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Abstract(19) FullText HTML(4) PDF 3955KB(0)
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Extinction-to-backscatter ratio is an important optical parameter of aerosols, which is related to aerosol type. In addition, it is an important error source in the retrieval of Mie-scattering Lidar. Nowadays, with the rapid development of Lidar in the field of atmospheric aerosol detection, it has become a research hotspot. Therefore, it is of great significance to investigate the retrieval methods of extinction-to-backscatter ratio for aerosol detection and research. According to the using instruments and the retrieval principles, this paper summarizes various methods and links them in terms of optical and microphysical properties. Among them, light scattering model method, passive optical remote sensing method and Lidar method are closely related and widely used, which provide important support for the detection and research of atmospheric aerosols. This paper mainly introduces these three kinds of relatively mainstream retrieval methods and summarizes the development of related methods. The application, advantages and disadvantages of these methods are analyzed, and the development trend in the future is forecasted.
Abstract(33) FullText HTML(12) PDF 7204KB(1)
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In order to obtain the 1.6 μm-band mode-locked pulse based on the soliton self-frequency shift effect, an erbium-doped fiber laser with nonlinear polarization rotation is designed, and the pulse is detected by a dual-output structure. At the pump power of 350 mW, by properly adjusting the polarization controller, the noise-like pulses with the central wavelength of 1560 nm are detected at the two outputs at the same time. The 3dB bandwidth is 17.5 nm, and the pulse duration is 968 fs. The pump power is further increased to 550 mW, the 1-port noise-like pulse remains fixed, the central wavelength of the 2-port noise-like pulse redshifts to 1614 nm, the 3 dB bandwidth becomes 64.4 nm, and the pulse duration becomes 302 fs. The maximum output power of the resonant cavity is 11.4 mW. The experiment also analyzes the influence of dispersion shifted fiber for the soliton self-frequency shift. The results show that within a certain range, the longer the length of the dispersion shifted fiber is, the smaller the frequency shift distance of the soliton self-frequency shift is. This 1.6 μm-band fiber laser has potential application value in the field of optical communications.
Abstract(32) FullText HTML(6) PDF 3651KB(0)
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A high-sensitivity surface plasmon resonance (SPR) sensor comprising an eccentric core ten-fold photonic quasi-crystal fiber (PQF) with a D-shaped structure and coated with indium tin oxide (ITO) is designed and analyzed numerically. The eccentric core D-shaped structure makes analysis of liquids more convenient and also strengthens the coupling between the core mode and SPP mode to improve the sensing sensitivity. The characteristics of the sensor are investigated by the finite element method (FEM). The wavelength sensitivity increases with increasing refractive indexes (RIs) and the maximum wavelength sensitivity and resolution are 60000 nm/RIU and 1.67×10−6 RIU, respectively. The sensor delivers excellent performance and has large potential applications in measurement of liquid refractive indexes.
Abstract(70) FullText HTML(41) PDF 5328KB(3)
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A visible/near-infrared real-time imaging spectrometer is designed for hyperspectral imaging. The spectrometer is designed on the basis of an acousto-optic tunable filter (AOTF). Its operating band range is 1.3 μm, in which the visible light camera works in the 400 nm−1000 nm band and the near-infrared camera works in 1000 nm−1700 nm band. A field-programmable gate array (FPGA) is used as the core processing unit of the spectrometer control system. The Cameralink interface is used to collect camera data, the AOTF frequency is controlled by the serial port. Through the organic combination of AOTF synchronization signal and the trigger signal outside the camera, the one-to-one correspondence between a continuous image and multi-wavelength cyclic acquisition is realized. Finally, the image data is transmitted to the upper computer through the USB3.0 interface for real-time display. The field test shows that the imaging quality of the spectrometer is good and the system works stably. For images with a 1024*1024 resolution, the real-time transmission rate of the image can reach up to 120 frame/s, which meets the design requirements. In practical engineering applications, the control system has a rich interface, high reliability, flexible interface and strong expansibility.
Abstract(91) FullText HTML(18) PDF 3675KB(20)
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The diffraction of optical fields is a universal phenomenon that can cause beams to spread during propagation in free space. Ideal non-diffracting (spatially stable) structured beams can propagate in free space without changing their initial field distribution at any plane orthogonal to the direction of propagation. Moreover, the non-diffracting structured beams also have the ability for self-recovery after encountering obstacles. Hence generating non-diffracting beams or structured beams is a very important field of research for overcoming the diffraction behavior of beams during propagation in free space. Any non-diffracting structured beams with a certain intensity, phase distribution, and propagation properties have special applications in the field of optics. Lately, some non-diffracting beams with complex structures are introduced one after another, such as Mathieu beams, parabolic beams, Lommel beams, asymmetric Bessel beams, and so on. The complex amplitude modulation is necessary to produce the nondiffracting beams with abundant structures. At present, no commercial optical modulator can modulate the phase and amplitude of light waves simultaneously. Based on binary computer-generated holography that can encode the two-dimensional transmission function distribution, a binary real amplitude computer-generated hologram with complex amplitude modulation functionality is designed and constructed. Binary real amplitude computer-generated holograms, which are a kind of binary optical diffracting element that generate non-diffracting beams with complex optical morphology, are designed and constructed by encoding the complex optical filed information by using the Lohmann-type detour phase coding method. For the Lohmann-type detour phase coding method, the coding principle is mainly that the complex field distribution information is transformed into amplitude and phase information. The complex field distribution is sampled, and one can obtain a matrix of point sources. Here, we extract the amplitude and phase information as input information to generate two 2D real value matrices for detour phase coding. By using the homemade projection imaging lithography system, the silver salt halide plate was exposed, developed and fixed, and then a binary mask is precisely machined. The homemade projection imaging lithography system can machine holograms with an ultrahigh resolution of 79, 874 × 79, 874 dpi and a maximum output of 156 mm × 156 mm. Using the mask, the non-diffracting beams with abundant structures can be produced accurately. Taking the nondiffracting Mathieu beam as an example, two kinds of binary real amplitude computer-generated holograms for generating Mathieu beams are constructed by using the Roman type detour phase coding method. In the process of the machine, the photolithography file is firstly divided into 47 unit patterns of 600 × 600 pixels, where each unit pattern is automatically inputted into a DMD (Digital micromirror) in proper sequence, and then subsequently scanned line-by-line for projection exposure. When the lithography is complete, the silver halide plate is processed to obtain the mask. In this experiment, the calculated CGH is 28, 000×28, 000 pixels, and the size of a pixel is 318 nm×318 nm. The size of the produced binary masks is 8.9 mm × 8.9 mm. The non-diffracting Mathieu beams with elliptic coefficient q=10 and topological charge number m=0, 1 are generated, which belong to the even type Mathieu beams of the first kind. Undoubtedly, the classes of nondiffracting Mathieu beams, including the even type Mathieu beams of the second kind, odd type Mathieu beams of the first kind, and odd-type Mathieu beams of the second kind can also be generated using the same encoding method and experimental setup. Since one can encode both the amplitude information and the phase information of optical field in sole spatial light modulation, the experimental system is simple in structure. The experimental results show that the coding method of binary computer-generated holography is an accurate, convenient and efficient way to generate high-quality non-diffracting beams with abundant structures.
Abstract(131) FullText HTML(55) PDF 3718KB(9)
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Objective  In response to the complex backgrounds of X-ray security images, serious overlap and occlusion phenomena, and the large differences in the placement and shape of dangerous goods, this paper improves the network structure of YOLOv4 for dangerous objects detection.  Method  On the basis of YOLOv4, this paper improves its network structure by combining atrous convolution with the atrous space pyramid pooling (ASPP) model to increase receptive field and aggregate multi-scale context information. Then, the K-means clustering method is used to generate an initial candidate frame that is more suitable for dangerous goods detection in X-ray inspection images. Cosine annealing is used to optimize the learning rate in model training to further accelerate model convergence and improve model detection accuracy.  Result  The experimental results show the proposed ASPP-YOLOv4 in this paper can obtain an mAP of 85.23% on the SIXRay dataset,  Conclusion  The model can effectively reduce the false detection rate of dangerous goods in X-ray security images and improve the detection ability of small targets.
Abstract(55) FullText HTML(23) PDF 5885KB(1)
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In order to realize the high-precision surface measurement of large-diameter elliptical optical flat mirrors and improve the image quality of large-aperture telescope systems, the absolute measurement algorithm for flat elliptical mirrors is studied in this paper. Firstly, the orthogonal polynomials fitting of an elliptical optical flat mirror is studied. Then, the absolute testing algorithm is studied theoretically. The orthogonal absolute testing algorithm can effectively separate the face error of the reference mirror from the mirror to be measured, which can realize the high-precision surface reconstruction of the elliptical flat mirror to be measured. To prove the actual testing accuracy of the above method, we carried out an absolute testing simulation and experiment on a 250 mm*300 mm mirror. In the simulation, the possibility that the reference surface error is high was considered. In the experiment, a 250 mm*300 mm elliptical testing area was selected in the Zygo300 mm standard flat surface. The above-mentioned elliptical area was tested by the 150 mm Zygo interferometer, and the surface reconstruction was realized based on the above-mentioned orthogonal absolute testing algorithm. The experimental results show that the surface error separation between the reference mirror and the elliptical mirror can be achieved by using the method described in this paper, and the residual RMS (Root-mean square) value of the absolute testing result is 0.29 nm, which proves the feasibility and accuracy of the method described in this paper. The high-precision surface reconstruction of the elliptical flat mirror can be achieved using the above method.
