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Improvement of Transmission Efficiency in Microwave Photonic Links Using EDFA
Xiao Yong-chuan, Wang chao, Zhang hao, Zhang Ya-biao, Yu Cai-bin, Qu Peng-fei, Sun Li-jun
Accepted Manuscript  doi: 10.37188/CO.2019-0195
Abstract(172) FullText HTML(79) PDF 2216KB(3)
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Photonics have long been viewed as an enabling technology that extends the sensing and signal processing performances of radio frequency (RF) remoting systems such as radar and electronic-warfare because of its inherent advantages in multi-octave operating frequencies, broad instantaneous bandwidth, low transmission loss, and good phase linearity. In order to improve the efficiency of the analog optical transmitter during electronic-to-optical conversion, an erbium-doped fiber amplifier (EDFA) combing with a low-bias modulator in an external intensity modulation direct detection link is applied. According to our analysis, the RF gain reduces linearly with modulator’s optical power output when the bias becomes close to its minimum. Thus, the gain provided by the EDFA to the optical signal was transferred to increase RF transmission efficiency. Experimental results indicated that the RF gain improved by 13.5 dB compared to that of conventional quadrature bias point transmissions. Meanwhile, a small penalty is introduced to system noise. Most importantly, this can be achieved by using off-the-shelf devices, which can drastically reduce the system’s cost. Finally, the proposed scheme can be widely used in electronic information equipment.
Research on the Influence of Proximity Focusing Structure and Electric Field Distribution on Electron Trajectory in the EBCMOS
WANG Wei, LI Ye, CHEN Wei-jun, SONG De, WANG Xin
Accepted Manuscript  doi: 10.37188/CO.2020-0063
Abstract(0) FullText HTML(0) PDF 3389KB(0)
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In order to realize high-resolution electron bombarded CMOS (EBCMOS) imaging devices, this paper studies the effect of electric field distribution on the electron trajectory in proximity focusing electron bombarded CMOS (EBCMOS) devices. Three different electric field distributions are obtained by EBCOMS structure design: the equipotential surfaces between the photocathode and the back thinned CMOS (BSB-CMOS) are not parallel, partially parallel and parallel to each other. The electron trajectories in each case are simulated according to electromagnetism theory and monte carlo simulation method. The results indicate that, when the BSB-CMOS is bombarded by photoelectrons, the scattering diameter can be reduced to 30 μm when the surface of the electron multiplying layer is covered with 30 nm ultra-thin heavily doping layer and the voltage between electrodes is maintained at 4000 V while the distance between photocathode and BSB-CMOS is 1 mm. This structure is helpful to realize electrons focusing and achieve EBCMOS with high resolution. The scattering diameter, which was influenced by the distance and voltage between the photocathode and BSB-CMOS, was studied further. Electron focusing was found to improve with higher voltage and smaller distance, due to the higher electric field strength. This is work will provide theoretical guidance for improving the resolution characteristics of electron bombarded CMOS imaging devices.
Optical system design of a wide-area fundus camera
CHEN Wei-lin, CHANG Jun, ZHAO Xue-hui, JIN Hui
 doi: 10.37188/CO.2020-0066
Abstract(68) FullText HTML(36) PDF 1302KB(8)
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In order to scan the retinae of infants, a wide-area fundus camera was designed, and the design method of the device’s illuminating and imaging systems was investigated. Based on James Polans’ wide-field human eye model and a set of ophthalmic anatomy data, an infant eye model was established. Then, a tapered fiber scheme was proposed for wide area illumination. Finally, the design method of a wide-area fundus camera imaging system, including the contact lens and relay lens, is introduced. The design example shows that the field of view (FOV) of the wide-area fundus camera can reach 130 °, and the object resolution of the fundus can reach 10 μm. The design results meet the national standards YY0634-2008 for fundus imaging equipment and meet the requirements for infant retina screening.
Algorithmic Study of Total Petroleum Hydrocarbons in Contaminated Soil by Three-dimensional Excitation-emission Matrix Fluorescence Spectroscopy
Gu Yan-hong, Zuo Zhao-lu, Zhang Zhen-zhen, Shi Chao-yi, Gao Xian-he, Lu Jun
Accepted Manuscript  doi: 10.37188/CO.2019-0216
Abstract(854) FullText HTML(320) PDF 3278KB(9)
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Assessment of total petroleum hydrocarbons (TPHs) from contaminated soils demands reliable measurement to analyze the types and contents of mixed petroleum hydrocarbons in soils. Three-dimensional excitation-emission matrix (3DEEM) fluorescence spectroscopy technique has been demonstrated as a powerful technology for rapid analyzing the mixed petroleum hydrocarbons by its abundant spectral information. However, the detection precision in soils needs to be improved. This study investigated the correction methods of 3DEEM fluorescence Assessment of total petroleum hydrocarbons (TPHs) in contaminated soil demands reliable measurement to analyze the types and contents of mixed petroleum hydrocarbons in soil. Three-dimensional excitation-emission matrix (3DEEM) fluorescence spectroscopy has been demonstrated as a powerful technology for rapidly analyzing mixed petroleum hydrocarbons by identifying its abundant spectral information. However, detection precision in soil still demands improvement. This study investigates the correction methods of 3DEEM fluorescence spectra to correct the complicated matrix and scatting effects of soils. To improve the analytical accuracy, parallel factor analysis (PARAFAC) and the alternating trilinear decomposition method (ATLD) were used to qualitatively and quantitatively analyze mixed petroleum contaminated soils. The methods were used to assess three commonly observed petroleum hydrocarbons: machine oil, lubricating oil, diesel oil, and their mixtures. Compared with the results of PARAFAC, the average recoveries increased from 85% to 95%, implying that ATLD can effectively distinguish between similar fluorescence spectra and is more effective in the detection of the components and total content of petroleum in soil. This work can have applications of risk assessment and remediation techniques.
The effects of metallic contacts on the lasing characteristics of organic thin films
HAO Yaru, DENG Zhaoqi
Accepted Manuscript  doi: 10.37188/CO.2020-0007
Abstract(241) FullText HTML(88) PDF 1086KB(3)
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Optical loss caused by metallic contacts are thought to be a major obstacle to the achievement of organic laser diodes. We find that multi-channel emissions and surface plasmons (SPs) using a proper distributed feedback structure can allow successful lasing in organic thin films in the presence of contacting electrodes and even show better lasing performance when compared to metal-free cases. A lower threshold (0.026 mJ/pulse) laser emission is achieved with the Ag metal electrode on the grating structure with a period of 740 nm. Since there is no increase in device thickness, the electrical properties have are not reduced when the optical properties are improved.
Influence of Turbulent Atmosphere on the Effect of Coherent Beam Combining
SONG Ji-kun, LI Yuan-yang, CHE Dong-bo, GUO Jin, WANG Ting-feng
Accepted Manuscript  doi: 10.37188/CO.2019-0197
Abstract(1129) FullText HTML(817) PDF 3879KB(6)
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Coherent beam combining is a promising technology for achieving a high-power laser beam with good beam quality. However, turbulent atmosphere is one of the key factors that restrict its application and development. This paper focuses on the influence of atmospheric Greenwood frequency on the correction effect of the coherent combination system based on stochastic parallel gradient descent (SPGD) algorithm. At first, the influence of different turbulence intensities on the correction effect of coherent combination systems is analyzed by numerical simulation under static atmospheric conditions. Then, a set of rotating phase screens that meet Kolmogorov’s statistical law are generated by numerical calculation to simulate the turbulent atmosphere and study the correction effect of coherent combination system at different atmospheric Greenwood frequencies. Finally, an experimental platform is established to demonstrate the coherent combination effect of two laser beams. The simulated and experimental results show that when the system's control algorithm iteration frequency (350 Hz) is constant, the disturbance of turbulent atmosphere to the phase and light intensity of laser beams will increase with atmospheric Greenwood frequency, making the effect of coherent combination worse.
