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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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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.
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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.
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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 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 the brightness compensation, according to the imaging characteristics and radiation attenuation mechanism of point light source, the relative radiation correction is used to compensate the channels of underwater image. This stage eliminates the brightness distortion caused by uneven light source, different optical path and so on. In the color restoration, firstly adaptive compensation and rough color balance are performed on the red channel. Then Retinex model is used to restore colors. The real seabed images are used for experiments. The results show that the proposed method has uniform brightness and natural color. Compared with the existing methods, the results by the proposed method are better overall both subjectively and objectively. At the same time, the method proposed in this paper does not need light source, camera and other characteristic parameters. Only the real detection images themselves are used for correction, and achieve better adaptability.
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In order to improve the tracking stability and accuracy of photoelectric tracking control system, the control method of photoelectric tracking servo system is studied in this paper. Firstly, in order to meet the requirements of system function and performance index, the structure of the servo turntable is designed. Then, the linear ADRC algorithm is designed, tracking differentiator and the linear extended state observer and state error feedback control law are obtained. Then, the model of tracking servo system based on ADRC algorithm is established with Matlab/Simulink, in which the position loop and speed loop adopt the second-order ADRC strategy, and the current loop adopts the PI control strategy. The simulation results show that zero overshoots can be realized during positioning tracking, and the fastest response speed can be achieved. When sudden disturbance is added, the maximum value of dynamic landing is 3%, and the sinusoidal tracking error can reach 0.02°, demonstrating that the photoelectric tracking control system based on ADRC algorithm has good results in fast response, steady-state accuracy and anti-interference performance.
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Abstract(62) FullText HTML(19) PDF 8587KB(18)
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In-situ observation and digital image correlation (DIC) analysis have gradually been widely used in the analysis of plastic deformation in metal cutting processes and become a major means of material deformation analysis due to the intuitive and accurate process of measurement and analysis. In order to meet the demand of obtaining a large observation field and making the displacement field analysis results clear and intuitive when analyzing metal micro orthogonal cutting in situ microscopy, this paper proposes an improved image size compression matching algorithm to detect and compensate for the displacement deviation between image sequences, and transform the cutting condition from the workpiece to the tool to do the feed motion. By comparing with the normalized product correlation matching algorithm, it is concluded that the proposed improved image size compression matching algorithm can significantly improve the execution efficiency and obtain high search accuracy at the same time. Finally, two images are extracted from the image sequence, and the displacement deviation compensation and DIC analysis of the displacement field in the deformation zone are performed. It is concluded that the compensation method in this paper can effectively compensate the displacement deviation caused by the feed motion of the workpiece and the vibration in the external environment, and make the relative motion trend between the sample materials in the deformation zone displacement field analysis more intuitive.
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The imaging performance and measurement accuracy of infrared radiation measurement systems are seriously affected by the non-uniformity of the focal plane array. Therefore, the non-uniformity of the raw infrared image needs to be corrected by the image processing algorithm. In order to further improve the nNon-Uniformity Correction (NUC) effect of cooled infrared detectors, an improved non-uniformity algorithm based on calibration is proposed in this paper. The algorithm is based on the single-point calibration and the two-point calibration NUC methods, which not only retains the consistency advantage of the two-point calibration NUC method in gain correction coefficient, but also combines the stability of the single-point calibration in the offset correction coefficient. The improved algorithm has a better correction effect. In order to verify the correction effect of the improved algorithm, a cooled medium wave infrared detector with a size of 640 pixel×512 pixel is taken as the research object, and an infrared imaging system with a pupil diameter of 25 mm is used to verify the performance of the proposed algorithm. The experimental results show that under the 1ms integral time, the single-point calibration method, the two-point calibration method and the improved algorithm correct the image's non-uniformity to 1.7833%, 0.2190% and 0.1481%, respectively. And under the 2 ms integral time,they correct the image's non-uniformity to 1.8257%, 2.2474% and 1.6546%, respectively. The improved algorithm further reduces the image's non-uniformity more effectively, so it's correction effect is better and the accuracy is higher.
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To meet the needs of the synchrotron radiation beamline station project under construction , a design scheme of variable cross-section bending ellipsoidal cylindrical mirror is proposed. In this scheme the calculation formula of the slope error of the variable-section (with sagittal focus) mirror is deduced based on the design theory of variable-width bending ellipticalcylindrical focusing mirrors , and the design is optimized. This project is designed based on the optical parameters of the focusing lens (object distance p, image distance q and grazing incidence angle θ), and the design error of mirror is calculated by finite element analysis software. The results show that within the given requirements, the optimal widths at both ends of the mirror are 49.5 mm and 90.5 mm. After calculating, simulating and optimizing, the slope error RMS value of the bending moments at both ends of the mirror is reduced from ~5.1368 μrad to ~0.0636 μrad (at 1 m of length), close to the system error ~0.0407 μrad, meeting the design requirements.
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In order to realize the passively harmonic mode-locking with high repetition rate in the fiber laser. A saturable absorber (SA) based on two dimensional (2D) topological insulators material of Bismuth telluride (Bi2Te3), combining with a side-polished fiber, was fabricated by laser deposition technology in this study. This device has a modulation depth of 23.96%, nonsaturable loss of 37.77% and saturable intensity of 31.5 MW/cm2. According to the adjustment of dispersion in the whole cavity and the excellent nonlinear saturable absorb character in topological insulator materials, a self-starting mode-locking is realized successfully when this SA device is applied in the Er-doped fiber laser, with a central wavelength of 1555.67 nm, pulse duration of 487 fs, repetition rate of 47.87 MHz and signal-to-noise ratio of 58 dB. A harmonic mode-locking is achieved when the pump power is over 150 mW. When we adjust and increase slightly the pump power till 250 mW, the harmonic mode-locking of 11 orders is achieved with the repetition rate of 528 MHz and the signal-to-noise ratio of 41.5 dB. These results demonstrate that with the evanescent field produced by the side-polished fiber, the damage threshold of materials can be improved and the passively harmonic mode-locking with high repetition rate is realized, which has a great significance for the materials in the application of ultrafast fiber laser with high repetition rate.
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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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At present, the mobile camera has the ability to obtain imaging information in the dimensions of space (X-Y direction) and depth (z direction), while the acquisition of spectral information has been stuck in RGB tricolor. Trapped by the size of the mobile platform, the traditional imaging spectrometer is difficult to be embedded into the mobile platform. Based on the integrated manufacturing technology of multi-channel array filter, micro-lens array imaging and integration, this paper completes the overall design of the system, the design and manufacture of key components and the overall assembly. And the spectral imaging is verified by experiments. The overall physical size of the system is less than ϕ 6 × 6 mm, spectral resolution 8nm, spectral range 0.53−0.68 μm. 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 for embedding in mobile phones, it is expected to promote the integrated application of imaging spectrometer on it.
