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Performance studies on laser absorbing coating
ZHANG Lei, XIE Xian-chen, WU Yong, WANG Ping, WU Jun-jie
 doi: 10.37188/CO.2020-0154
Abstract(116) FullText HTML(38) PDF 2857KB(3)
Abstract:
A laser loading model for coating samples is established. The coupling process of the laser energy is simulated based on the parameters of the materials and the temperature rise characteristics are analyzed at different parameters. The reflective characteristics of SiCN coating on a copper substrate are then investigated. Through a series of laser radiation experiments, the laser-induced damage of the coating is examined by recording the temperature threshold for the coating. This paper provides research support for the material selection and parameter design of laser energy measurement devices.
Two-dimensional material photodetector for hybrid silicon photonics
HU Si-qi, TIAN Rui-juan, GAN Xue-tao
 doi: 10.37188/CO.2021-0003
Abstract(53) FullText HTML(12) PDF 5071KB(27)
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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 their photodetection mechanisms, this paper reviews the research progress of silicon photonic integrated photodetectors based on 2D materials and summarizes existing photodetector devices’ structures and performances. Finally, prospects for strategies for obtaining 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, and emerging 2D materials.
Saliency detection combined with selective light field refocusing of camera array
FENG Jie, WANG Shi-gang, WEI Jian, ZHAO Yan
 doi: 10.37188/CO.2020-0165
Abstract(84) FullText HTML(26) PDF 3914KB(8)
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For the multiple salient targets scene, as well as a scene in which some areas of the salient target do not contrast significantly with the background area, the saliency maps obtained by existing algorithms are not fine enough or even loses some saliency regions. In this paper, a new significance detection method combined with selective light field refocusing of camera array is proposed. In this method, the light field dataset is selected and multi-viewpoint images of the same scene are used. First, we perform refocusing rendering combined with super-resolution on the central viewpoint image. Then, on the basis of the graph-based saliency detection method, we propose a propagation model combining global and local smoothness constraints to prevent false label propagation. Finally, the obtained coarse saliency map is refined through the object map to output the final saliency map. In addition, for the scene that contains multiple salient targets, by refocusing a certain depth layer in the scene, and producing varying degrees of blurring to other depth layers, the salient targets on the depth layer can be detected accurately and in detail. To a certain extent, the optional saliency detection is realized. Experiments on the 4D light field dataset show that the average Mean Absolute Error (MAE) between the ground truth and the saliency map obtained by the method proposed in this paper is 0.2128, which is lower than existing methods. The detection result contains more detailed information about the salient target, which improves the above-mentioned shortcomings of the existing salient detection methods.
Improvement of the ultrasonic testing accuracy of laser welding fusion width
HUANG Zhi-yi, WANG Chun-sheng, HE Shuai, GU Xiao-peng, DONG Juan, XU Guo-cheng
 doi: 10.37188/CO.2020-0149
Abstract(49) FullText HTML(16) PDF 3815KB(0)
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Due to the tiny dimensions of lap laser welding joints, there is significant error in weld width detection when using the traditional 6 dB method. In order to improve the method’s detection accuracy and study its source of error, the finite element analysis method is used to analyze the propagation law of incident ultrasonic waves and reflected ultrasonic echo characteristics inside a laser-welded joint. Based on a modified 6 dB method, a laser welding joint melt width evaluation model is constructed and verified through physical experiments. The experimental results show that the primary echo amplitude of the bottom surface of the upper plate can be used as a characteristic value that reflects the internal structure of the joint. When the center of the probe corresponds to the edge of the weld fusion line inside the joint, the attenuation of the primary echo amplitude varies with the thickness of the upper plate, and the traditional 6 dB method can be modified according to the attenuation degree which related to the upper plate’s thickness. Based on this, the effective weld width at the contact surface of the inner plate of the joint can be calculated quantitatively. The ultrasonic testing results of the actual laser welding joints confirmed that the melt width of the laser welding joints obtained by the modified 6 dB method agree with the results of the physical experiments, which means that this provides a very practical method for accurate ultrasonic testing of laser welding joints in real-world production.
Review of research on orthogonal frequency division multiplexing modulation techniques in visible light communication
XU Xian-ying, YUE Dian-wu
 doi: 10.37188/CO.2020-0051
Abstract(300) FullText HTML(57) PDF 3605KB(21)
Abstract:
With its unique advantages, Visible Light Communication (VLC) can compensate for limitations in radio frequency communication, allowing it to become a recent avid topic of research. Orthogonal Frequency Division Multiplexing (OFDM) has been widely used in VLC due to its high rate of data transfer and frequency selective fading resistance. We compare the performance of several OFDM modulation techniques in VLC, including unipolar schemes, enhanced schemes and hybrid schemes based on discrete Fourier transformation, as well as optical OFDM systems based on Hartley transform and LED index modulation. We perform these comparisons in terms of energy efficiency, spectral efficiency, bit error rate, and algorithm complexity. The principles of some kinds of optical OFDM systems are firstly illustrated and their spectrum efficiencies are theoretically analyzed and compared. We also research and analysis the improved design of receivers in optical OFDM systems. The challenges and upcoming research of OFDM systems in VLC are summarized. The research in this paper can provide a research reference and propose more efficient unipolar modulation schemes to further improve the spectral efficiency and reliability of optical OFDM systems.
Luminescence properties of Bi3+ doped Lu1-xO3: x%Ho3+ metal ion phosphors
ZHAO Hai-qin, WANG Lin-xiang, TUO Juan, YE Ying
 doi: 10.37188/CO.2019-0222
Abstract(74) FullText HTML(19) PDF 4045KB(2)
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Bi3+ doped Lu1-xO3: x%Ho3+ metal ion phosphors were prepared using the high-temperature solid-phase method. The crystal structures of Bi3+ doped Lu1-xO3: x%Ho3+ phosphors, the Bi3+→Ho3+ energy transfer rule in Lu2O3 matrix and the luminescent properties of a synthetic powder at different doping concentrations were investigated. X-ray diffraction results showed that Bi3+ and Ho3+ doping had no effect on the cubic phase structure of Lu2O3. Lu2O3: Ho3+, Bi3+ phosphor emitted 5S25I8 transition of Ho3+ at 551 nm under an excitation wavelength of 322 nm, and exhibited 1S03P1 characteristic transition of Bi3+ at 322 nm and 5I85F1 transition of Ho3+ at 448 nm under an emission wavelength of 551 nm. When the doping concentration of Bi3+ was 1.5%, the effect was most effective for the energy transfer of Ho3+, which increased by a factor of 34.8 compared to that of the single-doped Ho3+ sample. For the synthesis of 1%, 1.5%, 2% Bi3+ doped Lu98.5%O3: 1.5% Ho3+ samples, the luminescence intensity at 551 nm under 980-nm excitation increased by a factor of 13.3, 16.8 and 14.2, respectively, compared to that of under 322-nm excitation. The energy transfer critical distance between Bi3+ and Ho3+ was calculated to be 2.979 nm, and the energy transfer between Bi3+ and Ho3+ was achieved by dipole-quadrupole interaction.
Research progress on the modulation properties of new electro-optic materials
LÜ Xiao-lei, ZHAO Ji-guang, DU Xiao-ping, SONG Yi-shuo, ZHANG Peng, ZHANG Jian-wei
 doi: 10.37188/CO.2020-0039
Abstract(240) FullText HTML(69) PDF 3437KB(35)
Abstract:
Polarization modulation technology based on electro-optic crystals is playing an increasingly important role in the field of three-dimensional laser imaging. Due to the low field of view and high half-wave voltage of LN materials, it is difficult for traditional electro-optic modulation technology to further improve 3D imaging performance. As the preparation technology of perovskite-structured electro-optical materials becomes more mature, electro-optic modulation technology based on new materials will become an excellent means to create a breakthrough in the detection accuracy of laser 3D imaging. PMNT, PLZT and KTN three typical materials have excellent electro-optical properties and dielectric properties that might surpass the field of view and half-wave voltage limitation. However, their applications in electro-optic modulation has lead to difficulties such as a low modulation bandwidth for PMNT, poor transmission performance for PLZT, and low practical application bandwidth for KTN. Future research will focus on the practicality of this modulation technology. The technology’s electro-optic modulation performance can be improved by doping and the signal-to-noise ratio of the system can be optimized by establishing performance characterization models.
Optical testing path design for LOT aspheric segmented mirrors with reflective-diffractive compensation
WANG Feng-pu, LI Xin-nan, XU Chen, HUANG Ya
 doi: 10.37188/CO.2020-0218
Abstract(15) FullText HTML(5) PDF 3885KB(3)
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The primary mirror of the Large Optical Telescope (LOT) is a segmented mirror with an equivalent diameter of 12 meters and a focal ratio of F /1.6, and is assembled by a variety of different types of off-axis hexagonal mirror segments. The diagonal diameter of each segmented mirror is 1.44 m. In order to achieve high precision surface testing of the large diameter and long focal length off-axis segments, we designed a reflective diffractive compensation null testing system. Using a computer-generated hologram and a spherical mirror to compensate for normal aberration of the off-axis mirror. The design’s results show that the residual wavefront error of the optical path is close to zero. For a testing system, a non-axisymmetric off-axis structure corresponding to the CGH alignment optical paths is designed to ensure the feasibility of the assembly. Parameters of testing the optical path of different off-axis distance mirrors are the same. Rapid high-precision null testing of different types of segmented mirrors can be achieved simply by replacing the CGH at corresponding positions and adjusting the spatial positions of the mirror to be measured. Error analysis shows that the RMS error of the mirror surface to be measured is better than λ/40 (λ=632.8 nm), which is caused by the manufacturing error of the compensating elements, misalignment of the optical path, repeatability of the interferometer surface measurement and standard spherical wavefront deviation of the interferometer.
Research on Multi-optical Axis Parallelism Calibration of Space Photoelectric Tracking and Aiming System
WEN Zhong-kai, ZHANG Qing-jun, LI Shuang, LEI Wen-ping, DU Guo-jun
 doi: 10.37188/CO.2020-0133
Abstract(174) FullText HTML(39) PDF 4604KB(13)
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  Objective  To achieve multi-optical axis calibration of the Space Photoelectric Tracking and Aiming System in a vacuum.  Method  this paper first designed a set of multi-axis calibration systems based on the accuracy requirements for multi-axis consistency detection of the Space Photoelectric Tracking and Aiming System. Then, a detailed error analysis of each subsystem of the multi-axis calibration system was conducted, and the methods to limit error in the key subsystem were given. After that, the technical tests of the space photoelectric tracking and aiming system of the communications technology test satellite 3 were implemented in laboratory and vacuum environments, and the error sources and test accuracy of the multi-axis calibration system in the two test environments were analyzed to produce test results. Finally, the accuracy of the multi-axis calibration system was verified.  Result  The final results show that the calibration accuracy of the multi-axis calibration system designed in this paper is 0.998" in the laboratory test environment, and the calibration error of the parallelism of transmitter and receiver is 1.165"; the calibration accuracy is 1.219" in the vacuum test environment, and the calibration error of parallelism of transmitter and receiver is 1.359".  Conclusion  These results fully meet the 1.5" multi-optical axis detection accuracy requirements of the space photoelectric tracking system, and provides support for research in related engineering applications.
Polarization lidar gain ratio calibration method: a comparison
TONG Yi-cheng, TONG Xue-dong, ZHANG Kai, XIAO Da, RONG Yu-hang, ZHOU Yu-di, LIU Chong, LIU Dong
 doi: 10.37188/CO.2020-0136
Abstract(177) FullText HTML(57) PDF 6321KB(14)
Abstract:
Gain ratio calibration error is one of the most significant factors affecting the accuracy of a polarization lidar depolarization ratio. This paper analyzes the basic principles of various existing gain ratio calibration methods and compares the advantages and disadvantages of the +45° method, ±45° method, ∆45° method, rotation fitting method and pseudo-depolarizer method in practice though experiments. Results show that: the ∆45° method, ±45° method and rotation fitting method are relatively accurate when the misalignment angle is small, but the operation of the ±45° method and rotation fitting method are more complicated. The +45° method still has a large calibration error without a misalignment angle. The pseudo-depolarizer method is the easiest to operate, but it is restricted by a non-ideal pseudo-depolarizer. Through comparison of theory and experiment, this paper provides a suggestion for the best choice of gain ratio calibration method. It is recommended that the ±45° method be used for calibration with a half-wave plate, and the pseudo-depolarizer method be used for calibration with a high-precision depolarizer.