Abstract(53) FullText HTML(20) PDF 3916KB(5)
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Objective  Aiming at 640×512 long-wavelength infrared cooler detectors, a cooled long-wavelength infrared optical system was designed to track and detect an infrared target.  Method  The optical system adopts the secondary imaging structure pattern to ensure the system has 100% cold-shielding efficiency, and adopts a combination of optical material Ge and ZnS to achieve aberration correction and an achromatic design. By introducing the high-order aspheric surface, the high aberration of the system is well-corrected, thus the system structure is simplified. The optical system is composed of 6 lenses. The focal length is 400 mm, the working bands are 7.7 μm~9.3 μm, the field of view is 1.37°×1.10°, and the F-number is 2. The system adopts the secondary imaging structure to place the system’s exit pupil at the cold screen to ensure the system has 100% cold-shielding efficiency, and introduces the high-order aspheric surface to optimize and balance the aberration of the system.  Result  The design results show that at a spatial frequency of 33 lp/mm, the off-axis field of view MTF>0.24, which approaches the diffraction limit and has high imaging quality.  Conclusion  In the operating temperature range of −35 ℃~+55 ℃, the focusing lens is used to ensure the imaging quality under high and low temperature environments, which can be used for infrared tracking detection over a wide range of temperatures.
Abstract(19) FullText HTML(10) PDF 3720KB(3)
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Objetive  Ultraviolet detection technology has been widely used in various fields of human production and life. It is of great significance to study the system of ultraviolet (UV) imager with wide spectrum..  Method  Based on the theoretical formula of chromatic aberration, a scheme of correcting the chromatic aberration of the optical system of the wide-band UV imager with a single material was proposed. Combined with the performance index of the high-sensitivity dynamic UV imaging detector, the optical system of the 210−400 nm wide-band UV imager with only one lens material and all lenses being spherical was designed. The optical design software CODE V was used to optimize the system and evaluate the image quality.  Result  The results demonstrate that the modulation transfer function (MTF) in total fields of view and all waveband of the system is better than 0.6 at the Nyquist frequency of 40 lp/mm and RMS<7.8 μm, the system has good imaging quality.  Conclusion  The system does not contain aspheric optical elements, which is not only easy to be processed and assembled, but also reduces the developing cost, and lays a technical foundation for the development of a wide spectrum UV imaging spectrometer.
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Abstract(65) FullText HTML(29) PDF 4228KB(0)
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The technology of enhancing fluorescence emission can increase the sensitivity of fluorescence detection and the brightness of LEDs, and is of great significance in improving the performance of light-emitting devices. Since the metal structure has a good effect in enhancing the local field and enhancing the fluorescence emission, and the flexible dielectric material has flexible bendability characteristics, for the enhancement of the fluorescence emission, this paper proposes a flexible structure composed of metal-dielectric-metal (MDM). The influence of the structure on the directional emission enhancement of quantum dots is systematically studied by using the finite difference time domain method. Theoretical calculations show that the local undulations and arcs of the flexible MDM structure promote fluorescence enhancement, and can increase the quantum efficiency of the quantum dots located at the center of the structure by about 7 times. And the refractive index and thickness of the dielectric can be changed to achieve the tunability of the target wavelength. At the same time, the experimental verification shows that the flexible MDM structure does have a positive effect on the fluorescence enhancement. This discovery is useful for future display technologies and flexible light-emitting devices. It is of great value and has certain guiding significance for the development and application of high-efficiency flexible devices.
Abstract(74) FullText HTML(26) PDF 1245KB(3)
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Owing to the strong penetrating ability in the atmosphere, 532 nm wavelength green laser has wide applications including free space optical communications and laser three-dimensional mapping. A spectral filter, with a half-power bandwidth of less than 100 pm, is an important optical element to suppress the interference of background light. Therefore, an ultra-narrow band-pass filter based on optical interference film is designed and fabricated in this paper. The high and low refractive index film material is Tantalum pentoxide (Ta2O5) and Silicon dioxide (SiO2), respectively. The designed optical thin films are deposited on a fused quartz substrate by double ion beam sputtering deposition method. The transmission spectrums of the filters are measured by a tunable laser and a power meter. The half-power bandwidths of the filters are 60±2 pm, and the transmittance reaches 62.6%.
Abstract(80) FullText HTML(29) PDF 4599KB(12)
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To address the difficulty in measuring the strain limit of pliable composite film forming tests, a measurement method based on binocular stereo vision combined with digital image correlation is proposed. Firstly, to address the image matching problem in large deformations or cracks in thin films, a weak-correlation step-by-step matching method based on adaptive updating of image matching benchmarks is proposed according to the continuity of adjacent state deformation of series images. Then, according to the differences in the surface strain distribution of the film material is that of the steel parts, a strain field is proposed to fit the limit strain curve of the film material. The software and hardware system of visual measurement is built, and the limit strain curve of a Q235 steel specimen is measured and compared to results from the coordinate grid method. The limit strain accuracy can be improved by 0.02%, which proves the feasibility and accuracy of this method. The pliable composite film specimens prepared by PET, Nylon, Al foil, PP were each measured. The method and system successfully completed the measurement of the forming limit curve of the pliable composite film. The comparative experiments show that the proposed method can quickly and accurately measure the surface strain distribution of pliable composite film during forming. Compared with the coordinate grid method, it has obvious advantages and provides a highly reliable and highly precise method for solving the forming limit strain curve of film materials.
Abstract(71) FullText HTML(29) PDF 4447KB(6)
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When a micro-milling tool has a clamping angle on its spindle, the wear of the tool edge will accelerate and shorten the tool’s lifespan. In order to accurately observe the inclination state of the micro-milling tool on the machine, a three-dimensional pose reconstruction method based on the depth of field of a micro-milling tool is proposed. The laser coaxial digital holographic experimental device is used to obtain the micro-milling tool hologram, and the reconstruction image is obtained through the Fresnel reconstruction algorithm. The tool edge points are extracted as the key points in the reconstruction image, the wavelet transform local variance operator is used to obtain the degree of focus of the key points, and then the axial position corresponding to the milling tool is determined. The least square method is used to fit the key points and correct the reconstruction error, from which the three-dimensional pose reconstruction of the micro-milling tool is realized. The experimental results show that the reconstruction error of the micro-milling tool obtained by the three-dimensional pose reconstruction method is better than 0.1. This method can accurately measure a three-dimensional pose of a micro-milling tool, which can provide a reference for the subsequent correction of micro-milling tool clamping accuracy.
Abstract(74) FullText HTML(32) PDF 3938KB(3)
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Ultraviolet radiation of characteristic free radicals and blackbody radiation in combustion flames is essential to the quantitative analysis of flame temperature and fuel composition. An aperture-divided ultraviolet multiband imaging optical system is designed, which consists of an aperture-divided system and an image-combined system. The lens materials are fused silica and calcium fluoride. By placing multiband ultraviolet filters in each divided channel, the combustion flame can be imaged on the detector’s four regions with four ultraviolet bands, including 240−280 nm, 308 nm, 300−360 nm, and 390 nm. The parameters of the system are: a 2.85 F-number, a 10° field-of-view, and a 277.2 mm total length. The entrance pupil diameter of the aperture-divided system is 10 mm, and the single-channel focal length is 43.88 mm. The modulation transfer function (MTF) is close to the diffraction limit. The MTF value of the object surface at the edge of the image-combined system reaches 0.45 at 45 lp/mm. After optimizing the combination of the two parts, the MTF value of the total system surpassed 0.5 at 45 lp/mm in Nyquist frequency. Monte Carlo analysis on the tolerances gives a yield rate of more than 20%. The results show that this system is suitable for research and has practical value.
Abstract(57) FullText HTML(23) PDF 4131KB(5)
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In order to further improve the calculation accuracy and reduce the calculation time of the inverse algorithm in the Risley-prism structure, a new algorithm is proposed. It combines the forward iterative method is with the equivalent vector model of the Risley-prism to produce an equivalent vector iterative method of calculation. Firstly, the equivalent vector model of the wedge is established according to its deflection. Then, the vector coordinates of the light emitted from the Risley-prism are solved through vector superposition. The equivalent vector model is then substituted into the two-step inverse solution algorithm to calculate the approximate value of the rotation angle of the Risley-prism. Finally, the inverse equivalent vector iteration algorithm is proposed by using forward iteration and gradual approximation, and by calculating the rotation angle of Risley-prism. The experimental results show that the accuracy of the algorithm reaches 10 μm and the calculation time is less than 0.1 ms. The algorithm can effectively improve calculation accuracy, reduce calculation time, and has application prospects in the field of high-precision beams.