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Because the chromatic confocal technique has no axial scanning, high measurement speed, high precision, good axial tomography ability, and good axial resolution ability, it is widely used in industrial fields such as height measurement and transparent specimen thickness measurement. However, most chromatic confocal systems are coaxial illumination structures in which the illumination optical axis and imaging optical axis are perpendicular to the tested specimen which reduces its signal-to-noise ratio and light energy utility. However, the existing inclined illumination system has high light spot drift on the imaging surface, and the measurement accuracy and application range are limited. To overcome the above shortcomings, a chromatic confocal measurement method with inclined illumination is proposed in this paper. The "V-shaped" structure is changed to a triaxial structure, and the drift of the light spot is limited by adding an adjusting branch. Also, an array color camera is used as the photoelectric receiving device, and the height value is obtained by the light spot’s color processed by a color conversion algorithm. In this study, the calibration experiment was first carried out to determine the measurement range and accuracy of the device. Then, the self-made steps and transparent specimens were measured and the corresponding measured values were determined. In order to better verify the performance of the improved system under unchanged conditions, the V-shaped system was used for comparison. The experimental results show that the axial measurement range of the system is 350 μm, and the repeatability is greater than 1.69 μm. The axial measurement accuracy can reach the micron level and the system is highly capable of measuring the thickness of transparent specimens. Through comparison, it can be verified that the system has a good suppression effect on spot drift, and the measurement accuracy of the system has been significantly improved after suppression.
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A key factor limiting the performance of Adaptive Optics (AO) systems is the Non-Common Path Aberration (NCPA) caused by the difference between the wavefront sensor path and the science imaging path. Meanwhile, a static aberration will inevitably be introduced in the common path of the AO system. This paper proposes a correction technology based on a copy of the focal-plane Point Spread Function (PSF) to correct static aberration in the scientific imaging path of AO systems. This technology uses the PSF generated by the laser point light source as the reference PSF, and copies that to the science imaging path of the AO system through iterative optimization algorithms. Experimental results show that the Strehl Ratio (SR) increases from the initial 0.312 to 0.995 after correction. This technology can still stably and quickly obtain global optimization results, especially when the initial static aberration of the system is large.
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It is a common design method to reduce the volume and mass of aerial remote sensors by using the plane mirror to replace the light path. However, the introduction of a plane mirror puts forward stricter requirements for the alignment of the aerial remote sensor. We propose an alignment method for the plane mirror system of an aerial remote sensor. The mathematical model of the theodolite measurement is established by the coordinate transformation method, and the corresponding relationship between the angular deviation (pitch deviation and azimuth deviation) of the single plane mirror assembly and plane mirror system and the measured value of the theodolite is deduced. Then a method of measuring and adjusting the angle deviation of the plane mirror system with theodolite is proposed. Finally, the pitch angle deviation and azimuth angle deviation between the lens optical axis and the normal of the focal plane mounting surface meet the index requirements of being no more than 2′. More than 10 sets of aerial remote sensor plane mirror systems have been aligned using this method, which is both convenient and efficient. At the same time, this method can provide a solution for the angle calibration and alignment of the plane mirror in various optical instruments.
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The stimulated Brillouin scattering in As2S3 photonic crystal fibers were investigated at wavelength 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 megahertz order when the air filling rate 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 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.
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In order to achieve high spectral responsivity of the silicon avalanche photodiode in blue band (400−500 nm), Separated Absorption Control Mul-tiplication (SACM) basic device structure was designed. Based on multiple physical models, the effect of the thickness on the avalanche breakdown voltage and the photocurrent gain of the device and the effect of the doping concentration of the multiplication layer on the optical responsivity were investigated. Comprehensively considering the factors of light responsivity and breakdown voltage, the results show that the device has a low breakdown voltage Vbr-apd=34.2 V when the doping concentration of the surface non-depleted layer is 1.0×1018 cm−3, and the thickness is 0.03 μm; the doping concentration of absorption layer is 1.0×1015 cm−3, the thickness is 1.3 μm, the doping concentration of field control layer is 8.0×1016 cm−3, the thickness is 0.2 μm and the doping concentration of double layer is 1.8×1016 cm−3 and the thickness is 0.5 μm. When Vapd=0.95Vbr-apd, it has higher optical responsivity in blue band, i.e. SR=3.72~6.08 A·W−1. The above research results provide certain theoretical reference for the preparation of practical Si-APD devices with high blue light detection responsivity.
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Due to the difficulty of extracting the distinguishable features of a small number of terahertz spectra with low signal-to-noise ratio; second and the over fitting problem of the deep learning model itself caused by too few samples, the application of terahertz spectra and deep learning in myocardial amyloidosis detection exists some challenges. In this paper, we propose a classification model based on multi-modules sequential cascade for real-time detection of myocardial amyloidosis at the algorithm level. Firstly, we collect a small number of low SNR terahertz spectra and preprocess them. Secondly, we construct a deep learning model based on denoising autoencoder, multi-scale feature extraction module and dense connection module. Finally, we use the 5 folds cross validation strategy to predict the lesions to obtain stable and reliable results. The results of 10 times independent repeated experiment and comparative experiment show that this method can classify the spectra with noise accurately and stably, which possesses of a better performance. Experiments under different number of samples show that this method is adaptive to the change of dataset size: an accuracy of 95% is achieved corresponding to 100 samples; when the amount of samples is only 20, the model can still achieve an accuracy of 70%. Therefore, the proposed method is of great significance for the real-time, efficient and safe diagnosis of myocardial amyloidosis.
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The three-dimensional (3D) shape measurement of highly reflective surface is one of the common problems in the field of optical 3D measurement. In this paper, a 3D measurement method of highly reflective surface based on per-pixel modulation was proposed to solve the problem that the phase information could not be obtained due to overexposure. Firstly, the positions of saturated pixels were identified by the projecting maximum gray image. Then, the coordinate matching was carried out by projecting horizontal and vertical fringes under low gray-level condition, and the optimal projecting gray value of supersaturated pixels would be per-pixel modulated by combining with a new intensity mapping relationship between camera and projector. Finally, the reconstructed and adaptive fringe projection sequences were projected, phase recovery and 3D reconstruction were realized by using the multi-frequency heterodyne phase shift method. The experimental results showed that the average error and standard deviation of the proposed method were less than the measured values obtained by other methods, and compared with the traditional method, the average error was reduced by 61.9% and the standard deviation was reduced by 67.7%. The proposed method has the advantages of high modulation, fast speed and can ensure high measurement accuracy.
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In order to improve the detection efficiency of Micro Array Electrodes (MAE) and reduce the production cost, a technology combining Digital Micromirror Device (DMD) maskless projection lithography with electrochemical deposition was proposed. Firstly, a user-defined micro array was fabricated by using the advantages of lithography system such as high-resolution PZS motion and imaging flexibility of DMD. And a uniform Au microarray electrode (Au/MAE) was fabricated after obtaining an Au conducting layer by electrodeposition. Then, the electrochemical properties of Au/MAE with different structures were compared by cyclic voltammetry, and the optimized structural parameters were obtained. Finally, the current response of optimized Au/MAE to the glucose with different concentrations and pH values was studied, and the anti-interference of Au/MAE in glucose detection was tested by chronoamperometry. The electrochemical analysis shows that the simple Au/MAE has a significant amperometric response, a strong anti-interference ability and a sensitivity of 101 μA·cm−2·mM−1 in the electrochemical detection of glucose. This method has the advantages of high resolution, high consistency, simple process and low cost, which provides a feasible operation scheme for the fabrication of biosensor array.