Suppression of the influence of atmospheric turbulence during the propagation of a twisted laguerre-gaussian correlated beam
ZHANG Ying, MA Chao-qun, ZHU Shi-jun, LIU Xiao-xu, CAI He, AN Guo-fei, WANG You
 doi: 10.37188/CO.2020-0138
Abstract(148) FullText HTML(35) PDF 3876KB(5)
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During its propagation in atmospheric turbulence, the optical properties of a laser beam will be changed by the surrounding environment. Compared with a completely coherent laser, a partially coherent laser can more strongly resist the influence of atmospheric turbulence. In this study, a twisted Laguerre-Gaussian correlated beam was employed to deduce a cross-spectral density function for propagation in atmospheric turbulence. The cross-spectral density and M2 factor were also constructed by using the extended Huygens-Fresnel diffraction integral principle, Wigner distribution function, basic properties of the twisted phase, and power spectrum model of non-Kolmogorov turbulence. Then, the influence of atmospheric turbulence on the beam was numerically simulated, and the results were compared with those for different twist factors, transverse coherence parameters and mode orders. It has been demonstrated that a beam with a high twist factor, low transverse parameter, and high mode order can be used to effectively suppress the influence of atmospheric turbulence. The conclusions of this paper might be useful in improving the transmission performance of a laser beam in atmospheric turbulence.
Research on infrared dual-color filters with 3.2~3.8 μm and 4.9~5.4 μm bands
ZHOU Sheng, WANG Kai-xuan, LIU Ding-quan, HU Jin-chao, LI Yao-peng, WANG Shu-guang
 doi: 10.37188/CO.2020-0206
Abstract(66) FullText HTML(15) PDF 3966KB(2)
Abstract:
The dual-color (dual band-pass) filter is a new type of optical element that includes two precisely controlled spectral channels at any geometric position and can improve the target recognition ability of optical detection devices. Single crystal Ge is used as a substrate, and Ge and ZnSe are used as high (H) and low (L) reflective index thin films, respectively. An infrared dual-color filter is designed with two band-pass channels: 3.2~3.8 μm (channel 1) and 4.9~5.4 μm (channel 2). Thin films are fabricated by thermal evaporation in a high vacuum chamber, and the film thickness are monitored are using the POEM (percent of optical extreme monitoring) strategy. At a working temperature of 100 K, the average transmittance of channel 1 was 94.2%, and its top ripple amplitude was 5.7%. The average transmittance of channel 2 was 96.5%, and its top ripple amplitude was 0.6%. In the cut-off range between the two channels (4.0~4.7 μm), the average transmittance was no more than 0.16%. The infrared dual-color filter has good optical stability, which is conducive to the recognition of high-speed moving targets.
Pupil location algorithm applied to infrared ophthalmic disease detection
CAI Huai-yu, SHI Yu, LOU Shi-liang, WANG Yi, CHEN Wen-guang, CHEN Xiao-dong
 doi: 10.37188/CO.2020-0170
Abstract(50) FullText HTML(14) PDF 3755KB(1)
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In order to quickly, accurately and automatically locate a pupil in ophthalmic disease detection, a location algorithm for a pupil’s center based on radial symmetry transformation was proposed. Firstly, the gray integral projection method combined with the Maximum Class Square Error method was used to complete the rough segmentation of the pupil to isolate a Region Of Interest (ROI) solely containing and the pupil was extracted according to multi-lump screening conditions. Then the search radius range was set by using a minimum circumscribed rectangle on the ROI combined with gray-level morphological linear filtering. Finally, the pupil center was located using an improved radial symmetry transformation algorithm. The experimental results show that the location error of this algorithm is less than 8 pixels and the average processing time is 0.366 s. It can adapt to a large number of irrational states such as noise interference and an incomplete collection of human eye images and meets the pupil location performance requirements for many kinds of infrared ophthalmology disease detection equipment.
Rotational angle measurement of galvanometer using reflective circular grating
LIU Yong-kun, DING Hong-chang, Xiang Yang, LÜ Si-hang
 doi: 10.37188/CO.2020-0179
Abstract(85) FullText HTML(26) PDF 6003KB(5)
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In order to achieve high-precision measurement of the rotation angle of the galvanometer, an angle detection system using a reflective diffraction grating is designed, and its measuring principle, measuring process and measuring precision are designed, simulated and verified. Through a mirror designed coaxially with the galvanometer, with a reflective circular grating and a photosensitive detection device, the ±1st order diffracted light generated by the reflective circular grating is interfered to convert the angular displacement of the galvanometer into a change in the intensity of interference fringes. In this way, the measurement of the rotational angle of the galvanometer is realized. The experimental results show that the detection system can realize the measurement of the galvanometer's angle within ±10°, and the measurement accuracy is 10″. The high-precision measurement of the rotational angle of the galvanometer is realized, and the device has a compact structure to meet the requirements of the scanning galvanometer demand.
A fast blind denoising method for grating image
ZHANG Shen-hua, YANG Yan-xi, QIN Qiao-meng
 doi: 10.37188/CO.2020-0166
Abstract(62) FullText HTML(24) PDF 3473KB(5)
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The three-dimensional measurement technology based on the projection of sine grating fringe image is a hot-popic. However, due to the influence of noise, the quality of the captured grating image is worse, resulting in the disturbance of the extracted phase, which directly determines the accuracy of the measurement. Since the noise is unknown in actual measurement, a blind denoising method is proposed in this paper. Firstly, according to the residual model, the grating fringe image is separated into the true value and the noise, then the Principal Component Analysis (PCA) technology is introduced to estimate the variance of the noise. Finally, according to the estimated value of the variance, the filtering on multi-frame fringe images is replaced by employing Gaussian filtering on the phase map. In contrast to other methods, the results of the proposed method showed that the Root Mean Square Error (RMSE) decreased by 88.5% (up to most), which indicated that the phase values of the proposed method were closer to the ground-truth of the measured object. By employing the proposed method, the phase disturbance caused by noise were significantly suppressed in the shortest execution time. The proposed method can quickly deal with the phase error caused by the noise of the grating image and has strong practicability in the grating image projection measurement.
Star tracker lens mechanical automatic design system on parametric modeling
ZHU Jun-qing, SHA Wei, FANG Chao, WANG Yong-xian, WANG Zhi
 doi: 10.37188/CO.2021-0029
Abstract(13) FullText HTML(8) PDF 7714KB(0)
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In order to meet the standardized design requirements of the star tracker lens, a star tracker lens auxiliary design system based on parametric modeling was established, which shortened the product design cycle and improved the process quality and reliability of lens design. First, the design parameters of the star tracker lens designed by the optical alignment and edge removal process are chartered. Then, the parametric modeling of the optical system is carried out on the lens design, and the manufacturability indexes of the lens are calculated in real time to assist the designer to adjust the lens design reasonably. Design of structure parts carries out by parametric modeling of the revolving body polyline based on the dimension chain. The parameters include the lens installation method, orientation, structure size, etc. of the lens assembly. Assembly design combined with lens component design are automatically and graphically presented. So is the lens weight and other information. The system aided the designer by tackling massive repetitive design operations. It assists designers in rationally designing space layout and evaluating design results, thereby quickly iterating lens design. The results show that the assembly drawing design of the 9-lens star tracker lens has been reduced from about 15 hours to about 3 hours, which greatly improves the design efficiency, and guarantees the design quality and reliability, which satisfies the standard design requirements of the star tracker lens.
Blue-blocking protective optical thin films based on cutoff slope control
WANG Yu-si, ZHOU Xian-jian, LI Qing-yuan, YE Zhao-song, CAI Yuan-hai, LIU Jin-qiu, CHEN Nan, Bu Yin-kun
 doi: 10.37188/CO.2020-0212
Abstract(40) FullText HTML(22) PDF 4677KB(5)
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To reduce the damage to human eyes and ensure the beneficial regulation of the human rhythm by short-wave blue light, accurate control of the transmission slope of the 400−500 nm wavelength is particularly important in blue light protection. In this paper, a nonlinear Boltzmann function fitting method for long wave-pass thin films is proposed, and thin films (Z1) and (Z2) were obtained by optimizing the nonlinear and linear target, respectively. Admittance and transmittance diagrams of thin films (Z1) and (Z2) were shown to demonstrate that the thin film optimized by a nonlinear target has a controllable slope and better passband spectral performance. The blue-blocking thin film of 14 layers was fabricated using electron-beam evaporation assisted by an ion beam, which met the technical requirements of the new GB/T38120—2019 national standard. The results present that the average transmittance of the single-side thin film is less than 3.2% at 385−415 nm, 30.88% at 415−445 nm, more than 81.9% at 445−475 nm, and more than 95.5% at 500−800 nm. These promising results indicate that this design method provide a new solution for vision protection applications such as eyeglasses and computer desktop and mobile digital screens.
Research on a field-of-view splicing method for the optical system of a star simulator
FU Jing-yi, QIN Tian-xiang, HUANG Yun-han, LIU Zhi-ying
 doi: 10.37188/CO.2020-0221
Abstract(15) FullText HTML(3) PDF 3857KB(1)
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The large field-of-view star simulator provides wider star maps but the existing star simulator is limited by the size of the display chip, and the maximum field of view is not more than 30°. In order to increase the field of view of the star simulator, a method of splicing it is proposed. In order to reduce the cost, the overall weight and complexity of the system, and to achieve the largest splice with the least amount of splicing, the paper carries out detailed calculation and analysis of the overlapping area of the field of view and proposes a simplified splicing model based on plane splicing. It produces three typical splicing methods including a regular triangle, a regular quadrilateral and a regular hexagon, and deduces the calculation of the field of view utilization. It also provides a coordinate calculation method, determines the center position of each field of view, and obtains an accurate number of the stitching. The final comparison result shows that the regular hexagon splicing method has the outstanding advantages of a higher utilization of the field of view utilization and fewer splicing numbers, which provides a basis for the design of a large field-of-view star simulator.
A thermal dissipation design method for LED array structure illumination
WU Fu-pei, XIE Xiao-yang, LI Sheng-ping
 doi: 10.37188/CO.2020-0211
Abstract(20) FullText HTML(8) PDF 4066KB(3)
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Obtaining high-quality images plays an important role in active automatic optical inspection systems. Besides the traits of cameras, image quality is significantly affected by illumination thermal stability. To ensure the illumination thermal stability and capture high-quality images in optical inspection systems, a thermal dissipation design method for LED array structure illumination is proposed in this paper. Firstly, the thermal resistance model of a single LED is built by analyzing its thermal resistance characteristics. Secondly, a setup with two adjacent LEDs is taken as an example to analyze junction temperature characteristics of the same color light in a LED array, and then the junction temperature model of the LED array structure illumination is developed. Finally, the thermal dissipation design method for LED array structure illumination is illustrated based on the proposed junction temperature model. The thermal design method is decomposed into two sub-problems to simplify the design process. The experimental results show that the junction temperature deviation is within −0.33%~0.33% by simulation and is 2.28% by experiment, which validates the effectiveness of the proposed method.
3D small-field surface imaging based on microscopic fringe projection profilometry:a review
WANG Yong-hong, ZHANG Qian, HU Yin, WANG Huan-qing
 doi: 10.37188/CO.2020-0199
Abstract(12) FullText HTML(14) PDF 2290KB(8)
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Intelligent manufacturing has become more precise, miniaturized and integrated. Representative integrated circuit technology and its derived miniature sensors such as micro-electro-mechanical system (MEMS) have become widely used. Therefore, it is important for intelligent manufacturing development to accurately obtain the surface morphology information of micro-devices and implement rapid detection of device surface defects. Fringe projection profilometry (FPP) based on structural light projection has the advantages of being non-contact, highly precise, highly efficient and having full-field measurement, which plays an important role in the field of precision measurement. Microscopic fringe projection profilometry (MFPP) has been developed rapidly during recent decades. In recent years, MFPP has made great progress in many aspects, including its optical system structures, corresponding system calibration methods, phase extraction algorithms, and 3D coordinate reconstruction methods. In this paper, the structure and principle of a three-dimensional measurement system of microscopic fringe projection are reviewed, and the calibration problem of a small field-of-view system that is different from the traditional projection model is analyzed. After that, the development and improvement process of the micro-projection system structure is introduced, and the reflection problem caused by the system structure and metal measurement is analyzed. Also, we analyze the reflection problem caused by the system’s structure and metal measurement. On this basis, the prospects of the development of microscopic fringe projection of 3D measurement system are discussed.