Fabrication and Characterization of Ultra-thin GaN-based LED Freestanding Membrane
LI Xin, SHA Yuan-qing, JIANG Cheng-wei, WANG Yong-jin
Accepted Manuscript  doi: 10.37188/CO.2019-0192
Abstract(535) FullText HTML(300) PDF 1127KB(6)
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In order to deliver the emergent light of LED active layer easily, we study the fabrication process, morphological characterization and optical characterization of submicron-level LED freestanding membrane. We prepared ultra-thin GaN-based LED freestanding membrane based on GaN-on-silicon wafer by using the backside process with photolithography, deep reactive ion etching and fast atom beam etching. Through a white light interferometer, we found that the deformation of the prepared ultra-thin LED freestanding membrane is positively correlated with the diameter of membrane, but negatively correlated with the thickness of membrane. The deformation as a whole is a smooth nanoscale arch deformation. Through the reflection spectrum test, we found that the number of reflection modes of LED freestanding membrane is much smaller than that of unprocessed silicon-based gallium nitride wafer and that the overall light intensity of reflection spectrum of the membrane is obviously improved. In the photoluminescence test, we found that due to the stress release, the emergent spectral peak of LED freestanding membrane has a blue shift of 8.2 nm compared with silicon-based gallium nitride wafer. Moreover, obvious outgoing light can be detected on the backside of the ultra-thin LED freestanding membrane with most of epitaxial layer removed. It demonstrates that LED freestanding membrane is more beneficial to deliver the emitted light in the photoluminescence test. In this study, the LED freestanding membrane with small thickness, large area, small deformation and excellent optical properties has been realized. It provides a new way for the application of GaN-based LED in the field of MOMES.
Fan-shaped Mid-infrared Chiral Metamaterials Based on Indium Tin Oxide and Their Circular Dichroism
ZHU Ye-xin, LI Ya-nan, SHI Wei-jie, ZHANG Wen-tao, YAN Chang-chun
 doi: 10.37188/CO.2019-0190
Abstract(537) FullText HTML(321) PDF 1070KB(17)
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A mid-infrared chiral metamaterial was designed to overcome the problems of large volume and high cost of traditional mid-infrared laser polarization state controls, The fan-shaped chiral structure made of Indium Tin Oxide (ITO) was designed and its Circular Dichroism (CD) characteristics in the mid-infrared band were studied. The CD variation characteristics of the structure are analyzed by changing the filling material in the fan blade layer, the thickness of the fan blades, their size, their number, and their material. The simulation results show that the CD signal varies with changes in these parameters. When the filling material is silicon and the fan blade has six pieces, the strongest CD signal is 0.052 and is obtained near the 5.3 μm wavelength by selecting the appropriate fan thickness and size. The simulation results also show that the structure composed of ITO exhibits great broadband circular dichroism compared to that with silver and gold, which provides a new concept for the design of broadband polarization-state control devices in the mid-infrared band.
Fiber-reinforced silicon carbide and its applications in optical mirrors
ZHANG Wei, ZHANG Ge, GUO Cong-hui, FAN Tian-yang, XU Chuan-xiang
Accepted Manuscript  doi: 10.37188/CO.2020-0052
Abstract(63) FullText HTML(31) PDF 1241KB(4)
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Fiber-reinforced silicon carbide composites are widely used in aerospace, nuclear energy, automotive, chemical and many other fields because of their low density, high strength, high modulus, good thermal conductivity, low coefficient of thermal expansion, good fracture toughness, excellent frictional properties, and a high resistance to temperature and ablation. It has both high specific stiffness and fracture toughness, resists deformation and easily integrates into optical-structures, so it has high potential in optical mirror applications. This article describes the effects of fibers on composite properties, matrix and fiber interface layers, and provides information on the research and application of materials in the field of optical mirrors at home and abroad.
Optimal design of a 2.7 m standard spherical inspection mirror support
GAO Jing-jing, JIAO Chang-jun, HUANG Shen, ZHANG Zhen, BI Yong
Accepted Manuscript  doi: 10.37188/CO.2019-0225
Abstract(158) FullText HTML(85) PDF 5393KB(3)
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To solve the problem where an increase in the diameter of a spherical inspection mirror causes its inspection accuracy to decrease, the weight support parameters of the 2.7-meter standard spherical mirror are optimized and the structural design of its adjustment frame and support system is designed. Firstly, the 54-point equal-force support ring was optimized for the mirror body using a finite element and genetic algorithm. In order to increase the rigidity of the mirror body after the nesting hole increases, the bottom support force and the side support force of each ring were each optimized and the influence of support radius and support force error on the support deformation was statistically analyzed. Finally, based on the analysis results, a structural frame of the standard inspection mirror and a support system were designed. The analysis results show that after optimization of the 54-point support position of the standard spherical mirror, the support force of each ring bottom and the side support force, the spherical mirror support deformation was less than 1/115λ(λ=632.8 nm), the bottom support position was disturbed by ±2 mm and the side support position was disturbed by ±0.6 mm. Furthermore, the case of support force disturbance was ±3 N, the support deformation was less than 1/70λ, which shows little deterioration. This meets the requirements of standard spherical mirror support.
Optical system design and stray light suppression of catadioptric space camera
LÜ BO, FENG Rui, KOU Wei, LIU Wei-qi
Accepted Manuscript  doi: 10.37188/CO.2019-0036
Abstract(204) FullText HTML(92) PDF 1572KB(10)
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In order to achieve low-cost, compact, large-field-of-view and long-focal-ground observations, a lens group is used as an aberration correction group to solve the limited field of view angle and low imaging contrast at a large field of view in the coaxial two-mirror optical system. The lens group adopts reasonable optical power and pitch, it expands the field of view of two-reflection mirrors and improves imaging quality in the camera's full field of view. Taking an engineering application as an example, this paper designs and develops an optical system with a 750 mm focal length, a field of view of 2ω=3.45, an average transfer function better than 0.2 at 108 p/mm, and an optimized design for its secondary mirror hood that suppresses stray light without a main mirror barrel hood. Simulation stray light was optimized by using TracePro software. The results show that the stray light point source transmittance (PST) in the non-imaging field of view ranges from 10−3 to 10−6. The system meets the requirements for traditional ground target detection and imaging, the feasibility of a compact large-field refracting optical stray light suppression structure is verified, and a certain reference for the design and optimization of commercial coaxial refracting optical systems is provided.
Panoramic peripheral vision imaging and display technology based on a deformation eyepiece and OLED
LUO Jie-chao, GUO Jun-da, MI Feng-wen, QIU Su, DUN Xiong, JIN Wei-qi
Accepted Manuscript  doi: 10.37188/CO.2019-0214
Abstract(154) FullText HTML(87) PDF 3712KB(10)
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In narrow spaces, vehicles, carriers or for single guards on duty, traditional displays have a dilemma wherein it is difficult to balance a display’s field of view and its resolution. This paper studies panoramic/periodic imaging technology and a system based on deformable eyepieces, which is expected to provide a technical solution to effectively solve the above problems. The system uses three low-light cameras with 4 mm focal length lens to form a panoramic imaging field of view of 150°. Using the FPGA processing platform, it processes algorithms for panoramic image analysis, stitching, correction, and display. It also has a real-time zoom display; a display system consisting of OLED micro-displays; and an anamorphic eyepiece group. large eyepiece enlarges the video image horizontally by a factor of 3 and displays a panoramic high-resolution dynamic scene image in real time. The experiment verifies the feasibility of a day and night panoramic imaging display. The system has a wide array of possible applications inside and outside of the military.
An Automatic Focusing Method of a Telescope Objective Lens Based on the Defocusing Estimation of a Circular Edge Response
LUO Qi-jun, GE Bao-zhen
Accepted Manuscript  doi: 10.37188/CO.2019-0247
Abstract(188) FullText HTML(164) PDF 1854KB(8)
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A new defocusing estimation algorithm based on the response curve of a circular edge is proposed, through which the calibration of some focusing parameters and the automatic focusing of the telescope objective lens are achieved. The relationship between the gray-scale response of the edge of the circular pattern and the defocusing radius is established. Using the double threshold mean filtering of the defocusing radius around the circle, the accurate defocus radius of the blurred image is calculated and the influence of motion blur and noise is reduced. According to the linear relationship between defocus radius and focus distance, the broken line fitting method is used to obtain the focus distance. Then, by using multiple object and focus image distances, the parameters of the focusing model of the ranging method are optimized and the automatic focusing of the imaging system is achieved. Through simulation and experimentation, the feasibility and robustness of the defocusing estimation algorithm are verified. The images taken by the calibrated autofocus imaging system are clear, have a physical resolution that reaches half of their theoretical value, and have a resolvable line width better than 0.354 mm when the shooting distance is between 43 m and 52 m.
