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Abstract(24) FullText HTML(46) PDF 5496KB(76)
Abstract:

In order to satisfy the urgent needs of on-line real-time monitoring and analysis instrument for industrial pollution emission and sudden safety accidents, a panoramic bispectral infrared imaging interference spectrum measurement inversion instrument is proposed. Through the collaborative design of dual channel interference system, dual spectral imaging system, azimuth and elevation axis system, the measurement of image spectrum information of target scene with large field of view, wide spectral band and high resolution is realized. First, based on Fourier optics theory, the scalar diffraction theoretical model of interference imaging spectrum is established. Then based on broadband sampling and narrowband sampling theory, the sampling design of dual channel interference system is carried out. Based on the analysis of the interference imaging characteristics, the optical design of the dual band imaging system is carried out. Finally, the principle prototype is completed, and the telemetry experiment of the gas plume emitted by the chimney is carried out. The instrument can realize spectral measurement with resolution of 4 cm−1 in large field of view by 360°×60° and wide spectral range from 3~5 μm to 8~12 μm. The instrument can satisfy the application requirements of qualitative identification and quantitative analysis for gas emission monitoring.

Abstract(22) FullText HTML(9) PDF 7585KB(18)
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The rectangular primary mirror with aperture of 1.8 m×0.5 m is the crucial component of an off-axis Three Mirror Anastigmat (TMA) space optical system. In order to guaranty the structural stability and reliability of the Primary Mirror Assembly (PMA) and the surface ﬁgure error (RMS value) of the mirror, a bi-axial ﬂexural support has been proposed for the large-size rectangular mirror. First, based on the principle of kinematic equivalent, the initial structure of the bi-axial ﬂexural support was designed and the analytical formula for stiffness and its characteristic was studied as well. Then the mounting position and the key dimensions of the ﬂexural supports were studied and optimized. Finally, the ﬁnal optimization design scheme of the PMA was determined. Experimental results indicate that the surface figure error (RMS value) of the PMA under 1 G gravity in X and Y directions are 4.81 nm and 6.09 nm respectively when the optical axis is placed horizontally, which are less than λ/50 (λ=632.8 nm). The first-order natural frequency is 104 Hz, which can satisfy the design requirements. The dynamic tests have shown that the dynamic characteristics of the mirror assembly are good, and the flexural support system is stable and reliable. Now the mirror has been polished to have a surface figure better than λ/30 RMS. Zero Gravity optical testing has been performed under ±1 G respectively, which shows good coincidence with the analytical results.

Abstract(25) FullText HTML(16) PDF 6496KB(63)
Abstract:

The semi-active support is based on the semi-active optical technology, and the correction force is converted into a correction torque through a Warping Harness(WH) spring blade to correct the mirror low-order aberration introduced by error sources such as gravity and temperature. Aiming at the defects of traditional empirical design of mirrors, a new optimal design method for a mirror support system is proposed, that is, a comprehensive design optimization method of mirror support system based on structural size optimization combined with empirical design, and a set of semi-active mirror support systems based on WH is established. Firstly, the initial structure of the support system is designed according to the empirical formula; an L-shaped hollow WH spring blade is designed, and the nonlinear analysis and fatigue analysis are carried out to determine that the blade thickness is 2 mm and the service life is 1.2×106 times. Then, the RMS value of the mirror surface in the vertical and horizontal states of the optical axis was reduced from 119 nm and 106 nm to 13.3 nm and 4.8 nm by optimizing the position of the mirror support point, the position of the triangular plate flexure joint, and the key dimension parameters of the support system’s flexible parts; under the state of 1 °C temperature difference, the specular aberration is reduced from 2.8 nm to 1.9 nm; the first-order resonance frequency is increased from 80 Hz to 130 Hz. Finally, this method is used to verify the correction ability of the semi-active support system. The results show that the correction rate of the semi-active support system for mirror defocus, primary astigmatism, primary coma and primary spherical aberration can reach up to 99%. The amplitude of each aberration is less than 1 nm; the correction rate of the RMS value of the mirror’s surface shape can reach up to 46.5% under its own weight state at room temperature, and the correction rate is 31.28%

Abstract(20) FullText HTML(14) PDF 4698KB(34)
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Aiming at the problems of large parameters and low semantic segmentation accuracy of real-time semantic segmentation networks for true-color microvascular decompression (MVD) images. This paper proposes a U-shaped lightweight fast semantic segmentation network U-MVDNet (U-Shaped Microvascular Decompression Network) for MVD scenarios, which consists of encoder-decoder structure. A Light Asymmetric Bottleneck Module (LABM) is designed in the encoder to encode context features. Feature Fusion Module (FFM) is introduced in the decoder to effectively combine high-level semantic features and underlying spatial details. Experimental results show that for the MVD test set, U-MVDNet achieves 0.66 M parameters, 76.29% mIoU (mean Intersection-over-Union), and 140 frame/s speed on NVIDIA GTX 2080Ti. And when input image size is 640 × 480, the real-time (24 frame/s) semantic segmentation is realized on NVIDIA Jetson AGX Xavier embedded development board. The proposed network has no pretrained model, fewer parameters, and fast inference speed. The semantic segmentation performance is superior to other comparison methods, and a good trade-off between segmentation accuracy and speed is achieved. Furthermore, U-MVDNet can also be easily developed and applied on embedded platform with superior performance and easy deployment.

Abstract(44) FullText HTML(15) PDF 5353KB(67)
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Based on the requirement of multichannel detection for hyperspectral resolution imaging spectrometer, we design a hyperspectral resolution ultraviolet dual channel common optical path imaging spectrometer whose telescopic system adopts an off-axis three mirror structure with an off-axis field of view, and whose spectroscopic system applies a modified small and light weight Offner structure. Through the theoretical analysis of Offner spectrometer structures, initial structural parameters of a dual channel common optical path Offner that met the requirements of hyperspectral resolution were achieved. In order to improve the imaging quality of the imaging spectrometer, meniscus lenses were introduced into Offner structure, and the system was gradually optimized. Eventually, a dual channel common optical path imaging spectrometer was obtained with operating bands of 280~300 nm and 370~400 nm. When the Nyquist frequency is 27.8 lp/mm, the modulation transfer function (MTF) of both channels is better than 0.8, the full field mean square root radius (RMS) is less than 9 μm. and the spectral resolution is better than 0.1 nm. The design of this imaging spectrometer has important implications for the miniaturization and integration design of space-based hyperspectral detection imaging spectrometers.

Abstract(43) FullText HTML(21) PDF 2539KB(76)
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In order to meet the application requirements of airborne laser differential absorption lidar for small and lightweight light sources, a compact pulsed CO2 laser is developed with automatic wavelength tuning. First, the aperture matching relationship between an RF waveguide intracavity beam and a free space optical chopper beam was studied, and a beam conversion system was designed with real focus on the intracavity. The influence of the chopper aperture on a laser pulse waveform was verified experimentally. Secondly, the wavelength tuning characteristics of CO2 laser were studied, and the diffraction angle difference between adjacent laser spectral lines was analyzed. Tunable operation in the CO2 laser was realized using a high-precision electric turntable and metal blazed grating. Finally, the integration of a compact automatic tuning pulsed CO2 laser was completed using small lightweight modules. Experimental results indicate that the laser operates stably at 1 kHz with a pulse width of 350 ns and a peak power of 3.7 kW. There are 30 lines within 9.2~10.7 μm waveband. The total weight of the laser is 18 kg. It provides a miniaturized detection light source for airborne laser differential absorption lidar.

Abstract(24) FullText HTML(13) PDF 2818KB(56)
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The modulation Transfer Function (MTF) is an important evaluation index for remote sensing cameras, but at present, the research on the dynamic MTF characteristics of digital domain TDI CMOS cameras is very limited. In order to deeply research its image quality degradation mechanism, combined with the principle of digital domain Time Delay Integration Complementary Metal Oxide Semiconductor (TDI CMOS) imaging, a mathematical model of digital domain TDI imaging MTF degradation caused by pixel, electronic shutters, exposure time and vibration is established. Combined with the derived model, the prediction analysis and experimental verification are carried out. The results show that the regional distribution of effective pixels of the sensor will affect the image MTF with a greater intluence from smaller opening rates, and the rolling shutter of the CMOS sensor will lead to the decrease of the digital domain TDI imaging MTF with a more serious impact for slower rolling shutter speeds. When the rolling shutter speed changes from 6 μs to 10 μs, the corresponding image MTF decreases from 0.191 to 0.177. As the exposure time shortens, the MTF grows higher, especially when there is low-frequency image shift mismatch. When the exposure time is reduced from 180 μs to 100 μs, the MTF increases from 0.126 to 0.155 with some influence on the image signal-to-noise ratio. Therefore, the exposure time should be reasonably controlled in practical applications.

Abstract(66) FullText HTML(52) PDF 7030KB(70)
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The effective realization of desired optical system performances depends not only on the design results of imaging quality, but also on the realizability of various tolerances such as optical manufacturing tolerances, assembly tolerances, and environmental tolerances. An optical system with low error sensitivity relaxes tolerance requirements, which can better resist image quality degradation disturbed by errors. While reducing manufacturing costs, it effectively improves the realizability of an optical system, thereby reducing error sensitivity. It is an important link that should be considered in optical system design. This paper analyzes and summarizes the research status of optical system error sensitivity, summarizes typical optical system desensitization methods, and summarizes the application of these methods in optical system design. Finally, potential future development directions for low error sensitivity design methods for optical systems are provided.

Abstract(30) FullText HTML(3) PDF 11487KB(10)
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In order to solve the problems of low space utilization and small aperture of sub-eye in bionic compound eye system, a design method of large aperture compound eye system with hexagonal ring arrangement was proposed in this paper.Using the filling factor theory, Taking the traditional curved surface circular arrangement as the control group, it is demonstrated that the hexagonal band arrangement model can effectively improve the space utilization rate of the large-aperture compound eye system. Aiming at the limited target information acquisition of the single-band compound eye system, an infrared dual-band common optical path imaging form was designed, supplemented by a two-color image sensor, which enhanced the multi-dimensional ability of the compound eye system to obtain information. At the same time, a math model of the sub-aperture positioning of the hexagonal band arrangement is established. The bionic compound eye system is composed of 91 sub-apertures, with entrance pupil diameter of 16 mm, focal length of 48 mm and field of view of 9°. The combined total field of view of the sub-apertures is 96°×85°. The focal length of the relay system is 6.14 mm. In the temperature range of −40 °C−+60 °C, the sub-aperture system and the relay system basically have no influence of thermal difference. Cold reflection effect of detector can be ignored. The simulation results show that the RMS radius of each sub-channel is smaller than airy spot,optical distortion value of each sub-channel is less than 0.1%, The MTF of the edge sub-channel in MWIR/LWIR band is above 0.5 at 17 lp/mm.The system has compact structure and strong detection ability,and can be used for multi-target detection and recognition in complex environments.

Abstract(7) FullText HTML(2) PDF 596KB(10)
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Objetive: I In order to implement solar direct pumping slab high power laser, uniform linear high power density pump source is studied. Method

In this paper, the design method of high power density uniform linear light source is proposed by combining the first-order concentrating system with seven confocal ellipsoids to form the second-order concentrating system (composite ellipsoid cavity). Each ellipsoid realizes the equal radiation flux segmentation of the circular first focal spot. The mirror imaging characteristics make the peak power density not significantly decrease. After decomposition, the mirror spot forms a uniform linear light source at the second focus. The mathematical model of equal radiation flux is given by coordinate change, and the rotation and translation parameters of each ellipsoid are solved by annealing algorithm.

Result

: The first-order system is composed of a Fresnel lens with radius of 30 mm, focal length of 70 mm and a = 3.4 mm, c = 3.15 mm single ellipsoidal cavity. The second-order composite ellipsoidal cavity concentrating system is attached. The effective length is 12 mm, the peak power density is 1.09 × 106 W / m2, and the uniformity is 95.46 %.

Conclusion

Compared with the contribution of each ellipsoid parameter to the uniformity, the uniformity effect is significantly improved when the rotation parameter θ of the middle ellipsoid is 1.4°. The change of the edge ellipsoid parameter Δ has a significant influence on the effective length of the linear light source, and its optimal value is 0.53 mm.

Abstract(103) FullText HTML(29) PDF 3076KB(74)
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Non-blind image restoration is one of the most improtant research topics in the field of computer vision. It is also a typical ill-posed problem in mathematics. Its goal is to estimate a clear image from a blurred image when the point spread function is known. Its research focuses on how to make an appropriate compromise between improving clarity and suppressing noise. In the past 50 years, non-blind image restoration has made great progress. From the Wiener filtering to deep learning based methods, scholars have proposed hundreds of non-blind image restoration algorithms and applied them in various academic fields. This paper first introduces the basic concept and research significance of non-blind image restoration, then classifies and summarizes the main non-blind image restoration algorithms according to the algorithm attributes, which are generally divided into traditional methods and deep learning based methods. The traditional methods are divided into the direct method and iterative method, then are analyzed for their advantages and disadvantages. The performance of representative restoration algorithms is compared in a varity of typical experiments. Finally, the development trend and important research directions of non-blind image restoration algorithms are proposed.

Abstract(30) FullText HTML(19) PDF 6919KB(63)
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In order to realize the target of light and small, low radiation and large field of view of the long-wave infrared catadioptric optical system for deep-space low-temperature target detection, the local cooling optical system, topology optimization, metal based mirror design, additive manufacturing, Single Point Diamond Turning (SPDT) for metal mirrors and surface modification are studied. First of all, a compact catadioptric optical system with partially cooled is designed, in which the aperture is 55 millimeters, the focal length is 110 millimeters and the field of view is 4 degrees by 4 degrees. Secondly, the primary mirror assembly, the secondary mirror assembly and the connecting baffle are designed using the topology optimization theory, and the third order mode and fourth order mode reach 1213.7 Hz. Then, the front group optical mirrors assembly are developed by means of additive manufacturing, SPDT, surface modification and surface gold plating. We complete the optical mechanical assembly using the centering assembly method. Finally, the performance of the system after optical mechanical centering is tested. The test results show that the modulation transfer function (MTF) curves of the optical system reach the diffraction limit in the whole field of views, and the weight is only 96.04 grams. Additive manufacturing method can be used as an effective means to improve the performance of optical systems.