Carbon dioxide detection technology based on the laser occultation absorption spectrum
WANG Yu-Zhao, TAO Yu-Liang, SUN Hai-Qing, YANG Chao
 doi: 10.37188/CO.2020-0201
Abstract(7) FullText HTML(7) PDF 2656KB(0)
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The advantages and disadvantages of fixed-wavelength laser occultation differential absorption technology are analyzed, and the measurement principle of tunable laser direct absorption spectroscopy technology is introduced. The relationship between optimal wavelength transmittance and signal-to-noise ratio and the relationship between measurement error and background light interference are analyzed. According to the working wavelength range of the high-sensitivity detector, 6310.915 cm−1, 6310.893 cm−1, 6310.890 cm−1 and 6310.8834 cm−1 are selected as the absorption working wavelengths, and 6310.15 cm−1 is selected as the reference wavelength, and the detection ability of each wavelength is simulated and analyzed.. Simulation shows that the detection error of a CO2 concentration is better than 0.9% in the range of 5~35 km with a vertical resolution of 1 km, and the detection error is better than 0.4% in the range of 7~42 km. This technology reduces the cost and complexity of the system, and is beneficial to the design and implementation of space-borne products.
Research on night vision intelligent detection method of scatterable landmines
WANG Chi, YU Ming-kun, YANG Chen-ye, LI Si-yuan, LI Fu-di, LI Jin-hui, FANG Dong, LUAN Xin-qun
 doi: 10.37188/CO.2020-0214
Abstract(21) FullText HTML(7) PDF 3710KB(5)
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Night vision intelligent detection system and detection method of scatterable landmines based on machine learning is presented. Firstly, the intelligent detection network model of scatterable landmines is designed and optimized based on the YOLO series algorithm. Then, the model of measuring the distance between scatterable landmines and detection equipment is proposed based on the similarity principle of geometric optical imaging. Finally, an intelligent detection system for scatterable landmines was built, tested and analyzed. The experimental results show that, the optimized intelligent detection network model can detect scatterable landmines with an accuracy of 98.97%, a recall rate of 99.22%, and a mean average accuracy of 99.2%. Under the given experimental conditions, the optimized scatterable landmine ranging model has an error of ±10 cm in the calculated distance of scatterable landmines. The study shows that machine learning can perform intelligent and long-distance detection of scatterable landmines.
Experimental investigation on propagation characteristics of vortex beams in underwater turbulence with different salinity
Teng-fei Lu, 永欣 刘, Yong-xin Liu, 志军 吴
Abstract(15) PDF 440KB(0)
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We build a device which can control both the salinity and the intensity of underwater turbulence to study the propagation characteristics of vortex beams and a Gaussian beam in underwater turbulence. In addition, we set up another experimental device which can transmit a longer distance, and studied the scintillation characteristics of the vortex beam with topological charge m=2 and a Gaussian beam over a propagation distance of 20 meters.
基于三维边界元算法的石墨烯纳米圆盘表面等离子体共振特性研究
硕 王, 滨 胡, 娟 刘
Abstract(14) PDF 170KB(0)
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相对于有限元、有限时域差分等常用的仿真算法,边界元算法具有精度高、占用内存少、善于处理复杂结构的优点。本文给出了三维边界元算法的基本原理,编写了基于C++语言的三维边界元算法程序,并用其研究了石墨烯纳米圆盘结构的表面等离子体共振特性。本文计算了石墨烯纳米圆盘在不同化学势下的散射截面谱线,共振波长下电磁场分布等物理量,分析了石墨烯纳米圆盘在红外波段的电磁响应性质。考虑到加工过程中产生的缺陷会造成石墨烯材料的褶皱,研究了石墨烯纳米圆盘中心处产生凸起后,凸起结构的几何参数对共振强度、波长等参量的影响,并采用电荷运动的弹簧振子模型,对仿真结果进行了解释。
用于胶囊内窥镜的宽频圆极化石墨烯天线设计
仁侠 欧
Abstract(20) PDF 1KB(0)
Abstract:
为了提高胶囊内窥镜天线工作性能,提高天线抗干扰能力和兼容性,进一步缩小尺寸,设计了一种基于石墨烯的用于胶囊内窥镜的宽频圆极化天线。该天线由三层辐射单元和地板构成,利用石墨烯薄膜优良的导电性能,制作天线的各层辐射单元和地板,能够有效增强胶囊天线的工作带宽与增益,提高传输效率并降低损耗。通过四个短路探针使第一层与第二层辐射单元相连接,构成复合螺旋天线,进而产生圆极化特性,既能减少误码率又能抑制多径干扰,并且能够更加高效的耦合电磁能量,有效改善阻抗匹配并调节圆极化纯度。详细分析了第一层、第二层和第三层辐射单元开口圆环尺寸、石墨烯薄膜厚度、天线摄入胃、小肠、结肠等环境对天线性能的影响。测试结果表明,设计的体积仅为π×(4.5)2×1.905mm3,阻抗带宽为2.2~2.78GHz,轴比带宽为2.26~2.66GHz,增益为-22.9dBi,实际测量与仿真结果吻合良好,工作频段内辐射特性稳定,与现有技术相比,外形兼容性强,功能带宽更宽,具有宽频带、圆极化、抗干扰、电磁兼容性好、体积小等特点。该天线适用于ISM 2.4GHz频段,能满足胶囊内窥镜摄入不同消化器官的工作要求。
Development progress of Fe2+:ZnSe lasers
XU Fei, PAN Qi-kun, CHEN Fei, ZHANG Kuo, YU De-yang, HE Yang, SUN Jun-jie
 doi: 10.37188/CO.2020-0180
Abstract(90) FullText HTML(22) PDF 3594KB(15)
Abstract:
Mid-infrared lasers with emission spectrums located in the 3~5 μm atmospheric window have a wide range of possible applications in medical treatment, industrial processing, atmospheric remote sensing, space communication, infrared countermeasures and other fields. Transition metal (TM) doped Ⅱ~Ⅵ group sulfide crystals can be used as the gain medium to achieve mid-infrared laser output. Among them, Fe2 +:ZnSe lasers are advantageous for their high conversion efficiency, their wide tunable range in the mid-infrared band and their compact structure. They are one of the most effective ways of achieving a short pulse with high power and high energy and in the mid-infrared band. With the development of material technology in recent years, Fe2 +:ZnSe lasers have begun developing rapidly and have become a heavily researched topic. This paper reviews the development of a TM2+:Ⅱ~Ⅵ laser represented by a Fe2 +:ZnSe laser. The preparation methods of a Fe2 +:ZnSe gain medium are introduced and analyzed. The pump sources and factors affecting the performance of Fe2 +:ZnSe lasers are discussed. The output characteristics of the Fe2 +:ZnSe laser are reviewed. The latest development of Fe2 +:ZnSe lasers in room temperature and ultrashort pulse directions is summarized and prospected. The possible future development direction of Fe2 +:ZnSe lasers is discussed.
Simulation study on tunable graphene metasurface focusing mirror based on flexible substrate
LI Xiang-jun, HOU Xiao-mei, CHENG Gang, QIU Guo-hua, YAN De-xian, LI Jiu-sheng
 doi: 10.37188/CO.2020-0171
Abstract(130) FullText HTML(18) PDF 4230KB(11)
Abstract:
Ultra-thin focusing mirror with adjustable focal length has important applicant value in compact systems, especially on-chip terahertz spectroscopy, imaging systems and communication systems. By changing the geometric size and adjusting the chemical potential, the graphene subwavelength reflective structure can achieve a phase of 0-2π. Combined with the above properties and the dynamic stretching of polydimethylsiloxane (PDMS) flexible substrate, the ultra-thin terahertz focusing reflector with large dynamic adjustment range can be realized. In this paper, a dynamic focusing graphene metasurface focusing reflector based on flexible substrate with a working frequency of 1.0 THz, a width of 12 mm, a focal length of 60 mm and a thickness of 75 μm is designed and investigated. Firstly, by adjusting the chemical potential and width of the graphene unit strips, the reflective phase covers the 0-2π, and the reflective focusing effect can be achieved according to the predesigned phase spatial distribution. Then, the dynamic adjustment of the focal length of the reflective mirror can be realized by laterally stretching the flexible substrate. The simulation results demonstrate that when the length of the flexible substrate varies from 100% to 140%, the focal length of the reflective mirror increases from 53.4 mm to 112.1 mm, the dynamic focus rage can reach 109.7% of the minimum focal length, and the focus efficiency decreases from 69.7% to 46.8%. In addition, the performance of the reflective mirror in a wide frequency range has also been investigated in this paper, and the simulation results demonstrate that the good dynamic focusing for incident plane waves in the frequency range of 0.85−1.0 THz can be achieved. The proposed tunable metasurface design is highly versatile in the development of ultra-thin, multifunctional and tunable terahertz devices for various applications.
The influence of CCD nonlinearity effect on the three-dimensional shape measurement of dual frequency grating
QIAO Nao-sheng, SUN Ping
 doi: 10.37188/CO.2020-0143
Abstract(62) FullText HTML(20) PDF 3909KB(7)
Abstract:
The CCD nonlinearity effect in the measurement system will affect the measurement accuracy of complex optical three-dimensional surface. Therefore, a method to eliminate the CCD nonlinearity effect by using dual frequency grating projection is proposed, which can improve the measurement accuracy. Firstly, the influence of CCD nonlinearity effect on three-dimensional shape measurement is analyzed. The analytical derivation and physical explanation of spectrum aliasing are given. Then, the measurement principle of dual frequency grating under the CCD nonlinearity effect is discussed. The light intensity distribution of deformed fringe and the principle of obtaining aliasing spectrum by Fourier transform are analyzed. Finally, the method to judge the measurement accuracy by the equivalent wavelength is given. The basic formula of measuring the height information of three-dimensional surface by using dual frequency grating projection is derived, and the theoretical analysis is carried out. The object is simulated as the maximum absolute value and average absolute value are 24.3181 mm and 1.0839 mm, respectively. The maximum absolute height error and average absolute height error between the measured value and the actual value are 0.8950 mm and 0.0622 mm, respectively. After increasing the fundamental frequency of the dual frequency grating, the corresponding values are reduced to 0.3710 mm and 0.0232 mm, respectively. When the fundamental frequency of the dual frequency grating is increased by 2.5 times, the separation between the fundamental frequency and the advanced spectrum becomes better, and the measurement accuracy is improved. Therefore, using dual frequency grating projection to eliminate CCD nonlinearity effect has strong practicability and is highly advisable.
Optical design of visual and infrared large-aperture imaging system based on a space-based platform
LI Yi-ting, FU Yue-gang, WANG Ling-jie, ZHANG Yu-hui, LIU Ming-xin
 doi: 10.37188/CO.2019-0255
Abstract(96) FullText HTML(27) PDF 1984KB(18)
Abstract:
To solve the data transmission difficulties and long-signal acquisition and processing time problem caused by excessive data transmission of the Geostationary Orbit array staring spectrometer, a scheme for a large-aperture visual and infrared snapshot spectrometer based on compressive sensing is proposed, which takes advantage of the fact that a geostationary orbit platform can stay over the fixed area for a long time. This paper analyzes the physical model of compressive sensing spectral imaging. The structure of the optical system is designed, and the relevant parameters are calculated. The objective lens uses a coaxial three-mirror afocal optical system, and dichroic films are used to split the spectrum. The relevant parameters were calculated according to requirements and the system was designed using optical software. After optimization, the optical system was shown to have a width of 400 km◊400 km, a visible area of 40 m GSD, an MWIR area of 400 m GSD, and an LWIR area of 625 m GSD. The results show that the MTF of the visible area is higher than 0.455 at 78.125 lp / mm. In mid-wave infrared, the MTF is higher than 0.518 at 33 lp / mm, and the MTF is higher than 0.498 at 20.8 lp / mm in long-wave infrared. The spectral resolution of the visible light is 20 nm, the mediumwave infrared region’s resolution is 50 nm, and the long-wave infrared spectrum resolution is 150 nm. The second-order spectrum of the visual area is less than 0.05 mm. The optical system has good imaging performance and the imaging quality of each part of the optical system is close to the diffraction limit, which meets the needs of applications and indicators.