Abstract(40) FullText HTML(23) PDF 4839KB(2)
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In order to reduce the manufacturing cost of narrow-bandwidth metamaterial absorbers (MA) and broaden their applications in the field, this paper designs a dual-wavelength dielectric narrow-bandwidth MA based on the finite-difference time-domain method using dielectric materials. The MA is composed of an Au substrate, SiO2 dielectric layer and a Si dielectric asymmetric grating. Through simulation calculations, it was found that the narrow bandwidth MA proposed in this paper has ultra-high absorption efficiency at λ1=1.20852 μm and λ2=1.23821 μm, and its FWHM are only 0.735 nm and 0.077 nm, respectively. The narrow bandwidth absorption of MA at λ1 is mainly due to the formation of fabry-pérot (FP) cavity resonance in the SiO2 layer, while the narrow bandwidth absorption of Ma at λ2 is mainly due to the guided mode resonance effect of the incident light in the asymmetric grating. The theoretical calculation shows that the absorption wavelength and efficiency of MA can be tuned by changing the structural parameters of MA.
Abstract(65) FullText HTML(31) PDF 5213KB(6)
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To solve the real-time change of the camera poses caused by the rotation of cameras in free binocular stereo vision, a method for estimating the poses of free binocular cameras based on reprojection error optimization is proposed. The movement paraments of cameras are estimated by decomposing the homography matrix between two adjacent images. Then, the reprojection error of feature points in the overlapping area is calculated, and the objective function is constructed by using the movement parameters as initial values. Finally, the objective function is optimized by the nonlinear optimization algorithm, and the current camera poses are calculated by combining with the optimal movement parameters and the camera poses before rotation. Simulations indicate that the pose estimation error declines with a decrease in reprojection error and the proposed method can converge to a globally optimal solution both rapidly and stably. An experiment of 3D reconstruction of cement models indicates that 3D point clouds of models are generated effectively with the proposed method, the adjacent point clouds are stitched accurately, and the average error of distance between any two points on the stitched point clouds is 1.68%.
Abstract(75) FullText HTML(36) PDF 2180KB(2)
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The quick fabrication of ring-shaped colloidal photonic crystal was demonstrated on the circle-patterned photoresist substrate by spin-coating, which is promising for practical application. Latex spheres were designed with a hydrophobic core and a hydrophilic shell of poly(styrene-methyl methacrylate-acrylic acid). Scanning electron microscopy (SEM) images and reflectance spectra of the as-prepared ring-shaped colloidal photonic crystals were acquired. The influences of spinning speed, latex sphere concentration and different circle-patterned photoresist substrates on the morphology of the ring-shaped colloidal photonic crystal were investigated. The results indicate that the optimal parameters for a ring-shaped colloidal photonic crystal are achieved with a spinning speed of 2000 rpm, a latex sphere concentration of 7.5 wt% and a circle-patterned photoresist structure (diameters: 22.8 µm). The SEM images showed that the latex spheres were almost all deposited at the periphery of the ring and were dispersed with relative order, which was attributed to fast evaporation. This fast self-assembly method for preparing ring-shaped colloidal photonic crystals was achieved by spin-coating and relied on the physical confinement of patterned photoresist substrates and their wettability difference. It will have important applications in optical devices, sensing materials and anti-counterfeiting.
Abstract(363) FullText HTML(117) PDF 3808KB(24)
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Ultra-high quality optical elements are demanded by beamlimes on fourth generation synchrotron facilities and free-electron laser facilities. Bimorph mirror is effectively used to achieve ultr-high-precision surface profile control and wave front correction, yet it’s one of the bottlenecks of domestic technique to be dealt with. In order to meet this demand, a 200 mm long bimorph mirror with 36 elements of piezoelectric actuators was developed. The structure parameters of the bimorph mirror were optimized by numerical simulation, and the bimorph mirror was fabricated by domestic technology. The test results show that the surface profile error and slope error of the bimorph mirror can be reduced to 1.38 nm(rms) and 240 nrad(rms), thus the nanoscale control of the mirror surface profile was realized.
Abstract(76) FullText HTML(45) PDF 1147KB(5)
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With the development of underwater optical communication, it is very important to study the propagation characteristics of light beams in ocean turbulence. In order to get closer to the actual situation, we build a device which can control both the salinity and the intensity of underwater turbulence to study the propagation characteristics of vortex beams and a Gaussian beam in underwater turbulence. The results show that compared with the underwater turbulence without sea salt, the light spot will be more diffuse and the light intensity will be weaker in the underwater turbulence with sea salt. The scintillation index of the vortex beam with topological charge m=2 in the underwater turbulence with salinity of 4.35‰ is larger than that in the underwater turbulence with salinity of 2.42‰, no matter it is strong turbulence or weak turbulence. When the vortex beam with m=2 propagates to the same distance, the scintillation index increases with the increment of the salinity and the intensity of underwater turbulence. Under different salinity conditions, the radial scintillation index of the vortex beam with m=2 decreases firstly and then increases with the increase of the radial distance. In addition, we set up another experimental device which can transmit a longer distance. The scintillation index of the vortex beam with m=2 is much higher than that of the Gaussian beam in the underwater turbulence within 20 meters, and the scintillation indices of both the vortex beam with m=2 and the Gaussian beam increase with the increase of the propagation distance.
Abstract(181) FullText HTML(64) PDF 5881KB(18)
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Helmholtz-Kohlrausch effect (H-K effect) described the influence of color purity on the perceived brightness of a color object. Quantum dots (QD) based backlights can enhance the color quality of liquid crystal display (LCD) display with improved perceived brightness due to the well-known H-K effect. However, the H-K effect of QD embedded TV (also known as QLED TV) has not been fully demonstrated. In this paper, we investigated the H-K effect of QLED TV through a comparative study between QLED backlights and YAG-LED backlights. By comparing the viewers’ experimental results with the Kaiser and Nayatani model, we demonstrate that QLED TV shows significant H-K effect. To achieve the same perceived brightness with YAG-LED TV, the physical brightness of QLED TV was greatly decreased to 75% for pure red color, 86% for pure green color, and 74-88% for bright colorful images. Moreover, QLED TV is much preferred than the YAG-LED TV even when both QLED TV and YAG-LED TV show the same perceived brightness. The results imply the bright future of QLED TV toward health display.
Abstract(97) FullText HTML(45) PDF 3743KB(2)
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The single wedge compensation test method, as a testing method for large convex aspheric surface, has good applicability, robustness, and flexibility. However, various errors are coupled with one another during the test process and these errors are difficult to decouple; this affects the accuracy and reliability of the test process. To address this, a method is developed to calibrate the system error of single optical wedge test path using computer generation hologram (CGH). This study first analysed the source of the system error in the optical path of single optical wedge compensation test as well as the feasibility of using CGH for the calibration of an optical wedge compensation test system. In combination with engineering examples, a CGH is designed for optical wedge compensators with a diameter of 150 mm. Based on the analysis results, the calibration accuracy of the CGH is 1.98 nm RMS, and after calibration the test accuracy of single wedge compensation is 3.43 nmRMS, thereby meeting the high-precision test requirements of large convex aspheric mirrors. This shows that CGH can accurately calibrate the pose of single optical wedge compensators and test system errors of optical paths, address the problem of error decoupling in test optical paths, and improve the accuracy and reliability of the single optical wedge compensation method. Meanwhile, using CGH calibration, the system errors of the test optical paths, Tap#2 and Tap#3, are 0.023 and 0.011 λ RMS, respectively.
Abstract(51) FullText HTML(28) PDF 3776KB(1)
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An initial construction with satisfactory aberration balance and multi-constraint control is essential for the design of an off-axis multi-reflective optical system. This paper establishes a mathematical model for calculating the initial structure of an off-axis multi-reflective optical system based on the grouping design methods of spatial ray tracing and aberration correction, and proposes an improved particle swarm algorithm to solve the initial structural problems in off-axis multi-reflective optical systems. The particle swarm algorithm of natural selection with a shrinkage factor is applied to improve calculation accuracy and improve design efficiency, then the initial structure of the off-axis multi-reflection optical system is obtained. An extreme ultraviolet (EUV) lithography projection objective with six reflective aspheric mirrors is used as an example to verify the reliability and effectiveness of this method. A 0.33 numerical aperture EUV lithographic objective with wavefront error better than \begin{document}$1/80\lambda$\end{document} (λ=13.5 nm) RMS is achieved.
Abstract(165) FullText HTML(38) PDF 3209KB(16)
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In order to overcome the problems where traditional star trackers’ directional accuracy, field of view, volume, weight and other factors are difficult to balance, we studied a highly accurate interferometric star tracker structure based on a diffraction grating. By using the angular spectrum theory, the mathematical models between the incident angle of starlight, the centroid position of spots, the incident angle of starlight and the relative intensity of spots on the detector were established. Secondly, methods were determined that estimate a relative position of the star from the centriod of the spots on the detector and the relative fine position of the star from relative intensity of the spots. Then, we drew a conclusion that the angle resolution for a single star is affected by the grating period, the distance between the two gratings and the electric subdivision of the intensity signal. Finally, a computer simulation was used to confirm the feasibility of this relative fine positioning technique and this combination technique of coarse positioning and fine positioning. The results show that this measure is praticable, and the angle resolution for a single star can reach 0.1 arc-seconds when the grating period is 50, the distance between two gratings is 50 mm and the intensity signal of each period is subdivided by 1024 times. Compared with traditional star trackers, the accuracy is improved significantly.