Research on 2D grating displacement measurement technology
Jirigalantu, YIN Yun-Fei, YU Hong-Zhu, LIU Zhao-Wu, WANG Wei, LI Wen-Hao
Accepted Manuscript  doi: 10.37188/CO.2019-0237
Abstract(330) FullText HTML(207) PDF 5324KB(7)
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Ultra-precision displacement measurement technology is not only the basis for precision machining, but also plays a decisive role in the chip manufacturing industry that is rapidly developing such that it is following Moore's Law. The grating displacement measurement system based on the grating pitch is widely used in multi-degree-of-freedom displacement measurement. Compared with the laser displacement measurement system, the 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 systems based on two-dimensional gratings from recent years is introduced. The principle of zero-difference and heterodyne grating interferometry is also introduced. The optical structure based on a single-block two-dimensional grating is reviewed. The development history of the optical structure in two-dimensional grating coupling designs is summarized, the advantages and disadvantages of several two-dimensional grating displacement measurement systems are compared and analyzed, and then the development trend of two-dimensional grating displacement measurement system is speculated. Finally, the engineering process of the two-dimensional grating displacement measurement system is summarized.
Analysis of the corneal surface and peripheral defocus after orthokeratology
LIU Bao-kai, LIU Yong-ji, XIE Pei-ying, GUO Xi, GU Jian-da, YU Hao
Accepted Manuscript  doi: 10.37188/CO.2019-0248
Abstract(195) FullText HTML(100) PDF 915KB(2)
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In order to analyze the shape of human cornea after Orthokeratology, a new method of corneal shape analysis is proposed, which not only measures the influence of corneal thickness on the shape of cornea after Orthokeratology, but also reflects the asymmetry of a cornea. A reference surface was introduced into the analysis of the height data of the anterior surface of the cornea to eliminate the influence of corneal thickness, and then the anterior surface of the cornea was divided into the Optical Zone, Transition Zone and Peripheral Zone. The results show that the zone diameter of the Optical Zone is 1.9±0.27 mm, the radius of curvature is 8.32±0.38 mm, the zone diameter of the Transition Zone is 6.56±0.38 mm, the radius of the curvature is 7.48±0.55 mm, and the radius of curvature of the Peripheral Zone is 10.49±1.83 mm. After Orthokeratology, the horizontal refraction of the Transition Zone is lower than its vertical refraction. The refraction of the nasal side is greater than that of the temporal side and the refraction of the upper side is greater than that of the lower side. A semi-customized eye model was established based on the obtained parameters and the results show that its peripheral refraction was myopic after Orthokeratology and its refraction was asymmetrical in each direction, which is consistent with clinical observations.
The research progress of a K-B mirror high-precision surface metrology
ZHANG Shuai, HOU Xi
Accepted Manuscript  doi: 10.37188/CO.2019-0231
Abstract(266) FullText HTML(142) PDF 7939KB(7)
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The advanced light source introduced by the creation 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, especially in cases that require the surface precision of a K-B mirror. This key focusing optical element in advanced light sources should be less than tens of nanometers in 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 machine (NOM), and stitching. Current K-B mirror surface shape technology is summarized and the upcoming research progress is speculated.
Variable image distance bending using an elliptical bending mechanism with a constant cross-section mirror
ZHOU Bo-wen, WANG Nan, ZHU Wan-qian, XUE Song, TIAN Ying-zhong
Accepted Manuscript  doi: 10.37188/CO.2019-0250
Abstract(176) FullText HTML(106) PDF 1879KB(2)
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  Objective  In this paper, the surface slope error is studied when the image distance is adjusted drastically (when the position of the sample is changed) and when the object distance is fixed (when the position of the mirror in the light path is invariable).  Method  Based on theoretical analysis and the finite element analysis, slope error is calculated when it is caused by bending a mirror with a width equal to an elliptical cylinder with a different shape (different image distance). Then, a bending experiment of a prototype of the elliptical bending mechanism is conducted.  Result  Experimental results and analysis indicate that the slope error between the bending mirror and an ideal ellipsis will increase with a decrease in image distance, and the slope error of the mirror will increase more quickly as the image distance is shortened. When the initial slope error of the reflecting mirror is 0.397 μrad, the slope error of the bent mirror in the breadth (21.5-3.8 m) is between 0.402 μrad-0.560 μrad and the repeatable accuracy is 0.051 urad, which meets the design requirements of the beamline of the SSRF.  Conclusion  It is proven that in elliptically bending mirrors, continuous adjustment of the image distance from the focusing mirror can be achieved by using an equal section reflecting mirror bending mechanism.
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
Accepted Manuscript  doi: 10.37188/CO.2019-0241
Abstract(358) FullText HTML(161) PDF 1198KB(3)
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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.
A Femtosecond Laser-inscribed Fine-core Long-period Grating with Low Temperature Sensitivity
MING Xin-yu, GUO Qi, XUE Zhao-kang, PAN Xue-peng, CHEN Chao, YU Yong-sen
Accepted Manuscript  doi: 10.37188/CO.2020-0015
Abstract(155) FullText HTML(92) PDF 4497KB(6)
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In order to reduce crosstalk caused by temperature during refractive index and strain testing, the temperature, refractive index and strain response characteristics of fine-core long-period fiber gratings were studied. A long-period fiber grating with a period of 50 μm was successfully prepared on a single-mode fiber with a core diameter of 6 μm using the femtosecond laser direct writing method. The results show that long-period fiber gratings processed with low laser energy in fine-core fibers have lower temperature sensitivity, and maintain a larger extinction ratio and better spectral quality. The loss peak of this fine-core long-period fiber grating drifts only 1.7 nm in the 20 °C ~ 700 °C temperature range. The grating is also highly responsive to changes in the refractive index. Its ambient refractive index is in the 1.4065 ~ 1.4265 range, its sensitivity reaches 882.51 nm/RIU, and its strain sensitivity is −2.2 pm/με. This fine-core long-period fiber grating can better reduce crosstalk caused by temperature in the refractive index and strain tests.
Non-symmetrical Design of a Compact, Lightweight HMD Optical System
HUANG Song-chao, FENG Yun-peng, CHENG Hao-bo
Accepted Manuscript  doi: 10.37188/CO.2019-0193
Abstract(223) FullText HTML(92) PDF 2308KB(7)
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In non-symmetric optical systems, the field of view is narrow. The diameter of their exit pupil is narrow, their optical structure is complicated, their cost of manufacturing is high, and adjustment of their assemblies is troublesome. To address these problems, the design requirements and working principle of the dual mirror non-symmetrical optical system are firstly discussed. Then, the off-axis structure control method of the three-mirror non-symmetric optical system is analyzed. Finally, the XY polynomial free-form mirror is used to fold the optical path thus eliminating the obstruction, enlarging the field of view, correcting the off-axis aberration, and designing a non-symmetrical optical system suitable for helmet-mounted display. The designed dual mirror non-symmetrical optical system has a field of view of 60° x 30° and a pupil diameter of 8 mm. At a cutoff frequency of 52 lp/mm, the full field of view modulation transfer function value is greater than 0.25 and system distortion is less than 5%. This monocular system’s weight is about 190 g. The design results show that the non-symmetrical optical system has an improved field of view and image quality, is compact and lightweight, and can be applied to a helmet-mounted display.
Recent advances in high-power continuous-wave ytterbium-doped fiber lasers
DANG Wenjia, LI Zhe, LI Yuting, LU Na, ZHANG Lei, TIAN Xiao, YANG Huihui
Accepted Manuscript  doi: 10.37188/CO.2019-0208
Abstract(265) FullText HTML(157) PDF 3089KB(4)
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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 concluded by predicting the development prospects of high-power continuous-wave ytterbium-doped fiber lasers.
Generation of a 49-GHz, High-repetition-rate, All-polarization-maintaining, frequency-locked multicarrier
WANG Chao, XIAO Yong-chuan, LIN Shu-qing, YU Cai-bin, QU Peng-fei, LI Ru-zhang, SUN Li-jun
Accepted Manuscript  doi: 10.37188/CO.2019-0191
Abstract(208) FullText HTML(86) PDF 2236KB(4)
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Frequency-locked multicarrier with high-repetition-rate is an ideal tool for microwave channelization and optical communications. To meet the needs of those applications, we propose a multicarrier laser with a repetition frequency of 49 GHz. The IQ modulator works at the single-frequency shifting (SSB) state by carefully optimizing the radio frequencies (RFs) and their three bias points, resulting in a signal-to-noise ratio of 27.5 dB. The recirculating frequency shifter (RFS) architecture is employed to generate an optical comb with high flatness. By optimizing the power of RFs for the balance of intracavity loss, we successfully generate 28 frequency-locked subcarriers with flatnesses lower than 3 dB and tone-to-noise ratios (TNR) larger than 29 dB. Meanwhile, an FP etalon is used to increase the repetition-rate, resulting in 14 frequency-locked subcarriers with flatnesses lower than 2.7 dB, tone-to-noise ratios larger than 19 dB, average powers of more than 9 dBm and carrier spacings at 49 GHz. The system is built with all-polarization-maintaining components, showing one-push and long-term running properties. The power fluctuation of the multi-carrier frequency comb through the half-hour is only 0.5%, which shows that this scheme has great potential applications in channel communications and microwave channelization.