Research progress of the laser vibration measurement techniques for acoustic-to-seismic coupling landmine detection
LI Jin-hui, MA Hui, YANG Chen-ye, ZHANG Xiao-qing, LUO Xin-yu, WANG Chi
 doi: 10.37188/CO.2020-0134
Abstract(172) FullText HTML(39) PDF 4545KB(9)
Abstract:
Acoustic-to-seismic coupling landmine detection technology based on the unique mechanical characteristics of landmines and the acoustic-to-seismic coupling principle has broad application prospects in safe and effective detection of landmines. However, a significant amount of work must be done to study the practical landmine detection system. Among them, the acoustic coupled surface vibration signals are very weak and complicated, which has always been a challenging problem to detect such signals accurately and quickly. In this paper, the non-contact laser measurement techniques of surface vibrations based on the principle of the acoustic-to-seismic coupling landmine detection technology were reviewed, including laser Doppler interferometry, electronic speckle pattern interferometry and laser self-mixing interferometry, etc., and the application feasibility of electronic speckle-shearing pattern interferometry in acoustic-to-seismic coupling landmine detection was explored.
Influence of modulation performance on coating on repaired fused silica
JIANG Yong, LIAO Wei, WANG Biyi, ZHAO Wanli, LIU Qianghu, QIU Rong, GUO Decheng, ZHOU Lei, ZHOU Qiang, ZHANG Yuanheng
 doi: 10.37188/CO.2020-0110
Abstract(112) FullText HTML(47) PDF 3314KB(5)
Abstract:
In order to address the light modulation problem on repair spots created after using a CO2 laser to repair fused silica surface damage, this paper focuses on the change of the profile and the modulation of the repaired sites before and after coating them with antireflective film. The influence of the depth and width of the repaired site on the deposition of the colloid are discussed, with some attention also given to the influence of the modulation effect. The results indicate that the colloidal material significantly enriches the pits of a repair, which can effectively improve their topographic dimensions with regards to their depth. The maximum modulation locations of a repaired site will increase after being coated with the antireflective film. However, the maximum modulation caused by the repaired site is much smaller than that of the corresponding uncoated repair point. The results of this study can provide reference for further optimization of repair processes and light modulation regime control of the surface damage sites on fused silica.
Research progress on portable laser-induced breakdown spectroscopy
ZENG Qing-dong, YUAN Meng-tian, ZHU Zhi-heng, CHEN Guang-hui, WANG Jie, YU Hua-qing, GUO Lian-bo, LI Xiang-you
 doi: 10.37188/CO.2020-0093
Abstract(199) FullText HTML(48) PDF 3931KB(29)
Abstract:
As a new rapid element analysis technique, laser-induced breakdown spectroscopy (LIBS) has proven iteself to have great potential for applications in increasingly numerous industrial fields. However, due to harsh outdoor and industrial environments, newer and higher requirements are being demanded of the LIBS system, such as the size of its instruments and the ability to resist a harsh environment. The rapid development of new laser technology promotes instrumentation for LIBS, allowing it to gradually step outside the laboratory and into the industry, and allows the LIBS system to gradually move towards instrumentation, miniaturization and portability.In this paper, the development of a portable LIBS that was developed in recent years was reviewed. The application and latest research progress of different kinds of laser source (small lamp pumped solid-state laser, diode pump solid-state laser and micro laser, fiber laser) applied to the portable LIBS system were summarized and discussed, providing insight into both the fiber optic LIBS (FO-LIBS) and the handheld LIBS. In addition, the basic problems of current portable LIBS and the prospects of its future were proposed and discussed.
Real-time polarization imaging integrated technology for solid-state low-light imaging
LIANG Wan-yu, XU Jie, DAI Fang, CHANG Wei-jing, NA Qi-yue
 doi: 10.37188/CO.2020-0086
Abstract(273) FullText HTML(66) PDF 4215KB(31)
Abstract:
High-performance night vision light detection is the future direction of development in photoelectric detection. In this paper, a real-time polarization imaging technology for low-light imaging is proposed to solve issues where polarization images show large error due to low sensitivity. By introducing white light channels and 8 polarization channels in four polarization directions, detection can be achieved on EMCCD micro-optical devices. The experiment shows that the polarization information obtained by the polarization array is highly accurate, and also has advantages for its low difficulty in processing and its low cost.
Non-destructive Testing of Red Globe Grape Sugar Content and Moisture Content Based on Visible/Near Infrared Spectroscopy Transmission Technology
GAO Sheng, WANG Qiaohua
 doi: 10.37188/CO.2020-0085
Abstract(185) FullText HTML(52) PDF 4724KB(15)
Abstract:
  Objective  The sugar content and moisture of red globe grapes are important internal quality measurement indices. However, traditional detection methods use destructive biochemical detection.  Method  In this paper, a non-destructive detection method for the sugar and moisture content of red globe grapes based on visible/near-infrared spectroscopy transmission technology is studied. 360 red globe grape extract samples were collected and PLSR models were established by Standard Normal Variable transformation (SNV), SavitZky-Golay(S_G) and other spectral preprocessing methods to determine the one. Seven data dimensionality reduction methods of primary dimensionality reduction (GA, SPA, CARS, UVE) and secondary dimensionality reduction combinations (CARS-SPA, UVE-SPA, GA-SPA) were used to identify characteristic variables of spectra. PLSR and LSSVM content detection models of red globe grape extract sugar content and moisture content were established respectively, and the advantages and disadvantages of each model were compared and analyzed.  Result  The results show that the optimal PLSR model wavelength extraction method for red globe grape sugar content and moisture content is GA-SPA-PLSR, and the correlation coefficients of the optimal model were 0.958 and 0.938, respectively. The optimal LSSVM model wavelength extraction methods for red globe grape sugar and moisture content are CARS-SPA-LSSVM and UVE-SPA-LSSVM, respectively. The correlation coefficients of the optimal model are 0.969 and 0.942, respectively. The model built using LSSVM is better than that built using PLSR, but its operation time is longer.  Conclusion  The results show that: The non-destructive detection method of red globe grape sugar and moisture content based on visible/near-infrared technology is feasible, and that the detection accuracy of the two optimal detection models is high, which can meet detection requirements. Different models can be selected for different applications. The optimal model built by PLSR has shorter computation time and is suitable for online rapid detection. LSSVM has the best detection performance and can accurately predict red globe grape sugar and moisture content.
Investigations of optical environment changes in the dunhuang gobi site of the chinese radiometric calibration sites
LI Yuan, ZHANG Yong, HU Li-qin, LU Qi-feng, LU Nai-meng
 doi: 10.37188/CO.2020-0129
Abstract(232) FullText HTML(36) PDF 4273KB(12)
Abstract:
The Dunhuang Gobi Site of the Chinese Radiometric Calibration Sites (CRCS) has an irreplaceable role in the field radiometric calibrations and quantitative applications in remote sensing satellites. In 2016, the molten salt tower concentrating solar power (CSP) project in the south side of the Dunhuang Site completed and began operation. The scattered radiation of the heat collection tower has an impact on diffused sky radiation. The influence on the optical environment of the calibration site needs to be analyzed and evaluated in detail. This paper focuses on the scattered radiation of the heat absorber on the top of the heat collection tower. The influence of the heat absorber was analyzed quantitatively based on the Monte Carlo three-dimensional radiation transmission model simulation and in situ CE318 multi-channel photometer almucantar measurements. By measuring the data with a new cloud cover automatic observing instrument ASC200, the accuracy of clear sky measurements improved, and the development of the CE318 four-quadrant location correction algorithm effectively increased the amount of valid data that meets our threshold requirements. The effective data collected from January to March 2020 shows that the molten salt tower CSP project has no significant impact on the sky diffuse radiation outside the 550 nm channel. In the 500 nm channel, under the geometric parameters corresponding to the valid data (distance 0.87−3.07 km, observation zenith angle 77.30−51.32°), the impact of the molten salt tower heat absorber on diffuse sky radiation does not exceed 0.93%. Combined with the analysis of the model simulation results, it can be concluded that the relative change of the sky diffuse radiation caused by the scattered radiation of the large power station is less than 1.62% at 2 km away, and the relative change is less than 0.93% when it is at least 3 km away. The research results have positive significance for the use of Dunhuang Site to conduct quantitative applications in remote sensing and the accurate evaluation of the uncertainties introduced by power stations.
Reviews
Research advances in adaptive interferometry for optical freeform surfaces
ZHANG Lei, WU Jin-ling, LIU Ren-hu, YU Ben-li
2021, 14(2): 227-244.   doi: 10.37188/CO.2020-0126
[Abstract](452) [FullText HTML](125) [PDF 3333KB](153)
Abstract:
Optical free-form surfaces are difficult to detect due to their rich degrees of freedom. Interference detection methods are both highly precise and non-contact. However, the static compensator in a traditional interferometer faces difficulty in achieving in-situ tests of unknown surface shapes or those changing during fabrication. Therefore, programmable adaptive compensators for large dynamic ranges have become a well-researched topic in recent years. Combined with the research work in the field of freeform surface metrology, we introduce the latest research progress in adaptive interferometry for optical freeform surfaces. Adaptive interferometers based on a Deformable Mirror (DM) or Liquid Crystal Spatial Light Modulator (LC-SLM) are analyzed in detail. An adaptive controlling algorithm in the adaptive interferometer is introduced as well. Finally, the advantages and development bottleneck of the above two kinds of adaptive interferometry are summarized and the prospects for the future development of freeform surface adaptive interferometers are proposed.
Interrogation technology for quasi-distributed optical fiber sensing systems based on microwave photonics
WU Ni-shan, XIA Li
2021, 14(2): 245-263.   doi: 10.37188/CO.2020-0121
[Abstract](209) [FullText HTML](87) [PDF 3910KB](42)
Abstract:
Quasi-distributed fiber sensing systems play an important role in the fields of civil engineering, energy surveying, aerospace, national defense, chemicals, etc. Interrogation technology for quasi-distributed fiber sensing systems based on microwave photonics is widely used in high-speed and high-precision signal demodulation and sensor positioning in optical fiber multiplexing systems. Compared to conventional optical wavelength interrogation, this technology greatly improves system demodulation rate and compensates for the defects of traditional sensor positioning methods. This paper introduces the recent research progress of quasi-distributed fiber sensing interrogation technology based on microwave photonics; compares and analyzes the advantages and disadvantages of several existing microwave demodulation systems from the perspective of their fiber grating quasi-distributed sensing and fiber Fabry-Perot quasi-distributed sensing systems, respectively; and provides a summary of the prospective direction of future research in quasi-distributed fiber sensing interrogation technology based on microwave photonics.
Research progress of 0.9 ~ 1.0 μm near-infrared continuous-wave fiber lasers
DANG Wen-jia, LI Zhe, LU Na, LI Yu-ting, ZHANG Lei, TIAN Xiao
2021, 14(2): 264-274.   doi: 10.37188/CO.2020-0193
[Abstract](151) [FullText HTML](47) [PDF 2460KB](61)
Abstract:
Near-infrared continuous-wave fiber lasers with wavelengths of 0.9~1.0 μm have important application prospects in the fields of high-power blue and ultraviolet laser generation, high-power single-mode pump sources, biomedicine and lidars. They have thus become a heavily researched topic in recent years. At present, their gain mechanisms mainly include a rare earth ion gain or a nonlinear effect gain. In this paper, the research progress of 0.9~1.0 μm fiber lasers based on these two kinds of gain mechanisms are reviewed in detail, and the technical bottlenecks and solutions of these lasers are analyzed. Furthermore, the potential directions for the future of their research are proposed.
