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Projector calibration based on cross ratio invariance
YANG Jian-bai, ZHAO Jian, SUN Qiang
 doi: 10.37188/CO.2020-0111
Abstract(125) FullText HTML(55) PDF 3424KB(11)
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.
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
 doi: 10.37188/CO.2020-0130
Abstract(96) FullText HTML(33) PDF 3826KB(8)
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.
Time-delay interferometry for space-based gravitational wave detection
WANG Deng-feng, YAO Xin, JIAO Zhong-ke, REN Shuai, LIU Xuan, ZHONG Xing-wang
 doi: 10.37188/CO.2020-0098
Abstract(156) FullText HTML(34) PDF 9986KB(15)
The 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, the Time-delay Interferometry technique, TDI, 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.
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
 doi: 10.37188/CO.2020-0193
Abstract(46) FullText HTML(14) PDF 2438KB(7)
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.
Research advances in adaptive interferometry for optical freeform surfaces
 doi: 10.37188/CO.2020-0126
Abstract(182) FullText HTML(60) PDF 3241KB(33)
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, this paper introduces 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 prospects the future development of freeform surface adaptive interferometers are proposed.
Polarization changes of partially-coherent Airy-Gaussian beams in a slanted turbulent atmosphere
CHENG Ke, LU Gang, ZHU Bo-yuan, SHU Ling-yun
 doi: 10.37188/CO.2020-0095
Abstract(105) FullText HTML(26) PDF 2094KB(4)
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 in this paper may be useful for studying atmospheric communication, and show that optical information encoding can be achieved by selecting appropriate parameters.
Review of interrogation technology for quasi-distributed optical fiber sensing systems based on microwave photonics
WU Ni-shan, XIA Li
 doi: 10.37188/CO.2020-0121
Abstract(141) FullText HTML(61) PDF 3910KB(23)
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 on 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
 doi: 10.37188/CO.2020-0169
Abstract(47) FullText HTML(13) PDF 4062KB(3)
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. It can efficiency improve the output efficiency of narrow linewidth pumped mid-infrared MgO∶PPLN OPO.
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(45) FullText HTML(11) PDF 3984KB(2)
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 map of the existing algorithm is 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 objectness image to output the final saliency map. In addition, for the scene that contains multiple salient targets, by refocuing 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 between the saliency map obtained by the method proposed in this paper and the ground truth is 0.2128, which is lower than the existing method. The detection result contains more detailed information about the salient target, which improves the above-mentioned shortcomings of the existing salient detection methods.
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
 doi: 10.37188/CO.2020-0097
Abstract(221) FullText HTML(46) PDF 3336KB(5)
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 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 structure modulation
ZHAO Jia-wang, ZHANG Yun-hai, WANG Fa-min, MIAO Xin, SHI Xin
 doi: 10.37188/CO.2020-0120
Abstract(160) FullText HTML(81) PDF 4007KB(22)
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 wolth 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.
Establishment and analysis of the diffraction BRDF model for surface defects
LU Min, WANG Zhi-le, ZHANG Shu-qing
 doi: 10.37188/CO.2020-0162
Abstract(34) FullText HTML(7) PDF 3692KB(0)
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
 doi: 10.37188/CO.2020-0084
Abstract(164) FullText HTML(69) PDF 3833KB(14)
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, this paper proposes 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.
Research on 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
 doi: 10.37188/CO.2020-0050
Abstract(186) FullText HTML(68) PDF 1981KB(8)
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.
Solutions to inhomogeneous and unstable illumination in biological photoacoustic tomography
Meng Qi, Sun Zheng
 doi: 10.37188/CO.2020-0142
Abstract(69) FullText HTML(39) PDF 4420KB(5)
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.
Study on 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
 doi: 10.37188/CO.2020-0205
Abstract(23) FullText HTML(9) PDF 5056KB(4)
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 = 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.
Effects of the combination of sample temperature and spatial confinement on LIBS
YU Dan, SUN Yan, FENG Zhi-shu, DAI Yu-yin, CHEN An-min, JIN Ming-xing
 doi: 10.37188/CO.2020-0118
Abstract(84) FullText HTML(39) PDF 3891KB(1)
The signal intensity of laser-induced breakdown spectroscopy can be improved by increasing sample temperature and confining space confinement. The combination of the two techniques can further improve the spectral intensity of laser-induced breakdown spectroscopy. In this paper, the effects of increasing a sample’s temperature and spatial confinement on laser-induced breakdown spectroscopy (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.
Analysis of effects on the beam quality β factor of high power laser beams
WANG Yan-ru, WANG Jian-zhong, RAN Zheng-hui, DING Yu-jie
 doi: 10.37188/CO.2020-0137
Abstract(60) FullText HTML(19) PDF 3740KB(5)
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.
Hybrid plasmonic leaky-mode lasing on subwavelength scale
YAN Shan-Shan, WANG Shuang-Peng, SU Shi-Chen
 doi: 10.37188/CO.2020-0108
Abstract(43) FullText HTML(11) PDF 4792KB(3)
Surface plasmon polariton is a mode of electromagnetic surface waves that exists on two dielectric cross-sections (usually a metal and an insulator) with opposite signs of dielectric constant, which can break the diffraction limit. In an appropriate optical waveguide structure composed of metal and dielectric, light can be trapped at the subwavelength scale. Here, we propose an approach that integrates dielectric waveguiding with plasmonics by finite-element simulation. The hybrid optical waveguide consists of an active ZnO nanowire separated from a metal surface by a nanoscale dielectric gap (10 nm). The coupling between the surface plasmonic and waveguide modes allows energy to be stored and propagated in the subwavelength dielectric gap. The leaky modes of the ZnO nanowire lose part of their energy to the continuum of the dielectric layer during propagation. Due to gain guiding, the hybrid electric leaky mode makes it possible to observe leaky-mode lasing. This approach could lead to the true integration of subwavelength lasers based on nanoscale semiconductor-based plasmons and photonics.
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
 doi: 10.37188/CO.2020-0099
Abstract(167) FullText HTML(54) PDF 4622KB(18)
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 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.
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(20) FullText HTML(7) PDF 3787KB(0)
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, this paper uses the finite element analysis method to analyze the propagation law of incident ultrasonic waves and reflection of ultrasonic echo characteristics inside a laser-welded joint. Based on a modified 6 dB method, a laser welding joint melt width evaluation model was 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 is 6.77 dB. 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.