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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.
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The structure model (\begin{document}${\rm{ACG}}^{K_1}$\end{document}CB)NCGKC(\begin{document}${\rm{BCG}}^{K_2}$\end{document}CA)M of photonic crystal with graphene defect is constructed and the modulation effect of graphene defects on the light absorption characteristics of photonic crystals is studied by transfer matrix method and computer simulation. When graphene defect are introduced into the photonic crystal, the optical absorptivity of the photonic crystal are enhanced and an obvious narrow-band absorption peak appears. With the increase of period number M or K2, the optical absorptivity increases. When M=6, the absorptivity is 96.55%, when K2=4, the absorptivity is 43.30%. The absorption peak moves towards the short wave with the increase of M while towards the long wave with the increase of K2. With the increase of the period number K, the light absorption of photonic crystal increases to the maximum value first and then decreases, and the absorption peak moves towards the short wave. As dA, the thickness of A medium layer (monatomic silicon) increases, the optical absorptivity of photonic crystal is enhanced. When dA=178.25 nm, the absorptivity is 48.54%, and the absorption peak moves to the long wave direction; With the increase of the thickness dB of B (carbon tetrachloride) and dC of C (gallium arsenide) dielectric layer, the optical absorptivity of photonic crystals decreases. When dB=178.25 nm, the absorptivity is 33.12%, when dC=155.25 nm, the absorptivity is 25.89%, and the absorption peak moves to long wave direction. With the increase of incident angle θ, the optical absorptivity of photonic crystal first increases to the maximum and then decreases, and the absorption peak moves in the short wave direction. The result shows that graphene defects have a good modulation effect on the light absorption characteristics of photonic crystals, which provides a theoretical reference for the research and selection of novel optical absorbers, filters and total reflectors.
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In order to identify the elliptical components of space target, an ellipse detection method based on adaptive optical image is proposed. Firstly, the RL(Richardson-Lucy) method is used to restore the adaptive optics image. Next, the Arc-Support Line Segments (ASLS) method is used to detect the ellipse of the restored image. To tackle the problems of “arc segment over segmentation” and “semantic information difference” caused by Canny edge extraction, an improved edge extraction algorithm based on Multiscale Combinatorial Grouping (MCG) is proposed. Finally, for some false ellipses produced by using verification methods such as goodness measurement, a variety of geometric constraint measurement are comprehensively used to effectively eliminate the false ellipse. The experimental results show that the detection error of ellipse center point, the semi-major axis error and the direction angle error are less than 3 pixels, 4 pixels and 3 degrees, respectively. When the overlap area threshold is 0.65, the accuracy rate of this algorithm is 85.7%, the recall rate is 93.3% and the F value is 0.893. Our method is better than the traditional ellipse detection algorithms.
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In the process of structured light detection, the thin-walled blade is easy to produce a strong reflection due to its low surface roughness, which affects the solution of the principal value of the fringe phase. As a result, it cannot accurately reconstruct the three-dimensional point cloud. In this paper, the blade in the machining process is taken as the research object, and an image enhancement process based on the Retinex algorithm is proposed to restore the information of the stripes in the position with the highest reflectivity. Firstly, the reflective characteristics of thin-walled blades are analyzed. The gray range and ideal gray value of the optimal exposure are calibrated experimentally. The camera response curve model of the aperture rotation angle and the image’s average gray level is determined, and the gray level interval of the optimal exposure is used as the detection condition by adjusting the aperture and exposure time. Secondly, the fringe image is processed based on the Retinex algorithm. The improved bilateral filter replaces the commonly used Gaussian filter, which effectively retains the edge information of the fringe while removing its illumination. Finally, monocular structured light detection is carried out on the thin-walled blade. The experimental results show that, for the fringe image processed by this proposed algorithm, the number of stripes detected by the Canny operator is the largest, the average growth rate of image information entropy is 18.21%, and the phase principal value error of the solution is the smallest. Through the deviation analysis with the standard point cloud detected by the handheld laser scanner, the positive and negative deviations of the point cloud are reduced to 0.0589 mm and −0.0590 mm, which are reduced by 44.6% and 44.1% compared with the deviation of the origin cloud, respectively, and the surface quality is significantly improved. The image enhancement algorithm proposed effectively suppresses the reflection of the metal surface in the process of surface structured light detection.
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Catastrophic Optical Mirror Damage (COMD) on the cavity surface is one of the main factors that restrict the output power and reliability of semiconductor lasers. Quantum well intermixing technology is one of the most commonly used methods to avoid COMD. Si impurity-induced quantum well intermixing technology is explored for high-power, high-reliability laser diode devices. In this paper, a silicon dielectric layer is used as the diffusion source for a study of silicon impurity-induced disordering by annealing in a tube furnace. The effects of the dielectric film thickness, annealing conditions, quantum barrier material and sacrificial layer material on the wavelength blue shift of InGaAs/GaAs(P) quantum wells were analyzed. It is found that the degree of intermixing between quantum well and barrier increases with the increasing of annealing time and temperature, but is particularly sensitive to temperature. The wavelength blue shift of the InGaAs/GaAsP structure is 70.5 nm under 780 ℃ annealing temperature at a duration of 10 hours. Also, the GaAsP barrier structure has a larger blue shift than the GaAs barrier, and the epitaxial layer with an InGaP sacrificial layer has a larger blue shift than the AlGaAs sacrificial layer.
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In this study, the gradient characteristic of field-induced reorientation of nematic liquid crystal was investigated to accurately analyze the Polarization Conversion Length (PCL) and Polarization Conversion Efficiency (PCE) of an electronically controlled polarization rotator based on a liquid crystal optical waveguide. Firstly, according to the eigenvalue equation obtained from the liquid crystal magnetic field coupling equations, the corresponding relationship between PCL and the applied voltage was constructed. Then, the explicit expression of the iterative equations of the Alternating Direction Implicit Beam Propagation Method (ADI-BPM) was obtained by transverse finite-difference discretization of the electric field transmission equation, which was used to solve the propagation field in the liquid crystal optical waveguide and calculate the PCE. Finally, the eigenmode and propagation field were solved through a simulation experiment, and then the effects of the gradient characteristics of the liquid crystal director on PCL and PCE were analyzed. The results show that the effect of the gradient of the liquid crystal director on the PCL can be ignored, but the maximum PCE is about 20% lower than that of the uniform reorientation of the liquid crystal. This result will provide a certain theoretical reference for the practical development of an electronically controlled polarization rotator based on a liquid crystal optical waveguide.