Abstract(129) FullText HTML(74) PDF 5559KB(7)
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Objective  To monitor crop growth more efficiently, various kinds of hyperspectral spectrometers have been designed that detect chlorophyll fluorescence. In this paper, the traditional Offner spectrometer system is improved, and a structure with a higher spectral resolution is obtained.  Method  The double-reflection telescope system is selected, and the spectrometer adopts a highly dense linear reflective convex grating to achieve higher spectral resolution. On this basis, an amplifying lens is added to meet the need for a long slit. An Offner structure with a slit image plane on the same side of the grating is obtained. The initial structure of the telescope system and the spectrometer are optimized by Codev software  Result  The results show that the spectral resolution is 0.3 nm in the range of 670 nm−780 nm, the overall modulation transfer function (MTF) is greater than 0.75 at the cut-off frequency of 17 lp/mm, and the root mean square radius (RMS) of the speckle is less than 15 μm.  Conclusion  The proposed system can meet the requirements of highly precise real-time monitoring in crop growth chlorophyll detection.
Abstract(121) FullText HTML(47) PDF 2614KB(11)
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Ultra-low emission standards of flue gas emitted from stationary sources have been proposed, which creates a new challenge for continuous emission monitoring (CEM). Peak carbon dioxide emissions and carbon neutrality are frequently-mentioned concepts, which means the monitoring of CO2 will eventually be necessary. It is difficult to satisfy the strict limits of ultra-low emission standards with conventional continuous emission monitoring systems. A multi-component gas analysis system based on non-dispersive infrared is promoted in this paper to monitor trace gases of continuous emission. A gas filter correlation (GFC) model and interference filter correlation (IFC) model were established, which can describe the relationship of optical length, center wavelength, bandwidth of the filters and gas concentration using measurements and a reference signal. To confirm the measurement technique of gases, the GFC technique combines with the IFC technique to achieve a double-beam path. With the help of white cells, a small-scale, sub-ppm detection limit can be achieved. Zero and span drift are no more than ±2% of the full scale. SO2, NO, NO2, CO and CO2 can be simultenously and continuously monitored to satisfy the requirements of ultra-low and carbon emission monitoring. This technique is helpful for obtaining factual, accurate and comprehensive EM data.
Abstract(64) FullText HTML(25) PDF 5199KB(8)
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To apply hyperspectral technology to the field of microscopic imaging more conveniently, this paper designed and built a fully automatic push-broom hyperspectral microscopic imaging system. In this system, an inverted microscope was designed as the main body, a prism-grating component was used for spectrum splitting, a high precision two-dimensional motorized stage was applied for a push-broom. A motor focus module was used to control the focus, and a hyperspectral microscopic image was collected through a highly sensitive sCMOS scientific camera. The system has the advantages of low cost, easy installation and adjustment, real-time focusing and large-field-of-view imaging. The spectral range of the system ranged from 420 nm to 800 nm to meet the spectrum detection requirements of most biological samples. The spectral resolution was better than 3.5 nm, and the spatial resolution was better than 0.87 μm through the monochromatic collimated light scanning calibration method. Then, the system was given HE-stained breast cancer pathological slices as the research object. The samples were investigated and compared using passive and active focusing for push-broom imaging. The results were analyzed and summarized with mention of the advantages and disadvantages of the two focusing methods. It showed that both methods can meet the needs of large-field-of-view imaging, but active focus imaging is faster and clearer, and is more suitable for push-broom hyperspectral microscopy imaging systems. Through the design and research of a fully automatic push-broom hyperspectral microscopy imaging system, we solved real-time focusing in hyperspectral microscopic imaging and achieved 3.25 mm×3.25 mm field of view imaging of biological samples with a 40x objective lens. This system could be beneficial for promoting the application of hyperspectral technology in the biomedical field.
Abstract(169) FullText HTML(55) PDF 4734KB(12)
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Traditional temperature detection has certain limitations in terms of sensing accuracy and response time. Chip-level photoelectric sensors based on the thermo-optic effect recently aroused widespread interest not only because they can improve measurement sensitivity and speed, but also because they can help reduce system complexity and cost. State-of-art integrated optical temperature sensors mostly measure the optical interference of broadband light sources or tunable light sources in the micro-resonators to provide accurate and fast measurement solutions. However, these solutions are based on wide-spectrum detection cannot achieve real-time processing, are costly with complicated signal post-processing, and are difficult to implement in highly integrated systems. To solve the above problems, this paper shows a fast and high-precision temperature measurement method using a silicon-based integrated micro-ring array. The different responses of the cascaded micro-ring array are measured by a single-frequency laser at different temperatures. The results are utilized to model the relationship between the electrical response of the detector array and the real temperature, thereby realizing real-time high-precision temperature measurement. In addition, to enlarge the temperature detection range under a fixed-wavelength light source, a cascaded micro-ring structure is adopted. Based on the proposed structure, a silicon-based integrated temperature sensing system including a light source, a micro-ring array, a detector array, a signal post-processing unit and an output data unit is designed. Depending on the requirement of actual applications, the system can change the temperature measurement range resolution by separately designing the number of cascaded micro-rings, the center resonance wavelength, and the half-width of the resonance peak while ensuring low system power consumption and cost. Through the optimized design of the micro-ring array, a temperature sensor with a response range covering −20−105°C, accuracy better than 60 mK, and a response time as quick as 20 μs is demonstrated.
Abstract(82) FullText HTML(23) PDF 4815KB(4)
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Objective  In the “Taiji mission”, the laser jitter noise caused by satellite jitter is one of the main noise sources that affect the accuracy of laser interferometer. In order to ensure the measurement accuracy, the noise must be suppressed to 10 nrad/√Hz@10 mHz.  Method  Firstly, an angle sensor composed of a four-quadrant photodetector and a phase meter was used to measure the angle signal, and a Mach-Zehnder interferometer combined with proportional-integral-derivative control technology was used to build a ground-based laser jitter noise suppression system. Secondly, the feedback control capability of the system and the effectiveness of the system to suppress laser jitter noise were analyzed.  Result  The experimental results showed that the system could effectively suppress the laser jitter noise, and the laser jitter noise was <4 nrad/√Hz@10 mHz.  Conclusion  The experiment advanced the study of the “Taiji mission” on the level of laser jitter noise suppression, which laid a physical experimental foundation for laser interferometry.
Abstract(138) FullText HTML(41) PDF 6036KB(9)
Abstract:
In response to the need for the automated and rapid urine detection, microfluidic technology and biochemical analysis technology are adopted to design and fabricate a disc microfluidic chip used for urine biochemical detection. The chip consisted of microfluidic channels, capillary valve, siphon valve and ferrowax valve realizes the sequential transportation of the sample and reagent, mixing and detection. COMSOL multiphysics software is used to model the structure of capillary valve and siphon valve and optimize the rotary frequency. Next a fully automatic urine biochemical detection system is generated based on a disc microfluidic chip. The effects of light source fluctuations and background interference on test results are reduced by dual optical path and dual wavelength detection. The detection system is characterized by urinary retinol binding protein (RBP). The results demonstrate the coefficient of variation (CV) of the system is 1.3%−2.46%, indicating that the system has good repeatability. The calibration curve shows the linear correlation between urinary RBP concentration and the absorbance (R2=0.995). The four identical unit on the chip could perform a multi-sample or multi-parameter detection in parallel, in which it has a potential to be applied for the rapid of urinary protein detection.
Abstract(96) FullText HTML(41) PDF 3438KB(10)
Abstract:
The dual Mach-Zehnder interferometer system has received extensive attention and applications due to its unique advantages such as simple optical path, high sensitivity and wide frequency response. However, it is very susceptible to external environmental noise. Direct cross-correlation calculation method will lead to large error. This paper proposes a data signal processing scheme based on Hilbert-Huang transform (HHT) to realize high-precision distributed optical fiber vibration positioning detection. In this method, the eigenmode function is obtained by empirical mode decomposition of the two received optical signals. The Hilbert transform and superposition of all eigenmode functions are performed to obtain the Hilbert spectrum, which can be clearly and intuitively extracted. It can accurately calculate the vibration position information by calculating the time delay caused by the vibration signal through cross-correlation. Compared with the traditional direct cross-correlation calculation, this method can effectively identify and extract the characteristic information caused by the vibration signal in the dual M-Z system. Thereby it can effectively reduce the impact of external environmental noise on the system and reduce the positioning error. This paper analyzes the related theory of the proposed method and builds a dual M-Z system for related experimental verification. The experimental results show that, compared with the traditional direct cross-correlation method, this method can effectively reduce the amount of calculation of cross-correlation data. At the same time, it can effectively improve the positioning accuracy of the vibration position. Under MHz sampling rate, the positioning accuracy can reach 10 m. Therefore, the distributed optical fiber sensing technology based on the dual Mach-Zehnder interferometer system proposed in this paper has high application value.