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(34) FullText HTML(8) PDF 3594KB(7)
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.
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(22) FullText HTML(7) PDF 3675KB(0)
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 is proposed. Firstly, the gray integral projection method combined with the OTSU 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.
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(32) FullText HTML(8) PDF 3966KB(2)
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 was designed with two band-pass channels: 3.2~3.8 μm (channel 1) and 4.9~5.4 μm (channel 2). Thin films were fabricated by thermal evaporation in a high vacuum chamber, and the film thickness monitoring curves were designed using the POEM (percent of optical extreme monitoring) strategy. At a working temperature of 100K, 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 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.
Measurement of rotation angle of galvanometer using reflective circular grating
LIU Yong-kun, DING Hong-chang, Xiang Yang, LV Si-hang
 doi: 10.37188/CO.2020-0179
Abstract(42) FullText HTML(13) PDF 6034KB(4)
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 used to interfere to convert the angular displacement of the galvanometer into a change in the intensity of interference fringes. In this way, the measurement of the rotation angle of the galvanometer is realized. The experimental results show that the detection system can realize the measurement of the galvanometer's angle of ±10°, and the measurement accuracy is 10″. The high-precision measurement of the rotation angle of the galvanometer is realized, and the device has a compact structure to meet the requirements of a compact design of the scanning galvanometer demand.
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(75) FullText HTML(11) PDF 4230KB(7)
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.
A fast blind denoising method for grating image
ZHANG Shen-hua, YANG Yan-xi, QIN Qiao-meng
 doi: 10.37188/CO.2020-0166
Abstract(29) FullText HTML(12) PDF 3476KB(2)
The three-dimensional measurement technology based on the projection of sine grating fringe image is a highly active research area. 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 decomposed 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 Gaussian filtering method based on the phase map is employed. 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.
Double pumped composite cavity 501 nm cyan laser with tunable injection power ratio
WANG Lan, JIN Guang Yong, DONG Yuan, WANG Chao
 doi: 10.37188/CO.2020-0161
Abstract(41) FullText HTML(9) PDF 3422KB(1)
In order to explore the theoretical and technical basis for improving 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 that there is no gain competition of two kinds of fundamental frequency laser in the cavity, improve the output power of fundamental frequency laser, and 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, and the injection LBO optical power is adjusted. The sum frequency conversion efficiency and output power are compared 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). It fills the gap in the research on the controllability of the cyan light output power and conversion efficiency near 500 nm.
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(38) FullText HTML(10) PDF 3909KB(5)
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.
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(134) FullText HTML(47) PDF 6364KB(8)
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 \begin{document}$ + 45^\circ $\end{document} method, \begin{document}$ \pm 45^\circ $\end{document} method, \begin{document}$\Delta 45^\circ $\end{document} method, rotation fitting method and pseudo-depolarizer method in practice though experiments. Results show that: the \begin{document}$\Delta 45^\circ $\end{document} method, \begin{document}$ \pm 45^\circ $\end{document} method and rotation fitting method are relatively accurate when the misalignment angle is small, but the operation of the \begin{document}$ \pm 45^\circ $\end{document} method and rotation fitting method are more complicated. The \begin{document}$ + 45^\circ $\end{document} method still has a large calibration error without a misalignment angle. The pseudo-depolarizer method is the easiest to operate, but it is restricted by a non-ideal pseudo-depolarizer. Through comparison of theory and experiment, this paper provides a suggestion for the best choice of gain ratio calibration method. It is recommended that the \begin{document}$\Delta 45^\circ $\end{document} method be used for calibration with a half-wave plate, and the pseudo-depolarizer method be used for calibration with a high-precision depolarizer.
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(63) FullText HTML(20) PDF 1984KB(12)
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.
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(47) FullText HTML(10) PDF 4015KB(2)
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 in Lu2O3 matrix and the luminescent properties of a synthetic powder 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 increased by a factor of 13.3, 16.8 and 14.2, respectively, compared to that of under 322 nm of 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 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(132) FullText HTML(31) PDF 4545KB(9)
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.
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(110) FullText HTML(26) PDF 3846KB(3)
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 M2factor 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.
Performance studies on laser absorbing coating
Zhang Lei, Xie Xianchen, Wu Yong, Wang Ping, Wu Junjie
 doi: 10.37188/CO.2020-0154
Abstract(86) FullText HTML(32) PDF 3569KB(3)
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 with 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.
Variable step size search method of CGH encoding
Qiu Hong-wei, Jin Chun-shui, Yu Jie, Liu Yu, Zhang Hai-tao, Wang Li-ping, SUN Shi-zhuang
 doi: 10.37188/CO.2020-0124
Abstract(80) FullText HTML(34) PDF 3827KB(10)
In the field of aspheric testing, computer-generated hologram (CGH) technology has been widely used. CGH encoding, which is the conventional encoding method to achieve highly accurate coding, uses an amount of data that is often up to tens or even hundreds of gigabytes. Therefore, in order to achieve high encoding accuracy with a small amount of encoded data, this paper proposes a variable step size CGH encoding method. This method selects different sampling frequencies 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 had 3.142 nmRMS. In order to verify the credibility of the test results, this paper designs and makes a compensator to test the same aspheric surface. The test result had 3.645 nmRMS. The difference between the two results is 1.291 nmRMS, and shows that the encoding method can meet the requirements of high-precision testing of aspheric surfaces.
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(99) FullText HTML(43) PDF 3314KB(5)
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 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(134) FullText HTML(32) PDF 4603KB(7)
  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.
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(173) FullText HTML(44) PDF 3931KB(27)
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(225) FullText HTML(53) PDF 4215KB(28)
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(141) FullText HTML(41) PDF 4724KB(5)
  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(191) FullText HTML(28) PDF 4273KB(12)
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.
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(211) FullText HTML(48) PDF 3572KB(16)
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 present a comparative performance evaluation 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 provide research and analysis of the improved design of receivers in optical OFDM systems. The challenges and upcoming research of OFDM systems in VLC are summarized. We induce optical OFDM systems in this paper, providing a research reference and proposing more efficient unipolar modulation schemes to further improve the spectral efficiency and reliability of optical OFDM systems.