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As an important parameter of high-precision optical films, thickness uniformity plays a vital role in the performance of optical films. Especially large-size high-precision reflective films have extremely high requirements for thickness uniformity. In this paper, 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, the efficiency and accuracy of the uniformity correction of thin film are greatly improved. By this method, an aspherical deep ultraviolet reflector with a diameter of 320mm is prepared on a public autobiographical planetary evaporation deposition equipment. The average reflectance at ultraviolet 240~300nm is greater than 97.5%, and the uniformity is better than 0.5%. This research provides theoretical basis and technical support for the uniformity correction of large aperture aspheric films.
Abstract(49) FullText HTML(21) PDF 4983KB(10)
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The high temperature sensor of optical fiber Fabry-Perot interferometer has the advantages of small size, simple manufacture, high sensitivity, high temperature resistance and anti-electromagnetic interference, which make it widely used in 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 research progress and the performance parameters of optical fiber Fabry-Perot interferometer high temperature sensors at home and abroad are summarized. Thirdly, the cross-sensitivity problems and solutions of temperature and pressure of optical fiber Fabry-Perot interferometer sensors and the high temperature sensing characteristics of Fabry-Perot interferometers based on different kinds of optical fibers are introduced. Fourthly, according to the research progress of fiber Fabry-Perot interferometer high temperature sensors in recent years, 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.
Abstract(61) FullText HTML(11) PDF 5490KB(14)
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In the space gravitational wave detection, the telescope is an important part of the space laser interferometry system. The wavefront error at the exit pupil is coupled with the tilt-to-length (TTL) noise, which become the main sources of noise and affects the space gravitational wave detection. First, based on the interference model between the flat-top beam and the 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 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 requirements low-order aberration design proportion for TTL coupling noise control under different numerical wavefront errors at the exit pupil of the telescope optical system. Finally, based on the above theoretical analysis results and 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 within ±300 μrad of the beam jitter. Through tolerance analysis, the maximum TTL coupling noise is 15.50 pm/μrad, which meets the detection requirements of space gravitational waves.
Abstract(25) FullText HTML(11) PDF 3119KB(3)
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The aperture of a monoblock telescope can’t be infinitely large, to build a more than ten-meter aperture telescope, the technology of segmented mirror should be used. Therefore, the co-phasing detection technology of segmented mirror has become the key technology in the segmented process and maintaining the mirror quality. To solve the problem of the most widely accepted broadband and narrowband shack Hartmann method that the broadband method has long time consuming and the narrowband method has small range, the new method which the incoherent and coherent diffraction patterns of broadband light (400−700 nm) are used to realize precision coarse co-phasing of 250 nm precision and fine co-phasing of 10 nm precision is proposed, when the segmented is coarse co-phasing, the incoherent diffraction pattern of two hale circular holes is used as template and white light is used as light source, the cross-correlation algorithm is used to calculate the value of cross-correlation coefficient, then it can achieve the unlimited range and the detection precision of 0.25 μm detection by setting a reasonable threshold value of cross-correlation coefficient; when the segmented is fine co-phasing, the disk pattern of white light instead of the multiple coherent diffraction patterns with different piston errors is used as template to achieve the range of 0.27 μm and the detection precision of 0.01 μm detection. The theoretical and simulation results show that the detection range is the range of actuator and the measurement accuracy is better than 10 nm, theory and simulation show that this method is suitable for the detection of coarse and fine co-phasing of segmented mirror.
Abstract(37) FullText HTML(10) PDF 4781KB(6)
Abstract:
Oxide vertical cavity surface emitting lasers (VCSELs) are widely used in data communication. However, VCSELs are sensitI-Ve to electrostatic discharge (ESD), which is one of the main reasons for VCSELs failure. It is difficult to dig out the root cause of the problem when device failure. Therefore, different ESD models and electrical overstress(EOS) shocks were carried out for oxide VCSELs, including three typical ESD models: human body model (HBM), machine model (MM) and charge device model (CDM). Among them, voltage shocks of different polarity were used for HBM. 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 threshold, and the oxide VCSEL is susceptible to HBM and MM damage, but insensitive to CDM model. Defect characteristics associated with ESD failure were found, including increased reverse leakage, degradation of optical output power, and bright spots in EMMI. And TEM as the most direct and effective method, different ESD events show different defect size and location. 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.
Abstract(26) FullText HTML(16) PDF 5943KB(7)
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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, and reviews the research progress of various optical limiting materials with practical prospects, from 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.
Abstract(181) FullText HTML(115) PDF 2073KB(28)
Abstract:
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 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.
Abstract(115) FullText HTML(61) PDF 3390KB(18)
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Abstract(149) FullText HTML(83) PDF 10681KB(29)
Abstract:
To ensure the imaging quality of the off-axis three-mirror space telescope during the ground adjustment and on-orbit adjustment stages, this paper uses the Nodal aberration theory to reveal the coupling characteristics of the axial misalignment and the lateral misalignment on aberration 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 lateral misalignment can compensate for astigmatisms and comas induced by axial misalignment is proposed (defocus cannot be corrected) in orbit. 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 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 0.03λ compared with the design state (the best state of installation and alignment).
Abstract(122) FullText HTML(54) PDF 4786KB(19)
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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 with a Ti:Sapphire femtosecond laser with a pulse width of 35 fs. The damage morphology of the CsPbBr3 polycrystalline film was observed using a microscope under different laser energy densities, and the photoelectric performance of the Schottky-structure perovskite photodetector after damage from different energy densities was evaluated. Results suggest that the damage threshold of the self-made all-inorganic metal halide Schottky photodetectors is high at 2.1 W/cm2, and when the sample is slightly damaged, the photoelectric characteristics of the sample are improved to a certain extent as 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.
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2022, 15(2): 161-186.   doi: 10.37188/CO.2021-0143
[Abstract](717) [FullText HTML](233) [PDF 5743KB](257)
Abstract:
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
[Abstract](504) [FullText HTML](205) [PDF 7522KB](153)
Abstract:
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
[Abstract](482) [FullText HTML](167) [PDF 6613KB](129)
Abstract:
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(2): 224-232.   doi: 10.37188/CO.2021-0142
[Abstract](227) [FullText HTML](99) [PDF 2504KB](64)
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In this paper, we introduce a prefabricabed Ag@SiO2 nanostructure directly into tellurite luminescence glass composed of 70TeO2-25ZnO-5La2O3-0.5Er2O3. We find that the maximum enhancement of visible and infrared excitation spectra intensity of (A) Ag (1.6×10−6 mol/L)@SiO2(40 nm) @Er3+ (0.5%): tellurite glass relative to (B) Er3+ (0.5%): tellurite glass is about 149.0% and 161.5%, respectively. Their maximum enhancement of visible and infrared luminescence spectra intensity is 155.2% and 151.6%, respectively. We also find that sample (A) has a larger lifespan compared to sample (B). Because the surface plasmon absorption peak of Ag@SiO2 is located at 546.0 nm, it completely resonates with the luminescence peak of erbium ions which are also at 546.0 nm. Therefore, the resonance enhancement action of Ag@SiO2 on the luminescence of erbium-doped tellurite luminescence glass is significant. Thanks to the advantages of the step-by-step realization of the silver nano core-shell structure and the production of glass, it can successfully and smoothly control the size of Ag@SiO2. It also has the advantage of strong operability in the manufacturing process of Ag@SiO2@Er: telluride luminescence glass. Its costs are also minor. Moreover, it can not only ensure that the silver is not oxidized, but it can also successfully control the distance between the rare earth ion luminescence center and the silver surface plasma. It can also successfully reduce the back energy transfer, which allows the silver surface plasma to more effectively enhance the intensity of photo-luminescence.