Study of TDLAS Detection of Propylene with Complex Spectral Features
Zhong Li, Song Di, Jiao Yue, Li Han, Li Guolin, Ji Wenhai
Accepted Manuscript  doi: 10.37188/CO.2019-0203
Abstract(2102) FullText HTML(460) PDF 4583KB(15)
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  Objetive  To satisfy the need for propylene measurement in the olefin production process, tunable diode laser absorption spectroscopy (TDLAS) was studied to improve analytical performance.  Method  Propylene is a heavy hydrocarbon with high molecular weight and a complicated structure. Its spectral absorption lines overlap and it has a broad absorption base. Its spectral features are not well rounded in parameters and have no applicable analytical expression. Thus, a numerical simulation approach is proposed using absorbance from a spectral database to obtain the optimized design parameters, which is independent of spectral features. In the simulation, the effect of a wider linewidth laser on the absorbance profile was considered. Through the comparison of simulation results and experimental collection, the TDLAS-based propylene analysis apparatus was developed correspondingly. It has a 1628.5 nm center wavelength broad-tuning DFB laser. A differential method was utilized in demodulated spectral acquisition to eliminate bias voltage. The multivariate linear regression model was employed to address the strong spectral interference from the background components in the analysis.  Result  Based on the simulated field test, the max relative error is 0.55% in the 0-10000 ppm range for the step test. For the long-term test, the standard deviation (1σ) is 9.30 ppm at 2000 ppm. The best standard deviation is 1.33 ppm at 221.9 seconds of integration time through Allen variance analysis. In the anti-interference test, the max error of 19.17 ppm is demonstrated at 2000 ppm propylene concentration while methane and ethylene concentrations vary.  Conclusion  The disadvantages of traditional methods such as the gas chromatogram (GC) and soft measurement methods are overcome by modulated absorption spectroscopy. The TDLAS system for heavy hydrocarbon detection with complex spectral features was demonstrated to have distinct advantages in precision, stability and interference suppression through multivariate regression modeling.
Study on the Light Intensity and Spatial Coherence Characteristics of Laser Coherent Detection in a Turbulent Atmosphere
REN Jian-ying, SUN Hua-yan, ZHAO Yan-zhong, ZHANG Lai-xian
Accepted Manuscript  doi: 10.37188/CO.2019-0194
Abstract(563) FullText HTML(520) PDF 2514KB(8)
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In this paper, the cross-spectral density function of target reflected light in laser detection is obtained by using generalized huygens-fresnel principle and Goodman target scattering theory, and the expression of intensity distribution and spatial coherence length of target reflected light is obtained from that. The influence of different light sources and target reflected light parameters on the intensity distribution and coherent length of the target reflected light is simulated by using the expressions obtained in this paper under turbulent atmospheric conditions. The results show that: The coherence length of the light source has little effect on the normalized light intensity distribution; The coherence length of the received light is smaller with a larger beam waist radius and reflected light radius, and the transmission distance increases as the coherence length increases at a slower rate. In the process of weak turbulent atmospheric transmission, the influence of light source parameters on the received light is much stronger. The larger the beam waist radius, the smaller the received light intensity and coherence length value. During strong turbulent atmospheric transmission, the influence of atmospheric turbulence on the received light is dominant.
Design of a Freeform Curved Prism Imaging Spectrometer Based on an Anastigmatism
ZHANG Jia-lun, ZHENG Yu-qun, LIN Chao, JI Zhen-hua
Accepted Manuscript  doi: 10.37188/CO.2019-0049
Abstract(260) FullText HTML(147) PDF 1483KB(10)
Abstract:
In this paper, an algorithm for calculating the initial structure of the Offner freeform curved prism imaging spectrometer’s secondary mirror’s external reflection is designed. The ray tracing method is used to obtain the formula for the propagation of light on the optical surfaces of the secondary mirror’s external reflection on an Offner spectrometer. The formula can determine the structural parameters of the optical component. The off-axis beam astigmatism theory commonly used in the analysis of off-axis systems is used to analyze image quality, and a reasonable threshold is set to judge the structure algorithm. The initial structure that meets the design requirements is obtained through iterative optimization in Matlab and the initial structure is optimized in Zemax. To verify the performance of the proposed algorithm, the initial structure of a free-form prism spectrometer with a spectral range of 380−780nm, a numerical aperture of 0.15 and a spectral resolution of 6 nm was designed. After being optimized in Zemax, the system reached the design index and the smile and keystone were both less than 0.1 pixels. The algorithm of this paper can quickly calculate the initial structure such that the requirements are satisfied, and can simplify its optimization.
Method of Enhancing the Quality of In-Line Holographic Images for Micro-Milling Tool
CHENG Ya-ya, YU Hua-dong, YU Zhan-jiang, XU Jin-kai, ZHANG Xiang-hui
Accepted Manuscript  doi: 10.37188/CO.2019-0217
Abstract(486) FullText HTML(278) PDF 3593KB(9)
Abstract:
When tool setting with digital in-line holography, the zero-order image and defocused twin-image can form strong and complex background noise, which gets superimposed on the real image and seriously reduces the quality of the reconstructed image. To improve interferential images in digital in-line holography, a holographic image enhancement method using an improved self-snake model is proposed. The improved self-snake model selects a diffusion intensity according to the gradient of the initial image. The experimental results show that the improved self-snake model can avoid the appearance of jagged edges and “pseudo-contours” caused by large gradient background noise during the diffusion process. This improvement outweighs the shortcomings of the self-snake model in holographic imagery. In addition, compared with the phase retrieval and multi-plane reproduction approaches, the improved self-snake model filtering method proposed in this paper not only has better suppression for interferential images but also can enhance the edge of the tool, which is conducive to the actualization of tool-setting using on digital in-line holography.
Design and Analysis of Stress-free Clamping of Mirrors Used in Free-electron Laser
ZHAO Chen-hang, LU Qi-peng, SONG Yuan, GONG Xue-peng, WANG Yi, XU Bin-hao
Accepted Manuscript  doi: 10.37188/CO.2019-0131
Abstract(860) FullText HTML(273) PDF 4422KB(3)
Abstract:
The reflector is an important optical element in free-electron laser beamlines. Deformation error caused by gravity can seriously affect the image quality of a beamline. To reduce deformation error, a gravity compensation scheme based on the Bessel point theory is proposed and a stress-free clamping device is designed. Taking a 440 mm * 50 mm * 50 mm mirror as an example, the deformation error of a mirror clamped with the traditional support method is 1.647 μrad. Adopting the newly designed device, the results of a finite element analysis showed that the deformation error reduced to 0.0857 μrad, which is better than the engineering index of 0.1 μrad. To prevent the mirror from moving when switching modes, a small clamping force of no more than 2N can be added to the mirror, at which point the surface error of the mirror becomes 0.0939 μrad. Additionally, a dynamic analysis of the device was also carried out, which indicated that the device mutes the low natural frequency, which means that resonance will not occur during operation. Therefore, this scheme satisfies our requirements for the beamline.
Research on modification of Soluble Solids Content sorting line based on light source transmitting and receiving integrated probe
Liu Yande, Rao Yu, Sun Xudong, Xiao Huaichun, Jiang Xiaogang, Xu Hai, Li Xiong, Xu Jia, Wang Guantian
Accepted Manuscript  doi: 10.37188/CO.2019-0165
Abstract(876) FullText HTML(930) PDF 7566KB(4)
Abstract:
Traditional quality sorting methods have been unable to meet people's increasing demands for fruit flavour and quality. Producers must therefore develop their traditional quality sorting methods to achieve sugar content sorting and ensure favourable flavour and quality. To address this, the near-infrared reflection spectra of navel oranges were collected separately through two different detection methods. The spectral energy of their ring transmissions and diffuse reflections had to be stronger than that of the multi-point transmission and diffuse reflections. The positions of their peaks and troughs had to be approximately the same. The near-infrared diffuse reflectance spectra were preprocessed using baseline correction and multivariate scattering correction. First and second derivatives were used to reduce the influence of stray light and noise. A partial least squares (PLS) model for the sugar content information that was collected through the two different reflection detection methods was established for their comparison and analysis. The experimental results show that the baseline correction preprocessing method produced the best results between the two methods. Its predicted correlation coefficient of sugar under diffuse transmission and reception reflection detection was 0.82 and its root mean square error was 0.45° Brix. The estimated correlation coefficient of the sugar content model using the transmit and receive diffuse reflection detection method was 0.80 and its root mean square error was 0.48° Brix. This research shows that it is feasible to use PLS modeling and near-infrared diffuse reflectance spectrum to upgrade the sugar content sorting methodology used on production lines.