Research progress on the modulation properties of new electro-optic materials
LV Xiao-lei, ZHAO Ji-guang, DU Xiao-ping, SONG Yi-shuo, ZHANG Peng, ZHANG Jian-wei
 doi: 10.37188/CO.2020-0039
Abstract(208) FullText HTML(63) PDF 3432KB(25)
Polarization modulation technology using 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. With perovskite-structured electro-optical materials becoming more and more mature, electro-optic modulation technology using 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 PMNT modulation bandwidth, poor PLZT transmission performance, and low KTN practical application bandwidth. Future research will focus on the practicality of this modulation technology. The technology’s electro-optic modulation performance can be improved with doping and the signal-to-noise ratio of the system can be optimized by establishing performance characterization models.
Progress on two-dimensional quantum sheets and their optics
CHEN Zhe-xue, WANG Wei-biao, LIANG Cheng, ZHANG Yong
2021, 14(1): 1-17.   doi: 10.37188/CO.2020-0176
[Abstract](462) [FullText HTML](121) [PDF 14140KB](203)
Two-dimensional (2D) materials like graphene have attracted much attention due to their unique structures and exotic properties. With significantly reduced lateral sizes, 2D quantum sheets (2D QSs) are attracting an increasing level of interest. 2D QSs have opportunities for new applications because of their intrinsic characteristics of being 2D materials and having emerging quantum confinement and prominent edge effects. This review focuses on the conceptual interpretation of 2D QSs and the recent progress on their preparation and optical properties. Particular focus is given to the realization and significance of the universal and scalable production of intrinsic 2D QSs. In addition, the photoluminescence of 2D QSs and their applications in nonlinear optics and solid-state light-emitting devices are reviewed. At the end, the perspectives and challenges towards the future development of 2D QSs are discussed.
Progress on defect and related carrier dynamics in two-dimensional transition metal chalcogenides
WANG Yun-kun, LI Yao-long, GAO Yu-nan
2021, 14(1): 18-42.   doi: 10.37188/CO.2020-0106
[Abstract](1009) [FullText HTML](150) [PDF 5890KB](100)
Because of their unique physical properties, the monolayer and few-layer two-dimensional transition metal chalcogenides with atomic-level thickness are expected to play an important role in the next generation of optoelectronic devices. However, defects in two-dimensional materials affect their properties to a great extent. On one hand, defects reduce the fluorescence quantum efficiency, carrier mobility and other important device parameters. On the other hand, the control and utilization of defects have given birth to new techniques such as using single-photon sources. Therefore, it is very important to characterize, understand, handle and control the defects in two-dimensional materials. In this review, the research progress on defects and its related carrier dynamics in two-dimensional transition metal chalcogenides is summarized. This paper aims to sort out the great influence of defects and their related ultrafast dynamics on material performance in two-dimensional transition metal chalcogenides, and to support studies on fundamental physical properties and high-performance optoelectronic devices.
Recent progress and prospects of topological quantum material-based photodetectors
ZHANG Xing-chao, PAN Rui, HAN Jia-yue, DONG Xiang, WANG Jun
2021, 14(1): 43-65.   doi: 10.37188/CO.2020-0096
[Abstract](351) [FullText HTML](161) [PDF 5560KB](100)
The discovery of the topological quantum states of matter is a major milestone in condensed matter physics and material science. Due to the existence of special surface states (e.g. Dirac fermions, Weyl fermions, Majorana fermions), topological quantum materials can usually exhibit some novel physical properties (such as the quantum anomalous Hall effect, 3D quantum Hall effect, Zero-band gap caused by topological states, ultra-high carrier mobility, etc.), which are different from conventional semiconductors. Because of this, there is an abundance of prospects for applications in low-power electronic and optoelectronic devices, especially in broad-spectrum detection. However, the application of topological quantum materials in the field of photoelectric detection is still in the exploratory stage at present. This article reviews the characteristics and preparation methods of topological quantum materials and the development status with respect to optical-sensing materials in photodetectors. The structure and performance of the devices based on topological quantum materials are also mentioned as the development prospects in the field of broad-spectrum detection.
Research progress on organic self-assembling low-dimensional circularly polarized luminescent materials
WANG Meng-Zhu, DENG Yong-Jing, LIU Shu-Juan, ZHAO Qiang
2021, 14(1): 66-76.   doi: 10.37188/CO.2020-0192
[Abstract](164) [FullText HTML](71) [PDF 5044KB](34)
In recent years, materials with Circularly Polarized Luminescence (CPL) have received growing attention due to their wide applications in 3D displays, optical storage, optical security, etc. Supramolecular self-assembling is one of the most effective methods to construct CPL active materials, which can assemble different types of molecules into low-dimensional (0D, 1D and 2D) structures with unique functions. This review summarizes the research progress of self-assembled CPL active organic low-dimensional materials from recent years with emphasis on the driving force of supramolecular self-assembly. Firstly, the review systematically summarizes the current design strategies of self-assembled CPL active organic low-dimensional materials. Secondly, it focuses on their performance and applications. Finally, it discusses the future opportunities and challenges of this rapidly developing field.
Suppressed ion migration in halide perovskite nanocrystals by simultaneous Ni2+ doping and halogen vacancy filling
SUN Zhi-guo, WU Ye, WEI Chang-ting, GENG Dong-ling, LI Xiao-ming, ZENG Hai-bo
2021, 14(1): 77-86.   doi: 10.37188/CO.2020-0060
[Abstract](311) [FullText HTML](97) [PDF 4331KB](40)
Lead Halide Perovskites(LHPs) are promising candidates for next-generation optoelectronic application. However, defect-induced ion migration causes phase degradation in LHP nanocrystals. Therefore, material stability has become an urgent problem that impedes practical applications. In this paper, we aim to study the influence of doping cations on inhibiting the migration of halogen ions in perovskite nanocrystals. Through the measurement of ion migration activation energy and in-situ high-resolution transmission electron microscope technology, the effect of precursor dopants on the stability of LHPs were analyzed. Firstly, we synthesized two types of LHP nanocrystals with high crystal quality using nickel acetylacetonate and nickel bromide as precursor dopants, respectively. Secondly, the optical properties and component elements of the doped samples were analyzed by absorption-fluorescence spectroscopy, X-ray diffraction, X-ray photoelectron diffraction, and transmission electron microscopy. Finally, the ion migration activation energies of various LHP films were measured using temperature-dependent ion conductivity tests, and the influence of the precursor dopants on the stability of as-synthesized doped LHPs was compared with the results from high-resolution electron microscopy. The results showed that the activation energies of the doped CsPbBr3 samples were significantly improved compared to the intrinsic CsPbBr3 sample (0.07 eV), which were determined to be 0.238 eV for nickel acetylacetonate and 0.487 eV for nickel bromide. In addition, the electron irradiation experiments showed that the nickel bromide-doped perovskite nanocrystals exhibited higher structural stability. This is due to the strong bonding of doped Ni2+ to halogen and the synergistic passivation effect of halogen filling vacancy defects. It can be concluded that Ni2+ doping and halogen vacancy filling can effectively inhibit ion migration in halide perovskite nanocrystals.