2022, 15(2): 233-241.   doi: 10.37188/CO.2021-0205
[Abstract](145) [FullText HTML](70) [PDF 5931KB](46)
Abstract:
In order to develop an excellent Au nanostars therapeutic agent for photothermal therapy and optical coherence tomography, we research the preparation of gold nanostars, photothermal properties, photothermal therapy and applications in optical coherence tomography. By adopting the tip structure to enhance the local surface plasmon resonance properties of gold nanomaterials, the multi-branched Au nanostars is prepared by seed mediated method. The multi-tip structure enables the Au nanostars to have obvious photothermal effect, then its effect as a therapeutic agent for photothermal therapy and contrast agent for optical coherence tomography is explored. The experimental results showed that compared with Au nanoparticles, the multi-branched Au nanostars had a higher photothermal conversion efficiency of 42%, and has good biocompatibility. At the concentration of 100 μg/mL, the survival rate of human breast cancer cells is 82%. Human breast cancer cells are effectively killed by laser irradiation at the concentration of 100 μg/mL, and the survival rate is significantly reduced to 37%. At the same time, Au nanostars also has better optical coherence tomography imaging effect, significantly improving the signal intensity and imaging depth. Au nanostars is a promising multifunctional therapeutic agent with both efficient photothermal therapy and excellent optical coherence tomography imaging capability.
2022, 15(2): 242-250.   doi: 10.37188/CO.2021-0160
[Abstract](222) [FullText HTML](67) [PDF 3935KB](61)
Abstract:
With the development of optoelectronic countermeasures and ultrashort pulse laser technology, the study of the interaction between ultrashort pulse laser and monocrystalline silicon has a very important theoretical and practical significance. In order to further clarify the damage mechanism of 532 nm picosecond pulsed laser on monocrystalline silicon, we have conducted an experimental study to measure the damage threshold, clarify the damage mechanism, and discuss the pulse accumulation effect at low flux. Firstly, using a laser with a wavelength of 532 nm, a pulse width of 30 ps and a metallurgical microscope based on the 1-on-1 laser damage test method, the zero damage probability threshold is determined to be 0.52 J/cm2. Secondly, the damage effect of a picosecond laser irradiated on monocrystalline silicon was studied under different laser fluxes, and it was found that the damage of 532 nm picosecond laser to monocrystalline silicon is manifested as heated-effect damage and plasma impact damage. The increase in energy density can be divided into three stages according to the main damage mechanism: thermal effect (0.52~3 J/cm2), thermal ablation (3~50 J/cm2) and plasma effect (>50 J/cm2), and the damaged areas are corresponded to different growth laws with the laser energy density, respectively. Finally, an experiment for the multi-pulse cumulative effect was carried out at a low laser flux and it was found that at a laser energy density of 0.52 J/cm2, the surface was irradiated continuously for 16 shots. The formation of a heat-affected zone confirms that the cumulative effect of multiple pulses can lower the laser damage threshold on monocrystalline silicon.
2022, 15(2): 251-258.   doi: 10.37188/CO.2021-0158
[Abstract](194) [FullText HTML](71) [PDF 3808KB](48)
Abstract:
The Excess Noise Ratio (ENR) of traditional noise sources is usually less than 20 dB due to the limitation of the working frequency and the power of electronic devices. To solve the problem, we propose a technology to generate a millimeter-wave noise source with a high ENR by two incoherent light beams beating. First, two optical filters are used to filter and shape the broadband amplified spontaneous emission light source. Then, the two obtained beams of amplified spontaneous radiation light with different frequencies are coupled to the photodetector for the beat frequency, which can generate electrical noise signals. A theoretical analysis predicts that a noise source with an ENR larger than 50 dB can be obtained by adjusting the optical spectral, linewidth and optical power of the two incoherent light beams filtered from an amplified spontaneous emission source under the current level of photodetector responsivity. A proof-of-concept experiment achieved a millimeter-wave noise source with an ENR higher than 50 dB. This method could also generate millimeter-wave and even terahertz-wave noise with a high ENR if a higher-speed photodetector was used.
2022, 15(2): 259-266.   doi: 10.37188/CO.2021-0232
[Abstract](145) [FullText HTML](67) [PDF 6901KB](49)
Abstract:
When a hypersonic vehicle maneuvers at a high angle of attack, the jet generated by its off-orbit engine interferes strongly with the high-speed thin atmospheric flow, and the flow field is complicated, and the infrared radiation generated by the flow field is also a landmark event in space-based infrared system detection. In this paper, aiming at interference situation of the jet flow of hypersonic flight vehicle engine and thin flow, Navier-Stokes equations are numerically solved to simulate the interference flow field, and the infrared radiation characteristics of gas are obtained by the line-by-line integration method. Combining with the backward Monte Carlo method, the infrared radiation characteristic of exhaust plume are obtained when the aircraft flight′s altitude is 94 kilometers, with no wind, different incoming flow attack angles and different velocities are considered, and the observability of low orbit satellites is evaluated. The simulation results show that for a given observation position, the intensity of infrared radiation in each band is low when there is no wind, and the maximum value is 10−9 W/m2. Under the influence of incoming flow attack angles, the infrared signal intensity of the flow field increases significantly with greater attack angle and velocities and the maximum value reaches 10−6 W/m2. The atmospheric attenuation effect has great influence on the observability of different observation positions. The results can provide reference for infrared warning and anti-missile of hypersonic vehicle.
2022, 15(2): 267-275.   doi: 10.37188/CO.2021-0170
[Abstract](161) [FullText HTML](79) [PDF 3226KB](61)
Abstract:
To improve the high false-alarm rate and poor real-time capability in detecting infrared small dim targets, a novel algorithm based on visual saliency and local entropy is proposed in this paper. This method solves the problem from coarse to fine detecting of small targets. First, a local entropy method is used to obtain the region of interest. Then, an improved visual saliency method is used to calculate local contrast. Finally, a threshold segmentation method is used to extract dim infrared small targets. The method is verified using a contrast test with TOPHAT and LCM, and the results show that the performance of this method precedes the TOPHAT algorithm and LCM algorithm. The false alarm rate by this method decreases to 62.5% and 33.3% compared with the other two algorithms, and the time cost decrease to 38.6% of that of LCM. The method can achieve accurate detection of infrared dim and small targets in a complicated environment, solving the high false alarm rate and poor real-time capability issues to some extent.