Reviews
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](1439) [FullText HTML](611) [PDF 2774KB](64)
Abstract:
All-solid-state deep ultraviolet coherent light sources have important applications in frontier science, high technology and many other fields. An effective and feasible technical approach is to use commercially available visible and near-infrared all-solid-state lasers as the fundamental frequency light source to generate a deep ultraviolet laser through cascaded frequency conversion using nonlinear optical crystals. This paper reviews the research progress of deep ultraviolet nonlinear optical crystals and all-solid-state deep ultraviolet coherent light sources. Taking KBBF crystals as the representative example, their discovery, crystal growth, corresponding prism-coupled device technology, main optical properties, and ability to generate deep ultraviolet coherent light are each introduced. It was proven that KBBF crystals are excellent nonlinear optical crystals that can achieve deep ultraviolet laser output through direct frequency doubling. The applications of deep ultraviolet coherent light sources based on KBBF crystals and prism-coupled technology are discussed, with special focus given to ultra-high resolution photoelectron spectrometers. Finally, the future direction of the development of deep ultraviolet nonlinear optical crystals and all-solid-state deep ultraviolet laser technology are given.
Original Article
Optimization and analysis of a primary mirror for a laser incoherent combining system
TANG Wei, LIU Li-sheng, LIU Yang, SHAO Jun-feng, GUO Jin
2020, 13(3): 442-450.   doi: 10.3788/CO.2019-0161
[Abstract](520) [FullText HTML](285) [PDF 2320KB](29)
Abstract:
A primary mirror for a high-power laser incoherent combining system was designed and analyzed. Firstly, the material and the thickness of the primary mirror, it's supporting way and it's lightweight scheme were determined through theoretical analysis. Then, the thermal deformation of the primary mirror was calculated by the finite element method, and the topology optimization was executed according to thermal deformation results. Finally, the impact of gravity, base frequency and ambient temperature on the P-V value of the primary mirror was analyzed. The calculation results show that the temperature rise ΔT and the P-V value of the primary mirror gradually increase when irradiated by six lasers with a power of 10 kW over a greater amount of time. When laser irradiation time reaches 3 min, the temperature rise ΔT and the P-V value of the unoptimized primary mirror are 83.4 ℃ and 155 nm respectively, resulting in thermal deformation values in the irradiated area that are inconsistently affecting by the structure. Its D-value was about 1/6 that of the primary mirror. After topology optimization, the lightweight rate of the primary mirror was 54.5%, the thermal deformation value in the laser-irradiated area was consistent, and the P-V value of the primary mirror reduced to 1/3. The gravity deformation value of the primary mirror at different pitching angles was basically the same and the maximum P-V value was less than 10 nm. The ambient temperature causes distortion and defocus aberration, and with an increase in ambient temperature, the aberration grows. Modal analysis shows that the base frequency of the primary mirror meets the system requirement. These conclusions have a referential value for high power laser incoherent combining systems.
Numerical simulation of transmission spectra characterization of long-period fiber grating
ZHU Yu-yu, XI Ya-ru, ZHANG Ya-ni, JIANG Peng, XUE Lu, XU Qiang
2020, 13(3): 451-458.   doi: 10.3788/CO.2019-0152
[Abstract](965) [FullText HTML](714) [PDF 5090KB](38)
Abstract:
Based on the coupled-mode theory, the equation for the transmission spectrum of Long Period Fiber Gratings (LPFGs) is solved by using the transmission matrix method and the relationship between the spectral characteristics of LPFGs and grating parameters (such as grating period, writing length and the depth of refractive index modulation) is simulated. The results show that the resonant wavelength of LPFGs is red-shifted with an increase in the grating period and refractive index modulation depth, and that the resonant wavelength with higher-order mode is relatively more sensitive on the grating period. At the same time, the change in the spectral bandwidth mainly depends on the writing length of the grating. The bandwidth narrows gradually with an increase in the length of the grating and over-coupling occurs when the grating length is higher than 5.2 cm. With an increase in the refractive index modulation depth, the grating has the phenomena of incomplete coupling, complete coupling and over-coupling, and the position of the maximum resonance loss will gradually transfer to the lower-order mode. The results of this research have important referential significance for the theoretical research of LPFGs and parameter designs in practical applications.
Infrared polarization properties of targets with rough surface
LIU Yi, SHI Hao-dong, JIANG Hui-lin, LI Ying-chao, WANG Chao, LIU Zhuang, LI Guan-lin
2020, 13(3): 459-471.   doi: 10.3788/CO.2019-0123
[Abstract](547) [FullText HTML](330) [PDF 5411KB](31)
Abstract:
Infrared polarization imaging is advantageous for its ability to enhance image contrast and identify true-false targets. In order to improve detection and identification probability, it is necessary to accurately obtain the infrared radiation polarization properties of the targets. However, the traditional analytical model of infrared radiation polarization ignores the shadowing effect caused by rough surfaces. Based on the surface microelement bidirectional reflectance distribution function and by using a Muller matrix, the stocks analytical model of the infrared radiation polarization degree of the rough surface is constructed with a shadowing function. The effects of the incident angle and the surface roughness on the polarization of the metallic and nonmetallic targets are analyzed quantitatively. The analysis results show that the polarization degree of infrared spontaneous radiation decreases with an increase in the roughness of both the metal and the nonmetal, and the decrease of polarization degree of nonmetallic is greater than that of metal. Under the same roughness and temperature, the degree of polarization of the infrared radiation of the metal is always greater than that of the nonmetal. The polarization degree of infrared radiation firstly increases with the incident angle, and reaches a peak value within a specific range of incident angle, and then decreases dramatically. The difference in the degree of polarization between the metallic and nonmetallic infrared radiation reaches a maximum within a certain range of incident angle. This property is useful for distinguishing the metal and nonmetal. Finally, a long-wave infrared micro-polarization imaging system and near-infrared polarization imaging system are used to collect different images. The infrared radiation polarization properties of the targets are reasonably consistent with the results of the theoretical analysis. This research is of great significance for analyzing the polarization properties of real targets, designing infrared polarization systems and processing polarization images.
Simulation analysis of isolation between laser communication ground test equipments
ZHAO Meng, YAN Chang-xiang, WU Cong-jun
2020, 13(3): 472-481.   doi: 10.3788/CO.2019-0154
[Abstract](846) [FullText HTML](571) [PDF 5806KB](18)
Abstract:
The distance between a laser communication ground test platform and the terminal under test is far less than the actual communication distance due to space limitations. As a result, the backscattered stray light generated by the test platform optical device will enter the terminal under test, and the signal will seriously affect the performance of the terminal under test. Aiming at this problem, we research the isolation relationship between the tested terminal and the test platform based on the optical interference problem. The Cassegrain and off-axis three-mirror optical antenna are designed respectively. According to astigmatic transmission model, the stray light analysis software is employed to analyze the influence of optical antenna's structure and surface roughness on the isolation. The results of the analysis show that the isolation when applying the off-axis three-mirror optical antenna is significantly higher than that applying the Cassegrain optical antenna, and that this isolation increases with a decrease in the roughness of the optical surface. When the optical surface's roughness reaches 0.892 nm, the isolation is −86.22 dB. Finally, the relationship between the ABg model and the Harvey model parameters is derived. According to calculation formula of the roughness and TIS, the ABg model parameters with roughness of 0.7 nm and 0.5 nm are theoretically obtained. The isolation between the terminals is −94.39 dB and −97.3 dB, achieving an isolation rating of −90 dB.