Highly sensitive infrared detector based on a two-dimensional heterojunction
ZHANG Jin-yue, LYU Jun-peng, NI Zhen-hua
2021, 14(1): 87-99.   doi: 10.37188/CO.2020-0139
[Abstract](240) [FullText HTML](49) [PDF 6255KB](61)
To achieve weak signal detection, high sensitivity is required. Because of their strengths in optical and electrical properties such as wide spectral absorption, adjustable bandgap, and high carrier mobility, graphene, Transition Metal dichalcogenides (TMDs), Black Phosphorus (BP) and other two-dimensional (2D) materials have been used to fabricate infrared detectors. However, those 2D materials have disadvantages of weak light absorption, low carrier mobility and air instability, that restrict their applications in high-sensitivity infrared detection. Compared with single two-dimensional material, heterostructures consisting of two or more single 2D materials adopt the characteristics of each single material as well as some novel physical properties from heterojunctions/interfaces. In recent years, the heterostructure of 2D materials has been studied extensively in the field of high-sensitivity infrared detection. To gain a deep understanding of the factors affecting sensitivity, we provide a comprehensive review of the strategies that improve the sensitivity of infrared detectors and the development of high-sensitivity infrared detectors based on 2D heterojunctions in recent years. We summarize the figures of merit of these infrared detectors and identify the existing challenges impeding further improvements in sensitivity. Finally, by summarizing the challenges of future improving the sensitivity of infrared detection prospects for strategies to obtain high-sensitivity infrared detectors with good comprehensive performance and commercial applicability are presented with considerations for balancing the detector’s responsivity and response speed, large area two-dimensional heterojunction preparation, heterojunction interface optimization, and so forth.
Research progress of quasi-two-dimensional perovskite solar cells
WEI Jing, WANG Qiu-wen, SUN Xiang-yu, LI Hong-bo
2021, 14(1): 100-116.   doi: 10.37188/CO.2020-0082
[Abstract](468) [FullText HTML](137) [PDF 3585KB](113)
At present, the power conversion efficiency of perovskite solar cells exceeds 25%. Their rapidly increasing efficiency has made people increasingly optimistic about their commercial application, but the stability of perovskite remains the biggest obstacle to successful commercialization. Quasi-two-dimensional perovskite solves this problem. Utilizing the hydrophobicity and thermal stability of large organic spacer cations, quasi-two-dimensional perovskite can effectively improve the stability of perovskite and improved crystal formation energy while providing a more stable structure. Quasi-two-dimensional perovskite also invites significant improvement to the morphology of perovskite films, which can replace anti-solvent processes, simplify production, and meet the industrial production requirements of perovskite. However, the relatively large band-gap and low carrier mobility caused by insulated organic spacer cations hinder ion transmission, causing quasi-two-dimensional perovskite solar cells to be far less efficient than three-dimensional perovskite solar cells. Therefore, for quasi-two-dimensional perovskite, it is necessary to further study its characteristics and device applications to achieve further optimization of device performance. This article summarizes the research progress of quasi-two-dimensional perovskite solar cells, the molecular structure of quasi-two-dimensional perovskite, the methods and principles of quasi-two-dimensional doping that improves the stability of three-dimensional perovskite, and the phase distribution and carrier transport characteristics of quasi-two-dimensional perovskite. Then this paper analyzes the problems faced by quasi-two-dimensional perovskite solar cells and looks forward to their prospects. It is expected that it will provide a reference for the preparation of efficient and stable quasi-two-dimensional perovskite solar cells.
Strategies for improving the stability of quantum dots light-emitting diodes
LYU Mei, ZHANG Li, ZHANG Yan, YUAN Ming-jian
2021, 14(1): 117-134.   doi: 10.37188/CO.2020-0184
[Abstract](101) [FullText HTML](20) [PDF 5233KB](55)
Quantum dot Light-Emitting Diodes (QLEDs) are applied to the lighting and display industry for their unique photoelectric characteristics. Their External Quantum Efficiency (EQEs) is quickly meeting commercial requirements while the device’s lifetime is still one of their biggest challenges. The significant factors affecting the lifetime of QLEDs are divided into two aspects including the stability of the functional layer’s materials and charge imbalance. Various strategies for enhancing QLEDs stability are discussed including improving the stability of quantum dots, implementing Charge Transport Layers (CTLs) and promoting charge balance. With the deepening understanding of the degradation mechanism of QLEDs, more stable quantum dots and QLEDs devices have been developed. However, there are still some obstacles to the commercialization of QLEDs. For example, the high toxicity of Cd and the lifetime and efficiency of blue QLEDs are far lower than the corresponding levels of green and red QLEDs. In addition, the stability of QLEDs at high brightness (1000 cd m−2) is usually much shorter, which still limits the development of QLEDs. Therefore, research and development efforts for QLEDs should be further strengthened to overcome these technical obstacles and achieve the future commercialization of QLEDs.