Abstract(127) FullText HTML(116) PDF 3460KB(7)
Abstract:
In order to explore the continuous deep ultraviolet laser output within the wavelength of 200~280 nm, a 5 mm long Pr:YLF crystal was pumped by the combine of 1.4 W blue laser diode at 444 nm and 1.5 W blue laser diode at 469 nm, the BBO with a length of 7 mm was used as the frequency doubling crystal. By optimizing the resonator mirror coating and inserting a full wave plate for wavelength competition, it makes the output of weak spectra of Pr:YLF possible. At last, the continuous deep ultraviolet laser with a maximum power of 8.37 mW and center wavelength of 268.89 nm was achieved.
Abstract(87) FullText HTML(40) PDF 1017KB(3)
Abstract:
In order to improve the luminescent properties of rare earth ions, precious metal nanoparticles were doped into rare earth luminescent materials. Metal plasma resonance can produce local electric field, which acts on the luminescence process of rare earth ions, and can achieve the luminescence enhancement. Ag@SiO2 core-shell nanoparticles can effectively control the distance between metal Ag and rare earth ions, which can not only achieve the effect of plasmonic resonance enhancement, but also avoid the fluorescence quenching caused by non-radiation energy transfer when they are too close to the emission center. Firstly, the Ag@SiO2 nanoparticles with different concentrations were dropped on the quartz wafers by drop-casting method. Then, the Eu(dbm)3Phen:PMMA: dichloromethane mixed solution was spin-coated to prepare the Eu-PMMA composite film. The morphology characterization and luminescence measurement of the samples showed that the luminescence intensity of the film doped with Ag@SiO2 nanoparticles was enhanced,, and the maximum enhancement factor of the measured excitation spectrum was 2.50 times, and the maximum enhancement factor of the emission spectrum was 2.15 times. The luminescence lifetime of the film containing Ag@SiO2 nanoparticles was also prolonged by the results of the fluorescence lifetime measurement of the sample. The doping of Ag@SiO2 nanoparticles in the rare earth luminescent materials shows a good enhancement, and the experimental method is highly operable. It is a promising method to enhance the luminescent intensity of rare earth luminescent materials.
Abstract(86) FullText HTML(32) PDF 3583KB(4)
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In pure seawater, the blue-green and blue light bands’ transmission window has good transmission characteristics. This paper proposes an underwater wireless optical communication system that uses a 470 nm LED array stitching structure. At an underwater distance of 20 m, this system could successfully achieve reliable communication at a rate of 5 mbps (data rate) and a BER of 10−6, which lays a foundation for subsequent underwater dynamic laser communication systems.
Abstract(111) FullText HTML(32) PDF 3857KB(13)
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The large field-of-view star simulator provides wider star maps but the existing star simulator is limited by the size of the display chip, and the maximum field of view is not more than 30°. In order to increase the field of view of the star simulator, a method of splicing it is proposed. In order to reduce the cost, the overall weight and complexity of the system, and to achieve the largest splice with the least amount of splicing, the paper carries out detailed calculation and analysis of the overlapping area of the field of view and proposes a simplified splicing model based on plane splicing. It produces three typical splicing methods including a regular triangle, a regular quadrilateral and a regular hexagon, and deduces the calculation of the field of view utilization. It also provides a coordinate calculation method, determines the center position of each field of view, and obtains an accurate number of the stitching. The final comparison result shows that the regular hexagon splicing method has the outstanding advantages of a higher utilization of the field of view utilization and fewer splicing numbers, which provides a basis for the design of a large field-of-view star simulator.
Abstract(379) FullText HTML(140) PDF 1984KB(26)
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To solve the data transmission difficulties and long-signal acquisition and processing time problem caused by excessive data transmission of the Geostationary Orbit array staring spectrometer, a scheme for a large-aperture visual and infrared snapshot spectrometer based on compressive sensing is proposed, which takes advantage of the fact that a geostationary orbit platform can stay over the fixed area for a long time. This paper analyzes the physical model of compressive sensing spectral imaging. The structure of the optical system is designed, and the relevant parameters are calculated. The objective lens uses a coaxial three-mirror afocal optical system, and dichroic films are used to split the spectrum. The relevant parameters were calculated according to requirements and the system was designed using optical software. After optimization, the optical system was shown to have a width of 400 km◊400 km, a visible area of 40 m GSD, an MWIR area of 400 m GSD, and an LWIR area of 625 m GSD. The results show that the MTF of the visible area is higher than 0.455 at 78.125 lp / mm. In mid-wave infrared, the MTF is higher than 0.518 at 33 lp / mm, and the MTF is higher than 0.498 at 20.8 lp / mm in long-wave infrared. The spectral resolution of the visible light is 20 nm, the mediumwave infrared region’s resolution is 50 nm, and the long-wave infrared spectrum resolution is 150 nm. The second-order spectrum of the visual area is less than 0.05 mm. The optical system has good imaging performance and the imaging quality of each part of the optical system is close to the diffraction limit, which meets the needs of applications and indicators.
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2021, 14(5): 1039-1055.   doi: 10.37188/CO.2021-0003
[Abstract](348) [FullText HTML](119) [PDF 10280KB](72)
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Two-dimensional (2D) materials provide new development opportunities for silicon-based integrated optoelectronic devices due to their unique structure and excellent electronic and optoelectronic properties. In recent years, 2D material-based photodetectors for hybrid-integrated silicon photonics have been widely studied. Based on the basic characteristics of several 2D materials and the photodetection mechanisms, this paper reviews the research progress of silicon photonic integrated photodetectors based on 2D materials and summarizes existing device structure and performance. Finally, prospects for strategies to obtain high-performance silicon photonic integrated 2D material photodetectors and their commercial applicability are presented with considerations for large-scale 2D material integrations, device structure, and metal-semiconductor interface optimizations, as well as emerging 2D materials.
2021, 14(5): 1056-1068.   doi: 10.37188/CO.2021-0071
[Abstract](187) [FullText HTML](40) [PDF 5700KB](31)
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Optical Frequency Comb (OFC) possesses unique time(frequency) domain characteristics such as narrow pulse width, high frequency precision, stable frequency comb teeth and well-defined optical coherence, etc. Therefore, it has become a hot research topic in various fields including ultra-fast laser technology and metrology science in recent years. Meanwhile, OFC has also been developed into an important scientific research instrument. Recently, a novel light source based on the coherent synthesis of OFCs has been developed, which can realize the periodical, high-speed (up to radio frequency) and stable modulation of the polarization or the orbital angular momentum of light. In this review, we try to introduce recent developments on the fundamental principles, experimental techniques and characterization methods of the novel light source based on the coherent synthesis of OFCs, starting from the basic concepts of OFC and mainly covering two aspects: polarization modulation and orbital angular momentum modulation respectively. We also try to provide some perspectives on the applications of OFC based on the coherent synthesis techniques in the fields of solid-state spectroscopy, optical manipulation and the interaction between light and matter, etc.
2021, 14(5): 1069-1088.   doi: 10.37188/CO.2021-0044
[Abstract](215) [FullText HTML](114) [PDF 12124KB](36)
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Because of the large size and immobility working modes, traditional spectral imaging systems struggle to meet increasingly complex practical needs. Tunable micro-nano filtering structures show unique advantages for their lighter weight and greater flexibility, so they are promising candidates for achieving adaptive and intelligent operation in the future. This article summarizes a variety of tunable filtering methodologies and their operational principles both in domestic and foreign research within the last several years. It illustrates static tunable methods such as utilizing liquid crystal and phase-change materials, some dynamic tunable filtering structures such as Fabry-Pérot cavity, micro-nano tunable grating as well as some driving approaches like mechanical stretching, electrostatic driving, optical driving, etc. Meanwhile, this article also introduces some frontier researches based on microfluidic chips and graphene. In the end, it discusses the barriers, challenges and future trends of development for tunable micro-nano filtering structures.
2021, 14(5): 1089-1103.   doi: 10.37188/CO.2021-0022
[Abstract](128) [FullText HTML](73) [PDF 7589KB](23)
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The requirements of modern optical engineering in fields such as deep ultraviolet lithography, extreme ultraviolet lithography and advanced light sources drive the continuous development of advanced optical manufacturing technology. Modern optical engineering requires the surface roughness of ultra-smooth optical components to reach the atomic level and the surface shape profile error in the full spatial frequency to reach RMS(Root Mean Square) sub-nanometer or even a few dozen picometers. This drives the manufacturing requirements of ultra-smooth optical components to approach the processing limits. At present, there are still technical challenges to achieve the ultra-smooth polishing technology and equipment required for the above ultra-high precision needs. Atomic level ultra-smooth polishing of complex surfaces such as cylinders, ellipsoids and toroids is still a primary direction of research at both domestically and abroad. Elastic emission machining is an atomic-level ultra-smooth processing method with stable removal functionality and ultra-low subsurface defect creation, which can be used for manufacturing optical components with the above-mentioned accuracy requirements. We summarize the research progress of elastic emission machining and equipment at both domestically and abroad, the principles of elastic emission machining which contains fluid characteristics, the movement characteristics of polishing particles and chemical characteristics, the equipment of elastic emission machining, and the factors affecting the improvement of surface roughness and material removal rate of elastic emission machining. Then we analyze the problems faced by elastic emission machining and equipment and look forward to their prospects. It is expected that this paper will provide a reference for the further development and application of elastic emission machining.