Abstract(25) FullText HTML(20) PDF 3591KB(46)
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In order to realize the in-situ detection of large aperture plane mirrors, wavefront detection is achieved by a combination of the Ritchey-Common method and holographic detection through the differential transfer function, combined with the actual Ritchey-Common detection architecture, and through the occlusion code of the pupil. Firstly, the principle of large aperture plane mirror detection based on differential transfer function method is derived, and the existing large aperture wavefront is compared with the reconstructed wavefront. Finally, the detection light path is built by using deformable mirrors. The correlation between the surface shape obtained by this method and the input surface shape is not less than 70%. This paper is of great significance to the fundamental cosmological propositions such as the detection of the "first light" of the universe and the "one black, two dark and three origins".

Abstract(52) FullText HTML(43) PDF 7664KB(70)
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Single molecule biological detection technology is an efficient technology to understand the dynamic characteristics of various biomolecules at the single molecule level and explore their structure and function. The advantage of this technology is that it can detect the heterogeneity of free energy on a single molecule, which is beyond the traditional methods. Therefore, researchers use it to solve long-standing problems in complex biological systems, heterogeneous catalysis, biomolecular interactions, enzyme systems and conformational changes. In terms of medical detection, detecting specific information about single molecules or their interactions with biological factors is not only crucial for the early diagnosis and treatment of various diseases such as cancer, but also has great potential for real-time detection and precision medicine. The advantages of high specificity and high precision of single-molecule bioassays are used to real-time detection of single biomolecules in molecular populations, and can be combined with multiple high-throughput analysis for the precise diagnosis of clinical samples. In this paper, the principle of single molecule detection and the application of biosensing are introduced, and the detection methods and related applications are summarized. Finally, the prospect and development direction of this research direction are discussed.

Abstract(44) FullText HTML(18) PDF 7658KB(52)
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High-speed vertical-cavity surface-emitting laser (VCSEL) is one of the main light sources for optical communication. Driven by the rapid growth of data traffic, the high-speed VCSEL is developing towards larger bandwidth and higher bit rate. By optimizing the epitaxy design and the growth of VCSELs, the design and the fabrication of VCSELs, and the high-frequency characterization techniques, much remarkable progress of high-speed VCSELs with different wavelengths have been achieved in modulation bandwidth, transmission rate, mode, power consumption in Changchun Institute of Optical, Jine Machanics and Physics (CIOMP). The research progress of high-speed VCSELs includes: high-speed single-mode 940 nm VCSEL with 27.65 GHz modulation bandwidth and 53 Gbit/s transmission rate; 200 Gbit/s optical link based on 850 nm, 880 nm, 910 nm and 940 nm high-speed VCSELs via wavelength division multiplexing; ultra-low power consumption as low as 100 fJ/bit of high-speed VCSEL via optimization of photon lifetime; 1030 nm high-speed VCSEL with 25 GHz modulation bandwidth; 1550 nm high-speed VCSEL with 37 Gbit/s transmission rate. The developed high-speed VCSELs have important application prospects in optical communication.

Abstract(52) FullText HTML(20) PDF 2204KB(45)
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In order to realize the stable and safe output of lasers, a control system based on a 515-nm high-power laser is designed. Firstly, the pump drive module of the system is studied. The analog sampling of the module is completed by Field Programmable Gate Array (FPGA) and the calculation output is completed in Digtital Signal Processing (DSP). The closed-loop control of the constant current source is completed by using the digital Proportion-Integral-Derivative (PID) algorithm. Secondly, a Thermo Electric Cooler (TEC) is used to achieve the stable temperature control of the frequency doubling crystal module, and the Negative Temperature Coefficient (NTC) is used as the feedback to realize the temperature control. Finally, the human-computer interaction system of the laser is designed, which realizes the real-time monitoring, judgment and storage of the internal state of the laser. In order to verify the effectiveness of the control system, a pump is selected for testing. The experimental results show that the pump drive module can work continuously and stably, and the control system can monitor the internal state of the laser in real time, which is safe and reliable. The laser output center wavelength after frequency doubling is 514.98 nm, the power can reach 170 W, and the optical power stability is ±0.07 dB. All devices and equipment for the control system are made in China, meeting the system design requirements of 515-nm high-power laser.

Abstract(28) FullText HTML(8) PDF 16644KB(45)
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Different from the traditional point-to-point mapping imaging method, computational optical imaging combines the physical regulation of the front-end optical signal with the processing of the back-end digital signal to make the image information acquisition more efficient. This new imaging mechanism is expected to alleviate the contradiction between low manufacturing cost and high performance indicators under the framework of traditional imaging technology, especially in the acquisition of high-dimensional image information. Since the system architecture supported by physical devices is the cornerstone of computational optical imaging, aiming at the sub-technical field of compressive spectral imaging, in this paper we introduce the existing optical devices that can realize spatial or spectral modulation. Based on this, the architecture of multi-type compressive spectral imaging system is sorted out and summarized, which can be categorized as single-pixel spectral imaging, coded aperture spectral imaging, spatial-spectral dual-coded spectral imaging, microarray spectral imaging and scattering medium spectral imaging, based on the information modulation process. We focus on the information modulation and acquisition principles of various system architectures and their modulation effects on the spatial-spectral data cube, and then analyze and explore the common issues. Finally, the technical challenges faced are given, and the future development trend is discussed.

Abstract(70) FullText HTML(30) PDF 5632KB(79)
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With the continuous development of astronomical exploration, the aperture of telescopes is getting larger and larger. Segmented mirror technology offers a viable and much simpler alternative to a large single monolithic primary mirrors, and has become an important way of designing the primary mirror of large-aperture telescopes. This paper summarizes the current development status of various technologies with reference to the primary mirror design of typical segmented telescopes such as the JWST and TMT, and elaborates on the performance differences and mirror supports of different segmented primary mirror schemes under the background of large-scale sub-mirrors. Potential future development trends of this technology and co-phasing detection technology are provided. This research acts as a reference for the independent development of the next generation of very large aperture optical infrared telescopes in China.

Abstract(35) FullText HTML(41) PDF 10268KB(69)
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In this paper, the basic principle and reconstruction method of random filter spectral coding-decoding are discussed. According to the automatic feature extraction mechanism of a deep learning undercomplete autoencoder, a pixel mapping variable-resolution spectral imaging reconstruction network with high reconstruction accuracy and low delay is constructed. The parallel training of a 2×2 and 4×4 pixel array spectral reconstruction network is implemented by transforming the pixel mapping relationship. Finally, the network’s performance is verified by the remote sensing data with 512×616 with 120 bands spectral images. For a 2×2 pixel array with 40 band, the reconstruction PSNR is 53 dB, the reconstruction MSE is less than 0.002, and the reconstruction time is 0.85 s. For a 4×4 pixel array with 120 bands, the reconstruction PSNR is 64 dB, the reconstruction MSE is less than 10−5, and the reconstruction time is 0.5 s. The experimental results show that the pixel mapping variable-resolution spectral imaging reconstruction network has the dynamic transformation performance of high accuracy and low delay.

Abstract(44) FullText HTML(24) PDF 2829KB(64)
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In order to realize single mode, narrow linewidth and low magnetism field intensity operation of lasers, Vertical-Cavity Surface-Emitting Lasers (VCSEL) with integrated micro-lens extended cavity was designed and fabricated. First, an epitaxial structure suitable for the micro-lens integration was designed and grown by Metal Organic Chemical Vapor Deposition (MOCVD). The fabrication steps of the micro-lens integrated VCSEL was carried out and the magnetism-free material was used in the electrode deposition. Experimental results indicate that the operating temperature is 90 °C, the laser wavelength is 896.3 nm, the laser power is 1.52 mW, the side mode suppression ratio is as high as 36.3 dB and the operating magnetic field intensity is less than 0.03 nT. A narrow linewidth and magnetism-free VCSEL suitable for quantum sensing was demonstrated.

Abstract(50) FullText HTML(25) PDF 3506KB(77)
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As the requirements of space astronomy, situational awareness, environmental monitoring and other fields grow higher, space telescopes are developing toward large fields of view and large apertures. Large-scale focal plane stitching technology is the key technology of large-field space telescopes. The allocation method of the main focal plane flatness error (P-V value) is generally a direct assignment method based on experience, which is prone to unreasonable error allocation.In this paper, a method of splicing focal plane error allocation is proposed, which can accurately allocate important parameter errors through optical-structural-thermal integration analysis. Taking 4×4 mechanical direct splicing focal plane with 16 pieces of Complementary Metal Oxide Semiconductor(CMOS) image sensor, as an example, an error tree of splicing focal planes is established. The influence of important parameters such as gravity and temperature on the flatness of splicing focal plane is analyzed by the method of optical-structural-thermal integration analysis. The error distribution result is finally given. The analysis shows that the flatness errors caused by gravity under two different attitudes are 0.28 μm and 1.55 μm respectively, and the total flatness error caused by temperature is 5.5 μm. After leaving a 30% margin, the assigned values of the flatness error caused by gravity and temperature are determined to be 2 μm and 7.2 μm, respectively.

Abstract(80) FullText HTML(35) PDF 4726KB(77)
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High power diode lasers are widely used for pumping solid-state lasers and fiber lasers, material processing, laser radars, free-space optical communication, security and defense. However, conventional diode lasers suffer from large far-field divergence angles, poor beam quality and low brightness, which restricts their direct applications. Broad-Area diode Lasers (BALs) can achieve high output power and efficiency. However, their lateral mode is usually influenced by many physical mechanisms, leading to a large number of guided lateral modes at high-power operation. It results in a rapid increase of the far-field width and strongly deteriorated beam quality, limiting the improvement of diode lasers′ brightness. Therefore, the lateral modes should be carefully controlled. In this paper, the factors influencing the diode lasers′ lateral modes are reviewed, and the lateral mode characteristics, optical field distribution and their relations with the device construction are analyzed. Then, the current lateral mode control technologies are described in detail. The beam quality and brightness of the output beam can be enhanced via the suppression of high-order lateral modes and the far-field blooming effect. As a result of advanced lateral mode control, novel high-brightness diode lasers can be developed at the chip level, which is beneficial for developing new diode lasers applications and reducing their system cost.

Abstract(84) FullText HTML(60) PDF 6212KB(62)
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Ultraviolet photodetection technology is another dual-use detection technology after infrared detection and laser detection technology, which has broad application prospects. Vacuum photomultiplier tubes and Si-based photodiodes are common commercial UV detectors, but vacuum photomultiplier tubes are susceptible to high temperatures and electromagnetic radiation, and need to work under high pressure while Si-based photodiodes require expensive filters. Wide bandgap semiconductor ultraviolet photodetectors have overcome some of the problems faced by the above two devices, and are becoming the research hotspot. Among them, wide bandgap oxide materials have attracted extensive attention, due to the advantages of easy preparation for high response and high gain devices, and rich micro-structures and nano-structures. In this paper, ultraviolet photodetectors based on micro/nano-structured wide bandgap semiconductor oxide are combed, and some related researches in recent years are reviewed. The oxide materials involved include ZnO, Ga2O3, SnO2 and TiO2, etc. and the device structures involved include metal-semiconductor-metal devices, Schottky junction devices and heterojunction devices, etc.

Abstract(15) PDF 18984KB(24)
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Abstract(27) FullText HTML(17) PDF 4972KB(46)
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The large aperture sky survey telescope needs closed-loop error correction based on the feedback of its wavefront sensing system, so as to give it a better confirm to its limit detection ability. In this paper, firstly, the basic theoretical expression of sub region curvature sensing is derived. Then, a joint simulation model is established. The process of sub region curvature sensing is simulated and analyzed by using the combination of optical design software and numerical calculation software. Finally, by setting up a desktop experiment, the cross-comparison of single- and multi-target curvature sensors is carried out to verify the correctness of the algorithm. Compared to the traditional active optical technology, the method proposed in this paper can improve the detection signal-to-noise ratio and sampling speed by expanding the available guide stars. For the standard wavefront, compared with the single guide star curvature sensor, the error is 0.02 operating wavelengths (RMS), and the error is less than 10%, which can effectively improve the correction ability of the active optical system.

Abstract(23) FullText HTML(15) PDF 1891KB(28)
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In the process of dynamic 3D measurement based on phase-shifting and fringe projection, the ideal correspondence between object points, image points and phases in different fringe images is destroyed. On this condition, the application of traditional phase formulas will produce significant measurement errors. In order to reduce the dynamic 3D measurement error, the basic principle of the error is firstly analyzed, and the errors are equivalent to the phase-shifting errors between different fringe images. Then, a dynamic 3D measurement error compensation method is proposed, and this method combines the advanced iterative algorithm based on least squares and the improved Fourier assisted phase-shifting method to realize the high-precision calculation of random step-size phase-shifting and phase. The actual measurement results of a precision ground aluminum plate show that the dynamic 3D measurement error compensation technology can reduce the mean square errors of dynamic 3D measurement by more than one order of magnitude, and the dynamic 3D measurement accuracy after compensation can be better than 0.15mm.

Abstract(20) FullText HTML(55) PDF 6395KB(44)
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As an early component of modern super-resolution (SR) imaging technology, structured illumination microscopy (SIM) has been developed for nearly twenty years. With up to ~60 nm and 564 Hz frame rate, it has achieved an optimal combination of spatiotemporal resolution in live cells recently. Despite these advantages, SIM also suffers disadvantages, some of which originated from the intrinsic reconstruction process. Here we review recent technical advances in SIM, including SR reconstruction, performance evaluation, and its integration with other technologies to provide a practical guide for biologists.