A polarization-sensitive photodetector based on a AsP/MoS2 heterojunction
REN Zhi-hui, ZHONG Mian-zeng, YANG Jue-han, WEI Zhong-ming
2021, 14(1): 135-144.   doi: 10.37188/CO.2020-0189
[Abstract](159) [FullText HTML](42) [PDF 6956KB](25)
The ability to detect linearly polarized light is an important index for evaluating polarized photoelectric detectors. Black arsenic phosphorus (b-AsP) is a relatively stable anisotropic material, and is sensitive to linearly polarized light because of its anisotropy inside its planar structure. The material has important application value in polarization detection. This paper introduces a polarization-sensitive photodetector based on AsP/MoS2. Due to the anisotropic light absorption of AsP, effective carrier collection and strong carrier transport capacity of MoS2, as well as the suppression of dark current by a van der Waals heterojunction, the performance of the photodector shows relatively large on/off ratios. Moreover, the photodector has a current optical responsivity of 0.27 A/W and a detectivity of 2×1010 Jones, and more importantly, achieves a dichroic ratio of up to 3.06 at 638 nm. These experimental results show that AsP/MoS2 heterostructures have broad application prospects in the field of polarized photoelectricity detection.
Nanofluidic channel-resonant cavity structure for measuring micro-displacement of fluorescent substances
LI Lin-wei, CHEN Zhi-hui, YANG Yi-biao, FEI Hong-ming
2021, 14(1): 145-152.   doi: 10.37188/CO.2020-0076
[Abstract](166) [FullText HTML](78) [PDF 4084KB](29)
In order to measure the micro-displacement of a fluorescent substance, we propose a nanofluidic channel-resonant cavity structure. Firstly, by using the Finite-Difference Time-Domain (FDTD) method, the influences of the quantum dot’s polarization state and structural parameters on the coupling effect of fluorescence and structure are studied and the structure is optimized. Then, the micro-displacement of the fluorescent substance is detected by measuring the change in the optical power output of the coupled structure. Finally, the factors affecting the sensitivity of the sensors are studied. The results show that, compared with the traditional method, when the refractive index of the nanofluidic channel-resonant cavity coupling structure is in the 2.8~3.3 range, the structure can sense of the micro-displacement of a fluorescent substance with high accuracy. The results also show that the sensing sensitivity can be further improved by reducing the distance between the nanofluidic channel and the resonant cavity.
Fabrication and characterization of an LED based on a GaN-on-silicon platform with an ultra-thin freestanding membrane in the blue range
JIANG Cheng-wei, SHA Yuan-qing, YUAN Jia-lei, WANG Yong-jin, LI Xin
2021, 14(1): 153-162.   doi: 10.37188/CO.2020-0148
[Abstract](152) [FullText HTML](53) [PDF 3811KB](27)
In order to improve the opto-electronic performance and light extraction efficiency of LEDs based on a GaN-on-silicon platform, we proposed an LED device based on GaN-on-silicon with an ultra-thin freestanding membrane. By combining photolithography, deep reactive ion etching and inductively-coupled plasma reactive ion etching, we prepared an LED based on a GaN-on-silicon platform with an ultra-thin freestanding membrane, removing the silicon substrate of light-emitting area and most area of the electrodes, and thinning most of the GaN epitaxial layer. We performed three-dimensional morphology characterization for the LED device and found that the surface of the LED’s membrane is flat and that the membrane’s deformation is minimal. It is proved that the back process can solve the problem of membrane deformation caused by stress release between the GaN epitaxial layer and the silicon substrate. By characterizing the current-voltage and electroluminescence spectrum of the LED and comparing the LEDs with different structures and different light-emitting area sizes, we found that the opto-electronic performance and light output efficiency of the LED with an ultra-thin freestanding membrane are better than that of the common LED, and the change in size of the light-emitting area has a significant effect on the performance of the LED. Compared with the current of common LED, the current of the LED which has an ultra-thin freestanding membrane with 80-μm diameter light-emitting area increased from 4.3 mA to 23.9 mA under 15 V driving voltage. Under 3-mA current, the peak light intensity increased by about 5 times. The light-emitting efficiency of the LED with a 120-μm diameter light-emitting area is improved more perceptibly compared with that of LED with a 80-μm diameter light-emitting area. This research provides more possibilities for the development of high-performance LED devices with an ultra-thin freestanding membrane.
Size and temperature dependence of spectral transmittance for CdSe colloidal quantum dot film filters
WANG Jia-tong, HUANG Qi-zhang, GAO Jian-qiao, MA Yue, XING Xiao-xue, ZHANG Yu
2021, 14(1): 163-169.   doi: 10.37188/CO.2020-0198
[Abstract](106) [FullText HTML](28) [PDF 4525KB](25)
In order to reduce the size of spectrometers and make it suitable for military satellites and other fields, we used colloidal quantum dots as filter materials to study the optical properties of CdSe colloidal quantum dot filters. The high-quality CdSe colloidal quantum dots were synthesized by an organic phase reaction method and prepared into CdSe colloidal quantum dots thin film filters after p-phenylenediamine extinction treatment. The Transmission Electron Microscope (TEM) was used to characterize the morphology and particle size of the as-prepared samples. The UV-visible absorption and UV-visible transmittance were measured at different temperatures. The results indicated that the increase in particle size caused both absorption and transmittance to increase for CdSe colloidal quantum dots thin film filters at room temperature. Under a given particle size, the absorption and transmittance of the first exciton absorption peak red shifted with the rise in temperature. The red shift of absorption curve of CdSe colloidal quantum dots thin film filters did not exceed 1nm per 10 K temperature rising and the half-width increased. In addition, the stability and tunable characteristics of the CdSe colloidal quantum dots thin film filters have been verified through repeated experiments, and it is suitable as a cut-off filter. Therefore, CdSe colloidal quantum dots thin film filters have high value in micro-spectrometers.
Defects- and interface-enhanced Raman scattering in low-dimensional optoelectronic materials
HOU Xiang-yu, QIU Teng
2021, 14(1): 170-181.   doi: 10.37188/CO.2020-0145
[Abstract](272) [FullText HTML](214) [PDF 4136KB](48)
In recent years, a series of new low-dimensional optoelectronic materials with excellent properties have emerged. Combined with surface-enhanced Raman scattering (SERS) technology, they show great application potential and are expected to become highly sensitive SERS substrates. Defects and interface regulation of low-dimensional optoelectronic materials are important strategies for their applications in SERS technology. In this paper, the types and enhancement mechanisms of defects- and interface-enhanced Raman scattering in new low-dimensional optoelectronic materials are introduced. By looking forward to the application and research prospect of defects- and interface-enhanced Raman scattering, this work might inspire people to reconsider and further understand the study of SERS.