Time-delay interferometry for space-based gravitational wave detection
WANG Deng-feng, YAO Xin, JIAO Zhong-ke, REN Shuai, LIU Xuan, ZHONG Xing-wang
2021, 14(2): 275-288.   doi: 10.37188/CO.2020-0098
[Abstract](256) [FullText HTML](53) [PDF 9981KB](51)
Abstract:
The Time-delay Interferometry (TDI) technique is of important value for China’s gravitational wave detection program and other space-based laser interferometry missions. In space-based gravitational wave detection, laser interferometry is utilized to achieve ten-picometer precision in the displacement measurements between drag-free proof masses. Laser frequency noise and clock frequency noise are the two dominant noises in the measurement. In the European LISA (Laser Interferometer Space Antenna) program for gravitational wave detection, TDI technique is used to remove laser noise and displacement noise of optical platform by time-delaying and linearly combining the twelve phase measurement data of the three satellites and thus creating an interferometer with equal-length beams. For the cancellation of clock noise, the frequencies of onboard clocks are multiplied to GHz levels and then the GHz clock signals are added on inter-satellite laser links by phase modulation. Finally, the clock noise can be extracted from the generated clock-sideband beat note, eliminating the clock noise terms in the TDI data combination. For the time-delay operation in the data post-processing of the TDI, there is also a requirement for the precise measurement of the absolute distances between three satellites. Therefore, in the TDI scheme, there are three functions applicable to the inter-satellite laser links: displacement measurement, clock sideband modulation and absolute distance ranging. The latter two functions consume the power of the optical carrier by 10% and 1%, respectively. The TDI demonstration in the LISA’s ground-based testbed shows the laser noise and clock noise can be suppressed by the factor of 109 and 5.8×104, respectively.
Original Article
Speckle noise reduction in swept-source optical coherence tomography by retinal image registration
CAI Huai-yu, HAN Xiao-yan, LOU Shi-liang, WANG Yi, CHEN Wen-guang, CHEN Xiao-dong
2021, 14(2): 289-297.   doi: 10.37188/CO.2020-0130
[Abstract](145) [FullText HTML](45) [PDF 3876KB](29)
Abstract:
The averaging of multiple B-Scans is an effective method of reducing speckle noise in Swept-Source Optical Coherence Tomography (SS-OCT) and obtaining clear structural information. However, physiological characteristics such as eye tremor, drift, micro-saccade, and the optical structure of an SS-OCT system cause geometric transformation between images, resulting in poor multi-frame averaging. In this paper, we propose a registration algorithm based on the combination of gray distribution information and target geometric information. This method extracts the region of interest containing target information using the average gray distribution of an image, and corrects the transformation of the image with the collective effect of the phase correlation algorithm and the gray projection algorithm based on the fitting of the curve of its segments. Then, the process is repeated with the upper boundary of the retinal image fitted as the feature points to determine the optimal rotation parameters. The translation parameters are re-estimated again to achieve the rigid registration of the image. Finally, a one-to-one mapping method of axial scanning is used to achieve the non-rigid registration of the image with the energy function as the constraint. Experiments on live rabbit eyes show that the averaged image has clear boundaries, enhanced structural information, and its signal-to-noise and contrast-to-noise ratios are more than doubled their previous values on average. The algorithm is suitable for the registration of B-Scan images with strong speckle noise and can meet the averaging needs of many types of OCT systems. It has high robustness and image registration accuracy.
Multi-scale singular value decomposition polarization image fusion defogging algorithm and experiment
ZHOU Wen-zhou, FAN Chen, HU Xiao-ping, HE Xiao-feng, ZHANG Li-lian
2021, 14(2): 298-306.   doi: 10.37188/CO.2020-0099
[Abstract](234) [FullText HTML](75) [PDF 4855KB](37)
Abstract:
Aiming at the problems that the robust of existing polarization defogging algorithms is poor and image enhancement abilities are limited, an image fusion defogging algorithm based on Multi-scale Singular Value Decomposition (MSVD) is proposed. Firstly, considering the redundancy in polarization measurement information, the least square method is used to improve the accuracy of the polarization information in the traditional defogging algorithm for polarized images; then, with respect to the limitations of that algorithm, a qualitative analysis of the feasibility of image fusion defogging is implemented, and a polarized image fusion defogging algorithm based on multi-scale singular value decomposition is proposed. Finally, a verification experiment under different visibility conditions is designed and quantified. The results show that compared with the classic polarized image defogging algorithm, this algorithm does not require manual parameter adjustment, it has strong adaptability and robustness, and can effectively improve the halos and overexposure of sky areas that occur in the traditional algorithm. The image information entropy and the average gradient can be increased by 18.9% and 38.4% respectively, which effectively improves the quality of visual imaging under complex lighting conditions. The proposed algorithm has great application prospects.
Solutions to inhomogeneous and unstable illumination in biological photoacoustic tomography
MENG Qi, SUN Zheng
2021, 14(2): 307-319.   doi: 10.37188/CO.2020-0142
[Abstract](152) [FullText HTML](67) [PDF 4440KB](23)
Abstract:
In biological Photoacoustic Tomography (PAT), the images of initial pressure, optical deposition and optical properties are usually reconstructed from acoustic measurements based on an ideal assumption of uniform and stable illumination for simplicity. However, in practical applications, optical attenuation and inhomogeneous distribution of light fluence in tissues may occur after the imaging target is illuminated by short laser pulses, which results in inaccurate image reconstruction and reduced image quality. This paper summarizes current methods for reducing errors caused by inhomogeneous and unstable illumination in PAT under non-ideal conditions and discusses the advantages and limits of these methods.
Projector calibration based on cross ratio invariance
YANG Jian-bai, ZHAO Jian, SUN Qiang
2021, 14(2): 320-328.   doi: 10.37188/CO.2020-0111
[Abstract](167) [FullText HTML](69) [PDF 3431KB](32)
Abstract:
In order to improve the accuracy of the projector calibration in 3D shape measurement using digital fringe projection, a new projector calibration method that combines secondary projection technology and cross-ratio invariance is proposed. The secondary projection technology is used to solve the mutual interference between the projection pattern and the calibration pattern, and the cross-ratio invariance method is used to avoid introducing camera calibration error. A comparative experiment is carried out to verify the effectiveness of the proposed method. Compared with the traditional method of projector calibration that requires camera parameters and that using global homography, the RMS values of reprojection error of this method is reduced from (0.2275, 0.2264) and (0.1397, 0.0997) pixels to (0.0645, 0.0601) pixels, and the maximum value of the reprojection error is reduced from 1.222 pixels and 0.5617 pixels to 0.2421 pixels. In addition, this method allows the camera to be simultaneously calibrated during operation, and therefore the parameters of the entire 3D measurement system can be acquired. The above results show that the method proposed in this paper can prevent error propagation of camera calibration parameters and improve the calibration accuracy of a projector.
Double pumped composite cavity 501 nm cyan laser with tunable injection power ratio
WANG Lan, JIN Guang Yong, DONG Yuan, WANG Chao
2021, 14(2): 329-335.   doi: 10.37188/CO.2020-0161
[Abstract](88) [FullText HTML](29) [PDF 3435KB](11)
Abstract:
In order to explore the theoretical and technical basis for the application of high accuracy laser near 500 nm, a double pump source composite cavity combined with nonlinear sum frequency conversion is used to realize zero gain competition of two kinds of fundamental frequency laser in the cavity. This method can improve the output power of fundamental frequency laser, as well as carry out multiple nonlinear frequency conversion in the composite cavity. By adjusting the fundamental frequency laser injection power ratio, the photon number ratio in the cavity reaches 1∶1, which effectively improves the optical-to-optical conversion efficiency and sum-frequency output power. The theoretical model established for the first time is verified experimentally, and Nd:YAG and Nd:YVO4 are used as gain media to obtain 946 nm and 1064 nm fundamental frequency laser output respectively. LBO is sum-frequency crystal. The 946 nm and 1064 nm fundamental frequency laser without gain competition is realized by using the double pump source structure. By adjusting the injection LBO optical power, the sum frequency conversion efficiency and output power are researched when the injection power ratio is different. Finally, the maximum output power of 501 nm cyan laser is 923 mW when the injection power ratio is 1.48∶1 (i.e. the photon number ratio in the cavity is 1∶1).
Effects of the combination of sample temperature and spatial confinement on laser-induced breakdown spectroscopy
YU Dan, SUN Yan, FENG Zhi-shu, DAI Yu-yin, CHEN An-min, JIN Ming-xing
2021, 14(2): 336-343.   doi: 10.37188/CO.2020-0118
[Abstract](112) [FullText HTML](55) [PDF 3890KB](16)
Abstract:
The signal intensity of Laser-Induced Breakdown Spectroscopy (LIBS) can be improved by increasing sample temperature and confining space confinement. The combination of the two techniques can further improve the spectral intensity of LIBS. In this paper, the effects of increasing a sample’s temperature and spatial confinement on LIBS are studied in air, and the time-resolved spectra of laser-induced aluminum plasma are measured. The experimental results show that increasing the sample’s temperature can increase the signal intensity of LIBS since a sample with a higher temperature can absorb more laser energy; when the cylindrical cavity is used to confine the plasma, the spectral emission is further improved. The effect of the combination of the two experimental conditions is that the signal intensity of LIBS is significantly stronger than that of either condition alone. The intensity of Al (I) 396.2 nm increases to 1.4 times at 200 °C with higher temperature conditions alone, 1.3 times when spatial confinement is applied alone, and 2.1 times at 200 °C with spatial confinement. The emission intensity with the combined effects is higher than the sum of that under the two individual conditions. The effect of the combination is mainly based on the fact that laser irradiation of the sample under a higher temperature generates stronger shock waves that can more effectively compress a larger-sized plasma plume, thereby further improving the spectral intensity of LIBS.
The normal alignment method for freeform surfaces based on multiple laser sensor assembly
ZHANG Ying, DING Hong-chang, ZHAO Chang-fu, ZHOU Yi-gen, CAO Guo-hua
2021, 14(2): 344-352.   doi: 10.37188/CO.2020-0205
[Abstract](97) [FullText HTML](32) [PDF 5070KB](23)
Abstract:
In large aircraft product automation, the accuracy requirements for hole position detection are gradually increasing, and the vertical accuracy of a drill is the most important evaluation condition for this standard. When drilling and riveting are performed by automatic robotic systems, assembly error, bumps, offsets and other adverse conditions can reduce the accuracy of manufacturing and detection, and in turn the fatigue performance of the entire structure. To solve this problem, we proposed a technique for detecting a freeform surface’s normal-direction based on the adaptive alignment method using multiple laser sensor assemblies, built a mathematical model for posture alignment, and studied the calibration method and process required by the detection device. Additionally, we investigated techniques for error compensation using an electronic theodolite and other devices when the adaptive method is used for detection. In our verification experiments, multiple sets of results demonstrated that the key technical indicators were as follows: normal accuracy < ±0.5°, average deviation after correction is 0.0667°. This method can effectively compensate for the errors affecting hole making in automated manufacturing, and further improve the positioning accuracy and normal-direction detection accuracy of a robot.
Analysis of effects on the beam quality β factor of high power laser
WANG Yan-ru, WANG Jian-zhong, RAN Zheng-hui, DING Yu-jie
2021, 14(2): 353-360.   doi: 10.37188/CO.2020-0137
[Abstract](128) [FullText HTML](35) [PDF 5202KB](23)
Abstract:
The influencing factors of beam quality β factor of high-energy laser system is analyzed based on two-dimension chirp z transformation. The effects of the sampling number within the diffraction limit and the beam spot’s energy loss on the beam quality β factor are analyzed. The simulation results based on different sampling numbers indicate that a larger sampling number induces higher beam spot diffraction image resolution which is beneficial for more accurate calculation of a beam quality β factor. When the sampling number of the diffraction limit angle is no less than ten, the measurement error can be limited within 3%. Meanwhile, different wavefront aberrations have different sensitivities against beam spot energy loss. The beam quality β factor of high order wavefront aberration is larger than that of low order aberration with equal energy loss. Especially, the spherical aberration is most sensitive to energy loss, and about 5% energy loss can induce 15% to 30% calculation error of the β factor.