On-line detection of soluble solids content of apples from different origins by visible and near-infrared spectroscopy
LIU Yan-de, XU Hai, SUN Xu-dong, JIANG Xiao-gang, RAO Yu, XU Jia, WANG Jun-zheng
2020, 13(3): 482-491.   doi: 10.3788/CO.2019-0128
[Abstract](686) [FullText HTML](347) [PDF 4480KB](23)
Abstract:
In order to realize fast, on-line, non-destructive testing of the Soluble Solids Content (SSC) of apples from different origins, and to reduce the effect of origin variability on NIR models, a universal model for predicting the SSC of apples from different origins is established. Firstly, the diffuse transmission spectra of Fuji apples from Qixia, Luochuan and Huining are collected with fruit dynamic online detection equipment. Then, 58 characteristic variables are selected and a UVE-PLS universal model for predicting the SSC of apples is established using the Partial Least Squares (PLS) algorithm combined with Uninformative Variable Elimination (UVE). The root mean square errors of single-origin prediction sets and the total-origin prediction set are 0.50~0.74° Brix and 0.63° Brix, respectively, which increase by 23.2%~44.4% and 35.7% respectively compared to the original individual model. Finally, a new external sample set is used to assess the performance of the model, showing a residual prediction deviation of 2.33 and ratios of the predicted values within the error range of ±1.0° Brix and ±1.5° Brix of 85% and 100%, respectively. Experimental results indicate that the establishment of a universal model for on-line detection of the SSC of apples, including those from multiple origins can improve the robustness of predicting the SSC of the samples from other origins. The results also show that an appropriate wavelength screening method can simplify the model. The development of a common model for the internal quality of fruit from different origins has strong potential for applications in wavelength-limited spectroscopy equipment.
Study on the binding mechanism of cefoxitin sodium to lysozyme by synchronous fluorescence spectroscopy
ZHANG Hong-cai, LIU Bao-sheng, CHENG Xu
2020, 13(3): 492-500.   doi: 10.3788/CO.2019-0112
[Abstract](657) [FullText HTML](322) [PDF 3518KB](19)
Abstract:
Under simulated physiological conditions (pH=7.40), the interaction between tyrosine (Tyr) residue and tryptophan (Trp) residue in lysozyme (LYSO) and cefoxitin sodium (CFXS) was studied using synchronous fluorescence spectroscopy. The results showed that CFXS quenched the fluorescence of Tyr and Trp residue in LYSO by static quenching, and that the number of binding sites n was nearly 1. At 310 K, the fluorescence quenching ratio of CFXS with Trp residue NSFQR(Trp)(60.25%) was higher than that of NSFQR(Tyr)(39.75%), indicating that the binding position was closer to the Trp residue. The Hill coefficient nH was about 1, indicating that the binding of CFXS to the Tyr and Trp residues in LYSO did not affect the binding of subsequent ligands to proteins. The drug binding rate of CFXS to Tyr residue in LYSO was 0.19% to 0.13%, and the drug′s binding rate to Trp residue was 0.23% to 0.14%, respectively. The content of the free drug was almost unchanged. The results showed that the combination of Tyr and Trp residue in LYSO and CFXS did not affect the efficacy of the drug. The protein binding rate of Tyr residue was 52.69% to 54.67%, and the protein binding rate of Trp residue was 67.67% to 69.39%, implying the amount of free amino acid residue in the protein decreased significantly. The main force of the CFXS-LYSO binding system was a hydrophobic interaction. The results of molecular docking showed that there was still a hydrogen bond between the CFXS and LYSO, and the best binding position was near to the active center of the LYSO. The combination of the two substances changed the microenvironment for the amino acid residue at the active center.
High precision corneal curvature radius measurement system
LI Hua-jian, XIAO Zuo-jiang, LIU Ying, ZHAO Yuan-yuan, WANG Rui-zhi, HE Xiao-ying
2020, 13(3): 501-509.   doi: 10.3788/CO.2019-0174
[Abstract](680) [FullText HTML](533) [PDF 4246KB](12)
Abstract:
To achieve accurate alignment of the imaging keratometer along the optical axis and improve the measurement accuracy of corneal curvature, we design a high precision imaging corneal curvature measurement system. The imaging light source, imaging optical system and interferometry system of the measurement system are studied. A light source is formed using uniform irradiation of the target ring with an LED array; The imaging objective lens adopts a double telephoto lens to enlarge the depth of its field, which is conducive to the measurement of alignment. Meanwhile, the magnification of the imaging objective lens are not affected by the depth of field. By using low coherent interferometry, the distance between the corneal vertex and the measured light source is accurately measured using a grating ruler to monitor the position of the scanning mirror. In this paper, the stability of the imaging objective magnification and the error of the corneal curvature measurement of the system are analyzed, and an experimental prototype is made based on the theory. The designed prototype is used to test the standard corneal simulators and the measurement accuracy of the system is up to ±0.02 mm, which basically meets the requirements of corneal curvature measurement.
A high precision image angular displacement measurement device with self-adaptive installation
YU Hai, WAN Qiu-hua, SUN Ying, LU Xin-ran, JIA Xing-dan
2020, 13(3): 510-516.   doi: 10.3788/CO.2019-0107
[Abstract](556) [FullText HTML](450) [PDF 2594KB](10)
Abstract:
The angular displacement measurement technology based on image detector is a hot research to realize high-precision and high-resolution angular displacement measurement. In order to improve the robustness of the angular displacement measuring devices, a high precision image displacement measurement device with self-adaptive installation techniques is designed in this paper. The installation and adjustment processes are very simple, and high resolution and high precision measurement output can be guaranteed in the presence of eccentricity in the calibration grating. Firstly, the angle measurement device using dual linear imaging sensors is proposed and a single-ring absolute grating is designed. Then, a high-resolution subdivision algorithm based on a centroid algorithm is used to subdivide the image, and dual linear image sensors are used to compensate for the angle measurement error. Finally, an experimental device is designed to test the performance of the adaptive installation. Experiments show that when the eccentricity of the grating is within ±1 mm, the designed device can achieve highly precise angular displacement measurements with high resolution. The device designed in this paper guarantee the output accuracy when the grating has an installation eccentricity of ±1 mm, which lays a foundation for improving the adaptability of small angular displacement measuring devices.
Design of solid-state array laser radar receiving optical system
WEI Yu, JIANG Shi-lei, SUN Guo-bin, ZHANG Xing-xing, WANG Yu-ning
2020, 13(3): 517-526.   doi: 10.3788/CO.2019-0166
[Abstract](825) [FullText HTML](663) [PDF 4571KB](103)
Abstract:
With regards to the safety of solid-state area array lidars, in order to improve the energy uniformity of imaging plane and increase the energy received by the optical system, this paper works to ensure a low signal-to-noise ratio and the detectability of a target. The optical parameters are given by modeling the emitted and received laser energy. The factors affecting the image plane's illumination in the optical receiver are studied and the design elements of optical systems with large fields of view, large relative aperture, and high illumination uniformity are described. Through ZEMAX optimization analysis, a detailed implementation process is then provided. A lidar receiving lens with λ = 905 (±5) nm, a focal length of 15 mm, a relative aperture of 1/1.4, and a field of view 2ω = 76° was designed. The total system length was less than 77 mm, and the MTF value at the spatial frequency of 20 lp/mm was greater than 0.5. The relative distortion at the 0.85 field of view was less than 8% and the unevenness of the image plane illumination was less than 7.2%.This design meets the requirements for lidar detection.
A state perception method for infrared dim and small targets with deep learning
HUANG Le-hong, CAO Li-hua, LI Ning, LI Yi
2020, 13(3): 527-536.   doi: 10.3788/CO.2019-0120
[Abstract](484) [FullText HTML](289) [PDF 5546KB](16)
Abstract:
Aiming at the problems of low accuracy, high artificial interference and high data quality requirements of the current spatial infrared dim target state perception, a new deep learning-based discrimination algorithm is proposed. Firstly, the state change of weak spatial infrared dim target is analyzed and a special data set is established. Then, a convolutional neural network dedicated to target state perception is established and adjustments are made in its local annotations and adaptive threshold. Finally, simulation data is generated from the target's radiation intensity information that was collected in the laboratory and is used to train and test the algorithm. A target state perception evaluation indexing system is established to evaluate the experimental results. The experimental results show that the accuracy of this method is 98.27% when the continuous complete radiation intensity information is inputted. When the radiation intensity information of the segment is inputted, the accuracy of each state is greater than 90%. This algorithm makes up for the shortcomings of current methods, which are not sensitive to low false alarm rates and incomplete target information. It improves detection speed and accuracy and better satisfies the demand for spatial infrared weak target sensing tasks.