Room-temperature terahertz photodetectors based on black arsenic-phosphorus
DONG Zhuo, CHEN Jie, ZHU Yi-fan, YANG Jie, WANG Zhong-chang, ZHANG Kai
2021, 14(1): 182-195.   doi: 10.37188/CO.2020-0175
[Abstract](239) [FullText HTML](52) [PDF 3958KB](56)
Terahertz technology is indispensable in plenty of fields due to the abundant interactions between terahertz waves and matter. In order to meet the needs of terahertz applications, the development of highly sensitive and portable terahertz detectors based on distinctive physical mechanisms and various materials with excellent properties are urgently required. Black arsenic-phosphorus is a novel two-dimensional material that has a tunable band gap and transport characteristics with varying chemical composition, which has gained widespread interest in optoelectronic applications. Recent research on b-AsxP1-x mainly focuses on infrared detection, while the detection of terahertz has not yet been applied. Herein, an antenna-coupled terahertz detector based on exfoliated multilayer black arsenic-phosphorus is demonstrated. The terahertz response performance of the detector reflects two different mechanisms, which have a competitive relationship in the detection process. In particular, the detection mechanism can be tailored by varying the chemical composition of black arsenic-phosphorus. By balancing the band gap and carrier mobility, a responsivity of over 28.23 V/W and a noise equivalent power of less than 0.53 nW/Hz1/2 are obtained at 0.37 THz. This implies that black arsenic-phosphorus has great potential in terahertz technology.
Fabrication and optoelectronic characterization of suspended In2O3 nanowire transistors
JIANG Yi-yang, CHEN Yan, WANG Xu-dong, ZHAO Dong-yang, LIN Tie, SHEN Hong, MENG Xiang-jian, WANG Lin, WANG Jian-lu
2021, 14(1): 196-205.   doi: 10.37188/CO.2020-0062
[Abstract](181) [FullText HTML](39) [PDF 4710KB](17)
One-dimensional (1D) semiconductor nanowires have shown outstanding performance in nano-electronics and nano-photonics. However, the electrical properties of the nanowire transistors are very sensitive to interactions between the nanowires and substrates. Optimizing the device structure can improve the electrical and photodetection performance of nanowire transistors. We report a suspended In2O3 nanowire transistor fabricated by one-step lithography, showing a high mobility of 54.6 cm2V−1s−1 and a low subthreshold swing of 241.5 mVdec−1. As an ultraviolet photodetector, the phototransistor shows an extremely low dark current (~10−13 A) and a high responsivity of 1.6×105 A•W−1. This simple and effective method of suspending the channel material of a transistor can be widely used in manufacturing high-performance micro-nano devices.
Hybrid graphene/n-GaAs photodiodes with high specific detectivity and high speed
TIAN Hui-jun, LIU Qiao-li, YUE Heng, HU An-qi, GUO Xia
2021, 14(1): 206-212.   doi: 10.37188/CO.2020-0153
[Abstract](94) [FullText HTML](17) [PDF 3377KB](21)
Hybrid graphene/semiconductor phototransistors have attracted great attention because of their ultrahigh responsivity. However, the specific detectivity (D*) for such hybrid phototransistors obtained from source-drain electrodes is assumed to be 1/f noise. In this paper, D* of ~1.82×1011 Jones was achieved from source-gate electrodes. Compared with the same device which was measured from source-drain electrodes, D* was improved by ~500 times. This could be attributed to the carrier trapping and detrapping processes having been screened by the Schottky barrier at the interface. The rise and decay times were 4 ms and 37 ms, respectively. The temporal response speed also correspondingly improved by ~2 orders of magnitude. This work provides an alternative route toward light photodetectors with high specific detectivity and speed.
Writing nanopores on a ZnS crystal with ultrafast Bessel beams
CHANG Gai-yan, WANG Yu-heng, CHENG Guang-hua
2021, 14(1): 213-225.   doi: 10.37188/CO.2020-0101
[Abstract](231) [FullText HTML](105) [PDF 4709KB](28)
Zinc sulfide (ZnS) crystal is one of the important materials used to make the wide-spectrum infrared window. The ultrafast laser technology for manufacturing the nanopores with high aspect ratio provides an important approach to fabricate the photonic devices such as mid-infrared waveguide Fourier transform spectrometer etc. In this paper, a 40-times-demagnification ultrafast laser direct-writing system was built with a 4f system and a Gaussian-Bessel beam generated by a quartz axicon and a Yb:KGW laser source that operated at a wavelength of 1030 nm, a repetition rate of 100 kHz and a pulse width tunable from 223 fs to 20 ps. When the pulse energy was changed from 36 μJ to 63 μJ and the pulse duration was changed from 12.5 ps to 20 ps, the nanopore structure with a diameter of 80~320 nm was successfully written on the ZnS crystal. The surface morphology, diameter and depth of the nanopores were determined by FIB (Focused Ion Beams) ablation and SEM (Scanning Electron Microscopy) imaging. The influence of laser pulse energy and pulse width on the nanopores was studied. The results show that when the pulse width is 20 ps and the pulse energy is 48 µJ, the depth of a nanopore is about 270 µm.
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(705) FullText HTML(215) PDF 7413KB(116)
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(435) FullText HTML(104) PDF 3630KB(105)
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(226) FullText HTML(74) PDF 3727KB(45)
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(214) FullText HTML(103) PDF 4987KB(49)
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(314) FullText HTML(63) PDF 6952KB(70)
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(547) FullText HTML(171) PDF 2407KB(91)
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(484) FullText HTML(171) PDF 4616KB(120)
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(374) FullText HTML(138) PDF 4187KB(58)
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(1149) FullText HTML(393) PDF 1212KB(124)
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
2020, 13(4): 660-675.   doi: 10.37188/CO.2019-0231
Abstract(731) FullText HTML(331) PDF 8130KB(76)
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(727) FullText HTML(339) PDF 4354KB(91)
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(414) FullText HTML(195) PDF 1380KB(42)
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(1975) FullText HTML(825) PDF 2774KB(162)
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.