High efficiency mid-infrared 3.8 μm MgO:PPLN optical parametric oscillator pumped by narrow linewidth 1064 nm fiber laser
CHEN Bing-yan, YU Yong-ji, WU Chun-ting, JIN Guang-yong
2021, 14(2): 361-367.   doi: 10.37188/CO.2020-0169
[Abstract](109) [FullText HTML](31) [PDF 4044KB](27)
Abstract:
In this paper, a 1064 nm ytterbium-doped fiber laser with Main Oscillation Power Amplification (MOPA) was used as the pump source to achieve mid-infrared 3.8 μm MgO:PPLN Optical Parametric Oscillation (OPO) laser output. In the pump source, the Distributed Feedback Laser (DFB) was used as the seed source to realize the modulation of the narrow linewidth of the fiber laser. The linewidth of 2.5 nm was compressed to 0.1 nm, and the maximum output power was 40 W. The mid-infrared 3.8 μm MgO:PPLN OPO laser was researched under different pump linewidths. Finally, when the pump power was 18.1 W, the line width was 0.1 nm, the repetition frequency was 1 MHz, and the pulse width was 2 ns, the output laser with the maximum power of 2.06 W and the wavelength of 3822.5 nm was achieved. The corresponding optical-optical conversion efficiency is 11.38%, and the beam quality is M2 = 2.34. This research can efficiency improve the output efficiency of narrow linewidth pumped mid-infrared MgO:PPLN OPO.
CGH encoding with variable step size search
QIU Hong-wei, JIN Chun-shui, YU Jie, LIU Yu, ZHANG Hai-tao, WANG Li-ping, SUN Shi-zhuang
2021, 14(2): 368-374.   doi: 10.37188/CO.2020-0124
[Abstract](125) [FullText HTML](52) [PDF 5168KB](29)
Abstract:
In the field of aspheric testing, Computer-Generated Hologram (CGH) technology has been widely used. For CGH encoding, when applying the conventional encoding method to achieve highly accurate coding, it will use an amount of data that is often up to tens or even hundreds of GB. Therefore, in order to achieve high encoding accuracy with a small amount of encoded data, we propose a variable step size CGH encoding method. This method first obtains CGH fringe distribution through finding isophase surface, then selects different sampling steps by calculating the phase distribution gradient so that the CGH achieves high precision coding using as few points as possible. Finally, the method was used to CGH encode, then the resulting CGH was manufactured to test an aspheric surface. The test result is 3.142 nm (RMS). In order to verify the credibility of the test results, we design and make a compensator to test the same aspheric surface. The test result is 3.645 nm (RMS). The difference between the two results is 1.291 nm (RMS), and shows that the encoding method can meet the requirements of high-precision testing of aspheric surfaces.
Establishment and analysis of the diffraction bidirectional reflection distribution function model for surface defects
LU Min, WANG Zhi-le, ZHANG Shu-qing
2021, 14(2): 375-381.   doi: 10.37188/CO.2020-0162
[Abstract](86) [FullText HTML](28) [PDF 3701KB](13)
Abstract:
The purpose of this paper is to establish a diffraction Bidirectional Reflection Distribution Function (BRDF) model of surface defects including scratches and pits, and to analyze the model being applied in various fields. By using nonparaxial scalar diffraction theory, a coherent window function filtering method is proposed, which can obtain the BRDF model of surface defect diffraction under incoherent light conditions. The effectiveness of the model is verified in related work, and the scattering characteristics of surface scratches and pits are obtained. The method and the results obtained by the model have high value in surface defect detection, surface defect stray light analysis and image rendering technology.
Corrective method for spectral offset error caused by radial distortion in the large aperture static imaging spectrometer
AN Ling-ping, WANG Shuang, ZHANG Geng, LI Juan, LIU Xue-bin
2021, 14(2): 382-389.   doi: 10.37188/CO.2020-0084
[Abstract](217) [FullText HTML](85) [PDF 5206KB](28)
Abstract:
In order to improve the spectral calibration accuracy of the large aperture static imaging spectrometer when its field of view is increased, and to reduce the influence of radial distortion on its spectral accuracy, we propose a corrective method for spectral calibration coefficients based on a spectral distortion correlation model. To begin the process, the wave number and wavelength correction formulas are given. Using 594.1 nm and 632.8 nm gas lasers, a spectroscopic imaging experiment was performed on the imaging spectrometer, and the data was processed and analyzed. The results show that when there is a barrel distortion of 0.3%, the inversion spectrum at the edge of the field of view shifts approximately 2 nm. After implementing the corrective method of this paper, the line shift is reduced to approximately 0.1 nm. This method only needs to be corrected according to the lens distortion parameters, which simplifies the laboratory spectral calibration process and improves work efficiency. It can also be applied to the orbit parameter correction of spaceborne interference spectral data.
A 10−9-order point source transmission test facility
WANG Wei, LU Lin, ZHANG Tian-yi, WANG Wei-lu, LIU Yi-chen, MENG Qing-yu, XU Shu-yan
2021, 14(2): 390-396.   doi: 10.37188/CO.2020-0050
[Abstract](239) [FullText HTML](87) [PDF 9860KB](21)
Abstract:
In order to achieve the quantitative evaluation of the stray light attenuation in optical systems, we demonstrated a point source transmission test facility with 10−9-order sensitivity in this paper. We employed a pulsed source and measured the pulse to obtain the weak signal at the image plane, as well as to simplify the detection system. Using this scheme, we constructed a test facility with a maximum aperture of 600 mm and a test wavelength of 527 nm, and conducted the test with a 250 mm aperture optical system. Experimental results showed that the point transmission at a 60-degree incident angle is 1.68×10−9. The results prove that the test error of this facility is in the order of 10−9 or below, and the test facility has the ability to test 10−9-order point source transmissions. This technology can provide quantitative evaluation for various optical systems with strict stray light requirements, like astronomical telescopes, star sensors and spaced target monitor payloads.
Hybrid plasmonic leaky-mode lasing on subwavelength scale
YAN Shan-shan, WANG Shuang-peng, SU Shi-chen
2021, 14(2): 397-408.   doi: 10.37188/CO.2020-0108
[Abstract](84) [FullText HTML](29) [PDF 4787KB](18)
Abstract:
Due to the existence of diffraction limit as the basic characteristic of light, the lasing on subwavelength scale cannot be achieved by traditional methods. In order to break this diffraction limit, a stacked structure composed of metal, dielectric layer and semiconductor was designed in this paper to achieve lasing on the deep subwavelength scale and its influence on the propagation mode was discussed. In terms of structural design, we used silver, a metal with low dielectric constant, as the substrate, a 10 nm-thick LiF layer as the dielectric layer, and a ZnO semiconductor nanowire with hexagonal section as the high-dielectric-constant layer. We adopted the finite-difference eigen mode and Finite-Difference Time-Domain (FDTD) method to perform optical simulation of the designed structure. First, by changing the nanowire diameter and using the finite eigen mode, the optical modes in the dielectric layer were analyzed to obtain four mode distributions. Then the effective refractive indexes and losses of the four optical modes at different nanowire diameters were used to calculate the corresponding waveguide propagation distances and lasing threshold gains. Finally, the three-dimensional FDTD method was introduced to simulate the electric field distribution of the four modes during the steady-state laser emissionin of the nanowire. The results showed that there were hybrid plasmonic mode and hybrid electric mode in the dielectric layer between the nanowire and the metal substrate. When the diameter of ZnO nanowire was smaller than 75 nm, there was no effective physical optical mode, that is, both the hybrid plasmonic mode and the hybrid electric mode were cut off. When the nanowire diameter was larger than 75 nm, the hybrid plasmonic mode could effectively exist. The hybrid electric mode did not appear until the nanowire diameter reached 120 nm. Although the hybrid plasmonic mode could be better confined to the dielectric layer, its loss was too large and its propagation distance was relatively small. In addition, the hybrid electric mode traveled a longer distance than hybrid plasmonic mode. At the given diameter of the micron wire (D = 240 μm), the hybrid electric mode propagated for over 50 μm. In conclusion, the hybrid leaky mode on the deep subwavelength scale can break the optical diffraction limit and realize lasing.
Polarization changes of partially-coherent Airy-Gaussian beams in a slanted turbulent atmosphere
CHENG Ke, LU Gang, ZHU Bo-yuan, SHU Ling-yun
2021, 14(2): 409-417.   doi: 10.37188/CO.2020-0095
[Abstract](153) [FullText HTML](38) [PDF 2094KB](19)
Abstract:
Investigating polarization changes in a turbulent atmosphere holds great significance because polarization is one of the most important parameters in laser communication. Based on the extended Huygens-Fresnel principle and the unified theory of coherence and polarization, an analytical expression for the degree of polarization (DoP) in partially-coherent Airy-Gaussian beams propagating in a slanted turbulent atmosphere is derived. It is then used to study the dependence of polarization changes in turbulent parameter, coherence length, zenith angle, truncation and distribution factor. The polarization between the slanted and horizontal paths is also compared. Compared with horizontal turbulence, the beams traverse a longer distance to recover their initial polarization in slanted turbulence. An increase in the zenith angle, receiving height and truncation factor, or a decrease in the coherence length can increase the DoP. A smaller distribution factor or a higher coherence length is beneficial to reducing the effect of the zenith angle on the polarization. Analysis of the influence of the distribution factor on polarization also shows that maintaining the polarization of a Gaussian beam with higher coherence in a horizontally turbulent atmosphere has a greater advantage to that of a pure Airy beam from the view of keeping polarization invariance. The results show that optical information encoding can be achieved by selecting appropriate parameters, which is useful for studying atmospheric communication.
Enhanced dye-sensitized up-conversion luminescence of neodymium-sensitized multi-shell nanostructures
WANG Dan, XUE Bin, TU Lang-ping, ZHANG You-lin, SONG Jun, QU Jun-le, KONG Xiang-gui
2021, 14(2): 418-430.   doi: 10.37188/CO.2020-0097
[Abstract](263) [FullText HTML](59) [PDF 3354KB](20)
Abstract:
Lanthanide-ion-doped upconversion luminescence is limited by the small absorption cross-section and narrow absorption band of lanthanide ions, which results in weak luminescence. Recently, a dye-sensitized method has proven to be an effective strategy of increasing upconversion luminescence. However, simply attaching dye molecules to nanoparticles with classic Yb-doped nanostructures cannot effectively activate the sensitizing ability of the dye molecules. In response to this problem, we designed Nd-sensitized core/shell/shell (NaYF4:Yb/Er (20/2%)@ NaYF4:Yb (10 %)@ NaYF4:Nd (80 %)) nanostructures, compared with the classic IR-806 sensitized NaYF4:Yb/Er nanostructure, their upconversion luminescence (500 to 700 nm) was approximately enhanced by a factor of 38. Through analysis of the nanostructure’s emission and luminescence lifetime data, the enhancement was confirmed by the effective overlap of Nd absorption with the emission of near-infrared dye molecules and the protective effects of the shell structure on the luminescent center (the lifetime of Er (4S3/24I15/2) was increased by 1.7 times). In addition, we found that the doping Yb3+ in the outermost layer will decrease the dye-sensitized luminescence intensity. Furthermore, this Nd-sensitized core/shell/shell structure also achieved enhancement in the sensitized upconversion luminescence of the luminescence centers of Ho and Tm, which establishes a foundation for enhanced dye-sensitized upconversion luminescence.
Line-scanning confocal microscopic imaging based on virtual structured modulation
ZHAO Jia-wang, ZHANG Yun-hai, WANG Fa-min, MIAO Xin, SHI Xin
2021, 14(2): 431-445.   doi: 10.37188/CO.2020-0120
[Abstract](207) [FullText HTML](103) [PDF 3948KB](33)
Abstract:
Resolution in a confocal microscope is limited by the diffraction limit. Structured modulation has been proven to be able to achieve super-resolution in confocal microscopy, however, its limited speed in image acquisition limits its applicability in practical applications. In order to improve its imaging speed, we introduce a method that can achieve rapid super-resolution confocal microscopy by combining line-scanning and structured detection. A cylindrical lens is used to focus the light into a line, and a digital mask with a sinusoidal function is used to modulate the descanned image in the light detection arm. Unlike the virtual structured method, there is no need for a subsequent frequency shift process. In order to improve the isotropic resolution of the system, a scanning angle of 0 ° and 90 ° is achieved by rotating the sample. Simulation and experiment results indicate that the spectrum width of coherent transfer function expands and the resolution is 1.4 times as large as that of a conventional confocal microscope. This method increases the system’s imaging acquisition speed 104-fold when compared with a confocal structured modulation microscope that uses spot-scanning.