Linkage tracking control technology of space laser communication network mirror
WANG Jun-yao, SONG Yan-song, TONG Shou-feng, JIANG Hui-lin, DONG Yan, DONG Ke-yan, CHANG Shuai
2020, 13(3): 537-546.   doi: 10.3788/CO.2019-0176
[Abstract](1128) [FullText HTML](818) [PDF 1837KB](22)
Abstract:
In order to improve the energy utilization efficiency of the optical antenna and realize the space laser communication networking, we study the mirror linkage tracking control technology. The principle of system composition is described, and a mirror linkage tracking control strategy based on a single-detector multi-actuator is discussed in detail. By analyzing the energy of a laser link, its linkage tracking constraints and error requirements are obtained. A mathematical model of double mirror linkage tracking is established. The servo controller is designed and simulated, and the prototype is built to test its tracking performance. The experimental results show that the system can track the target stably, the tracking target accuracy is better than 83 μrad, the double mirror linkage accuracy is better than 26 μrad and the received optical power of the system is significantly improved. The research in this paper lays a foundation for space one-to-many laser communication link networking.
Design of optical antenna for laser communication based on an off-axis freeform surface
GU Xi-xi, CUI Zhan-gang, QI Bo
2020, 13(3): 547-557.   doi: 10.3788/CO.2019-0157
[Abstract](917) [FullText HTML](560) [PDF 4315KB](28)
Abstract:
We propose a design for a large-field two-mirror afocal optical antenna based on an off-axis freeform surface to improve the working range of space laser communication systems and simplify the structure of optical systems. The optical antenna adopts an afocal structure without using collimating lens elements, which can greatly simplify the system structure, overcome the problems of traditional focusing optical antennae such as them being too large in volume or having a power density that is too high at the focus when using high power light source. First, based on third-order aberration theory, the aberration-free formula of this class of two-mirror afocal optical antenna is derived, and relative results are analyzed. Then, an afocal optical antenna is designed according to the analyzed results and practical requirements. The effective aperture of the system is 100 mm, the magnification is 5, the range of the wavelength is 500~1 100 nm, the full field of view is 0.6°, the primary mirror is part of the concave paraboloid and the secondary mirror is a freeform surface characterized by XY polynomials. MATLAB software is used to simulate the freeform surface of the secondary mirror. The design results show that the total field of view wavefront error of the optical system is better than λ/14 (λ=500 nm), the Strehl ratio is greater than 0.8, the system has a higher energy concentration, and the image quality is close to the diffraction limit. The field of view of the freeform surface optical system increased by 26.7% compared with that using traditional conic surface system. Therefore, this antenna structure is highly applicable and shows strong prospects for development in the field of laser communication.
Effects of a misaligned photodetector in autocollimators on angle measurements
LUO Jing, ZHANG Xiao-hui, HE Xu, YE Lu, ZHANG Tian-yi
2020, 13(3): 558-567.   doi: 10.3788/CO.2019-0207
[Abstract](572) [FullText HTML](332) [PDF 3053KB](25)
Abstract:
As one of the key errors in autocollimators, misalignment of the photodetector is analyzed and modeled carefully in this paper. Effect of misalignment of the photodetector on angle measurements is characterized, when the photodetector in any position and orientation in space with respect to the theoretical image plane of autocollimators. It is shown that the angular measurement errors of autocollimators induced by a misaligned photodetector increase with greater measuring range L, larger angle θ and smaller focal length f of the collimating object lens. When f=300 mm, L=100 mm, θ=20″, the angular measurement error caused by a misaligned photodetector is 0.004 5″. The effects of each photodetector misalignment error on angle measurements in autocollimators are characterized. The model proposed in this paper is validated. Among all kinds of photodetector misalignment errors, the defocusing error has the greatest influences on autocollimators. Hence, it is critical to choose an imaging objective with longer focal length, reduce the measurement distance, and improve the installation accuracy of the photodetector along the axis. The model proposed in this paper helps to systematically obtain the angular measurement errors caused by a misaligned photodetector, which will play a key role in building a better error analysis model for autocollimators.
Uncertainty analysis in cross-calibration and optimization calculation of calibration coefficients
GAO Shuai, LI Yuan, BAI Ting-zhu, ZHANG Yu-xiang, ZHENG Xiao-bing
2020, 13(3): 568-576.   doi: 10.3788/CO.2019-0215
[Abstract](465) [FullText HTML](322) [PDF 3375KB](12)
Abstract:
The general cross-calibration method uses the ordinary least square method to regress the calibration coefficient by data points selected after time, spatial, observation geometrics and spectral collocation. However, the ordinary least square algorithm would reduce the validity of the regressed result because of ignoring the differences in quality between each data point. An optimized method based on the calculation of uncertainty was proposed. This uncertainty analysis method was used to quantify the uncertainty of the radiation standard value for each data point, and their weight factors were calculated. The weighted least square method was used to regress the calibration coefficient. Using HYPERION as a radiance standard, the calibration coefficients of MODIS channels 1 to 7 were each regressed using the ordinary least squares method and the weighted least squares method. The regressed coefficients were compared with the official calibration coefficient. The results show that the calibration coefficients calculated using the weighted least squares method were closer to the official coefficients of MODIS channels 1, 2, 4, 5, 6, and 7. The maximum relative error reduced to 3%~5% and the average relative error decreased to 0.5%~1.5% compared with the ordinary least squares method, which indicates that the weighted least squares method proposed in this paper can further improve the calculation accuracy of cross-calibration.
Modeling and numerical simulation of a semiconductor switching device applied in an ultra-short pulse CO2 laser
GAO Yue-juan, CHEN Fei, PAN Qi-kun, YU Hang-hang, LI Hong-chao, TIAN You-peng
2020, 13(3): 577-585.   doi: 10.3788/CO.2019-0159
[Abstract](1345) [FullText HTML](1160) [PDF 3641KB](12)
Abstract:
The physical mechanism are studied for ultra-short pulse CO2 laser output realized by semiconductor switching technology. Firstly, based on the analysis of the generation, recombination and diffusion mechanism of laser-produced carriers, we introduce direct absorption, Auger recombination, plasmon-assisted recombination, an ambipolar diffusion process and according to Drude theory, we improve the theoretical model of semiconductor switching. Secondly, we simulate and analyze the generation of ultra-short CO2 pulses by two-stage semiconductor optical switches employing this model. The results show that the model is in good agreement with the latest experimental results reported abroad, which implies the rationality and correctness of the model. Finally, the model is used to analyze the effect of control pulse duration on the efficiency of the two-stage switching. It is found that a short control pulse is more conducive to intercepting high-quality ultra-short CO2 pulses accurately and efficiently. Semiconductor switching is an effective technique to realize the output of an ultra-short CO2 laser with an adjustable pulse width.
Development of the inverted-cone diversion type heat-stop for solar telescopes
ZHANG Yu-chen, WANG Fei-xiang, XU Fang-yu, HUANG Shan-jie, TAN Xu, LU Wen-long, XIAO Jian-guo, JIA Yu-chao, LUO Hong
2020, 13(3): 586-594.   doi: 10.3788/CO.2019-0139
[Abstract](462) [FullText HTML](261) [PDF 3727KB](9)
Abstract:
For large-aperture ground-based open-structure solar telescopes, an increase in heat-stop temperature will result in deterioration of image quality. In particular, heat-stop, located closely to the light-passing hole, has a great influence on image quality. This is one of the problems for the Chinese Giant Solar Telescope (CGST) development plan. For solving the heat-stop temperature control problem, the overall cooling efficiency should be high and further strengthen is implemented at key locations to achieve uniform temperature control. According to the above problem, an Inverted-Cone Diversion Type (ICDT) heat-stop design is proposed, which can reduce the temperature of the light-passing hole and make the hottest area away from the light-passing hole. The simulation results of cooling efficiency and heat-stop temperature field show that this scheme is obviously superior to its predecessor. The temperature of ICDT′s heat-stop is up to 3 ℃ above ambient, which is better than GREGO′s temperature difference of 7 ℃. The research team also carried out the heat-stop temperature field measurement experiment and verified the accuracy of the temperature field simulation′s results showing that ICDT heat-stop design has good temperature control capability.
Design of co-aperture antenna for airborne infrared and synthetic aperture radar
WU Wen-da, ZHANG Bao, HONG Yong-feng, ZHANG Yu-xin
2020, 13(3): 595-604.   doi: 10.3788/CO.2019-0160
[Abstract](1324) [FullText HTML](373) [PDF 3897KB](28)
Abstract:
In order to adapt to increasingly complex detection environments and detection requirements, airborne detection platforms often integrate multiple detection systems. As an ideal integration method, the common aperture composite not only combines the advantages of various types of detection systems, but also reduces the total volume of the system and reduces the burden on the platform. In this paper, a Cassegrain-type common-aperture antenna of infrared and Synthetic Aperture Radars (SAR) is calculated and designed. Firstly, the primary mirror is calculated according to the radar design requirements; then, the Cassegrain structure is designed by equations consisting of aberration coefficients and aspheric parameters; next, under the limitation of the front Cassegrain structure, the cold stop parameters and infrared system parameters, the lens parameters of the infrared system are calculated by the aberration formula in PW form. The proposed radar antenna has a diameter of 1.22 m and a gain of 40.9 dB. The infrared system has a focal length of −1 000 mm and a full field of view of 0.704°. The obscuration ratio of the secondary mirror is less than 0.33, and the MTF value is greater than 0.4 for each temperature level at 33 lp/mm. All the parameters of the proposed co-aperture antenna meet the requirements of expected applications.