2022, 15(2): 276-285.   doi: 10.37188/CO.2021-0157
[Abstract](206) [FullText HTML](131) [PDF 4176KB](48)
Abstract:
Non-contact detection of various physiological parameters has attract great attention. In this paper, a method of estimating physiological parameters based on imaging photoplethysmography from videos of people’s faces recorded by mobile phone is proposed. First, a "wavelet transform-principal component analysis-blind source separation" algorithm is proposed to extract the video’s RGB three-channel pulse wave signal with a high signal-to-noise ratio. Then, the green channel signal is processed separately in the frequency and the time domains to estimate heart and respiratory rates. The pulse wave signals of the red and blue channels are processed, and combined with the oxygen saturation detected by an oximeter to perform data fitting, the best linear equation for estimating the oxygen saturation value from the facial video is found. Finally, the error of the estimation results of various physiological parameters under natural light is compared, and the estimation results of each parameter under three lighting environments are analyzed. The results show that under the three lighting environments, the average error of heart rate detection is 0.5512 time/min, the average error of respiration rate is −0.6321 time/min , and the average error of oxygen saturation is −0.2743%. In summary, the non-contact physiological parameter estimation method proposed in this paper is highly accurate, universally applicable and stable. Its estimation results are highly consistent with the measurement result of standard instruments, which meets the needs of daily physiological parameter measurement.
2022, 15(2): 286-296.   doi: 10.37188/CO.2021-0152
[Abstract](222) [FullText HTML](98) [PDF 3781KB](51)
Abstract:
To improve the accuracy and efficiency of the dynamic speckle metric for non-destructively detecting far-field target hit-spot intensity in a Target-In-the-Loop (TIL) system, a multi-channel cooperative detection system for acquiring speckle signals is established. The theory of dynamic speckles, the simulation model of this system and the spatial-temporal spectral fusion characteristics are also investigated. As a first step, the power spectrum is obtained by filtering, auto-correlating and Fourier transforming the intensity fluctuations of dynamic speckle detected by the point detector. Then, the feasibility of speckle-metric, obtained by multiplying the spectrum with weights, is explored to monitor the target-focused spot. As a second step, the approach of splicing the temporal signals obtained from different spatial locations on the receiving plane is proposed. Moreover, the prerequisites of this approach are listed. Finally, the effectiveness of the proposed speckle metric obtained by fusing the spectrum is verified through simulations and experiments. The results show that the speckle metric decreases with an increase in the hit-spot size, and the four-channel space-averaging metric can improve the accuracy by a factor of 2 when each group of signals is uncorrelated. Moreover, the metric obtained by spatial-temporal fusion spectrum not only guarantees accuracy but also quadruples the system’s bandwidth. Therefore, the multi-channel cooperative acquisition of the speckle metric can monitor the hit-spot change of far-field moving targets more rapidly than current solutions.
2022, 15(2): 297-305.   doi: 10.37188/CO.2021-0162
[Abstract](176) [FullText HTML](84) [PDF 2581KB](40)
Abstract:
The scattering of light by water is an important factor in the deterioration of underwater image quality. In order to quantitatively analyze the influence of water scattering under the irradiation of a specific light source, the scattering model of underwater light transmission is established, and the Fredholm integral equation for solving the distribution of underwater light field is derived. Under conditions where the light energy underwater decays exponentially with an increase in distance and the volume scattering function of the water is constant, the numerical iterative solution method of the integral equation with boundary conditions is given and the high-precision underwater light field distribution can be obtained. Taking the sun, uniform sky brightness, and underwater and overwater point light sources as examples, the calculation results of their underwater light fields when the water surface is calm are given. This method can be extended to solve the distribution of underwater light fields under arbitrary light source configurations and arbitrary boundary conditions, which lays a foundation for strictly deriving a point spread function and modulation transfer function for water bodies.
2022, 15(2): 306-317.   doi: 10.37188/CO.2021-0130
[Abstract](243) [FullText HTML](88) [PDF 4869KB](95)
Abstract:
The adaptive optical correction technology can effectively improve the beam quality of solid slab lasers, but with the increase of laser output power, the output beam aperture and the system volume increase gradually, which make the design of adaptive optical correction system more difficult. Therefore, under the premise of meeting the requirements of conjugate detection in the adaptive optical correction system, it is of certain research significance to optimize the size parameters of the detection system as a whole, and realize the detection of multiple parameters such as wavefront phase and beam quality evaluation. In this paper, we realized the multi-parameter detection of 160 mm×120 mm rectangular beam emitted by slab laser under the condition that the overall size of the system is 350 mm×180 mm×220 mm (length × width × height). According to the technical requirements of large detection apertures, limitation of tube length and long exit pupil distance, firstly, the dual-Gaussian initial structure was used to eliminate the aberration. Combined with the aspheric surface technology, the design scheme of splitting detection after high-ratio beam compression was adopted to realize the simultaneous detection and evaluation of multiple parameters. Secondly, the initial parameters of the system were determined based on the principles of telephoto imaging and conjugate imaging. Thirdly, the simulation model of the detection system was established to analyze the imaging quality and the tolerance of the system, which were implemented to provide the basis for the construction of the experiment. Finally, the experiments were carried out to verify the design results. Results indicate that the conjugate wavefront detection, light intensity uniformity detection and beam quality evaluation of 160 mm × 120 mm rectangular beam can be realized under the conditions of the object-image conjugation and size constraint conditions. In the experiment, the β factor of the measured beam is 1.24 times the diffraction limit, and the uniformity is 73.8 %, which meet the technical requirements.
2022, 15(2): 318-326.   doi: 10.37188/CO.2021-0106
[Abstract](326) [FullText HTML](136) [PDF 7371KB](49)
Abstract:
In order to realize the high-precision surface measurement of large-diameter elliptical optical flat mirrors and improve the image quality of large-aperture telescope systems, the absolute measurement algorithm for flat elliptical mirrors is studied in this paper. Firstly, the orthogonal polynomials fitting of an elliptical optical flat mirror is studied. Then, the absolute testing algorithm is studied theoretically. The orthogonal absolute testing algorithm can effectively separate the surface error of the reference mirror from the mirror to be measured, which can realize the high-precision surface reconstruction of the elliptical flat mirror to be measured. To verify the actual testing accuracy of the above method, we carried out an absolute testing simulation and experiment on a 250 mm×300 mm mirror. In the simulation, the possibility that the reference surface error is high was considered. In the experiment, a 250 mm×300 mm elliptical testing area was selected in the Zygo300 mm standard flat surface. The above-mentioned elliptical area was tested by the 150 mm Zygo interferometer, and the surface reconstruction was realized based on the above-mentioned orthogonal absolute testing algorithm. The experimental results show that the surface error separation between the reference mirror and the elliptical mirror can be achieved by using the method described in this paper, and the residual RMS (Root-Mean Square) value of the absolute testing result is 0.29 nm, which proves the feasibility and accuracy of the method described in this paper. The high-precision surface reconstruction of the elliptical flat mirror can be achieved using the above method.