Abstract(131) FullText HTML(72) PDF 6277KB(81)
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Besides its advantages in volume, power and beam quality, a monolithic integration Master-oscillation Power-amplifier (MOPA) can also realize a narrower linewidth and dynamic single-mode by integrating Bragg grating. Its application value is high in the fields of frequency doubling, pumping, optical communication and sensing, which makes it a popular research topic in recent years. This paper firstly went over the mainstream structure and characteristics of monolithic integrated MOPA, including a tapered amplifier, ridge amplifier, Bragg grating and three-section MOPA. Based on their working principles and performance characteristics, we introduce the main research directions and the latest development trends in combination with their problems. Aiming at the problem of beam quality degradation at high power in monolithic integrated MOPAs’ epitaxial layer, facet optical film and electrode aspects, we then summarized the optimal design of monolithic integrated MOPAs. After that, we sorted out the research progress of MOPAs with different performance characteristics for various application requirements including high power, narrow linewidth, high beam quality and high brightness. Finally, we prospected the development trend of monolithic integrated MOPA.

Abstract(18) FullText HTML(7) PDF 5307KB(31)
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At present, the simulation research of arc actuator is only limited to obtaining the working characteristics of the plasma generated by the actuator, such as potential, pressure, temperature and velocity, while the plasma state is only limited to diagnosing its electron temperature and electron density by spectrum. The two are separated. This paper attempts to unify the two. Therefore, the arc jet plasma actuator designed here adopts the finite element method to solve the nonlinear multi physical equations. The working characteristics of the arc jet plasma actuator are numerically simulated, and the potential, pressure, temperature and velocity distributions inside the actuator are obtained. On this basis, the electron density is calculated, The simulation calculation model of the plasma state (electron temperature and electron density) of the actuator is obtained from the working condition of the actuator. Then the spectral diagnosis of jet plasma is carried out by using the emission spectral diagnosis method, and the electron density of plasma is calculated by using the intensity ratio method of discrete spectral lines. The diagnostic experiment of arc plasma actuator shows that the maximum electron temperature is 10505.8 k and the maximum electron density is 5.75 e + 22 m−3. For the plasma electron temperature and plasma density under different working conditions, the experimental and simulation results increase with the increase of inlet gas flow and discharge current. It shows that our simulation model of plasma state is reasonable and applicable for our miniaturized arc jet actuator with high jet velocity. At the same time, it also shows that our unified consideration is basically successful. Of course, there are still areas worthy of further improvement.

Abstract(49) FullText HTML(8) PDF 5050KB(41)
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Measurement repeatability is the largest uncertainty component of the light pressure measurement device, which directly affects the accuracy of the measurement results. In order to improve the accuracy of the measurement power in the process of the high power laser measurement, A high power laser measuring device based on light pressure is built, and the quality measurement repeatability experiment and the laser power measurement repeatability experiment were carried out, and the results of the two experiments were compared and analyzed. The experimental results show that the measurement repeatability of the light pressure measuring device gradually decreased with the increase of the measured mass and the measured laser power, indicating that the light pressure method has more advantages in measuring high power lasers. In the laser power measurement repeatability experiment, the influence of eccentric load and airflow disturbance is avoided, so the laser power measurement repeatability is better than the measurement repeatability calculated according to the equivalent mass. The research results have guiding significance for further improving the measurement accuracy of the light pressure method in the future.

Abstract(16) FullText HTML(11) PDF 3779KB(32)
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The traditional laser spot center positioning algorithm in a vibrating environment has problems such as long processing time and low accuracy. This paper proposed a laser spot center positioning method based on a genetic algorithm optimized BP neural network. This algorithm uses a BP neural network to predict the spot center position and a genetic algorithm to optimize the neural network. Based on the BP neural network, the spot center position derived by the gray weighted centroid method, centroid method, Gaussian fitting method, and the radius of laser spot obtained by the centroid method are used to predict the actual center position of the spot. Genetic algorithms are used to optimize the weights and thresholds of neural networks to improve prediction accuracy. An experimental platform is established to simulate the vibration environment by applying perturbations to the optical system and the data is collected for neural network training and algorithm verification. The experimental results show that the number of calibration test iterations before and after optimization is 55 and 29, and the average errors are 0.81 pixels and 0.45 pixels, respectively. Under the optimization of the genetic algorithm, the iteration speed and prediction accuracy of the neural network algorithm is improved.

Abstract(27) FullText HTML(23) PDF 18910KB(44)
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Two-dimensional (2D) Bi2O2Se has attracted broad attention in the field of electronic and optoelectronic applications in the UV-Vis-NIR region due to its unique crystal structure, energy band, high carrier mobility, and excellent stability. In this paper, we review the recent research progress in the material synthesis and optical characterization of Bi2O2Se. Firstly, the synthetic method and growth mechanism of 2D Bi2O2Se are introduced, including chemical vapor deposition (CVD), wet chemical process, molecular beam epitaxy (MBE) and pulsed laser deposition (PLD), etc. Via steady-state spectrum study, the properties change of 2D Bi2O2Se with thickness change can be studied, such as the band gap. The defect type, temperature coefficient and thermal conductivity of 2D Bi2O2Se material can be further studied by focusing on the crystal vibration mode. Transient spectrum techniques can benefit the study of relaxation process and carriers transport properties in 2D Bi2O2Se materials. Finally, we summarize the existing challenges and application prospects for the promising Bi2O2Se field.

Abstract(48) FullText HTML(37) PDF 4516KB(47)
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This paper studies the coherence of magnetic surface plasmons in one-dimensional metallic nano-slit arrays and proposes a double-dip sensing method to improve sensitivity. Different from the conventional way of scanning wavelength at a fixed incident angle, coherence of surface plasmons is investigated by changing the incident angle at a fixed wavelength. Due to the retardation effect, two coherence dips move in opposite directions as the refractive index of the surrounding medium changes. Compared with one dip used for sensing, two oppositely moving dips can efficiently improve the sensitivity. The sensitivity of two dips can reach 141.6°/RIU while the sensitivities of two single dips are 39.2°/RIU and 102.4°/RIU respectively. Besides, the inconsistency between the refractive index of slit medium and upper medium has few influences on the sensing performance, which can lead to wide practical applications.

Abstract(20) FullText HTML(14) PDF 679KB(34)
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In order to promote the application of Laser-induced breakdown spectroscopy (LIBS) in the field of nuclear industry, in this paper, a femtosecond LIBS (fs-LIBS) system was used to quantitatively analyze the element of Thorium (Th) in high purity graphite matrix. According to the Th concentration in the Thorium-based fuel, a total of 9 homemade Th2O3-graphite mixture samples with Th concentrations varied from 0.35% to 35.15% were prepared by standard addition method. The favorable experimental parameters such as the treatment methods for LIBS detection, laser pulse energy and delay times were studied before the quantitatively analysis. The results show that the signal intensity of the fs-LIBS spectrum acquired by the scanning with moving method is significantly higher than that of the without moving method. For the Th I 396.21 nm line, the Relative standard deviation (RSD) value of multiple measurements for the scanning method was just 5.7%, which was much lower than that of the without moving method (20.4%). The Th spectral lines showing obvious saturation effect due to self-absorption effect were found in the higher concentration region, and thus the basic calibration method was no longer applicable. Therefore, an exponential function was used to fit the spectral line intensity and concentration in the whole concentration region, and the concentration saturation threshold\begin{document}$t$\end{document}values corresponding to the analytical lines Th I 394.42, 396.21, and 766.53 nm were obtained. The basic calibration method has good detection performance when the calibration curves were constructed by using the lower concentration below the saturation threshold. For the peak area and peak intensity of each analytical line, using the internal standard method with the internal standard line (C I 247.85 nm), a good linear relationship can be found between them and the Th concentrations in the whole concentration region, especially for the case of the analytical line Th I 766.53 nm with a higher saturation threshold, the internal standard method had good prediction performance for unknown samples with higher concentration. The above results show that fs-LIBS has the potential to monitor and analyze the thorium concentration in the thorium-based fuel cycle.

Abstract(29) FullText HTML(21) PDF 687KB(36)
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Aiming at the problems of complexity and low accuracy of the classification for benign and malignant brain tumors, a classification model was proposed based on the fusion of multi-scale feature and channel feature. The model took ResNeXt as the backbone network. First, the multi-scale feature extraction module based on dilated convolution was used to replace the first convolution layer, which can make full use of dilation rate to obtain the image information from different receptive fields, and combine the global features with significant subtle ones. Second, the channel attention mechanism module was added in the network to fuse the feature channel information in order to increase the attention to the tumor, reduce the attention to the redundant information. Finally, the combination optimization strategy, the MultiStepLR strategy of learning rate, the label smoothing strategy of image and the transfer learning strategy on medical images, was adopted to improve the learning ability and the generalization ability of the model. The experiments were carried out on BraTS2017 Dataset and BraTS2019 Dataset, and the classification accuracy are 98.11 % and 98.72 %, respectively. Compared with other advanced methods and classical models, the proposed classification model can effectively reduce the complexity of the classification process and improve the accuracy of benign and malignant brain tumors.

Abstract(26) FullText HTML(10) PDF 750KB(35)
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Airborne lidar is an important means to achieve long-range accurate atmospheric monitoring. The laser wavelength is consistent with the absorption spectrum of most atmospheric pollutants and chemical substances, which makes it an important laser source for airborne lidar. However, it is difficult to design a temperature control system for airborne CO2 laser to work in a wide temperature range of −40 °C−55 °C under the condition of controlling volume and weight. This paper proposes a temperature control method. In the method, the laser characteristic and environment temperature are used as input, thermo electric cooler and forced air cooling are combined to control the laser temperature. According to the structure and heat transfer characteristics of laser, thermo electric cooler and forced air cooling, the finite element model of temperature control method is established, and the temperature control performance of laser is optimized based on the model. In the high temperature environment of 55 °C, the temperature of the laser is controlled at 40 °C, after the temperature control system works for 25 min. In the low temperature environment of −40 °C, the laser temperature is controlled at 25 °C after the temperature control system works for 20 minutes, which meets the normal working requirements of the laser. According to the laser and the established temperature control method, the experimental research on the working ability of the laser in high and low temperature environment is carried out, the temperature data of the laser in the experimental process is collected, and the laser output power is measured under high and low temperature conditions. The experimental results show that the experimental measured temperature data is consistent with the finite element simulation results, the error between them is less than 10%. The laser with proposed temperature control method can work steadily, and the output power of the laser is consistent with that of the laser at room temperature.

Abstract(35) FullText HTML(34) PDF 1469KB(51)
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Single-molecule imaging is widely used for reconstruction of three-dimensional subcellular structure. The point spread function is an important window to analyze the information of single molecule. Besides 3D coordinates, it also contains abundant additional information. In this paper, we reviewed the recent progress of multi-dimensional single-molecule imaging, including spatial location, fluorescence wavelength, dipole orientation and interference phase, etc. We also briefly introduced the latest methods for molecule localization and discussed the further directions.

Abstract(52) FullText HTML(26) PDF 7608KB(78)
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The fields of modern biology and biomedicine urgently need wide-field-of-view, high-resolution microscopic technology and instruments for trans-scale observation of biological samples to meet the research of major scientific issues need. Limited by the spatial bandwidth product, traditional commercial microscopes cannot meet this demand. Besides, the existing high spatial bandwidth product microscopy systems have problems such as bulky volume and high implementation costs. In this paper, based on the HiLo optical sectioning technology and the self-designed wide-field-of-view and high-resolution objective, a wide-field-of-view and high-resolution HiLo optical sectioning microscopy system was developed. The field of view (FOV) and imaging resolution of this system were tested. Brightfield imaging experiments were carried out on mouse brain slices by this system and OLYMPUS commercial microscope. At the same time, widefield fluorescence imaging comparison experiments were carried out on wheat seed fluorescent slices. The experiment results show that the FOV of this system reaches 4.8 mm×3.6 mm (the diagonal FOV is 6.0 mm), the lateral resolution reaches 0.74 μm, and the axial resolution reaches 4.16 μm. The comparative experiment proved that this system has the advantages of wide FOV, high resolution and the ability of fast optical sectioning imaging simultaneously. This system can carry out rapid 3D imaging of large-volume biological samples, which will provide strong technical support for researches such as embryonic development, brain imaging, and digital pathology diagnosis.

Abstract(51) FullText HTML(45) PDF 10500KB(64)
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In this paper, we propose a non-diffraction light sheet fluorescence microscopy (LSFM) technique, which readily enables multi-scale 3D imaging of diverse biological samples with size ranging from microns to centimeters. To solve the problem of heavy sidelobes in conventional non-diffraction Bessel LSFM, we invent a double-ring-modulated approach which can generate non-diffraction light sheet with ~0.4 to ~5 µm tunable thickness and suppressed sidelobes lower than 30%. Then we build a multi-scale LSFM system based on this novel approach and demonstrate its versatile multi-scale imaging abilities, such as dual-color 3D dynamic imaging of single live cell, 3D super-resolution imaging of expansion cells and high-throughput 3D mapping of entire meso-scale organs. Therefore, we demonstrate that this multi-scale imaging modality can substantially improve the efficiency of LSFM for advancing various biomedical studies, such as cell biology, tissue pathology, and neuroscience.

Abstract(37) FullText HTML(20) PDF 4373KB(56)
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A novel photonic quasi-crystal fiber (PQF) sensor based on surface plasmon resonance (SPR) is designed for simultaneous detection of methane and hydrogen. In the sensor, Pd-WO3 and cryptophane E doped polysiloxane films deposited on silver films are the hydrogen and methane sensing materials, respectively. The PQF-SPR sensor is analyzed numerically by the full-vector finite element method and excellent sensing performance is demonstrated. The maximum and average hydrogen sensitivities are 0.8 nm/% and 0.65 nm/% in the concentration range of 0% to 3.5% and the maximum and average methane sensitivities are 10 nm/% and 8.81 nm/% in the range between 0% and 3.5%. The sensor provides the capability of detecting multiple gases and has large potential in device miniaturization and remote monitoring.