Research advances in adaptive interferometry for optical freeform surfaces
ZHANG Lei, WU Jin-ling, LIU Ren-hu, YU Ben-li
2021, 14(2): 227-244.   doi: 10.37188/CO.2020-0126
Abstract(452) FullText HTML(125) PDF 3333KB(153)
Abstract:
Optical free-form surfaces are difficult to detect due to their rich degrees of freedom. Interference detection methods are both highly precise and non-contact. However, the static compensator in a traditional interferometer faces difficulty in achieving in-situ tests of unknown surface shapes or those changing during fabrication. Therefore, programmable adaptive compensators for large dynamic ranges have become a well-researched topic in recent years. Combined with the research work in the field of freeform surface metrology, we introduce the latest research progress in adaptive interferometry for optical freeform surfaces. Adaptive interferometers based on a Deformable Mirror (DM) or Liquid Crystal Spatial Light Modulator (LC-SLM) are analyzed in detail. An adaptive controlling algorithm in the adaptive interferometer is introduced as well. Finally, the advantages and development bottleneck of the above two kinds of adaptive interferometry are summarized and the prospects for the future development of freeform surface adaptive interferometers are proposed.
Interrogation technology for quasi-distributed optical fiber sensing systems based on microwave photonics
WU Ni-shan, XIA Li
2021, 14(2): 245-263.   doi: 10.37188/CO.2020-0121
Abstract(209) FullText HTML(87) PDF 3910KB(42)
Abstract:
Quasi-distributed fiber sensing systems play an important role in the fields of civil engineering, energy surveying, aerospace, national defense, chemicals, etc. Interrogation technology for quasi-distributed fiber sensing systems based on microwave photonics is widely used in high-speed and high-precision signal demodulation and sensor positioning in optical fiber multiplexing systems. Compared to conventional optical wavelength interrogation, this technology greatly improves system demodulation rate and compensates for the defects of traditional sensor positioning methods. This paper introduces the recent research progress of quasi-distributed fiber sensing interrogation technology based on microwave photonics; compares and analyzes the advantages and disadvantages of several existing microwave demodulation systems from the perspective of their fiber grating quasi-distributed sensing and fiber Fabry-Perot quasi-distributed sensing systems, respectively; and provides a summary of the prospective direction of future research in quasi-distributed fiber sensing interrogation technology based on microwave photonics.
Research progress of 0.9 ~ 1.0 μm near-infrared continuous-wave fiber lasers
DANG Wen-jia, LI Zhe, LU Na, LI Yu-ting, ZHANG Lei, TIAN Xiao
2021, 14(2): 264-274.   doi: 10.37188/CO.2020-0193
Abstract(151) FullText HTML(47) PDF 2460KB(61)
Abstract:
Near-infrared continuous-wave fiber lasers with wavelengths of 0.9~1.0 μm have important application prospects in the fields of high-power blue and ultraviolet laser generation, high-power single-mode pump sources, biomedicine and lidars. They have thus become a heavily researched topic in recent years. At present, their gain mechanisms mainly include a rare earth ion gain or a nonlinear effect gain. In this paper, the research progress of 0.9~1.0 μm fiber lasers based on these two kinds of gain mechanisms are reviewed in detail, and the technical bottlenecks and solutions of these lasers are analyzed. Furthermore, the potential directions for the future of their research are proposed.
Time-delay interferometry for space-based gravitational wave detection
WANG Deng-feng, YAO Xin, JIAO Zhong-ke, REN Shuai, LIU Xuan, ZHONG Xing-wang
2021, 14(2): 275-288.   doi: 10.37188/CO.2020-0098
Abstract(256) FullText HTML(53) PDF 9981KB(51)
Abstract:
The Time-delay Interferometry (TDI) technique is of important value for China’s gravitational wave detection program and other space-based laser interferometry missions. In space-based gravitational wave detection, laser interferometry is utilized to achieve ten-picometer precision in the displacement measurements between drag-free proof masses. Laser frequency noise and clock frequency noise are the two dominant noises in the measurement. In the European LISA (Laser Interferometer Space Antenna) program for gravitational wave detection, TDI technique is used to remove laser noise and displacement noise of optical platform by time-delaying and linearly combining the twelve phase measurement data of the three satellites and thus creating an interferometer with equal-length beams. For the cancellation of clock noise, the frequencies of onboard clocks are multiplied to GHz levels and then the GHz clock signals are added on inter-satellite laser links by phase modulation. Finally, the clock noise can be extracted from the generated clock-sideband beat note, eliminating the clock noise terms in the TDI data combination. For the time-delay operation in the data post-processing of the TDI, there is also a requirement for the precise measurement of the absolute distances between three satellites. Therefore, in the TDI scheme, there are three functions applicable to the inter-satellite laser links: displacement measurement, clock sideband modulation and absolute distance ranging. The latter two functions consume the power of the optical carrier by 10% and 1%, respectively. The TDI demonstration in the LISA’s ground-based testbed shows the laser noise and clock noise can be suppressed by the factor of 109 and 5.8×104, respectively.
Development status and trend of micro-satellite laser communication systems
GAO Shi-Jie, WU Jia-Bin, LIU Yong-Kai, MA Shuang, NIU Yan-Jun, YANG Hui-sheng
2020, 13(6): 1171-1181.   doi: 10.37188/CO.2020-0033
Abstract(892) FullText HTML(241) PDF 7413KB(164)
Abstract:
With its high speed, small size, light-weight and low power consumption, space laser communication has become an indispensable and effective means of high-speed communication between satellites, especially in micro-satellite applications, which can benefit more strongly from the advantages of laser communication. This paper provides a detailed introduction of the latest research progress in the field of micro-satellite laser communication technology. On this basis, key techniques such as light miniaturization of identical orbital terminals, light miniaturization of different orbital terminals and turbulence mitigation technologies are summarized, and the development trends of the technology’s applications, duplex communication, single-point to multi-point, localization and batch production capacity are concluded.
Review of laser speckle target detection technology
GAO Wei-ke, DU Xiao-ping, WANG Yang, YANG Bu-yi
2020, 13(6): 1182-1193.   doi: 10.37188/CO.2020-0049
Abstract(521) FullText HTML(127) PDF 3630KB(131)
Abstract:
Target detection technology based on laser speckles is a kind of laser detection technology that has been ignored for a long time. In this technology, the laser speckle, which is regarded as noise in the traditional laser detection technology, is used as a new source of information. By analyzing the formation mechanism of a laser speckle pattern, the relationship between the statistical characteristics and the physical characteristics of the target is explored, and the effective analysis and inversion methods are combined to obtain the target’s shape, size, surface roughness and dynamic parameters. Compared with traditional laser detection technology, target detection technology based on laser speckles has a simple structure, has low optical system requirements, is sensitive to the physical and fretting characteristics of the target’s surface, and has been widely used in aerospace, medicine, industry, military and other fields. This paper classifies and summarizes the various kinds of speckle-based target detection technologies from recent years, compares and analyzes their applications, advantages and disadvantages, as well as the environmental restrictions. Finally, this paper prospects the trend for the future development of target detection methods based on laser speckles.
Review of the active control technology of large aperture ground telescopes with segmented mirrors
FAN Wen-qiang, WANG Zhi-chen, CHEN Bao-gang, LI Hong-wen, CHEN Tao, AN Qi-chang, FAN Lei
2020, 13(6): 1194-1208.   doi: 10.37188/CO.2020-0032
Abstract(267) FullText HTML(82) PDF 3727KB(63)
Abstract:
Segmented mirror technology is one of the three ways to realize optical synthetic aperture telescope, and it is an important area of development for future large aperture telescopes. A telescope’s active control system of its segmented mirrors directly determines its large aperture mirror’s optical performance. This paper focuses on the active control technology of large aperture ground telescopes with segmented mirrors. In this paper, we introduce the development process of a segmented mirror telescope and the main structure of the segmented mirror active control system, then summarize and analyze the domestic and foreign development of active control systems of segmented mirrors. In this paper, the key technologies of segmented mirror active control systems and how they achieve active adjustment and active maintenance are summarized. Their applications and the direction of their development are also proposed with respect to deep learning theory in closed-loop control, co-phase detection and correction, system-level simulation modeling technology. This paper provides guidance for the design of a segmented mirror control system in the next generation of ground-based large aperture telescopes in China.
Progress in ultrafast laser space-selective welding
ZHANG Guo-dong, CHENG Guang-hua, ZHANG Wei
2020, 13(6): 1209-1223.   doi: 10.37188/CO.2020-0131
Abstract(309) FullText HTML(119) PDF 4987KB(65)
Abstract:
The development of ultrafast laser technology has continuously injected new impetus into fundamental research and production, promoted the emergence of new disciplines and technologies. As a new materials welding and joining technique developed in recent years, ultrafast laser welding has attracted extensive attention due to the potential application in the fields of aerospace, precision machinery, optoelectronics, biomedical, etc.. Based on the intrinsic characteristic of non-linear space-selective energy deposition, ultrafast laser welding possesses extremely high material applicability and spatial selectivity, and can realize high-quality space-selective welding involving transparent materials with no need inserting an absorption layer. In this paper, we firstly give an overview on the progress of this field. Then, the physical mechanism, key influencing factors, and application scope of ultrafast laser welding are elaborated. At last, the future development and key challenges of ultrafast laser welding are discussed.
Overview of 2D grating displacement measurement technology
YIN Yun-Fei, LIU Zhao-Wu, JIRIGALANTU, YU Hong-Zhu, WANG Wei, LI Xiao-Tian, BAO He, LI Wen-Hao, HAO Qun
2020, 13(6): 1224-1238.   doi: 10.37188/CO.2020-0237
Abstract(397) FullText HTML(82) PDF 6952KB(91)
Abstract:
Ultra-precision displacement measurement technology is not only the basis of precision machining, but also plays a decisive role in the chip manufacturing industry that is rapidly developing in Moore's Law. The grating displacement measurement system based on the grating pitch is widely used in multidimensional measurement system. Compared with the laser displacement measurement system, grating displacement measurement system greatly reduces the environmental requirements for humidity, temperature and pressure. In this paper, the development status of the optical structure of displacement sensing system based on two-dimensional grating in recent years is introduced. The principles of zero-difference and heterodyne grating interferometrys are introduced. The optical structure based on single-block two-dimensional grating is reviewed. The development history of the optical structure in single-block two-dimensional grating to coupling designs of multi-block two-dimensional gratings is summarized, the advantages and disadvantages of several two-dimensional grating displacement measurement systems are compared and analyzed, and the development trend of two-dimensional grating displacement measurement system is prospected. The engineering process of two-dimensional grating displacement measurement system is summarized.
Research progress on nitrogen-doped carbon nanodots
LI Di, MENG Li, QU Song-nan
2020, 13(5): 899-918.   doi: 10.37188/CO.2020-0035
Abstract(614) FullText HTML(183) PDF 2407KB(118)
Abstract:
In recent years, carbon nanodot (CDs) have been widely researched due to their unique luminescent properties, good biocompatibility, low toxicity and high photostability. These characteristics invite potential applications in optoelectronic devices, visible light communication, tumor therapy, biological imaging and other fields. There are a variety of CDs according to the different starting materials and synthesis routes. In this paper, we will systematically review nitrogen-doped CDs synthesized from citric acid and urea as the main precursor materials in our group in recent years, discuss their physicochemical properties, explore the methods and principles of CDs energy band regulation, and introduce the application progress of CDs.