2022, 15(2): 327-338.   doi: 10.37188/CO.2021-0144
[Abstract](249) [FullText HTML](133) [PDF 4328KB](51)
Abstract:
In order to correct the measurement error caused by a glass medium in high-temperature deformation measurement, we take a glass medium as a part of the camera calibration model. Based on photogrammetry technology and digital image correlation, a binocular camera calibration method in a complex environment is proposed and applied to high-temperature deformation measurements. Firstly, aiming at the calibration difficulty caused by the poor image quality in complex environments, the camera imaging model with distortion correction is adopted to achieve binocular camera calibration by bundle adjustment camera calibration method, which improves the success rate and stability of calibration. Secondly, to solve the problem of low calibration accuracy of binocular cameras in complex environments, the influence of lens focal length, ambient light interference and the distance between glass and camera on the calibration results are analyzed, and the optimal calibration parameters are given, so that the calibration reprojection error is reduced from 0.832 pixels to 0.132 pixels. Finally, the measurement error of the calibration method with and without glass is compared by using the measurement environment with a glass medium, which proves that this method can greatly reduce the measurement error. The test results show that this method can effectively reduce the measurement error of a displacement field caused by glass medium in a high-temperature environment. The maximum decrease of measurement error of the displacement field in the X, Y and Z axes is 70.16%, 76.51% and 40.05%, respectively. The method in this paper can achieve high-precision camera calibration in complex environments, and has good calibration stability. It is an effective way of realizing accurate measurement of high-temperature deformation.
2022, 15(2): 339-347.   doi: 10.37188/CO.2021-0132
[Abstract](346) [FullText HTML](124) [PDF 7406KB](84)
Abstract:
In order to obtain the true optical characteristics of a Digital Micro-mirror Device (DMD), a test method for the stray light distribution of the micro-mirror unit was proposed and an experimental device was built to test the stray light distribution of a micro-mirror unit in the 2×2 array area.First, a stray light test method is proposed. Then, in view of the small size of the micro-mirror unit and the flexible configuration mode, an illumination system with a continuously adjustable convergent spot size and an imaging system that can clearly image the micro-mirror unit was designed. Finally, the stray light distribution of the micro-mirror unit in the 2×2 array area was obtained through experimentation.The test results show that the reflection energy near the center channel of a single micro-mirror unit is strong, while the reflection energy near the edge is relatively weak. In addition, the micro-mirror unit also reflects part of the energy outside the test area. The maximum absolute stray light intensity of the micro-mirror unit in the test area appears near the central channel, and its gray value is 6.86. The maximum absolute stray light intensity of the micro-mirror unit close to the test area also appears near the central channel, and its gray value is 4.01, which indicates that the stray light near the central channel is strong. The relative intensity of stray light in the test area is relatively weak, which increases sharply from the edge of the test area and reaches the value of 293.5% after about two micro-mirror units, and then decreases sharply.
2022, 15(2): 348-354.   doi: 10.37188/CO.2021-0119
[Abstract](405) [FullText HTML](162) [PDF 5283KB](84)
Abstract:
A visible/near-infrared real-time imaging spectrometer is designed for hyperspectral imaging on the basis of an Acousto-Optic Tunable Filter (AOTF). Its operating band range is 1.3 μm, in which the visible light camera works in the 400−1000 nm band and the near-infrared camera works in 1000−1700 nm band. A Field-Programmable Gate Array (FPGA) is used as the core processing unit of the spectrometer control system. The Cameralink interface is used to collect camera data, the AOTF frequency is controlled by the serial port. Through the combination of AOTF synchronization signal and the trigger signal outside the camera, the one-to-one correspondence between a continuous image and multi-wavelength cyclic acquisition is realized. Finally, the image data is transmitted to the upper computer through the USB3.0 interface for real-time display. The field test shows that the imaging quality of the spectrometer is good and the system works stably. For images with a 1024×1024 resolution, the real-time transmission rate of the image can reach up to 120 frame/s, which meets the design requirements. In practical engineering applications, the control system has a rich interface, high reliability, flexible interface and strong expansibility.
2022, 15(2): 355-363.   doi: 10.37188/CO.2021-0089
[Abstract](427) [FullText HTML](174) [PDF 5767KB](55)
Abstract:
When a micro-milling tool has a clamping angle on its spindle, the wear of the tool edge will accelerate and shorten the tool’s lifespan. In order to accurately observe the inclination state of the micro-milling tool on the machine, a three-dimensional pose reconstruction method based on the depth of field of a micro-milling tool is proposed. The laser coaxial digital holographic experimental device is used to obtain the micro-milling tool hologram, and the reconstruction image is obtained through the Fresnel reconstruction algorithm. The tool edge points are extracted as the key points in the reconstruction image, the wavelet transform local variance operator is used to obtain the degree of focus of the key points, and then the axial position corresponding to the milling tool is determined. The least square method is used to fit the key points and correct the reconstruction error, from which the three-dimensional pose reconstruction of the micro-milling tool is realized. The experimental results show that the reconstruction error of the micro-milling tool obtained by the three-dimensional pose reconstruction method is better than 0.1°. This method can accurately measure a three-dimensional pose of a micro-milling tool, which can provide a reference for the subsequent correction of micro-milling tool clamping accuracy.
2022, 15(2): 364-372.   doi: 10.37188/CO.EN.2021-0010
[Abstract](191) [FullText HTML](92) [PDF 2384KB](32)
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In this paper, an averaged intensity and spectral shift of Partially Coherent Chirped Optical Coherence Vortex Lattices (PCCOCVLs) in biological tissue turbulence are investigated with emphasis on optical lattice structures in monochromatic optical fields and spectral rapid transitions in polychromatic optical fields. It is found that the beam profile evolves from annular structures with a vortex core into a periodic array of lobes with a dark zone, and finally presents a Gaussian-like pattern in biological tissue. Although lattice parameter modulates beam profile, it cannot affect the spectral behavior in biological tissue turbulence. The analysis of spectral shift also shows that a smaller distance is beneficial to spectral rapid transition where the transverse coordinate decreases with an increase in chirp parameter and a decrease in pulse duration. The accumulated turbulences over a longer distance can suppress not only spectral transition but also spectral shift. The reduction of spectral shift is accompanied by stronger biological tissue turbulence. The results have possible application in image recognition, medical devices and noninvasive optical diagnoses in biological tissue.
2022, 15(2): 373-386.   doi: 10.37188/CO.2021-0149
[Abstract](308) [FullText HTML](113) [PDF 4758KB](56)
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With the advantages such as simple structure, simple process and easy interface control, the photoelectric devices based on carbon nanomaterial/bulk semiconductor van der Waals (vdW) heterojunctions can fully realize the ultrahigh carrier mobility of carbon nanomaterials and the excellent photoelectric properties of bulk semiconductors. Especially, the novel mixed-dimensional vdW heterojunctions can be prepared by controlling the diameter/chirality and Fermi level of single-walled carbon nanotubes (SWCNTs) to form atomic-level interfaces and match bandgaps with bulk semiconductors. Here, we reported a self-powered broadband photodetector based on the pn vdW heterojunctions by combining (6, 5)-enriched semiconducting SWCNT film with n-type GaAs, and used graphene to reduce the probability of carrier recombination in SWCNT film and to promote the carrier transport. The experimental results suggest that the self-powered device exhibits high-sensitivity photoelectric response toward the incident photons in the 405~1064 nm range, and that the max photoelectric responsivity of 1.214 A/W and the specific detectivity of 2 × 1012 Jones could be achieved at zero bias.