Abstract(260) FullText HTML(104) PDF 8543KB(77)
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Rare earth-doped upconversion luminescence nanomaterials have received considerable attention from researchers due to their great potential for applications in many fields such as information security, biomedicine, optical fiber communication, display, and energy. Especially, the recently developed upconversion luminescence nanoparticles with orthogonal excitation- emission properties, whose distinct luminescence outputs can be dynamically modulated by switching the excitation conditions. The orthogonal luminescence properties further endow such nanocrystals with a set of new features and functionalities, which will largely expand their application areas. This review summarizes the progress in the development of orthogonal upconversion luminescence of rare earth ions, and provides a systematic discussion on design principles and construction strategies of orthogonal excitation-emission systems based on core-shell structure, as well as introduces their recent advances in various fields of applications including data storage, security anti-counterfeiting, display, sensing, bioimaging and therapy. Furthermore, the possible opportunities and challenges in the future research of orthogonal luminescence systems are also prospected.

Abstract(83) FullText HTML(93) PDF 10812KB(101)
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With the characteristics of real-time, high-resolution and non-invasive, optical microscopy can scale from cells, tissues to whole living organisms, which has greatly expanded our understanding to the nature of life. However, due to the limited space-bandwidth product (SBP), it is hard for a conventional optical microscope to achieve a large field of view with a high resolution. This makes it very difficult for microscopic imaging in large field of view biological imaging applications, such as imaging of neural circuits between the synapse of the brain neural networks. Recently, large field-of-view imaging technology has received increasing attention and experienced rapid development. The SBP has been improved ten times or even a hundred times as compared to a traditional optical microscope and the field-of-view has been expanded without sacrificing resolution, which, in turn, has resolved some major problems in biomedical research. This review introduces the progress, characteristics and corresponding biological applications of several typical trans-scale optical imaging techniques in recent years, and gives an outlook on their future development.

Abstract(41) FullText HTML(31) PDF 17296KB(70)
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With the continuous development of optical imaging technology and the growing demand for remote sensing applications, cross-scale high-resolution optical technology has been widely used in the field of remote sensing. In order to obtain more detailed information on the target, domestic and foreign researchers have carried out relevant research in different technical directions. In this paper, through the technical classification of remote sensing imaging, introduces a representative aerospace optical remote sensing high-resolution imaging optical imaging system. It focuses on monomer structure, block expandable imaging, optical interference synthesis aperture imaging, diffraction main mirror imaging, optical synthetic aperture and other technologies. It provides a new development idea for the development of high-resolution optical remote sensing loads on the ground.

Abstract(38) PDF 2784KB(55)
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We investigate a family of the cosh-Pearcey-Gaussian vortex (CPeGV) beams, obtain the general propagation expressions of a CPeGV beam, and study the longitudinal and transverse Poynting vector and angular momentum density (AMD) when the CPeGV beams propagate in uniaxial crystals. The effects of the cosh modulation parameter, topological charge, and propagation distance on the propagation properties of CPeGV beams are discussed. A larger cosh modulation parameter can lead the energy transfer significantly along the transverse Poynting vector direction. Moreover, we also investigate how the cosh modulation parameter and topological charge influence the propagation properties in the far-field. A larger cosh modulation parameter can lead AMD to present four-lobes structures rather than usual parabolic curves. Our investigation will provide a better understanding of the state of the CPeGV beams propagating in uniaxial crystals and be useful for applications in information transmission.
Abstract(73) FullText HTML(60) PDF 11931KB(79)
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The advantage of two-photon microscopy in maintaining good spatial resolution in thick biological tissues has led to its application in in vivo brain imaging studies soon after its birth. As neural networks have cross-scale multidimensional spatio-temporal properties, two-photon microscopy has developed rapidly and significantly in recent years to meet the demand for in vivo cross-scale imaging of the brain. This paper firstly introduces the working principle of two-photon microscopy, then reviews the new progress of two-photon microscopy in five aspects: imaging field of view, imaging flux, imaging depth, resolution, miniaturization, and analyzes the difficulties and future challenges of cross-scale two-photon in vivo microscopic imaging technology.

Abstract(29) FullText HTML(17) PDF 7177KB(74)
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In order to improve the suitability of the fiber hydrophone towing line array, a flexible fiber grating hydrophone array was proposed.The sound pressure sensitivity of three flexible fiber grating hydrophones was calculated according to the mechanical theoretical model,and the influence factors were compared and analyzed. The 2-element flexible fiber hydrophone sample arrays with diameters of 10 mm,12 mm and 16 mm were developed through finite element simulation for frequency response analysis. The sensitivity was measured by vibration liquid column experiment. The experimental results show that the response is flat within the frequency range of 200−800 Hz, and the average sound pressure sensitivities of hydrophone arrays with different structural parameters are −160.87 dB, −154.59 dB, and −156.73 dB, respectively. The theory and simulation analysis are verified. By further optimizing the material and structure parameters and using weak reflection fiber grating, the integrated flexible hydrophone array with hundreds elements can be constructed according to the design in this paper.

Abstract(32) FullText HTML(17) PDF 5334KB(80)
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In order to generate double doughnut-shaped focal spots in adjustable position along axial direction. Based on a formula of annular radius derived from vector diffraction integral, a vortex phase zone plate was designed to produce the double doughnut-shaped focal spots in axial direction. The focusing properties of the modulated vortex phase zone plate was further investigated in tightly focused system. First, integral formulas of linearly and circularly polarized vortex beams were calculated under high NA focusing condition. Then the intensity distributions of linearly and circularly polarized vortex beams in high NA focusing system were simulated by the integral formulas with various axial shifting distances and topological charges. Finally, the corresponding experimental results of linearly and circularly polarized light were also given, utilizing a spatial light modulator loaded on double doughnut-shaped phase patterns. The double doughnut-shaped focal spots with the topological charge of 1 and axial distances of ±10 μm and ±15 μm were produced when the incident light was linear polarization. As well as the double doughnut-shaped focal spots with axial distances of ±20 μm and topological charge of 1−4 were also produced when the incident light was circular polarization. The simulated and experimental results demonstrated that two doughnut-shape focal spots with controllable axial shifting distance and dark spot size could be produced in the tight focusing region of a high NA objective when it modulated by the vortex phase zone plate. This kind of vortex phase zone plate could be applied in the field of optical micromanipulation, two-beam super-resolution nanolithography, and stimulated-emission-depletion fluorescence microscopy (STED).

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Abstract(131) FullText HTML(31) PDF 6251KB(101)
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Digital pathology has brought new opportunities for remote pathological consultation and joint consultation owing to its convenient storage, management, browsing and transmission. However, because of the limited field of view of the microscope, panoramic imaging cannot be achieved while ensuring the resolution. The proposal of panoramic digital pathology makes up for this defect and achieves panoramic imaging while ensuring resolution. However, a single slice can only detect a single target, and disease diagnosis needs to observe the expression of multi-target at the same time. In recent years, multi-target panoramic digital pathology technology has developed rapidly. It has attracted much attention because of its great application potential in drug research and development, clinical research and basic research. Owing to the large field of view, many colors and high flux, the system can detect the expression of various biomarkers on the whole tissue section in situ in a short time, to identify the phenotype, abundance, state, and relationship of each cell in the tissue. Firstly, this paper reviews the development process of digital pathology, panoramic digital pathology and multi-target panoramic digital pathology, as well as the update and iteration of technology in the development process, and illustrates the importance of developing multi-target panoramic digital pathology. Then, the multi-target panoramic digital pathology is described in detail from three parts: biological sample preparation, multi-color imaging system and image processing. Next, the application of multi-target panoramic digital pathology in biomedical fields, such as tumor microenvironment and tumor molecular typing are described. Finally, the advantages, challenges and future development of multi-target panoramic digital pathology are summarized.

Abstract(60) FullText HTML(34) PDF 8727KB(89)
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Panoramic endoscopic imaging technology can effectively reduce the observation blind area of internal organs. It has many advantages, such as shortening the operation time, reducing the risk of intraoperative bleeding, improving the prognosis and shortening the postoperative recovery time. It has important application value in minimally invasive surgery and preoperative examination. It is a research hotspot in recent years. This paper combs the panoramic endoscopic imaging technology from two aspects: principle and product application. Firstly, various panoramic endoscopic imaging technologies based on two-dimensional and three-dimensional imaging are reviewed, their implementation methods are described, and their indexes and performance are analyzed. Secondly, the capsule endoscope, panoramic enteroscope and other different types of products derived from panoramic endoscopic imaging technology are compared and analyzed, and the development trend and application prospect of panoramic endoscopic imaging technology are prospected.

Abstract(111) FullText HTML(39) PDF 8515KB(104)
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Due to the advantages of high resolution, multi-scale, multi-dimensional, low radiation andeasy to integrate, opticalimaging technology plays an important role in biomedical field. In the field of endoscopy, how to carry out the acquisitionof endoscopic image information, processing and visualization of endoscopic image information is the core of the problem what optical imaging technology need to solve in the field of endoscopy.The obtaining of trans-scaleimageendoscopic image of patients wherethesurgeoncareaboutin the medical clinicalis more advantageous to the surgeon for the diagnosis of patients and improve in accuracy of the operation.Thereview starts with the application of trans-scale optical imaging technology in the field of endoscopy, focusing on the different optical systems to obtain trans-scale images in clinical endoscopy,includingtrans-scaleopticalzoom system, multi-channel imaging system,fiber-scanningimaging system,and expounds its progress and future trends.