Diffraction characteristics analysis of multi-depth phase modulation grating in terahertz band
YANG Qiu-jie, HE Zhi-ping, MI Zhong-liang
2020, 13(3): 605-615.   doi: 10.3788/CO.2019-0147
[Abstract](704) [FullText HTML](415) [PDF 3766KB](21)
Abstract:
To meet the requirements of terahertz spectral imaging for wide spectral range, high efficiency and real-time detection of spectrometers, a Multi-depth Phase Modulation Grating (MPMG) in terahertz band is proposed. The phase modulation of incident light is realized by introducing optical path difference resulted from the change of groove depth, so that different regions of reflecting terahertz wave front have different phase information. Based on the analysis of the intensity distribution of the diffraction field of the MPMG, the influence of grating parameters on the distribution of the diffraction field is discussed. The diffraction characteristics of the MPMG are verified by experiments. The experiment results indicate that the measurements of the 0th- and ±1st-order diffraction efficiency at 0.5 and 0.34 THz obtained by experiment and simulation are in good agreement. It suggests that 0th order diffraction of the MPMG has the ability of splitting light.
Analysis of the effect of lens shutter on image motion in aerial camera
YU Chun-feng, CHEN Zhi-chao, JIA Ping, WANG Nai-xiang, HOU Han
2020, 13(3): 616-626.   doi: 10.3788/CO.2019-0127
[Abstract](524) [FullText HTML](243) [PDF 2726KB](24)
Abstract:
In order to improve the photographic resolution of aerial remote sensing cameras and obtain high-resolution aerial images, besides optical system with high modulation transfer function and high-quality imaging medium, the exposure time of shutter should be controlled correctly to ensure that the detector can obtain an appropriate image motion value. Based on the structure and working principle of the lens shutter of an aerial mapping camera, we establish the matrix relationship between the ground object and the image through coordinate transformation method, that is, the relationship between the exposure time of the shutter and the image motion value is determined. The image motion value and residual error of the image motion are analyzed by combining the parameters of the camera speed-height ratio and the pixel size. According to the different installation modes of the aerial camera, when the residual error of the image motion value is more than 1/3 of a pixel in size, the Image Motion Compensation (IMC) mechanism is necessary to the imaging system. Thus a theoretical basis for the design of the IMC mechanism in an aerial camera is provided. The analysis is validated by a static test and flight test. The test results show that the aerial camera clearly captures images and the spatial resolution of its images reaches 36.8 lp/mm, which meets the requirements of our technical index.
Mid-infrared plasmon regulation based on graphene nanoribbons
HAN Jing, GAO Yang, JIAO Wei-yan, FAN Guang-hua, GAO Ya-chen
2020, 13(3): 627-636.   doi: 10.3788/CO.2019-0185
[Abstract](634) [FullText HTML](343) [PDF 2576KB](26)
Abstract:
Surface plasmon can be produced in graphene in the mid-infrared and terahertz waveband regimes, and the regulation for surface plasmon can be achieved by a reasonable design. On the basis of above, a resonant tunable structure was designed. By depositing single layers of graphene ribbons with different widths on a dielectric substrate, discontinuities in nanoscale were introduced, thereby effectively controlling the interaction of graphene with light. The spectral and electromagnetic field distributions of the structure were theoretically studied using the finite difference time domain method. The results showed that when the designed structure was coupled with the incident light, there would be multiple resonance enhanced absorption peaks. By changing the number, width and distance of the graphene ribbons in each period, the number, position, intensity of the resonance peak can be controlled. In addition, the Fermi energy level of graphene can be changed by applying different bias voltages, so the position and intensity of resonance peak can be adjusted dynamically. Therefore, with this structure graphene plasmon resonance can be regulated over a wide spectral range. This study provides a theoretical basis for the design of the graphene-based sensors, filters and absorbers in infrared regime.
Eigen generalized Jones matrix method
SONG Dong-sheng, ZHENG Yuan-lin, LIU Hu, HU Wei-xing, ZHANG Zhi-yun, CHEN Xian-feng
2020, 13(3): 637-645.   doi: 10.3788/CO.2019-0163
[Abstract](817) [FullText HTML](586) [PDF 2731KB](22)
Abstract:
A differential generalized Jones matrix method (dGJM) was recently introduced by Ortega-Quijano and colleagues to derive the GJM for modelling uniaxial and biaxial crystals with arbitrary orientations in laboratory coordinate systems. Later, we propose an eigen generalized Jones matrix method to simulate the phase and polarization of fully polarized light propagating in an anisotropic crystal when the optical axis orientations and light directions are both arbitrary. In our method, we use physics that are equivalent in principle to those of Ortega-Quijano, but we use a modified mathematical technique. We introduce the eigen generalized Jones matrix in the intrinsic coordinate system to precisely calculate the phase and polarization of the light, which overcomes the limitations of the differential generalized Jones matrix method. The simulation results indicate that our method can be used to calculate the polarization distribution, regardless of how the light beam and optical axis positioned, or whether the light beam has a vortex.
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(1215) FullText HTML(728) PDF 3187KB(135)
Abstract:
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(1232) FullText HTML(664) PDF 4890KB(59)
Abstract:
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(799) FullText HTML(399) PDF 2481KB(24)
Abstract:
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(987) FullText HTML(587) PDF 4222KB(44)
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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(1093) FullText HTML(658) PDF 2768KB(51)
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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(832) FullText HTML(459) PDF 8834KB(46)
Abstract:
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(965) FullText HTML(489) PDF 6598KB(29)
Abstract:
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.
Development of additively manufacturing metal mirrors
TAN Song-nian, DING Ya-lin, XU Yong-sen, LIU Wei-yi
2020, 13(1): 75-86.   doi: 10.3788/CO.20201301.0075
Abstract(747) FullText HTML(373) PDF 4338KB(27)
Abstract:
With the rapid development of optical measurement and remote sensing, the demand for weight, volume and environmental adaptability in folding optical systems are continuously increasing. Metal mirrors based on additive manufacturing technology are gradually gaining the attention and research of scholars at home and abroad for their easy to realize optimum design, rapid manufacturing process and high processing performance. Compared to conventional metal mirrors, additively manufacturing metal mirrors strengthen the stiffness of the mirror and achieve a higher degree of weight reduction simultaneously. Furthermore, additively manufacturing mirrors can meet the environmental adaptability and rapidity requirements of optical systems. This paper first discusses the evaluation indicators of metal mirrors. Second, the development status and technical parameters of metal mirrors based on additive manufacturing technology are reviewed. The design and preparation of metal mirrors for additive metal fabrication and the post-treatment of substrates are discussed. Then, through analysis, the preparation process and key technologies of additively manufacturing metal mirrors are summarized. Finally, prospects for additively manufacturing mirror applications are presented.
Advances in organic nonlinear crystals and ultra-wideband terahertz radiation sources
XU De-gang, ZHU Xian-li, HE Yi-xin, WANG Yu-ye, YAO Jian-quan
2019, 12(3): 535-558.   doi: 10.3788/CO.20191203.0535
Abstract(1194) FullText HTML(681) PDF 10967KB(158)
Abstract:
Nonlinear optical(NLO) crystals are the determinant in nonlinear optics. Recently, a variety of new organic crystals have been developed to further improve the output energy and conversion efficiency and to broaden the bandwidth of THz waves based on nonlinear optical frequency conversion technology. These crystals have become an ideal material for generating THz waves with their excellent performance in nonlinear optics. In this paper, the properties of different organic crystals are introduced in the classification of ionic crystals and nonionic molecular crystals, and the progress of THz sources that use the different organic crystals are summarized. At the same time, the applications and the trends in the development of broadband THz radiation using organic crystals are analyzed.
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(1730) FullText HTML(379) PDF 2700KB(43)
Abstract:
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(706) FullText HTML(349) PDF 4295KB(86)
Abstract:
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(1318) FullText HTML(432) PDF 8142KB(78)
Abstract:
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

CODEN ZGHUC8

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