2022, 15(2): 387-403.   doi: 10.37188/CO.2021-0174
[Abstract](149) [FullText HTML](60) [PDF 5548KB](57)
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A wide-band and narrow-band switchable bi-functional metamaterial absorber is presented in this paper. The phase change material vanadium dioxide (VO2) is introduced in the structure of the metamaterial absorber, and different functions can be achieved by using only a single switchable metasurface. The mutual conversion of different functions is realized by the reversible phase transition between the VO2 insulating state and the metal state. When VO2 is in metallic state, the designed structure can be regarded as a metamaterial wide-band absorber. The simulation results show that the absorption is over 98% in the frequency range of 1.55 THz to 2.21 THz. When VO2 is in the insulating state, the structure acts as a narrow-band absorber, and the absorption at resonance frequencies of 2.54, 2.93 and 3.34 THz is over 95%. In addition, the effect of geometric parameters on the absorption of metamaterial absorber is discussed. Because of the symmetry of the element structure, the absorber is insensitive to the polarization when the electromagnetic wave is vertically incident, and it can keep good absorption performance with the large incident angle. Therefore, the switchable bi-functional metamaterial absorber proposed in this paper can be widely used in terahertz modulation, thermal emitters and electromagnetic energy acquisition, etc.
2022, 15(2): 404-404.
[Abstract](102) [FullText HTML](53) [PDF 349KB](40)
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2022, 15(2): 161-186.   doi: 10.37188/CO.2021-0143
Abstract(717) FullText HTML(233) PDF 5743KB(257)
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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
Abstract(504) FullText HTML(205) PDF 7522KB(153)
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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
Abstract(482) FullText HTML(167) PDF 6613KB(129)
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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
Abstract(1071) FullText HTML(529) PDF 3910KB(368)
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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
Abstract(1912) FullText HTML(560) PDF 10280KB(436)
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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
Abstract(762) FullText HTML(200) PDF 5700KB(150)
Abstract:
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
Abstract(881) FullText HTML(343) PDF 12124KB(138)
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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
Abstract(636) FullText HTML(224) PDF 7589KB(112)
Abstract:
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
Abstract(1126) FullText HTML(301) PDF 4286KB(127)
Abstract:
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
Abstract(591) FullText HTML(166) PDF 6378KB(72)
Abstract:
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
Abstract(507) FullText HTML(170) PDF 6559KB(93)
Abstract:
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
Abstract(1590) FullText HTML(504) PDF 5479KB(331)
Abstract:
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
Abstract(1650) FullText HTML(293) PDF 3209KB(546)
Abstract:
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
Abstract(907) FullText HTML(387) PDF 15001KB(204)
Abstract:
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
Abstract(791) FullText HTML(160) PDF 6901KB(228)
Abstract:
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
Abstract(1098) FullText HTML(423) PDF 3489KB(299)
Abstract:
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.
2021, 14(4): 812-822.   doi: 10.37188/CO.2021-0023
Abstract(810) FullText HTML(169) PDF 4757KB(197)
Abstract:
Polaritons are half-light, half-matter quasi-particles formed by the interaction of light and different polarons. They can be applied for light-control at sub-wavelength scales and have shown intriguing potential for optical imaging, enhanced nonlinear optics and novel metamaterial design. Recent advances in the twistronics of two-dimensional van der Waals materials have enabled a vast variety of extraordinary phenomena associated with moiré physics, which also inspired new direction for the research of polaritons. In this article, we briefly review the rise of “twist-photonics”, including plasmon polaritons in twisted graphene system, exciton polaritons in a twisted transition-metal dichalcogenide system and phonon polaritons in a twisted h-BN and α-MoO3 system. Twist van der Waals materials may offer new directions to manipulate light-matter interactions at nanoscale.
2021, 14(4): 831-850.   doi: 10.37188/CO.2021-0014
Abstract(1423) FullText HTML(464) PDF 3928KB(354)
Abstract:
Traditional optical lenses and optical systems implement electromagnetic wave control based on the light propagation effect. So they usually suffer from the bulky size. Recently, metasurfaces comprised of artificial subwavelength structures have been widely studied, since they take great advantages of their subwavelength thickness and provide arbitrary control of electromagnetic waves. Here, the electromagnetic wave control mechanism is introduced. Then, we analyze the monochromatic aberrations and chromatic aberrations of the metalens and the corresponding image quality evaluation methods. Also, we discuss the research progress and applications of metalens for imaging. The exist problems and future goals are pointed out at the end of the review. Based on the advantages of portability and a high degree of design freedom, metalens are expected to replace the traditional imaging devices in many applications. High efficiency, large field of view, broadband, reconfigurable and tunable imaging devices based on metasurfaces will help in important future development directions.
2021, 14(4): 851-866.   doi: 10.37188/CO.2021-0069
Abstract(726) FullText HTML(234) PDF 4678KB(123)
Abstract:
Metasurfaces, composed of subwavelength-scale artificial nanostructures, can realize the versatile modulation of multiple attributes of light such as amplitude, phase and polarization, providing an excellent platform for nanophotonic devices. As a new type of layered material, 2D materials manifest peculiar optical and electrical properties compared to 3D bulk materials. The combination of 2D materials with metasurfaces offers new possibilities for the development of nanoscale planar optical devices. This paper reviews the development of metasurfaces based on 2D materials with atomic thicknesses, introduces the mechanism of light field modulation of various 2D material metasurfaces. An outlook on the challenges and potential applications for the development of atomic layer thickness metasurfaces are provided finally.
2021, 14(4): 867-885.   doi: 10.37188/CO.2021-0036
Abstract(959) FullText HTML(403) PDF 6720KB(218)
Abstract:
As one type of novel two-dimensional artificial micro-nano structure, metasurfaces have exhibited strong potential for application in light manipulation in recent decades. However, there is a substantial calling for next-generation optical metasurfaces endowed with remarkable reconfiguration capabilities for practical applications in increasingly miniaturized and integrated opto-electronic devices. In this paper, we review the recent progress of deformable optical metasurfaces mainly fabricated by focused-ion-beam-based nano-kirigami and focus on their excellent performance and applications in the active control of phase, polarization, optical chirality, nonlinear radiation, etc. Deformable metasurfaces with their exceptional flexibility and reconfigurability provide a novel and feasible strategy for the design of functional micro-nano-optoelectronic devices, and immensely promote the development of emerging strainoptronics.

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

ISSN 2095-1531

CN 22-1400/O4

CODEN ZGHUC8