Abstract(118) FullText HTML(92) PDF 8364KB(126)
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Optical imaging has become the dominant method for characterizing information in biological systems. The rapid, non-destructive and comprehensive characterization of biological samples in recent years has placed high demands on the resolvable volume of imaging systems. Digital holography records the entire complex wavefront, including both the amplitude and phase of the light field by interference imaging. Due to its advantages of fast, non-destructive, and 3D imaging, it has been used in numerous applications such as digital pathology, label-free observation and real-time monitoring of in vitro cells. First, this paper introduces the main ways to achieve high-throughput imaging, and analyzes the advantages of digital holography and the evolutionary of spatial bandwidth. Secondly, a theoretical framework for high-throughput multi-channel multiplexing digital holography based on Hilbert transform is presented. Then, an extended field of view digital holographic microscope is introduced based on this theoretical framework. Experimental results indicate that the system achieves an 8 times space-bandwidth product higher than that of conventional off-axis holographic microscopes without sacrificing spatial and temporal resolution. This high-throughput digital holographic multiplexing technology can make full use of the redundant spatial bandwidth of single intensity image, which verifies the feasibility of high-throughput multi-channel multiplexing digital holography.
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doi: 0.37188/CO.2022-0077
Abstract(106) FullText HTML(115) PDF 10648KB(45)
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Lipid droplets are a kind of spherical organelle in eukaryotic cells and are relevant to many cellular physiological processes. To visualize and study lipid droplets, fluorescence imaging techniques are one of the most powerful tools. However, the conventional wide-field microscopy and confocal microscopy can only provide a resolution of about 250 nm due to the limitation of optical diffraction. This resolution is quite insufficient for visualizing the small lipid droplets, especially the nascent ones (size of about 30-60 nm). In this context, emerging super-resolution microscopes that can break the diffraction limit (such as stimulated emission depletion microscopy, structured illumination microscopy and photoactivated localization microscopy) have gradually attracted much interest in recent years. To obtain high-resolution fluorescence images of lipid droplets, the advanced fluorescent probes which meet the special requirements of the corresponding super-resolution microscopes are highly essential. This review paper will briefly introduce the working principles of various super-resolution microscopes, discuss their special requirements on the photophysical properties of fluorescent probes, and further systematically summarize the research progress of super-resolution imaging of lipid droplets employing with these fluorescent probes. Meanwhile, this review will compare the advantages and shortcomings of different super-resolution techniques for lipid droplets imaging, and prospect their future possible trends.
Abstract(81) FullText HTML(54) PDF 5395KB(14)
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Terahertz (THz) technology becomes increasingly important nowadays, especially in testing and security related fields. How to extend the field of view and increase the imaging quality are both vital challenges for THz imaging. To address these problems, we build a THz light field imaging system based on single-camera scanning configuration, which could utilize the 4D information of the spatial and angular distribution of the THz waves. Based on the 4D plenoptic function and the parameterization method with two parallel planes, the intensity consistency of THz propagation is used for refocusing calculation, then a series of refocused images can be obtained by integrating original light field image corresponding to different imaging distances and views. Compared with the primitive THz imaging, the field of view and the imaging quality of the THz light field imaging are effectively improved. In our experiment, the field of view was enlarged by 1.84 time and the resolution increased from 1.3 mm to 0.7 mm. Besides, information of some obscured targets could also be retrieved by defocusing the obstructions. This method could improve the imaging quality of THz imaging as well as expand its functions, which inspires a new way of THz nondestructive testing (NDT) and security inspection.
Abstract(85) FullText HTML(65) PDF 9813KB(9)
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In order to accurately measure the laser intensity distribution, this paper proposes a method based on tomographic imaging. Firstly, numerical studies were performed to validate the correctness of the imaging model and convergence of the reconstruction algorithm. Reconstruction errors were less than or equal to 7.02% with different laser intensity distribution phantoms employed and less than 8.5% with the addition of different random noise levels under 10%. Additionally, a demonstration experiment was performed with the employment of a customized fiber bundle to realize the measurement from seven views. Seven views are distributed along a semi-circle plane which is perpendicular to the propagation direction of the laser beam. The distance from the laser beam to each view is nearly 160 mm and the angle coverage range of the seven views is about 150°. Laser-induced fluorescence obtained after the laser passed through a rhodamine-ethanol solution was collected by the tomographic imaging system. Then, the laser intensity distribution was obtained through absorption-corrected three-dimensional (3D) reconstruction. The correlation of the projection and re-projection of the one view was used to quantitatively access the accuracy after the other six views were adopted in the reconstruction. The results show the feasibility of the method with a correlation coefficient of 0.9802. It can be predicted that the 3D laser intensity measurement scheme proposed in this work has a broad prospect in the field of laser applications.
Abstract(137) FullText HTML(56) PDF 7219KB(26)
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In the Taiji program, laser interferometry is utilized to detect the tiny displacement produced by the gravitational wave signals. Due to the large-scale unequal arm, the laser frequency noise is the largest noise budget in the space interferometer system. To reduce the influence of laser frequency noise, a technology called the Time Delay Interferometry (TDI) is utilized to deal with it. The TDI is a kind of data post-processing method, which forms the new data stream by the method of the time delay to initial data. But the premise of TDI needs to obtain accurate absolute arm length between satellites. Thus, for that requirement, we discuss the ranging system scheme and implement a ground electronics verification experiment. The ranging system is based on Direct Sequence Spread Spectrum (DS/SS) modulation, and it mainly includes three parts, which are the signal structure, a Delay Locked Loop (DLL), and a data processing algorithm. In DS/SS modulation, types of pseudo-random code can make a difference to the quality of correlation and the ranging accuracy. Therefore, to design the optimal pseudo-random code, we compare the correlation and flexibility in choosing lengths of the m sequence, gold sequence, and Weil code. Weil code that has a shift-cutoff combination with the best autocorrelation is chosen as the ranging code. The ground electronics verification experiment is set up for simulating the physical process of signal transmission and verifying system performance. The main device of the experiment is a FPGA card based on the K7 chip from Xilinx, which is used to simulate the function of communication and ranging between satellites. Meanwhile, we change the length of the Radio Frequency (RF) coaxial cable to correspond to different ranges. The experimental process can be summarized as follows. Firstly, 16-bit data at 24.4 kbps and 1024-bit Weil code at 1.5625 Mbps are modulated with Binary Phase Shift Keying (BPSK) in the 50 MHz sampling frequency. Then the signal is transmitted through RF coaxial cables of 10 to 60 m in length. In receiving end, the signal is consolidated by DLL and the ranging information is collected. To measure the range accurately, we use a centroid method to optimize the collected data. The results show that the ranging accuracy is better than 1.6 m within 60 m. In conclusion, this experiment proves the principle of the scheme and its feasibility, laying a technical foundation for optical system verification in the future.
Abstract(107) FullText HTML(54) PDF 6408KB(12)
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In order to realize the efficient and automatic measurement of complex curved surface parts, this paper proposes a view planning method of surface structure light scanning based on an improved grid method, and applies it to the automatic measurement of complex curved surface automobile parts. Firstly, aiming at the problem of serious redundancy and poor scanning integrity of a manual teaching viewpoint, a scanning viewpoint planning algorithm for surface structured light based on an improved grid method is proposed. According to the effective measurement range of a surface structured light scanner, the grid size is determined, and the candidate viewpoint generation strategy is improved. The effective measurement range of candidate viewpoints is obtained by the measurement constraint condition of the scanner, and the optimal viewpoint is determined by the viewpoint quality evaluation function. Secondly, in view of the low efficiency of the algorithm and the low accuracy of feature reconstruction in the process of viewpoint planning, the voxel grid method is used to simplify the model. The complex surface model is segmented by the octree algorithm, and the voxel grid size is determined according to the normal vector consistency error. For the models with different geometric characteristics, the influence of the weight coefficient on the scanning quality is analyzed, and the optimal weight coefficient is given. Finally, the scanning viewpoint planning and measurement experiments of automobile sheet metal parts and reducer shell are carried out. The results show that the viewpoint planning of the automobile sheet metal parts takes 21.93 s, the scanning integrity is 99.124 %, and the scanning accuracy is 0.025 mm. The viewpoint planning of automobile reducer shell takes 158.29 s, its scanning integrity is 93.231 %, and its scanning accuracy is 0.032 mm. This method can quickly complete the viewpoint planning of complex curved surfaces, and the model with planning viewpoint scanning has good integrity and high precision, which can meet the requirements of automatic measurement of complex curved surface parts.
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Abstract(116) FullText HTML(68) PDF 6652KB(18)
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In order to improve the performance of lane detection algorithms under complex scenes like obstacles, we have proposed a multi-lane detection method based on dual attention mechanism in this paper. Firstly, we designed a lane segmentation network based on a spatial and channel attention mechanism. With this, we obtain a binary image which shows lane pixels and the background region. Then, we introduced HNet which can output a perspective transformation matrix and transform the image to a bird’s eye view. Next, we did curve fitting and transformed the result back to the original image. Finally, we defined the region between the two-lane lines near the middle of the image as the ego lane. Our algorithm achieves a 96.63% accuracy with real-time performance of 134 FPS on the Tusimple dataset. In addition, it obtains 77.32% of precision on the CULane dataset. The experiments show that our proposed lane detection algorithm can detect multi-lane lines under different scenarios including obstacles. Our proposed algorithm shows more excellent performance compared with the other traditional lane line detection algorithms.
Abstract(75) FullText HTML(45) PDF 4571KB(10)
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In order to account for the transverse effect of semiconductor lasers, the dynamic equation of a semiconductor laser with transverse effect is given by modifying the dynamic model describing it, and the influence of the transverse effect on its output characteristics is analyzed. On this basis, the synchronization transmission technology of a semiconductor laser’s output signal with transverse effect is further studied. The results show that the output of the semiconductor laser presents a new spatiotemporal chaotic state after considering the transverse effect, and is very sensitive to the dependence of the initial value. At the same time, whether the synchronization transmission of single-channel or multi-channel signals is carried out by a semiconductor laser, its transmission performance is very stable. The synchronization technology is very simple and easy to apply in practice.
Abstract(129) FullText HTML(44) PDF 4544KB(21)
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Tunable diode laser absorption spectroscopy (TDLAS) is a recently laser spectral gas detection technology developed. Compared with common oxygen sensors such as electrochemical devices and ionic conductive ceramics, TDLAS has the advantages of high selectivity and sensitivity, fast response, on-line measurement and strong anti-background spectral interference ability. Oxygen (O2) is an important gas in habitable environments and is greatly significant to industrial production and human life, and the detection of O2 concentration is also widely used in these fields. Based on this, this paper adopts TDLAS technology to carry out high sensitivity measurements of O2 in air. Using a semiconductor laser with an output wavelength of 760 nm as the light source, the oxygen concentration in the environment is 20.56 % by direct absorption spectroscopy, and the minimum detection limit is 283.27×10−6. In the wavelength modulation spectroscopy method, the laser wavelength modulation depth is optimized to obtain a complete second harmonic waveform, which can be used to calibrate the oxygen concentration. The SNR of the system is 380.74, and the minimum detection limit is about 540×10−9. The system realized in this paper has good oxygen detection ability and can be widely used in various fields of oxygen concentration detection.
Abstract(84) FullText HTML(48) PDF 3938KB(13)
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With the continuous development of digital display technology, display methods have also changed. Pepper's ghost images that adopt modern display methods require the light environment of the exhibition space to ensure the effect and ensure better visual comfort. In order to explore the influence of the lighting environment on the display effect based on Pepper's ghost images, a virtual imaging display space is set up to analyze the factors and trends affecting the imaging effect. A virtual imaging display space is set up in which 12 sets of LED lighting conditions with different illuminances and color temperatures are generated. 25 observers were used to conduct a psychophysical experiment. Conclusion: color temperature has no significant effect on the evaluation of color authenticity, detail expressiveness and stereoscopic expressiveness for Pepper's ghost images; Illumination has no strong effect on the evaluation of the color authenticity of Pepper's ghost images, but has a significant effect on their detail expressiveness and stereoscopic expressiveness. Under the lighting environment where the color temperature is 3500 K and the illumination is 10 lx, the detailed expressiveness and stereoscopic expressiveness of the display effect are relatively high and the visual comfort of 2500 K and 10 lx is better.
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Fluorescence emission difference microscopy is a super-resolution imaging technique with strong universality and low phototoxicity from fluorescent dyes. However, due to the limitation of its principle, traditional fluorescence emission difference microscopy has a high system complexity, low stability and limited imaging speed. In order to improve these defects, this paper designs and builds a set of multi-color virtual fluorescence differential microscopy systems, and their imaging methods and parameters are analyzed. On the basis of the existing principle of multicolor virtual fluorescence emission difference microscopy, the influence of the signal-to-noise ratio and background is further considered, and a virtual fluorescence emission difference microscopy imaging model that can be verified experimentally is established. The experiments show that the system and method have the characteristics of simple structure, strong background denoising ability, strong universality of fluorescent dyes, and low phototoxicity. Its imaging resolution is 1.9 times higher than that of confocal, and its imaging speed is doubled compared to the traditional fluorescence emission difference microscopy system. It has obtained good imaging results at three wavelengths, and has been experimentally verified in biological cell imaging.
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Objective  In order to reduce the space needed on a satellite, this paper proposes a design method for a free-form reflector for collimating illumination of integrating spherical light sources. By using this method, a square irradiance distribution with small diameter can be achieved.   Method  Firstly, the mathematical model of off-axis reflection lighting of free-form surface is established through the point light source model, then the free-form surface is discretized by Chebyshev points, and the free-form surface model that satisfies the point light source illumination is solved. Finally, the light source characteristics of the integrating sphere are analyzed. The method of free-form surface energy distribution completes the transformation from the point light source illumination model to the integrating sphere illumination model   Result   The analysis shows that when the illumination area is set at 140 mm*140 mm, the irradiance non-uniformity of the target surface is less than 0.02.   Conclusion  This method can meet the requirements of light weight, short light path and simple structure for spaceborne calibration.
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The damage threshold of an interline transfer CCD irradiated by different wavelength nanosecond Raman lasers was studied and an experiment with 496 nm, 532 nm, 632 nm Raman and multispectral Raman laser-irradiated CCD was carried out. The damage threshold interval of dot damage, line damage and total damage were observed and collected by adjusting the energy of each focused Raman laser. By careful fitting, the damage threshold interval and the damage possibility curve of the CCD at different laser energy densities with each Raman laser were estimated. Results showed that the multispectral Raman laser including a residual pump laser is most effective for damaging the CCD than the monochrome Raman laser, and the 630 nm Raman laser acts better than 574 nm and the 496 nm Raman laser. The microscopic images of the damaged CCD were reviewed, and the electronic characters of the damaged CCD were also tested to understand the damage and blindness mechanism of a Raman laser pulse-irradiated CCD.
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An optical switch based on a scanning mirror was designed in this paper. The optical switch is programmable and controlled by an embedded Linux system that switches between the fiber array channels on the UI of the touch display. Meanwhile, the switching sequence and residence time of the optical switch can be preset. In addition, the optical switch can be self-calibrated to obtain the maximum output power of each channel. The principle of the optical switch is analyzed and the performance of the optical switch is measured experimentally. The experimental results show that the average insertion loss is less than 17 dB for the single mode fiber array, the average crosstalk between adjacent channels is more than 30 dB, and the switching time between the adjacent channel is less than 1.3 mS. The average insertion loss is less than 2.4 dB for the multi-mode fiber array. It has the advantages of low loss, low delay, high precision, good stability, high repeatability, low cross-talk between the adjacent channel, and good man-machine interaction for the application of the WDM test device.
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Abstract:
In the tower solar thermal power plant, the heliostat mirror shape errors have an important impact on the optical efficiency of the heliostat field, so it is necessary to measure the heliostat surface shape error. The heliostat is generally made up of splicing multiple sub-mirrors, the tilt angle error of the sub-mirror is an important part of the heliostat mirror shape errors. This paper proposes a measurement method for the tilt angle errors of the heliostat sub-mirror based on the photogrammetry. That is, under the condition of known the shape size of the heliostat sub-mirror, the spatial position coordinates of the 4 corner points of the heliostat sub-mirror are calculated by using the principle of photographic imaging. Then the normal direction of the sub-mirror is found, and the tilt angle of the sub-mirror is calculated by using the normal line obtained. Finally, the purpose to measure the tilt angle error of the heliostat sub-mirror is achieved. The measurement principle of the method is elaborated, the calculation formula is derived, and relevant verification experiments were carried out using planar mirrors and cameras. By measuring the plane mirror with different tilt angles at different distances, the deviation between the measured tilt angle and the actual tilt angle of the plane mirror is about 0.1°−0.3°, and the experimental results show that the method can accurately measure the tilt angle error of the sub-mirror of heliostat, thus the correctness and feasibility of the method are verified.
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2022, 15(4): 609-624.   doi: 10.37188/CO.2021-0219
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Abstract:

The high temperature sensor of the optical fiber Fabry-Perot interferometer has the advantages of small size, a simple manufacturing process, high sensitivity, high temperature resistance and anti-electromagnetic interference, which make it widely used in the aerospace energy industry, environmental monitoring and other fields. Firstly, this paper introduces the sensing principle, sensing performance, sensing characteristics and fabrication method of optical fiber Fabry-Perot interferometer high temperature sensors. Secondly, the temperature, pressure and strain sensitivity and measurement range are summarized and the domestic and foreign research progress and the performance parameters of optical fiber Fabry-Perot interferometer high temperature sensors are summarized. Thirdly, the cross-sensitivity problems of temperature and pressure of optical fiber Fabry-Perot interferometer sensors and it’s solutions, and the high-temperature sensing characteristics of Fabry-Perot interferometers based on different kinds of optical fibers are introduced. Fourthly, according to the recent research progress of fiber Fabry-Perot interferometer high temperature sensors, several fiber Fabry-Perot interferometer high temperature sensors for two-parameter measurement are introduced. Finally, the future development trend and prospect of optical fiber Fabry-Perot interferometer high temperature sensors are prospected.

2022, 15(4): 625-639.   doi: 10.37188/CO.2021-0195
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Laser protection materials are of great significance in protecting human eyes and optical components from strong laser pulses. Among them, solid optical limiting materials based on the principle of nonlinear optics will be the main carriers for laser protection. This article introduces the research background, working mechanism, parameters and testing techniques of optical limiting materials, and reviews the research progress of various optical limiting materials with practical prospects, including inorganic semiconductor materials, conjugated organic polymers, inorganic metal clusters, carbon nanomaterials, and two-dimensional materials. And the development prospects of optical limiting materials are discussed.