Progress of OLEDs prepared by inkjet printing
LIU Xin, YE Yun, TANG Qian, GUO Tai-liang
2020, 13(2): 217-228.   doi: 10.3788/CO.20201302.0217
Abstract(1574) FullText HTML(842) PDF 3187KB(196)
In recent years, OLED(Organic Light Emitting Diode) devices have been widely used in small-and medium-sized displays, and have gradually been popularized in large area display applications, such as in TVs and lighting. With the continuous development of organic light-emitting technology, higher requirements drive research on the color and pattern of OLED devices. Compared with the traditional vacuum evaporation process, inkjet printing technology easily colors large-area devices and patterns composite functional materials. It is also simple to implement, low in cost and has a more flexible process. In this paper, the current progress of inkjet-printed OLED devices is reviewed. Furthermore, this paper systematically introduces the development of inkjet printing equipment, by optimizing bank structures to improve the resolution of their display screens, by optimizing the ink formulation and composition ratio to suppress the coffee ring effect of inkjet droplets, and improves the uniformity of display luminescence. Finally, this paper summarizes and provides prospects for the future development of this technology at home and abroad.
Research progress on rock removal by laser technology
GUAN Bing, LI Shi-bin, ZHANG Li-gang, CHEN Shuang-qing
2020, 13(2): 229-248.   doi: 10.3788/CO.20201302.0229
Abstract(1501) FullText HTML(741) PDF 4890KB(75)
Laser technology in rock removal is an important research direction in the field of applied optics. It is a complex, high-temperature and high-pressure physical and chemical process with multi-phase, multi-coupling and multi-scale applications. In order to clarify the core difficulties in laser-rock interaction research and to provide an effective theory reference and trend information for researchers, an overview of research on laser rock removal technology is summarized. Firstly, the mechanism of rock removal using lasers is clarified. Then, existing research of laser rock removal is summarized and analyzed from different perspectives, including laser equipment for petroleum drilling and completion, its influencing factors, the phase-change heat transfer of temperature fields, its physical and mechanical properties, and its feasibility in the oil and gas industry. Finally, the advantages of rock removal by laser technology compared with traditional drilling and completion methods are elaborated. In view of the existing problems in laser-rock interaction research, the future development trend of rock removal by laser technology is predicted. The research results show that rock removal by laser technology can lead to research breakthroughs in field-supporting facilities, multi-factor evaluation, multi-field coupling mechanisms and theoretical systems of underground applicability.
Application of planar antenna in field-effect transistor terahertz detectors
WANG Xiao-Dong, YAN Wei, LI Zhao-feng, ZHANG Bo-wen, HUANG Zhen, YANG Fu-hua
2020, 13(1): 1-13.   doi: 10.3788/CO.20201301.0001
Abstract(1055) FullText HTML(510) PDF 2481KB(47)
In order to improve the responsivity and reduce the noise equivalent power of Field-Effect Transistor (FET) THz detectors, a suitable planar antenna structure is necessary.In this paper, we investigate the research progress of FET THz detectors integrated with planar antenna structures. Firstly, we analyze the working principle of FET THz detectors and clarify that an integrated planar antenna could effectively improve the detector's performance by enhancing its coupling efficiency with terahertz waves. Secondly, we present some typical planar antennas and discuss their pros and cons. These include the dipole antenna, the patch antenna, the slot antenna, the grating-gate, and others, which are each compared with respect to responsivity for the detectors. Finally, we find that the responsivity of the FET THz detectors can be greatly improved when applying planar antenna structure and that each type of antennas contributes uniquely. This work introduces several planar antennas integrated into FET THz detectors, including the performance and research progress of various antennas.Some existing problems are described and some predictions of the future development trends for this technology are summarized.
Progress of quantum dot backlight technology
YE Yun, YU Jin-hui, LIN Shu-yan, CHEN En-guo, XU Sheng, GUO Tai-liang
2020, 13(1): 14-27.   doi: 10.3788/CO.20201301.0014
Abstract(1416) FullText HTML(769) PDF 4222KB(83)
Quantum dots (QDs) have received widespread attention because of their adjustable emitted wavelength of light, color purity and high quantum efficiency, which have great potential in applications requiring high-color-quality displays with photoluminescence. In this paper, the progress of QD backlights based on each QDs on-chip, QDs on-surface and QDs on-edge are reviewed, including their principle, structures and current applications. Then, several other novel QD backlight structures are also introduced, prompting a proposal for two novel QD backlight technologies. One is the QDs scattering diffusion plate, which is prepared by injecting molding with a mixture of QDs and polymer at a low temperature. The other is a QD microstructure light guide plate, which is fabricated by transferring QDs on the surface of a light guide plate through screen printing or inkjet printing. Both of these two QD plates can achieve high color gamut while being simple to process, being low in cost and holding high production efficiency. These have wide applications in high color gamut liquid crystal displays.
Research progress on laser-produced plasma light source for 13.5 nm extreme ultraviolet lithography
ZONG Nan, HU Wei-min, WANG Zhi-min, WANG Xiao-jun, ZHANG Shen-jin, BO Yong, PENG Qin-Jun, XU Zu-yan
2020, 13(1): 28-42.   doi: 10.3788/CO.20201301.0028
Abstract(2089) FullText HTML(1223) PDF 2768KB(185)
The semiconductor industry is the backbone of the high-tech and information age. Lithography technology, one of the core technology of the semiconductor industry, has become a key research subject all around the world. This article mainly discusses the light source of 13.5 nm Extreme Ultraviolet Lithography (EUVL) by using Laser-Produced Plasma (LPP). It makes a brief introduction to the principles behind this technology and the development history of this field at home and abroad. The introductions include the materials used in the multilayer mirror, and rationale for the selection of materials, the shape and design of the target and the type of laser. At the same time, this article points out that the main problems for the EUVL are light debris reduction and the conversion efficiency improvement of EUV light.This paper also gives special analysis of the light source output devices of 13.5 nm EUVL machines produced by international famous companies——Gigaphoton of Japan and ASML of the Netherlands, which can generate more than 100 W level EUV power. Finally, this article summarizes and forecasts future research related to this technology.