2021, 14(5): 1104-1119.   doi: 10.37188/CO.2021-0033
[Abstract](357) [FullText HTML](76) [PDF 4286KB](33)
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As the technology node of large-scale integrated circuits continues to shrink, the focus control of the lithographic tools becomes particularly difficult. In order to ensure the exposure quality of wafers, it is necessary to quickly and accurately adjust the wafer in the Depth of Focus (DOF) to a degree as small as few dozen of nanometers. For this reason, people need to carefully analyze the various factors that cause defocusing or process window changes in the lithographic process, make a reasonable focus control budget, and control the various error factors within a certain range. This paper focuses on Extreme Ultraviolet (EUV) lithography, reviews the factors that affect focus control in the optical path of an advanced EUV lithographic tool and summarizes their principles, simulation and experimental results. It can provide a reference when conducting advanced lithography focus control budget research.
2021, 14(5): 1120-1132.   doi: 10.37188/CO.2021-0125
[Abstract](82) [FullText HTML](24) [PDF 6378KB](8)
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Tunable fiber light sources with wavelength near 1 μm are widely used in optical fiber sensing, laser cooling, photochemical, spectroscopy and medical fields. They have thus become an area of focus in fiber light source research in recent years. The development history of fiber light sources with wavelength tuning ability is firstly summarized systematically. Then, their problems and possible solutions are analyzed. Finally, the future developments of tunable fiber light sources near 1 μm are prospected.
2021, 14(5): 1133-1145.   doi: 10.37188/CO.2020-0216
[Abstract](143) [FullText HTML](59) [PDF 6559KB](22)
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Chaotic lasers are widely used in secure communication, lidar, optical detection and other applications due to their noise-like randomness, excellent anti-interference and other advantages. Moreover, as semiconductor lasers have small size, stable structure and other advantages, it has become one of the main lasers to produce optical chaos. However, the chaotic laser output from conventional optical feedback semiconductor lasers has the problems of narrow signal bandwidth and delay characteristics, which seriously affect their applications. With consideration for these problems, a comprehensive introduction to reduce the delay characteristics and optimize the chaotic laser bandwidth are reviewed based on recent literatures. This paper also summarizes the research progresses of chaotic secret communication, which is very important in the synchronization of chaotic lasers. The chaotic output of semiconductor lasers and the applications of chaotic lasers are also summarized, and then their development and potential future applications are discussed.
2021, 14(5): 1146-1161.   doi: 10.37188/CO.2021-0032
[Abstract](374) [FullText HTML](124) [PDF 5479KB](87)
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Augmented reality (AR) display technology has developed rapidly in recent years, and has become a research hotspot and development focus of the global information technology industry. It has the potential to revolutionize the ways we perceive and interact with various digital information. Recent advances in micro-displays and optical technologies offer new development directions to further advance AR display technology. This review analyzes the optical requirements of human visual systems for AR head-mounted displays and compares them with current specifications of AR head-mounted displays to demonstrate their current levels of development and main challenge. The basic principles and parameters of various micro-displays and optical combiners in AR head-mounted displays are introduced to explain their advantages and practicability, and their development trends are summarized.
2021, 14(5): 1162-1168.   doi: 10.37188/CO.2021-0001
[Abstract](142) [FullText HTML](61) [PDF 2526KB](7)
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In order to realize accurate positioning during the puncture surgery, a high-resolution optical system with a 90° field of view and 0.67 mm focal length is designed and developed for the visual puncture needle. A 45° viewing angle is chosen to make the optical axis perpendicular to the inclined edge surface by using a reflection prism. The retrofocus structure is used and the formulas for the initial structure parameters calculation are derived. The imaging performance of the optimized system is nearly diffraction-limited and the maximum size of the optical component is less than 1.5 mm. The optical system is developed, and it is assembled in a 4 mm diameter puncture needle with a miniature CMOS image sensor. The assembled visual puncture needle is evaluated with the Modulation Transfer Function (MTF) measurement and the imaging experiment. The measurement results show that the imaging quality of the optical system is good and its object-space resolution reaches 18.03 lp/mm, thus it can realize the requirement for high-resolution imaging.
2021, 14(5): 1169-1176.   doi: 10.37188/CO.2021-0005
[Abstract](125) [FullText HTML](42) [PDF 5527KB](5)
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In order to improve the performance of the capsule endoscope antenna and its anti-interference ability and compatibility, and further reduce its size, a graphene-based and wide-band circular polarized antenna for capsule endoscopes is designed. The antenna is composed of three layers of radiation units and a floor. By making use of the excellent electrical conductivity of multi-layer graphene film, the radiation units and the floor of each layer of the antenna can enhance the working bandwidth and gain of a capsule antenna, improve the transmission efficiency and effectively reduce the loss. Four short-circuit probes are used to connect the radiation units of first layer and second layer to form a composite spiral antenna, thus generating circular polarization characteristics, which can not only reduce bit error rate but also inhibit multipath interference. In addition, it can couple electromagnetic energy, improve impedance matching and adjust the purity of circular polarization. The effects of the size of the radiation units of first, second and third layers on the performance of the antenna, such as the size of the opening ring, the thickness of the multilayer graphene film, and the antenna intake environment of the stomach, small intestine and colon are analyzed in detail. The test results show that the antenna volume is only π×4.52×1.905 mm3, the impedance bandwidth is 2.2~2.78 GHz, the axial ratio bandwidth is 2.26~2.66 GHz, and the gain is −22.9 dBi. The actual measurement results agree well with the simulation results, and the radiation characteristics in the working frequency band are stable. Compared with the existing technology, this antenna is more compatible and its functional bandwidth is wider. The antenna has a wide band, circular polarization, good anti-interference, good electromagnetic compatibility and a small volume. The antenna is suitable for the ISM 2.4 GHz band, which can meet the working requirements of a capsule endoscope intake for different digestive organs.
2021, 14(5): 1177-1183.   doi: 10.37188/CO.2021-0020
[Abstract](82) [FullText HTML](28) [PDF 8582KB](6)
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The large field of view bio-imaging analyzer can quickly and accurately detect rare cells and trace pathogenic microorganisms, playing an extremely important role in life sciences, food and drug testing, environmental safety, etc.. Based on the theory of coaxial three-mirror imaging, a large field of view biological imaging analyzer was designed by means of an coaxial three-dimensional objective lens as the core component for imaging analysis. It has a spectral range of 350~1100 nm, a magnification β=−1, a field of view of 150 mm×20 mm and NA=0.1. The root mean square of the dot column diameter is less than 3.5 μm. At the 178 lp/mm spatial cutoff frequency, the MTF mean of the full field of view is greater than 0.35 and the distortion is zero. The imaging system has a large field of view and high resolution, and the detection rate of the biological imaging analyzer system with a large field of view is 98%. The proposed objective lens is of good quality and can meet the application requirements.
2021, 14(5): 1184-1193.   doi: 10.37188/CO.2020-0218
[Abstract](210) [FullText HTML](85) [PDF 5767KB](16)
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In order to achieve high precision surface testing for the large diameter and long focal length off-axis segmented mirrors, we designed a reflective diffractive compensation null testing system. Using a computer-generated hologram and a spherical mirror to compensate for normal aberration of the off-axis mirror. The design results show that the residual wavefront error of the optical path is close to zero. For a testing system, CGH alignment optical paths corresponding to the non-axisymmetric off-axis structure are designed to ensure the feasibility of the assembly. Parameters of the optical path testing for different off-axis distance mirrors are the same. Rapid high-precision null testing of different types of segmented mirrors can be achieved simply by replacing the CGH at corresponding position and adjusting the spatial positions of the mirror to be measured. Error analysis shows that the RMS error of the mirror surface to be measured is better than λ/40 (λ=632.8 nm), which is caused by the manufacturing error of the compensating elements, misalignment of the optical path, repeatability of the interferometer surface measurement and standard spherical wavefront deviation of the interferometer.
2021, 14(5): 1194-1201.   doi: 10.37188/CO.2020-0220
[Abstract](131) [FullText HTML](42) [PDF 5647KB](22)
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At present, most of the research on super-resolution imaging technology is focused on the super-resolution reconstruction algorithm, but the influence of the alignment error of an optical system on the super-resolution imaging results has not been reported. To solve this problem, We researche the influence of alignment error on super-resolution imaging. First, the basic imaging model of super-resolution imaging optical system based on Digital Micro-mirror Device (DMD) is established. A DMD super-resolution imaging optical system with operating band of 8~12 μm is designed, and a method used to analyze the influence of the alignment error on super-resolution imaging quality is proposed. In the imaging model, alignment errors such as eccentricity, tilt, lens spacing error and defocus are introduced, and the reconstruction results are analyzed. Finally, the range of tolerance of the super-resolution imaging optical system is obtained. The results show that the total eccentricity error in the X direction is controlled within ± 0.07 mm, and that in the Y direction is within ±0.05 mm; the total tilt error in the X and Y directions is controlled within ±0.06°; the overall lens spacing error is controlled within ±0.02 mm; the defocusing amount of the imaging object lens is controlled within ±0.04 mm; the defocusing amount of the projection objective lens is controlled within ±0.05 mm, and within this range, the super-resolution imaging optical system can ensure the quality of super-resolution imaging.