2022, 15(4): 640-659.   doi: 10.37188/CO.2021-0191
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Polyvinylidene fluoride (PVDF) and its copolymers films have been extensively used in photoelectric functional devices such as photoelectric conversion, optical regulation, optical switch. They are the most important polymeric ferroelectricity materials with excellent electro-active properties, high diffraction efficiency and significant nonlinear optical effect. We summarize the progress in nonlinear optical effect of polyvinylidene fluoride and its copolymers films both in domestic and foreign research within the last several years. We illustrate that the development direction of the films will be nanoscale-doping, blending modification and ultrathin. The nonlinear optical properties should be investigated by the first-principle and photonic band gap calculations, and measured by the means of the high sensitivity Z-scan, Marker fringe combing with ellipsometry. This study can provide an insight for the development and utilization for polyvinylidene fluoride and its copolymers films in future.

2022, 15(4): 660-667.   doi: 10.37188/CO.2022-0057
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In order to make sure a microwave photonic filter both have wide tuning range and high frequency selectivity, a microwave photonic filter with a wide tuning range and narrow filter bandwidth based on a Brillouin oscillator is proposed and verified for the first time. The core of the filter is a Brillouin fiber oscillator with a cavity length of 10 m, and the stimulated Brillouin scattering pump and optical carrier signal are provided by two different tunable lasers. After the Brillouin gain spectrum interacts with the optical modulation sideband, the Brillouin fiber oscillator is used to narrow the spectral linewidth to realize narrowband microwave photonic filtering. By changing the pump wavelength, the filter passband can be tuned stably. The experimental results show that the microwave photonic filter can be stably tuned in the frequency range of 0−20 GHz. The out-of-band rejection ratio is found to be about 20 dB, and its 3-dB bandwidth and maximum Q value are 6.2 kHz and 3.222×106, respectively.To the best of our knowledge, this is the highest value of a high-Q single-passband MPF reported to date. At the same time, the MPF has the advantages of wide tunability, high side mode suppression and a simple structure.

2022, 15(4): 668-674.   doi: 10.37188/CO.2021-0196
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To understand the effects of femtosecond lasers on the optical performance of the photodetectors, the damage characteristics of a CsPbBr3 back-to-back Schottky photodetector irradiated by femtosecond pulses and its photoelectric performance under various laser energy densities were evaluated. A CsPbBr3 microcrystal film on the ITO interdigital electrode was deposited by chemical vapor deposition and a back-to-back Schottky type all-inorganic perovskite photodetector was prepared. The CsPbBr3 photodetector was irradiated by a Ti:Sapphire femtosecond laser with a pulse width of 35 fs. The damage morphology of the CsPbBr3 polycrystalline film under different laser energy densities was observed using a microscope, and the photoelectric performance of the Schottky-structure perovskite photodetector damaged under different energy densities was evaluated. Results suggest that the damage threshold of the self-made all-inorganic metal halide Schottky photodectector is as high as 2.1 W/cm2, and when the sample is slightly damaged, the photoelectric characteristics of the sample are improved to a certain extent and the spectral responsivity is broadened by 50 nm. As part of the film is heated off, the sample still maintains a certain level of detection performance.

2022, 15(4): 675-688.   doi: 10.37188/CO.2022-0124
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In order to effectively integrate the spectral saliency information of infrared and visible light images and improve the visual contrast of the fused images, a fusion method of infrared and visible light images based on weighted visual saliency and maximum gradient singular value is proposed in this paper. Firstly, the new algorithm uses the rolling guidance shearlet transform as a multi-scale analysis tool to obtain the approximate layer components and multi-directional detail layer components of the image. Secondly, for the approximate layer components that reflect the energy characteristics of the image subject, visual saliency weighted fusion is used as its fusion rule. This method uses the saliency weighted coefficient matrix to guide the effective fusion of spectral saliency information in the image, and improves the visual observation of the fused image. In addition, the principle of maximum gradient singular value is used to guide the fusion of detail layer components. This method can restore the gradient features hidden in the two source images to the fused image to a great extent, so that the fused image has clearer edge details. In order to verify the effectiveness of this algorithm, we have adopted five groups of independent fusion experiments. The final experimental results show that this algorithm has higher contrast and richer edge details. Compared with the existing typical methods, the objective parameters such as AVG, IE, QE, SF, SD and SCD are improved by 16.4%, 3.9%, 11.8%, 17.1%, 21.4% and 10.1%, respectively, so it has better visual effect.

2022, 15(4): 689-702.   doi: 10.37188/CO.2021-0211
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Active optical imaging detection is an important method for seabed topography and environment detection, which is widely used in ocean exploration. However, due to the attenuation effect of light in seawater, the optical images often suffer uneven illumination, color distortion and low contrast. According to the property of underwater active optical imaging, an underwater image enhancement method based on relative radiometric correction is proposed in this paper. The procedure is divided into brightness compensation and color restoration. In brightness compensation, according to the imaging characteristics and radiation attenuation mechanism of a point light source, the relative radiation correction is used to compensate for the channels of underwater images. This stage eliminates the brightness distortion caused by an uneven light source, varying optical paths and so on. In the color restoration, adaptive compensation and rough color balance are performed first on the red channel. Then, the Retinex model is used to restore colors. The real seabed images are used for experiments. The results show that the enhanced images by the proposed method have uniform brightness and natural look. Compared with the other methods, the results of the proposed method are better overall both subjectively and objectively. At the same time, the method proposed in this paper does not need the properties of light source, camera and others. Only the real detection images themselves are used for correction, and achieve better adaptability.

2022, 15(4): 703-711.   doi: 10.37188/CO.2022-0009
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Micro-Electro-Mechanical Systems (MEMS) have the characteristics of miniaturization and high integration. As the high aspect ratio of MEMS increases, the measurement of MEMS feature size faces greater challenges. Through-focus Scanning Optical Microscopy (TSOM) technology is a high-precision and nondestructive optical measurement method. TSOM images are captured along the scanning direction by collecting a set of defocused images and the size information of the structure is extracted from TSOM images by the library matching method. This method is highly sensitive and suitable for nano-scale structure measurements, but it is difficult to build a database for micron-scale features and is susceptible to environmental interference. In this paper, a TSOM optical system is established and traditional optical microscopy is used to collect a set of defocused images. The TSOM’s feature vector set is obtained by the image feature extraction method and is combined with machine learning to establish MEMS groove regression prediction models with different feature sizes. The results show that the above method can achieve nano-scale high precision measurement of a MEMS groove width and the single point repeatability measurement has great performance. The Relative Standard Deviation (RSD) of 2 μm width is about 1%, and the RSD of 10 μm and 30 μm width are respectively lower than 0.2% and 0.35%. This method has very high application prospects for micron MEMS groove structure measurement.

2022, 15(4): 712-721.   doi: 10.37188/CO.2022-0042
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This paper aims to meet the new requirements of modern analytical and testing technology development, and to promote the application of Laser-Induced Breakdown Spectroscopy (LIBS) in the field of element analysis, especially for the measurement of rare earth element in soil. A LIBS system combined with calibration curve method was used to quantitatively analyze samarium (Sm) in the soil of Bayan Obo rare earth mining region. Firstly, the samples containing 1%, 5%, 10% and 20% Sm2O3 were prepared by Standard Addition Method (SAM) with the soil of national standard material GBW07402a as the base. Secondly, through analyzing the substrate excited by different laser pulse energy parameters, the influence of laser pulse energy parameters on the spectral line intensity and Signal to Back Ratio (SBR) was researched, an optimum laser pulse energy parameter was finally selected for the next measurement. Thirdly, in order to get and study the linearity of the calibration curve constructed between the peak area and the Sm concentration, the original spectra data were processed with multiple peak Lorentz fitting method without background subtraction (MFM) and Concatenation-based Integration Method (CIM) with background retention, respectively. Finally, according to the calibration curve, the concentration prediction was carried out, and the detection performance of LIBS for Sm in soil samples of rare earth mining area was preliminarily evaluated. The results show that the matrix effect of the soil can significantly broaden the emission lines of Sm element, which makes it impossible to distinguish them from each other. However, the effect of the soil matrix on sodium (Na), potassium (K), Titanium (Ti) and iron (Fe) is much weaker than that on Sm. By comparing the spectral region of interest, the 410 nm-band and 470.44 nm emission lines were identified and selected as the analysis lines, and subsequently used for quantitatively analysis. Results show that calibration curves for Sm element constructed by the peak area and concentration have good linear correlations and most of the linear relationships of the regression coefficients (R2) for the Sm emission lines are better than 0.99. Compared with the results by using MFM, CIM could obtain better linear correlation, and the maximum of was 0.99927 for the 410 nm-band. The better analytical predictive skill of LIBS measurement by using the leave-one-out method with CIM data was found as well, the relative errors of the prediction for both the analysis lines were all within 1% for the 3# sample with the Sm concentration of 4.310%. The achievements of this study demonstrate that the LIBS spectral analysis is capable of monitoring special elements in the rare earth mineral sample, which meets new requirements of modern analysis technology, and provides an experimental basis for the development of portable rare earth element detector as well.

2022, 15(4): 722-730.   doi: 10.37188/CO.2021-0226
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Oxide Vertical Cavity Surface-Emitting Lasers (VCSELs) are widely used in data communication. However, VCSELs are sensitive to ElectroStatic Discharge (ESD), which is one of the main reasons for their failure. It is difficult to identify the root cause of this problem. Therefore, 3 different ESD models including Human Body Model (HBM), Machine Model (MM) and Charge Device Model (CDM) and Electrical OverStress (EOS) shocks were applied to carry out the failure analysis of oxide VCSELs. Among them, voltage shocks of different polarities were used for HBM while reverse I-V, forward L-I-V scan, emission microscopy (EMMI) and Transmission Electron Microscopy (TEM) were used for characterization. The results show that different ESD models show significantly different damage voltage thresholds, and the oxide VCSEL is susceptible to damage in the HBM and MM models but insensitive in the CDM model. Defect characteristics associated with ESD failure were found including increased reverse leakage, degradation of optical output power, and bright spots in the EMMI. TEM was the most direct and effective method where different ESD events showed different defect sizes and locations. These research results are of great significance to confirm whether the failure mode is caused by ESD and to judge the specific ESD models in detail.

2022, 15(4): 731-739.   doi: 10.37188/CO.2021-0197
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The rapid detection and identification of organic macromolecules can be realized by using the unique fringerprint spectrum of the terahertz band, but the measurement of terahertz absorption spectrum of trace analyte is still challenging. We proposed a detection scheme of enhancement of terahertz absorption spectrum for trace organic analyte based on angle multiplexing of the dielectric metasurface. The substrate and the cross-unit structure of metasurface are both high-resistance silicon which has high-Q resonances. The resonance frequency of the metasurface under terahertz incident with different angles can cover 0.50−0.57 THz. When a lactose film with the thickness of 0.5−2.5 μm as analyte is placed on the metasurface, the amplitude of the resonance peak corresponding to each incident angle changes greatly with the absorption spectrum of the analyte. The enhanced absorption spectrum built by the resonance frequencies envelope is 82.59 times larger than that without the cross-unit structure. The simulation results show that the metasurface has great potential to enhance the terahertz absorption spectrum through angle multiplexing, and it can be used to detect trace organic substances with different characteristic peaks after optimized design.

2022, 15(4): 740-746.   doi: 10.37188/CO.2022-0005
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As an important parameter of high-precision optical films, thickness uniformity plays a vital role in their performance. Large-size high-precision reflective films have especially high requirements for thickness uniformity. In this paper, the efficiency and accuracy of the uniformity correction of thin films are greatly improved by studying the emission characteristics and film thickness distribution of the evaporation source, combining Mathcad software to establish precise mathematical and physical models, writing automatic programs, and simulating the correcting mask shape. Through this method, an aspherical deep ultraviolet reflector with a diameter of 320 mm is prepared on public autobiographical planetary evaporation deposition equipment. The average reflectance at 240−300 nm ultraviolet waveband is greater than 97.5%, and the uniformity is better than 0.5%. This research provides a theoretical basis and technical support for the uniformity correction of large aperture aspheric films.

2022, 15(4): 747-760.   doi: 10.37188/CO.2021-0164
Abstract(384) FullText HTML(241) PDF 10804KB(185)
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To ensure the imaging quality of the off-axis three-mirror space telescope during the ground adjustment and on-orbit adjustment stages, we reveal the coupling characteristics of the effect of the axial misalignment and the lateral misalignment on aberration based on the Nodal aberration theory from the internal mechanism level. This paper focuses on the compensation relationship generated by the coupling characteristics of two types of misalignments: (1) axial misalignment compensates for lateral misalignment, which reveals a type of working condition where the system image quality may be at a local extreme during the alignment process on the ground; (2) lateral misalignment compensates for axial misalignment. A compensation strategy wherein astigmatisms and comas introduced by in orbit lateral misalignment can compensate for astigmatisms and comas induced by axial misalignment is proposed (defocus cannot be corrected). Taking the off-axis three-mirror system in the laboratory as an example, the accuracy of the analytical relationships can be verified. Simulations and experiments have proven that the imaging quality of the system may reach the diffraction limit (1/14λ), but the system’s image quality is at a local minimum in the presence of both axial and lateral misalignment. When the telescope is misaligned in orbit and the defocus is small, the system image quality can be corrected by properly aligning the lateral misalignment first. The RMS wavefront error after compensation changes less than 0.02λ compared with the design state (the best state of installation and alignment).