Recent progress in tunable metalenses
LIN Yu, JIANG Chun-ping
2020, 13(1): 43-61.   doi: 10.3788/CO.20201301.0043
Abstract(1117) FullText HTML(646) PDF 8834KB(113)
Emerging optical devices demand miniaturized, integrated and intelligent optical zoom systems, thus stimulating development in nano-optoelectronics. Metalenses are two-dimensional planar structures with lens function composed of arrays arranged specifically to equally focus wavelengths of light. Due to their ultrathin and lightweight properties and their ease of integration, it is expected that they will revolutionize optics by replacing the conventional bulky, curved lenses used that pervade optical devices. However, once the micro/nano-structures of a metalens are fabricated, their shape and size cannot be modified, which can not realize the real-time adjustment of focusing and will limit the further development of metalenses' functions and applications. Currently, substantial effort is being devoted to solving this problem. One of the most attractive aspects of metalenses is in the way they combine metasurface lenses with smart materials. In this article, we first provide an overview of novel tunable metalenses. Then, we elaborate and analyze their regulatory principles and device performance, respectively. Finally, we summarize the current problems and difficulties facing the development of tunable metalenses and describe the direction of their future development.
Research progress of quantum dot enhanced silicon-based photodetectors
ZHU Xiao-xiu, GE Yong, LI Jian-jun, ZHAO Yue-jin, ZOU Bing-suo, ZHONG Hai-zheng
2020, 13(1): 62-74.   doi: 10.3788/CO.20201301.0062
Abstract(1324) FullText HTML(674) PDF 6598KB(82)
Silicon-based photodetectors have been widely investigated due to their high reliability, easy integration and low cost. With the development of artificial intelligence and autonomous vehicles, research and performance enhancement of silicon-based photodetectors is an important field of research. Quantum dots are excellent light-conversion and light-modulation materials due to their superior absorption coefficient, tunable spectra, high photoluminescence quantum yield and simple integration. The tunable light absorption and phototuminesence properties of quantum dots make them suitable materials for enhancing the detection. Quantum dots enhanced silicon-based photodetectors are emerging as a new technique to advance the performance of detection and imaging. In particular, they show potential to expand the functionality of CCD and CMOS devices and further satisfy increasing demands for detection. In this review, we summarized the progress of quantum dot-enhanced silicon-based photodetectors in the field of ultraviolet detection, infrared imaging, polarization detection and spectral detection, hoping to attract the attentions of domestic colleagues.
Image processing method for ophthalmic optical coherence tomography
CAI Huai-yu, ZHANG Wei-qian, CHEN Xiao-dong, LIU Shan-shan, HAN Xiao-yan
2019, 12(4): 731-740.   doi: 10.3788/CO.20191204.0731
Abstract(2082) FullText HTML(599) PDF 2700KB(66)
Optical coherence tomography(OCT) has become a hot research topic in the field of clinical medicine due to its features including micron-level high resolution, non-invasive imaging and instantaneity, which has developed rapidly and made much progress and break throughs in recent years. In this paper we briefly review the applications of OCT in ophthalmology, discuss the methods of speckle noise reduction in the spatial and frequency domains of OCT images, and summarize the precise positioning and stratification method of each layer of tissue in the OCT anterior segment and retina image. The advantages and disadvantages of the segmentation methods based on gray value search, active contour model, graph and pattern recognition algorithms are analyzed and compared. In addition, the existing problems with segmentation methods are discussed and the corresponding solutions and feasible optimization schemes are proposed. Analysis and evaluation of clinical diagnostic indicators of ophthalmic diseases are discussed. According to the needs in ophthalmology and the current status of OCT image processing, the development trends and level of OCT image processing are discussed and analyzed.
The regularized phase tracking technique used in single closed interferogram phase retrieval
WANG Xian-min, LIU Dong, ZANG Zhong-ming, WU Lan, YAN Tian-liang, ZHOU Yu-hao, ZHANG Yu-peng
2019, 12(4): 719-730.   doi: 10.3788/CO.20191204.0719
Abstract(999) FullText HTML(422) PDF 4295KB(100)
Different kinds of modulation methods are usually adopted when physical quantities, such as temperature, forces and deformation, are measured in interference. Fringe patterns carry measurement information of those quantities and are usually later analyzed for its retrieval. Single closed fringes are generally what is recorded by CCD. When the experimental conditions are not conducive to phase shifting, loading wave and other modulation means, the regularized phase tracking(RPT) technique can retrieve a continuous phase map directly from a single interferogram, making it the most effective method. In recent years, RPT technique has been improved to achieve higher processing power, algorithm robustness and retrieval accuracy for complex fringe patterns, ultimately making it more practical. In this paper, we introduce the basic algorithm principle and how the RPT technique is applied in the retrieval of single interferograms, review the technique's relevant modifications and developments in recent years, cite some examples used for phase retrieval and speculate the direction of its future development.
Realization of a watt-level 319-nm single-frequency CW ultraviolet laser and its application in single-photon Rydberg excitation of cesium atoms
WANG Jun-min, BAI Jian-dong, WANG Jie-ying, LIU Shuo, YANG Bao-dong, HE Jun
2019, 12(4): 701-718.   doi: 10.3788/CO.20191204.0701
Abstract(1703) FullText HTML(623) PDF 8142KB(82)
In order to meet the demand for single-photon Rydberg excitation of cesium atoms in the field of atomic physics, we investigated the key technolgies of single-frequency continuous wave(CW) tunable ultraviolet(UV) laser at 318.6 nm. Combining the fiber lasers, fiber amplifiers and the nonlinear crystals, we achieved 318.6 nm UV laser over 2 Watt output with cavity-enhanced second-harmonic generation following the sum-frequency generation of two infrared lasers at 1 560.5 nm and 1 076.9 nm in PPLN crystal. The typical root-mean-square fluctuation of UV laser power was less than 0.87% within 30 minutes. The electronic side-band locking scheme based on a temperature controlled hyper-fine ultra-stable ultra-low-expansion cavity placed in an ultra-high vacuum chamber was used to achieve the continuously tuning of UV laser in a wide range while still keeping it locked. The continuously tunable range was larger than 4 GHz and the residual frequency fluctuation of UV laser was about 16 kHz. We employed this high-power single-frequency continuously tunable UV laser system for the direct 6S1/2nP3/2(n=70-100) Rydberg excitation of cesium atoms with atomic vapor cells in experiments. After that, relevant theoretical analysis and research have been done. With a magneto-optical trapped cesium atomic ensemble, single-photon Rydberg excitation using the UV laser system was achieved with a pure optical detection scheme.

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



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