2021, 14(5): 1202-1211.   doi: 10.37188/CO.2020-0214
[Abstract](168) [FullText HTML](65) [PDF 5045KB](16)
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Night vision intelligent detection method of scatterable landmines based on machine learning is presented. Firstly, the intelligent detection network model of scatterable landmines is designed and optimized based on the YOLO series algorithm. Then, the model measuring the distance between scatterable landmines and detection equipment is proposed based on the similarity principle of geometric optical imaging. Finally, a night vision intelligent detection system for scatterable landmines is built, tested and analyzed. The experimental results show that the optimized intelligent detection network model can detect scatterable landmines with an accuracy of 98.97%, a recall rate of 99.22%, and a mean average accuracy of 99.2%. Under the given experimental conditions, the optimized scatterable landmine ranging model has an error of ±10 cm in the calculated distance of scatterable landmines. The study shows that machine learning can perform intelligent and long-distance detection of scatterable landmines.
2021, 14(5): 1212-1223.   doi: 10.37188/CO.2020-0219
[Abstract](93) [FullText HTML](32) [PDF 3914KB](8)
Abstract:
With the increase in cars on the road, the reliability of automobile braking systems has received increasing attention. The detection accuracy of the compensation hole’s parameters of an automobile’s brake master cylinder based on machine vision is key to determining automobile safety and the reliability of parking technology. As an important part of automobile brake master cylinders, the compensation hole can play an important role in regulating the brake fluid in its reservoir and pressure chamber. Its dimensional accuracy and processing quality are strictly controlled, so accurately obtaining an image of the compensation hole is a priority in compensation hole parameter detection. By introducing the correction method of plane drilling rivet hole normal line into the image acquisition process, the four-point micro-plane normal line detection method is combined with image processing to realize high-efficiency and high-precision normal line correction. Experiments show that the algorithm's normal alignment accuracy is higher than 0.05°, which is better than the traditional detection accuracy of 0.5°, and the detection time is less than 1 s. The algorithm proposed in this paper is simple and has good real-time performance while meeting accuracy requirements. It also has good robustness and meets the requirements of the brake master cylinder production industry for detection speed and accuracy.
2021, 14(5): 1224-1230.   doi: 10.37188/CO.2021-0008
[Abstract](127) [FullText HTML](52) [PDF 3635KB](20)
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Temperature and pressure are very important parameters in oil and gas well exploitation. The downhole environment is harsh so it is difficult for traditional electronic sensors to achieve long-term and stable monitoring of downhole parameters. In this paper, a fiber Bragg grating temperature and pressure sensor based on a carbon-fiber sensitized tube is proposed. The sensor is composed of a hollow tubular structure woven of carbon fibers as a skeleton. The composite carbon fiber tubes are cured by high-temperature resistant epoxy resin as an elastomer, and the high-temperature resistant fiber Bragg grating is embedded on the surface as a sensing element to realize the simultaneous measurement of downhole temperature and pressure. The experimental results show that the sensor can work stably in environments of 0~150 ℃ and 0~80 MPa, and the maximum pressure sensitivity can reach −50.02 pm/MPa. The sensor has a good linear response. By adding a reference grating as a temperature compensation grating, the cross-sensitivity problem in the process of the simultaneous measurement of temperature and pressure is solved, and the accuracy requirements in the process of underground mining are met. This technique provides an experimental basis for the design of high-temperature and high-pressure optical fiber sensors in oil and gas wells.
2021, 14(5): 1231-1242.   doi: 10.37188/CO.2020-0129
[Abstract](437) [FullText HTML](130) [PDF 4279KB](24)
Abstract:
In order to effectively evaluate the influence of scattered radiation of the heat collection tower on the optical environment of the Dunhuang Gobi Site of the Chinese Radiometric Calibration Sites (CRCS), the Monte Carlo three-dimensional radiation transmission model simulation combined with in situ CE318 multi-channel photometer almucantar measurements was applied to solve the problem that it is difficult to quantitatively evaluate the scattered radiation mixed with the background radiation. By measuring the data with a new cloud cover automatic observing instrument ASC200, the accuracy of clear sky measurements improved, and the development of the CE318 four-quadrant location correction algorithm effectively increased the amount of valid data that meets our threshold requirements. The effective data collected from January to March 2020 shows that the molten salt tower Concentrating Solar Power (CSP) project has no significant impact on the sky diffuse radiation outside the 550nm channel. In the 500 nm channel, under the geometric parameters corresponding to the valid data (distance 0.87−3.07 km, observation zenith angle 77.30−51.32º), the impact of the molten salt tower heat absorber on diffuse sky radiation does not exceed 0.93%. Combined with the analysis of the model simulation results, it can be concluded that the relative change of the sky diffuse radiation caused by the scattered radiation of the large power station is less than 1.62% at 2 km away, and the relative change is less than 0.93% when it is at least 3 km away. The research results have positive significance for the use of Dunhuang Site to conduct quantitative applications in remote sensing and the accurate evaluation of the uncertainties introduced by power stations.
2021, 14(5): 1243-1250.   doi: 10.37188/CO.2021-0018
[Abstract](136) [FullText HTML](59) [PDF 4299KB](8)
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2021, 14(5): 1251-1258.   doi: 10.37188/CO.2020-0068
[Abstract](135) [FullText HTML](41) [PDF 2279KB](17)
Abstract:
Optical properties of periodic double-well potential are one of the frontier research fields in laser physics and quantum optics. In this work, we have employed time-periodic double-well potential for the investigation of Fano-type resonant tunneling of photon-assisted Dirac electrons in a graphene system. Using a double quantum well structure, it is found that the resonant tunneling of electrons in a thin barrier between the two quantum wells splits the bound state energy levels, and the Fano-type resonance spectrum splits into two asymmetric resonance peaks. The shape of Fano peak is regulated by changing the phase, frequency, and amplitude, that can directly modulate the electronic transport properties of Dirac in graphene. Our numerical analysis shows that the relative phase of two oscillating fields can adjust the shape of the asymmetric Fano type resonance peak. When the relative phase increases from 0 to \begin{document}${\text{π}}$\end{document}, the resonance peak valley moves from one side of the peak to the other. In addition, the asymmetric resonance peak becomes symmetric at critical phase \begin{document}${{3{\text{π}} }/{11}}$\end{document}. Furthermore, the distribution of Fano peaks can be modulated by varying the frequency and amplitude of oscillating field and the structure of the static potential well. Finally, we suggest that these interesting physical properties can be used for the modulation of Dirac electron transport properties in graphene.
2021, 14(5): 1259-1272.   doi: 10.37188/CO.2020-0204
[Abstract](49) [FullText HTML](25) [PDF 4132KB](6)
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In order to realize the demodulation of the cavity length of the fiber-optic FP sensor, a new optical wedge-type non-scanning correlation demodulation system is proposed, and the characteristics and structure of the devices used in the system are analyzed and studied. First, by simulating the light sources with different spectral distributions and the optical wedges with different surface reflectivities, the correlation interference signals are analyzed and the optimal structure parameters of the system components are given. Then by comparing the light intensity distribution characteristics of the Powell prism and cylindrical lens on the linear array CCD, more uniform spectral distribution is achieved. Finally, the specific implementation scheme and data processing method of the demodulation system are given. The experimental results show that when the light source spectrum has a Gaussian distribution and large spectral width and the reflectivity of the wedge surface is \begin{document}$R = 0.5$\end{document}, the characteristics of the correlation interference signal are obvious and convenient for demodulation. Finally, the demodulation system achieves the demodulation effect with an error of less than 0.025% within the cavity length range of 60 μm-100 μm. This optical wedge-type non-scanning correlation demodulation method can realize the sensing demodulation of the fiber-optic FP cavity and improve the power adaptability of different types of fiber-optic FP sensors.