2022, 15(4): 761-769.   doi: 10.37188/CO.2022-0018
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In space gravitational wave detection, the telescope is an important part of the space laser interferometry system. The wavefront error at the exit pupil of the telescope is coupled with the Tilt-To-Length (TTL) noise, which becomes the main source of noise in space gravitational wave detection. Firstly, based on the interference model between a flat-top beam and a Gaussian beam, the Fringe Zernike polynomial is used to characterize the wavefront error at the exit pupil of the telescope, and the LISA Pathfinder (LPF) signal is used to analyze the coupling mechanism of the wavefront error at the exit pupil and the TTL noise. Secondly, the Monte Carlo analysis method is used to study the influence of the proportion of low-order aberrations on the TTL coupling noise under different numerical wavefront errors, and determine the low-order aberration proportions which meets the requirements of TTL coupling noise control at the exit pupil in the design of the telescope optical system under different numerical wavefront errors. Finally, based on the above theoretical analysis results and the aberration control requirements, the optical design of the space gravitational wave detection telescope is completed. The diameter of the entrance pupil of the telescope is 200 mm, and the RMS value of the wavefront error at the exit pupil is 0.01908λ. The proportion of low-order aberrations is not higher than 50%. The analysis results show that the TTL coupling noise does not exceed 8.25 pm/μrad when the beam jitter is within ±300 μrad. Through tolerance analysis, the maximum TTL coupling noise is determined to be 15.50 pm/μrad, which meets the requirements of space gravitational wave detection.

2022, 15(4): 770-779.   doi: 10.37188/CO.2021-0209
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At present, the mobile camera has the ability to obtain imaging information in the space (x-y direction) and depth (z direction) dimensions while the acquisition of spectral information has been stuck in RGB tricolor. Limited by the size of the mobile platform, the traditional imaging spectrometer is difficult to be embedded. Based on the integrated manufacturing technology of multi-channel array filters, micro-lens array imaging and integration, this paper completes the overall design of the system, the design and manufacture of the key components and overall assembly. The spectral imaging is verified experimentally. The overall physical size of the system is less than Φ6 × 6 mm, the spectral resolution is 8nm, and the spectral range is 0.53−0.68μm. The experimental results show that the spectral curves of any part of the object can be obtained by imaging the object with different colors, which verifies the design index of the snapshot spectrometer. With the basic conditions of embedding the technology into mobile phones, the system is expected to promote the integrated applications of imaging spectrometers.

2022, 15(4): 780-788.   doi: 10.37188/CO.2022-0023
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In order to meet the requirements of long and highly precise heat flux measurement under laboratory conditions, a new radiative heat flux meter was developed based on the principle of electrical substitution measurement. The radiative heat flux meter can be traced to the International System of Units through self-calibration. Firstly, the system structure of the radiative heat flux meter is briefly described. Combining with the measuring principle of the radiative heat-flux meter, the measurement uncertainty of nine uncertainty components and their combined standard uncertainty in the process of radiative heat-flux meter self-calibration are analyzed and calculated. Then, the uncertainty of a radiometric heat-flux meter is verified by direct comparison with a standard detector calibrated by the National Institute of Metrology of China. Finally, according to the experimental data and analysis results, this paper provides a reference for the optimization design of the heat-flux meter. The experimental results show that the relative standard uncertainty of the radiative heat-flux meter is better than 0.26%, and the normalized error is 0.60, which verifies the validity of the uncertainty evaluation results. The experimental results will guide the development of radiative heat flow meters in the next stage and further improve its performance.

2022, 15(4): 789-796.   doi: 10.37188/CO.2022-0064
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For high-precision refractive index measurements of amorphous fluids, the minimum deviation angle method was used to design a novel thermostatic hollow trigonal prism device. The optical path and thermostatic compenents of the device are precisely designed. The device can be used not only to measure the refractive index of liquids, but also to quantify the measurement results and uncertainties. Firstly, the precise design and machining of the optical plane helps to precisely control the measurement light. Secondly, the tortuous hollow tube inside the thermostatic jacket is designed, which allows temperature fluctuations and uniformity of the liquid to be sufficient for high-precision refractive index measurements. Finally, the device is applied to measure a liquid’s refractive index, and the measurement uncertainty of each influence factor is quantitatively analyzed. The experimental results show that the refractive index measurement of three liquids, namely water, isooctane and tetrachloroethylene, could achieve an accuracy of 10−7 at 10−5 of uncertainty. Thus, the device provides a method for highly-precise measurements of the refractive index of liquids.

2022, 15(4): 797-805.   doi: 10.37188/CO.2021-0234
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Considering that the aperture of a monoblock telescope is limited in size, to build an aperture telescope that is greater than ten meters, the technology of segmented mirrors should be used. Therefore, the co-phasing detection technology of segmented mirrors has become the key technology in the segmented process and in maintaining the mirror quality. To solve the problem that the broadband method demands a long time consuming and the narrowband method has a small range in the most widely accepted broadband and narrowband shack Hartmann method, a new method is proposed combining the incoherent and coherent diffraction patterns of broadband light (400−700 nm) to realize coarse co-phasing of 250 nm precision and fine co-phasing of 10 nm precision. When a segmented mirror is coarse co-phasing, the incoherent diffraction pattern of two hale circular holes is used as a template and white light is used as the light source. The cross-correlation algorithm is used to calculate the value of cross-correlation coefficient, and then it can achieve the unlimited range and a detection precision of 0.25 μm by setting a reasonable threshold value for the cross-correlation coefficient. When segmented mirror is fine co-phasing, a disk pattern of white light instead of multiple coherent diffraction patterns with different piston errors is used as a template to achieve a range of 0.27 μm and a detection precision of 0.01 μm. The theoretical and simulation results show that the detection range is the range of actuator and the measurement accuracy is less than 10 nm. Both the theoretical analysis and simulation show that this method is suitable for the detection of a coarse and fine co-phasing of segmented mirror.

2022, 15(4): 806-811.   doi: 10.37188/CO.2022-0112
Abstract(96) FullText HTML(50) PDF 4899KB(64)
Abstract:

In this paper, the drive control circuit using C8051F120 and CPLD single chip microcomputer is optimized and designed based on the performance test of brushless DC motor. By using the minimum torque ripple control method of PWM_ON, both the speed and position closed-loop control of brushless DC motor are realized. The experimental results show that the designed control system has the characteristics of fast response and high station accuracy. The speed fluctuation is less than 7% at low speed of 1°/s, and the accuracy of large angle position step is less than 1 code. The proposed method has realized wide speed range and high precision control of brushless motor and the effectiveness of the drive and algorithm is verified.

2022, 15(4): 812-824.   doi: 10.37188/CO.EN.2022-0001
Abstract(115) FullText HTML(68) PDF 7507KB(51)
Abstract:

The mapping relationship between the mode shapes of a plastic landmine’s upper casing and its laser speckle interference signal was studied. The mode shape function of a landmine’s upper casing is established according to the vibration equation of its thin circular plate. Then, based on the principle of laser shearing speckle interference and the time-average method of a CCD camera, we mapped the out-of-plane displacement of the mode shape to the phase of the interference laser. The study shows that the different mode shapes of the landmine correspond to the unique Bessel fringes. Furthermore, the Bessel fringes of two modes are simulated, and the corresponding experiments were carried out. Both the numerical and experimental results confirm the theoretical conclusions, the research in this paper can provide theoretical evidence for realizing the rapid scanning technology of acoustic-optics landmine detection.

2022, 15(4): 825-834.   doi: 10.37188/CO.EN.2021-0011
Abstract(287) FullText HTML(181) PDF 3442KB(85)
Abstract:

2022, 15(4): 835-844.   doi: 10.37188/CO.EN.2022-0003
Abstract(137) FullText HTML(102) PDF 6927KB(83)
Abstract:

Stimulated Brillouin scattering in As2S3 photonic crystal fibers was investigated at wavelengths of 2 μm to 6 μm by the finite element method. The numerical results indicate that the proposed photonic crystal fiber can maintain single-mode operation when the air filling factor is less than 0.6. The Brillouin frequency shift is mainly influenced by the pump wavelength and fiber structure. The Brillouin frequency shift decreases by 4.16 GHz when the pump wavelength is increased from 2 μm to 6 μm, while the Brillouin frequency shift changes by the order of megahertz when the rate of air filling increases from 0.5 to 0.6. The FWHM of the Brillouin gain spectrum depends on the phonon lifetime, and the FWHM of the Brillouin gain spectrum is nine times wider at a pump wavelength of 2 μm than that at a pump wavelength of 6 μm. The maximum Brillouin gain of the proposed fibers with air filling fractions of 0.5 and 0.6 are 2.413×10−10 m/W and 2.429×10−10 m/W, respectively. The Brillouin threshold is positively correlated with the pump wavelength for the same effective fiber length, and is 27.8% and 19.6% larger at a pump wavelength of 6 μm than that at 2 μm with air fill factors of 0.5 and 0.6, respectively. The numerical results are of great significance for the design and fabrication of optical devices or optical sensors based on the proposed fibers in the mid-infrared band.

2022, 15(4): 845-861.   doi: 10.37188/CO.2021-0201
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In order to control the group velocity of slow light, a graphene plasmon time crystal slow light waveguide was constructed and used for the waveguide to construct the Zigzag topology interface channel for transmission. When the structure is fixed, the external bias voltage of the graphene nano-disk can be dynamically adjusted to obtain the dispersion curves at different times. The corresponding group velocity is studied. First, the graphene plasmon time crystal is obtained by applying the bias voltages periodically varying with time to different regions of the honeycomb arranged graphene nano-disks. When the time translation symmetry of the crystal is destroyed, the crystal band gap will periodically appear and disappear with time, and exhibit the band topology effect. The Zigzag topology interface is constructed to analyze the topological interface state and its slow light mode existing at different moments. Then the corresponding group velocity is calculated according to the dispersion curve. Finally, a slow light waveguide model is established through numerical simulation, and the field enhancement process is detected at the light energy capture point of the waveguide. Simulation results show that the waveguide designed based on the graphene plasmon time crystal can achieve a good slow light transmission effect, and the group velocity of the light can be dynamically adjusted when the waveguide structure is fixed. Under slow light transmission, the light energy capture point realizes the field enhancement effect. The slow light waveguide with simple structure can be dynamically tuned, and has broad application prospects in slow light modulation devices and optical storage devices.

2022, 15(4): 862-862.
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2022, 15(4): 609-624.   doi: 10.37188/CO.2021-0219
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The high temperature sensor of the optical fiber Fabry-Perot interferometer has the advantages of small size, a simple manufacturing process, high sensitivity, high temperature resistance and anti-electromagnetic interference, which make it widely used in the aerospace energy industry, environmental monitoring and other fields. Firstly, this paper introduces the sensing principle, sensing performance, sensing characteristics and fabrication method of optical fiber Fabry-Perot interferometer high temperature sensors. Secondly, the temperature, pressure and strain sensitivity and measurement range are summarized and the domestic and foreign research progress and the performance parameters of optical fiber Fabry-Perot interferometer high temperature sensors are summarized. Thirdly, the cross-sensitivity problems of temperature and pressure of optical fiber Fabry-Perot interferometer sensors and it’s solutions, and the high-temperature sensing characteristics of Fabry-Perot interferometers based on different kinds of optical fibers are introduced. Fourthly, according to the recent research progress of fiber Fabry-Perot interferometer high temperature sensors, several fiber Fabry-Perot interferometer high temperature sensors for two-parameter measurement are introduced. Finally, the future development trend and prospect of optical fiber Fabry-Perot interferometer high temperature sensors are prospected.

2022, 15(4): 625-639.   doi: 10.37188/CO.2021-0195
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Laser protection materials are of great significance in protecting human eyes and optical components from strong laser pulses. Among them, solid optical limiting materials based on the principle of nonlinear optics will be the main carriers for laser protection. This article introduces the research background, working mechanism, parameters and testing techniques of optical limiting materials, and reviews the research progress of various optical limiting materials with practical prospects, including inorganic semiconductor materials, conjugated organic polymers, inorganic metal clusters, carbon nanomaterials, and two-dimensional materials. And the development prospects of optical limiting materials are discussed.

2022, 15(4): 640-659.   doi: 10.37188/CO.2021-0191
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Polyvinylidene fluoride (PVDF) and its copolymers films have been extensively used in photoelectric functional devices such as photoelectric conversion, optical regulation, optical switch. They are the most important polymeric ferroelectricity materials with excellent electro-active properties, high diffraction efficiency and significant nonlinear optical effect. We summarize the progress in nonlinear optical effect of polyvinylidene fluoride and its copolymers films both in domestic and foreign research within the last several years. We illustrate that the development direction of the films will be nanoscale-doping, blending modification and ultrathin. The nonlinear optical properties should be investigated by the first-principle and photonic band gap calculations, and measured by the means of the high sensitivity Z-scan, Marker fringe combing with ellipsometry. This study can provide an insight for the development and utilization for polyvinylidene fluoride and its copolymers films in future.