Optical coherence tomography: principles and recent developments
LU Dong-xiao, FANG Wen-hui, LI Yu-yao, LI Jin-hua, WANG Xiao-jun
2020, 13(5): 919-935.   doi: 10.37188/CO.2020-0037
Abstract(558) FullText HTML(192) PDF 4616KB(135)
Abstract:
Optical Coherence Tomography (OCT) is a new imaging technique that uses interference in low coherent light by measuring the delay and magnitude of backscattered or reflected signals from the sample. OCT technology can provide real-time structural information with one-dimensional depth and two- and three-dimensional tomography at micron-scale resolution. Besides its high spatial resolution, OCT imaging is beneficial for its non-contact and non-invasive methodology. The system is also easy to operate and relatively portable. OCT technology is mainly applied in the biomedical imaging field for diagnoses, making up for the shortcomings of the low penetration depth in confocal microscopes and the low resolution in ultrasonic imaging. At present, OCT technology has been used as the clinical standard for the diagnosis of retinal diseases, and the combination of OCT technology and endoscope technology has become an important tool for the clinical diagnosis of cardiovascular and gastrointestinal diseases. It also provides references for early cancer diagnosis, surgical guidance and postoperative rehabilitation of musculoskeletal diseases. To broaden the application of OCT technology and improve its medical detection capabilities, researchers are committed to increasing the penetration depth of OCT imaging in biological tissue, improving the system's resolution and signal-to-noise ratio, and optimizing its overall performance. This review introduces the principle and classification of OCT systems, their applications and their recent progress in various biomedical fields.
Review on scientific detection technologies for ancient paper relics
YAN Chun-sheng, HUANG Chen, HAN Song-tao, HAN Xiu-li, YING Chao-nan, DU Yuan-dong
2020, 13(5): 936-964.   doi: 10.37188/CO.2020-0010
Abstract(448) FullText HTML(159) PDF 4187KB(62)
Abstract:
This paper comprehensively discusses all kinds of modern scientific and technological detection methods for paper raw materials, inks, inkpads, and pigments used in ancient paper cultural relics, including imaging and spectrometric technologies. Relevant imaging methods include photography, tomography and microscopic imaging methods. Photographic methods include light transmission, infrared, ultraviolet, X-ray and neutron activation photography to display macroscopic information on a sample’s surface or inside. Tomography methods include X-ray, terahertz, and optical coherence tomographic methods to display layered information beneath the sample’s surface. Microscopic imaging methods include optical, scanning electron, transmission electron and atomic force microscopic imaging methods to display the sample’s microscopic information. Spectroscopy methods with fingerprint characteristics based on the principles of wave-matter interactions include chromatography, mass spectrometry, electron paramagnetic resonance spectroscopy, nuclear magnetic resonance spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, X-ray fluorescence spectrum, molecular fluorescence spectrum, Raman spectrum, UV-Vis-NIR-MID-THz absorption spectrum and hyperspectral methods. It shows that the comprehensive applications, complementary advantages and mutual confirmations of the above technologies are powerful means to reveal important traits of paper cultural relics, such as one’s manufacturing process, artistic features, preservation history, disease status, authenticity, method of reparation, etc.
Application of emerging transition metal dichalcogenides in ultrafast lasers
SUN Jun-jie, CHEN Fei, HE Yang, CONG Chun-xiao, QU Jia-yi, JI Yan-hui, BAO He
2020, 13(4): 647-659.   doi: 10.37188/CO.2019-0241
Abstract(1295) FullText HTML(409) PDF 1212KB(139)
Abstract:
Ultrafast laser technology is one of the most active research frontiers in lasers, physics and information science. It is widely applied in industrial processing, biomedicine, lidar and other fields. Because of their unique physical structure and excellent photoelectric properties, two-dimensional materials have a wide operating band, controllable modulation depth and short recovery time when they are employed as saturable absorbers in ultrafast lasers. Among them, transition metal dichalcogenides have become a focus of research because their band-gap is continuously adjustable. In this paper, we introduce the characteristics of transition metal dichalcogenides and the fabrication methods of saturable absorber devices. The research progress of ultrafast lasers based on emerging transition metal dichalcogenides is reviewed, and the development trend is highlighted.
Research progress of high-precision surface metrology of a K-B mirror
ZHANG Shuai, HOU Xi
2020, 13(4): 660-675.   doi: 10.37188/CO.2019-0231
Abstract(827) FullText HTML(347) PDF 8130KB(83)
Abstract:
The advanced light source represented by the new generation of the diffraction limit synchrotron radiation source and the full-coherent X-ray free-electron laser has become an indispensable research tool in many fields. The continuous development of advanced light sources drives the rapid progress of ultra-precision optical manufacturing. The surface precision of a K-B mirror, a key focusing optical element in advanced light sources, is an important factor, which should be less than tens of nano radians. However, high precision K-B mirror surface metrology still has great technical challenges and is now a research hotspot in the scientific community. This paper introduces typical K-B mirror surface metrology, including reflection profile measuring technology such as the Long Trace Profiler (LTP), the Nanometer Optical component Measuring (NOM), and stitching interference metrology. Current K-B mirror surface shape technologies are summarized and the upcoming research progress is prospected.
Recent advances in high-power continuous-wave ytterbium-doped fiber lasers
DANG Wen-jia, LI Zhe, LI Yu-ting, LU Na, ZHANG Lei, TIAN Xiao, YANG Hui-hui
2020, 13(4): 676-694.   doi: 10.37188/CO.2019-0208
Abstract(811) FullText HTML(355) PDF 4354KB(103)
Abstract:
High power continuous-wave ytterbium-doped fiber lasers have unique advantages such as high electro-optical efficiency, excellent beam quality and good thermal management. For these reasons, these fiber lasers are widely used in industrial processing, national defense and military, and scientific research. However, their non-linear and thermal effects at high-power conditions limit the further improvement of their output power. In this paper, the formation mechanism and corresponding suppression methods of stimulated raman scattering and thermally induced mode instability are analyzed. We hope that these analyses can provide some reference for the design and integration of high-power fiber laser systems. The research results for overcoming these limited factors introduced since 2015 are then discussed in detail. This paper is concluded by predicting the development prospects of high-power continuous-wave ytterbium-doped fiber lasers.
Fiber-reinforced silicon carbide and its applications in optical mirrors
ZHANG Wei, ZHANG Ge, GUO Cong-hui, FAN Tian-yang, XU Chuan-xiang
2020, 13(4): 695-704.   doi: 10.37188/CO.2020-0052
Abstract(475) FullText HTML(210) PDF 1380KB(47)
Abstract:
Fiber-reinforced silicon carbide composites with excellent mechanical and thermal properties are widely used in aerospace, nuclear energy, automobile, chemical industry and many other fields, especially in optical mirrors. This paper introduces the characteristics of fiber-reinforced silicon carbide composites. The advantages and disadvantages of different preparation processes of fiber-reinforced silicon carbide composites are compared. The protective effects of different interface layers on fibers and composites are expounded. The application progress of fiber-reinforced silicon carbide composites in the field of optical mirrors at home and abroad is summarized. Finally, the research direction to be carried out for realizing large-scale application of fiber-reinforced silicon carbide mirror blanks is analyzed.
Research progress of deep-UV nonlinear optical crystals and all-solid-state deep-UV coherent light sources
WANG Xiao-yang, LIU Li-juan
2020, 13(3): 427-441.   doi: 10.3788/CO.2020-0028
Abstract(2045) FullText HTML(853) PDF 2774KB(171)
Abstract:
All-solid-state deep ultraviolet coherent light sources have important applications in frontier science, high technology and many other fields. An effective and feasible technical approach is to use commercially available visible and near-infrared all-solid-state lasers as the fundamental frequency light source to generate a deep ultraviolet laser through cascaded frequency conversion using nonlinear optical crystals. This paper reviews the research progress of deep ultraviolet nonlinear optical crystals and all-solid-state deep ultraviolet coherent light sources. Taking KBBF crystals as the representative example, their discovery, crystal growth, corresponding prism-coupled device technology, main optical properties, and ability to generate deep ultraviolet coherent light are each introduced. It was proven that KBBF crystals are excellent nonlinear optical crystals that can achieve deep ultraviolet laser output through direct frequency doubling. The applications of deep ultraviolet coherent light sources based on KBBF crystals and prism-coupled technology are discussed, with special focus given to ultra-high resolution photoelectron spectrometers. Finally, the future direction of the development of deep ultraviolet nonlinear optical crystals and all-solid-state deep ultraviolet laser technology are given.
Research progresses of planar super-oscillatory lenses for practical applications
LI Wen-li, YU Yi-ting
2019, 12(6): 1155-1178.   doi: 10.3788/CO.20191206.1155
Abstract(412) FullText HTML(133) PDF 14797KB(34)
Abstract:
Due to the diffraction limit, it is difficult to achieve far-field super-resolution focusing and imaging for traditional optical systems. The appearance of planar superlenses based on the super-oscillation principle provides a possible solution to the problem. It can achieve far-field super-resolution focus without using evanescent waves. By precisely adjusting the diffraction and interference effects among the diffractive elements, electric field oscillation that is higher than the highest spatial frequency of the system can be measured in the local area of the focal plane, and thus the transverse and axial sizes of the diffractive focal spot can be precisely controlled. Compared with conventional optical lenses, planar Super-Oscillatory Lenses(SOLs) hold advantages for their arbitrary control over the optical field, large degree of freedom in design and easy integration with optical systems. Due to the above-mentioned reasons, SOLs have attracted extensive attention from researchers in the fields of diffractive optics and micro-nano optics. In this paper, concerning practical applications, the research state-of-the-art and application scenarios of planar SOLs are presented and discussed. Finally, the system's problems and its corresponding solutions are also described.
Review on progress of variable-focus liquid lens
HUANG Xiang, LIN Si-ying, GU Dan-dan, BU Zhen-xiang, YI Wei-jin, XIE Pei-qin, WANG Ling-yun
2019, 12(6): 1179-1194.   doi: 10.3788/CO.20191206.1179
Abstract(485) FullText HTML(140) PDF 5581KB(62)
Abstract:
Compared with the traditional mechanical zoom lens, the variable-focus liquid lens has a smaller lens, faster response time, lower cost and higher integration capabilities. These lenses are widely used in image acquisition, target tracking and feature recognition. The performance and applications of liquid lenses are determined by the focal length adjustment method. This paper summarizes the progress of liquid crystals, dielectrophoresis, electrochemistry, electrowetting principle-based function control variable-focus lenses, electrostatic force, electromagnetic force, pressure regulation, and environmental-response-technology-based mechanical driven variable-focus lenses. The integrated applications of variable-focus liquid lenses in optofluidic chips are introduced. Also, the major obstacles and the settlement are described. Furthermore, the development potential and future research direction of the variable-focus liquid lens are also predicted and summarized.
Spectroscopic ellipsometry and its applications in the study of thin film materials
ZHU Xu-dan, ZHANG Rong-jun, ZHENG Yu-xiang, WANG Song-you, CHEN Liang-yao
2019, 12(6): 1195-1234.   doi: 10.3788/CO.20191206.1195
Abstract(928) FullText HTML(159) PDF 11094KB(50)
Abstract:
Spectroscopic ellipsometry is used to measure the relative amplitude and phase change of linearly polarized light reflected by a material surface, so as to obtain the ellipsometric parameters. The optical properties of a material can be deduced by fitting these parameters. This technique is advantageous for being non-contact, highly sensitive, non-destructive, so it is widely used in physics, chemistry, materials science and microelectronics, etc, being an indispensable optical measurement method. This article first introduces the development history of the technology, and then presents the basic principle of the traditional ellipsometer. According to different measurement principles, ellipsometers can be divided into two types:extinction and photometric. The basic structure, measurement principle and related application of these two different types of ellipsometer are briefly clarified. After comparing these various ellipsometers, their advantages and disadvantages are introduced. At this point, a double Fourier transform infrared ellipsometry system developed by Fudan University is highlighted. Then, according to the basic steps of ellipsometric parameter manipulation, a measurement, modeling and fitting process is introduced. The equations of various optical dispersion models used for parameter fitting are introduced in detail and application examples are illustrated. Finally, the future development direction of spectroscopic ellipsometry is proposed.

Supervisor: Chinese Academy of Sciences

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

Editor-in-Chief: Wang Jiaqi, Academician

ISSN 2095-1531

CN 22-1400/O4

CODEN ZGHUC8

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