2022, 15(3): 405-417.   doi: 10.37188/CO.2021-0198
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Terahertz (THz) imaging technology has recently become one of the most cutting-edge technologies in many fields and has made great progress in its development over the past two decades. With the increasing demands of scientific research, medical treatment, military and industrial applications, high-resolution THz images have become indispensable. To obtain high-resolution THz images, super-resolution imaging has become a research hotspot. In this paper, the imaging methods of a THz system are reviewed, including continuous wave imaging and pulse wave imaging. On this basis, THz super-resolution imaging systems and THz signal processing technologies are described in detail. The super-resolution imaging systems include near-field imaging, super lens and terajet effect, etc. The THz signal processing technologies could be grouped as either super-resolution reconstruction and convolution calculations. Finally, the shortcomings of current super-resolution imaging technologies were discussed. There are still some bottlenecks that need to be resolved such as the high manufacturing process requirements of the system, the slow acquisition speed, and the low resolution of the learning samples used to reconstruct images. With this analysis, the research direction of super-resolution imaging is proposed.
2022, 15(2): 161-186.   doi: 10.37188/CO.2021-0143
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Optical Systems using aspheric components (especially for free-form ones) have remarkable advantages over traditional spherical systems in that they can satisfy complicated requirements with simple optical-mechanical structures relying on abundant optional design parameters. Surface testing is an essential process for ensuring accuracy in manufacturing. Therefore, plenty of testing methods have been developed to meet varying testing demands of different types of surfaces at different stages in manufacturing. This paper summarizes the history of aspheric surface testing technology, classifies available techniques by whether they use interferometry, then introduces corresponding technical indexes, applicable conditions, research progress and applications. This paper highlights the high-precision interferometric methods, basic principles, optical layout and testing performances of every measurement method classified into Null and Non-null testing. The pros and cons of each method are compared, relative algorithms are introduced and precise adjustment methods are discussed.
2022, 15(2): 187-209.   doi: 10.37188/CO.EN.2021-0012
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Oxide Vertical Cavity Surface Emitting Lasers(VCSELs) are widely used in high-speed optical communications. The reliability of VCSELs is a very important index that requires a high lifetime and low failure rate in the application process. Understanding the root causes and mechanisms of VCSEL failure is necessary and helpful to improve device reliability. In this paper, we summarize and analyze the most common failure modes, causes and mechanisms observed in oxide VCSELs from the perspective of design, manufacturing and application, then apply some appropriate measures and suggestions to prevent or improve them. Moreover, the three dominating factors leading to the failure of VCSELs including oxide layer stress, Electronic Static Discharge (ESD) and humidity corrosion are introduced in more detail. At last, we simply introduce the VCSEL failure cases encountered in the actual accelerated aging verification process. This article can be used as a good VCSEL failure analysis library for chip development and production researchers.
2022, 15(2): 210-223.   doi: 10.37188/CO.2021-0176
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With the development of the computer vision technology, research on recording and modeling the real world accurately and efficiently has become a key issue. Due to the limitation of hardware, the resolution of a point cloud is usually low, which cannot meet the applications. Therefore, it is necessary to study the super-resolution technology of point clouds. In this paper, we sort out the significance, progress, and evaluation methods of 3D point cloud super-resolution technology, introduce the classical super-resolution algorithm and the super-resolution algorithm based on machine learning, summarize the characteristics of the current methods, and point out the main problems and challenges in current point cloud data super-resolution technology. Finally, the future direction in point cloud super-resolution technology is proposed.
2022, 15(1): 1-13.   doi: 10.37188/CO.2021-0115
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Electro-optic modulators based on lithium niobate (LiNbO3, LN) thin-film platforms are advantageous for their small volume, high bandwidth and low half-wave voltage. They have important application prospects in the field of optical fiber communication and optical fiber sensing, and thus have became a heavily researched topic in recent years. In this paper, the research progress of the waveguide structures, coupling structures and electrode structures of LN thin-film modulators are reviewed in detail. The fabrication process of a LN thin-film waveguide is summarized, and the performances of different modulator structures are analyzed. Based on SOI and LNOI, a platform modulator is realized with VπL<2 V∙cm, a bilayer inversely tapered coupling scheme achieves a coupling loss <0.5 dB/facet , and a traveling wave electrode structure achieves a modulation bandwidth >100 GHz. Thin-film LN modulators are better than commercial LN modulators in most aspects. It can be predicted that in the near future, with the further improvement in waveguide technology, thin-film LN will become a popular scheme of LN modulators. Finally, the potential directions for the future of their research are proposed.
2021, 14(5): 1039-1055.   doi: 10.37188/CO.2021-0003
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Two-dimensional (2D) materials provide new development opportunities for silicon-based integrated optoelectronic devices due to their unique structure and excellent electronic and optoelectronic properties. In recent years, 2D material-based photodetectors for hybrid-integrated silicon photonics have been widely studied. Based on the basic characteristics of several 2D materials and the photodetection mechanisms, this paper reviews the research progress of silicon photonic integrated photodetectors based on 2D materials and summarizes existing device structure and performance. Finally, prospects for strategies to obtain high-performance silicon photonic integrated 2D material photodetectors and their commercial applicability are presented with considerations for large-scale 2D material integrations, device structure, and metal-semiconductor interface optimizations, as well as emerging 2D materials.
2021, 14(5): 1056-1068.   doi: 10.37188/CO.2021-0071
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Optical Frequency Comb (OFC) possesses unique time(frequency) domain characteristics such as narrow pulse width, high frequency precision, stable frequency comb teeth and well-defined optical coherence, etc. Therefore, it has become a hot research topic in various fields including ultra-fast laser technology and metrology science in recent years. Meanwhile, OFC has also been developed into an important scientific research instrument. Recently, a novel light source based on the coherent synthesis of OFCs has been developed, which can realize the periodical, high-speed (up to radio frequency) and stable modulation of the polarization or the orbital angular momentum of light. In this review, we try to introduce recent developments on the fundamental principles, experimental techniques and characterization methods of the novel light source based on the coherent synthesis of OFCs, starting from the basic concepts of OFC and mainly covering two aspects: polarization modulation and orbital angular momentum modulation respectively. We also try to provide some perspectives on the applications of OFC based on the coherent synthesis techniques in the fields of solid-state spectroscopy, optical manipulation and the interaction between light and matter, etc.
2021, 14(5): 1069-1088.   doi: 10.37188/CO.2021-0044
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Because of the large size and immobility working modes, traditional spectral imaging systems struggle to meet increasingly complex practical needs. Tunable micro-nano filtering structures show unique advantages for their lighter weight and greater flexibility, so they are promising candidates for achieving adaptive and intelligent operation in the future. This article summarizes a variety of tunable filtering methodologies and their operational principles both in domestic and foreign research within the last several years. It illustrates static tunable methods such as utilizing liquid crystal and phase-change materials, some dynamic tunable filtering structures such as Fabry-Pérot cavity, micro-nano tunable grating as well as some driving approaches like mechanical stretching, electrostatic driving, optical driving, etc. Meanwhile, this article also introduces some frontier researches based on microfluidic chips and graphene. In the end, it discusses the barriers, challenges and future trends of development for tunable micro-nano filtering structures.
2021, 14(5): 1089-1103.   doi: 10.37188/CO.2021-0022
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The requirements of modern optical engineering in fields such as deep ultraviolet lithography, extreme ultraviolet lithography and advanced light sources drive the continuous development of advanced optical manufacturing technology. Modern optical engineering requires the surface roughness of ultra-smooth optical components to reach the atomic level and the surface shape profile error in the full spatial frequency to reach RMS(Root Mean Square) sub-nanometer or even a few dozen picometers. This drives the manufacturing requirements of ultra-smooth optical components to approach the processing limits. At present, there are still technical challenges to achieve the ultra-smooth polishing technology and equipment required for the above ultra-high precision needs. Atomic level ultra-smooth polishing of complex surfaces such as cylinders, ellipsoids and toroids is still a primary direction of research at both domestically and abroad. Elastic emission machining is an atomic-level ultra-smooth processing method with stable removal functionality and ultra-low subsurface defect creation, which can be used for manufacturing optical components with the above-mentioned accuracy requirements. We summarize the research progress of elastic emission machining and equipment at both domestically and abroad, the principles of elastic emission machining which contains fluid characteristics, the movement characteristics of polishing particles and chemical characteristics, the equipment of elastic emission machining, and the factors affecting the improvement of surface roughness and material removal rate of elastic emission machining. Then we analyze the problems faced by elastic emission machining and equipment and look forward to their prospects. It is expected that this paper will provide a reference for the further development and application of elastic emission machining.
2021, 14(5): 1104-1119.   doi: 10.37188/CO.2021-0033
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As the technology node of large-scale integrated circuits continues to shrink, the focus control of the lithographic tools becomes particularly difficult. In order to ensure the exposure quality of wafers, it is necessary to quickly and accurately adjust the wafer in the Depth of Focus (DOF) to a degree as small as few dozen of nanometers. For this reason, people need to carefully analyze the various factors that cause defocusing or process window changes in the lithographic process, make a reasonable focus control budget, and control the various error factors within a certain range. This paper focuses on Extreme Ultraviolet (EUV) lithography, reviews the factors that affect focus control in the optical path of an advanced EUV lithographic tool and summarizes their principles, simulation and experimental results. It can provide a reference when conducting advanced lithography focus control budget research.
2021, 14(5): 1120-1132.   doi: 10.37188/CO.2021-0125
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Tunable fiber light sources with wavelength near 1 μm are widely used in optical fiber sensing, laser cooling, photochemical, spectroscopy and medical fields. They have thus become an area of focus in fiber light source research in recent years. The development history of fiber light sources with wavelength tuning ability is firstly summarized systematically. Then, their problems and possible solutions are analyzed. Finally, the future developments of tunable fiber light sources near 1 μm are prospected.
2021, 14(5): 1133-1145.   doi: 10.37188/CO.2020-0216
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Chaotic lasers are widely used in secure communication, lidar, optical detection and other applications due to their noise-like randomness, excellent anti-interference and other advantages. Moreover, as semiconductor lasers have small size, stable structure and other advantages, it has become one of the main lasers to produce optical chaos. However, the chaotic laser output from conventional optical feedback semiconductor lasers has the problems of narrow signal bandwidth and delay characteristics, which seriously affect their applications. With consideration for these problems, a comprehensive introduction to reduce the delay characteristics and optimize the chaotic laser bandwidth are reviewed based on recent literatures. This paper also summarizes the research progresses of chaotic secret communication, which is very important in the synchronization of chaotic lasers. The chaotic output of semiconductor lasers and the applications of chaotic lasers are also summarized, and then their development and potential future applications are discussed.
2021, 14(5): 1146-1161.   doi: 10.37188/CO.2021-0032
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Augmented reality (AR) display technology has developed rapidly in recent years, and has become a research hotspot and development focus of the global information technology industry. It has the potential to revolutionize the ways we perceive and interact with various digital information. Recent advances in micro-displays and optical technologies offer new development directions to further advance AR display technology. This review analyzes the optical requirements of human visual systems for AR head-mounted displays and compares them with current specifications of AR head-mounted displays to demonstrate their current levels of development and main challenge. The basic principles and parameters of various micro-displays and optical combiners in AR head-mounted displays are introduced to explain their advantages and practicability, and their development trends are summarized.
2021, 14(4): 717-735.   doi: 10.37188/CO.2021-0030
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Nanophotonic systems have attracted tremendous attention due to their exotic abilities to freely control electromagnetic (EM) waves. In particular, much attention has been given to metasurfaces consisting of multiple plasmonic/dielectric meta-atoms coupled in different ways. Compared to simple systems containing only one type of resonator, coupled photonic systems exhibit more fascinating capabilities to manipulate EM waves. However, despite the great advances already achieved in experimental conditions, theoretical understandings of these complex systems are far from satisfactory. In this article, we summarize the theorized tools for developing nanophotonic systems including both coupled resonators and periodic metasurfaces. We aim to understand the EM properties in closed and open systems, and introduce methods of employing them to design new functional metasurfaces for various applications. We will mainly focus on works done in our own group and we hope that this short review can provide useful guidance and act as a reference for researchers in related fields.
2021, 14(4): 736-753.   doi: 10.37188/CO.2021-0095
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Exploring topological phases of matter and their exotic physics appeared as a rapidly growing field of study in solid-state electron systems in the past decade. In recent years, there has been a trend on the emulation of topological insulators/semimetals in many other systems, including ultracold quantum gases, trapped ions, photonic, acoustic, mechanical, and electrical circuit systems. Among these platforms, topological circuits made of simple capacitive and inductive circuit elements emerged as a very competitive platform because of its highly controllable degrees of freedom, lowercost, easy implementation, and great flexibility for integration. Owing to the unique advantages of electrical circuits such as arbitrary engineering of long-range hopping, convenient realization of nonlinear, nonreciprocal, and gain effects, highly flexible measurement, many of the nonlinear, non-abelian, and non-Hermitian physics can be potentially realized and investigated using the electrical circuit platform. In this review, we provide the first short overview of the main achievements of topological circuits developed in the past six years, primarily focusing on their theoretical modeling, circuit construction, experimental characterization, and their distinction from their counterparts in quantum electronics and photonics. The scope of this review covers a wide variety of topological circuits, including Hermitian topological circuits hosting nontrivial edge state, higher-order corner state, Weyl particles; higher dimensional topological circuits exhibiting nodal link and nodal knot states; non-Hermitian topological circuits showing skin effects, gain and loss induced nontrivial edge state; self-induced topological edge state in nonlinear topological circuit; topological circuit having non-Abelian gauge potential.
2021, 14(4): 764-781.   doi: 10.37188/CO.2021-0096
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Metasurface consists of the arrangement of the specially designed subwavelength nano units, which is the two-dimensional counterpart of metamaterial. Metasurface can modulate the electromagnetic field on a microscopic scale to allow the arbitrary wavefront manipulation. At present, it has been used to flexibly control various optical parameters such as phase, polarization, and amplitude. Among all of the applications based on metasurfaces, metalens is no doubt one of the most important and basic research interset. Because its thickness is on the order of wavelength, compared with traditional optical lenses, it can significantly increase the integration of optical devices and reduce the systematic complexity. However, the chromatic aberration caused by the inherent dispersion of the material of the unit structure and the diffraction effect of the structural geometry will severely influence the imaging quality of the metalens, and hence isolating us from a rich variety of advanced applications. Herein, we firstly discuss the principle of controlling chromatic aberration with metalens. Then we review several important imaging applications, including discrete wavelength achromatic, broadband focus imaging, light field imaging and other important imaging systems. Finally, this article makes some prospects for the incoming development direction and potential applications of metalens.
2021, 14(4): 792-811.   doi: 10.37188/CO.2021-0066
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In the last two decades, optical vortices carried by twisted light wavefronts have attracted a great deal of interest, providing not only new physical insights into light-matter interactions, but also a transformative platform for boosting optical information capacity. Meanwhile, advances in nanoscience and nanotechnology lead to the emerging field of nanophotonics, offering an unprecedented level of light manipulation via nanostructured materials and devices. Many exciting ideas and concepts come up when optical vortices meet nanophotonic devices. Here, we provide a minireview on recent achievements made in nanophotonics for the generation and detection of optical vortices and some of their applications.

Sponsors: the Changchun Institute of Optics, Fine Mechanics, and Physics (CIOMP), CAS

ISSN 2097-1842

CN 22-1431/O4

CODEN ZGHUC8