2021, 14(5): 1273-1287.   doi: 10.37188/CO.2021-0015
[Abstract](107) [FullText HTML](43) [PDF 3895KB](4)
Abstract:
In order to realize the separation and release of nucleated red blood cells from peripheral blood and develop a safe and effective non-invasive technique to separate nucleated red blood cells for prenatal diagnosis of fetal diseases, an automatic cell smear preparation system based on hydrogel material was established, and a laser focusing and microscopic imaging system for recognizing and releasing nucleated red blood cells was constructed. Firstly, the mechanical structure of cell smear preparation machine was designed, the upper computer control software was designed based on single chip microcomputer, and a hydrogel membrane substrate smear was prepared by optimizing the slide-pushing angle and speed. MXene, a two-dimensional material, was introduced into temperature-sensitive hydrogel gelatin, and the near-infrared light response was realized on the surface of hydrogel membrane by using the near-infrared photothermal conversion characteristics of MXene. Then, the whole cell smear experiment was carried out on the surface of the hydrogel substrate membrane. A monolayer cell smear was prepared by optimizing the parameters of blood slide. Finally, the optical path of laser focusing and microscopic imaging was established. After the nucleated red blood cells were recognized and located, the light from an 808 nm laser source passed through a collimator lens and a convergent lens and was focused on the surface of the cell smear, which released cells under photothermal effect. A monolayer cell smear was processed and prepared, and then a photothermal effect was produced under the near-infrared light of 808 nm. After the control of the laser focusing system, a fixed cell-releasing area with a spot diameter of 300 μm was finally obtained. In this paper, the automatic slide-pushing technology was applied to the preparation of a monolayer cell smear based on hydrogel membrane, and the optical path of laser focusing and microscopic imaging was established. By using the near-infrared response and a thermal response of hydrogel membrane, the recognition and fixed-point release of nucleated red blood cells were realized, and the efficiency of separation and enrichment of nucleated red blood cells was improved. This technology has a broad application prospect in the field of prenatal screening and diagnosis.
2021, 14(5): 1288-1304.   doi: 10.37188/CO.2021-0004
[Abstract](132) [FullText HTML](31) [PDF 4191KB](6)
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Compared with the commonly used simulation algorithms such as Finite Element Method (FEM) and Finite-Difference Time-Domain (FDTD) method, the Boundary Element Method (BEM) has the advantages of high accuracy, small memory consumption, and ability to deal with complex structures. In this paper, the basic principle of three-dimensional BEM is given, the corresponding program based on C++ language is written, and the Surface Plasmon Resonance (SPR) characteristics of a graphene nano-disk structure are studied. The Scattering Cross-Section (SCS) spectral lines of a graphene nano-disk under different chemical potentials, as well as the distributions of electromagnetic fields at the resonance wavelengths are calculated. The electromagnetic response of the graphene nano-disk in the infrared band is analyzed. In addition, considering the common corrugations of graphene materials caused by defects during processing, we study the influence of the geometric parameters of a convex structure in the center of the graphene nano-disk on the resonance intensity, wavelength and field distributions. A spring oscillator model of charge movement is used to explain the simulation results.
2021, 14(5): 1039-1055.   doi: 10.37188/CO.2021-0003
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Two-dimensional (2D) materials provide new development opportunities for silicon-based integrated optoelectronic devices due to their unique structure and excellent electronic and optoelectronic properties. In recent years, 2D material-based photodetectors for hybrid-integrated silicon photonics have been widely studied. Based on the basic characteristics of several 2D materials and the photodetection mechanisms, this paper reviews the research progress of silicon photonic integrated photodetectors based on 2D materials and summarizes existing device structure and performance. Finally, prospects for strategies to obtain high-performance silicon photonic integrated 2D material photodetectors and their commercial applicability are presented with considerations for large-scale 2D material integrations, device structure, and metal-semiconductor interface optimizations, as well as emerging 2D materials.
2021, 14(5): 1056-1068.   doi: 10.37188/CO.2021-0071
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Optical Frequency Comb (OFC) possesses unique time(frequency) domain characteristics such as narrow pulse width, high frequency precision, stable frequency comb teeth and well-defined optical coherence, etc. Therefore, it has become a hot research topic in various fields including ultra-fast laser technology and metrology science in recent years. Meanwhile, OFC has also been developed into an important scientific research instrument. Recently, a novel light source based on the coherent synthesis of OFCs has been developed, which can realize the periodical, high-speed (up to radio frequency) and stable modulation of the polarization or the orbital angular momentum of light. In this review, we try to introduce recent developments on the fundamental principles, experimental techniques and characterization methods of the novel light source based on the coherent synthesis of OFCs, starting from the basic concepts of OFC and mainly covering two aspects: polarization modulation and orbital angular momentum modulation respectively. We also try to provide some perspectives on the applications of OFC based on the coherent synthesis techniques in the fields of solid-state spectroscopy, optical manipulation and the interaction between light and matter, etc.
2021, 14(5): 1069-1088.   doi: 10.37188/CO.2021-0044
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Because of the large size and immobility working modes, traditional spectral imaging systems struggle to meet increasingly complex practical needs. Tunable micro-nano filtering structures show unique advantages for their lighter weight and greater flexibility, so they are promising candidates for achieving adaptive and intelligent operation in the future. This article summarizes a variety of tunable filtering methodologies and their operational principles both in domestic and foreign research within the last several years. It illustrates static tunable methods such as utilizing liquid crystal and phase-change materials, some dynamic tunable filtering structures such as Fabry-Pérot cavity, micro-nano tunable grating as well as some driving approaches like mechanical stretching, electrostatic driving, optical driving, etc. Meanwhile, this article also introduces some frontier researches based on microfluidic chips and graphene. In the end, it discusses the barriers, challenges and future trends of development for tunable micro-nano filtering structures.
2021, 14(5): 1089-1103.   doi: 10.37188/CO.2021-0022
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The requirements of modern optical engineering in fields such as deep ultraviolet lithography, extreme ultraviolet lithography and advanced light sources drive the continuous development of advanced optical manufacturing technology. Modern optical engineering requires the surface roughness of ultra-smooth optical components to reach the atomic level and the surface shape profile error in the full spatial frequency to reach RMS(Root Mean Square) sub-nanometer or even a few dozen picometers. This drives the manufacturing requirements of ultra-smooth optical components to approach the processing limits. At present, there are still technical challenges to achieve the ultra-smooth polishing technology and equipment required for the above ultra-high precision needs. Atomic level ultra-smooth polishing of complex surfaces such as cylinders, ellipsoids and toroids is still a primary direction of research at both domestically and abroad. Elastic emission machining is an atomic-level ultra-smooth processing method with stable removal functionality and ultra-low subsurface defect creation, which can be used for manufacturing optical components with the above-mentioned accuracy requirements. We summarize the research progress of elastic emission machining and equipment at both domestically and abroad, the principles of elastic emission machining which contains fluid characteristics, the movement characteristics of polishing particles and chemical characteristics, the equipment of elastic emission machining, and the factors affecting the improvement of surface roughness and material removal rate of elastic emission machining. Then we analyze the problems faced by elastic emission machining and equipment and look forward to their prospects. It is expected that this paper will provide a reference for the further development and application of elastic emission machining.
2021, 14(5): 1104-1119.   doi: 10.37188/CO.2021-0033
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As the technology node of large-scale integrated circuits continues to shrink, the focus control of the lithographic tools becomes particularly difficult. In order to ensure the exposure quality of wafers, it is necessary to quickly and accurately adjust the wafer in the Depth of Focus (DOF) to a degree as small as few dozen of nanometers. For this reason, people need to carefully analyze the various factors that cause defocusing or process window changes in the lithographic process, make a reasonable focus control budget, and control the various error factors within a certain range. This paper focuses on Extreme Ultraviolet (EUV) lithography, reviews the factors that affect focus control in the optical path of an advanced EUV lithographic tool and summarizes their principles, simulation and experimental results. It can provide a reference when conducting advanced lithography focus control budget research.
2021, 14(5): 1120-1132.   doi: 10.37188/CO.2021-0125
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Tunable fiber light sources with wavelength near 1 μm are widely used in optical fiber sensing, laser cooling, photochemical, spectroscopy and medical fields. They have thus become an area of focus in fiber light source research in recent years. The development history of fiber light sources with wavelength tuning ability is firstly summarized systematically. Then, their problems and possible solutions are analyzed. Finally, the future developments of tunable fiber light sources near 1 μm are prospected.
2021, 14(5): 1133-1145.   doi: 10.37188/CO.2020-0216
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Chaotic lasers are widely used in secure communication, lidar, optical detection and other applications due to their noise-like randomness, excellent anti-interference and other advantages. Moreover, as semiconductor lasers have small size, stable structure and other advantages, it has become one of the main lasers to produce optical chaos. However, the chaotic laser output from conventional optical feedback semiconductor lasers has the problems of narrow signal bandwidth and delay characteristics, which seriously affect their applications. With consideration for these problems, a comprehensive introduction to reduce the delay characteristics and optimize the chaotic laser bandwidth are reviewed based on recent literatures. This paper also summarizes the research progresses of chaotic secret communication, which is very important in the synchronization of chaotic lasers. The chaotic output of semiconductor lasers and the applications of chaotic lasers are also summarized, and then their development and potential future applications are discussed.
2021, 14(5): 1146-1161.   doi: 10.37188/CO.2021-0032
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Augmented reality (AR) display technology has developed rapidly in recent years, and has become a research hotspot and development focus of the global information technology industry. It has the potential to revolutionize the ways we perceive and interact with various digital information. Recent advances in micro-displays and optical technologies offer new development directions to further advance AR display technology. This review analyzes the optical requirements of human visual systems for AR head-mounted displays and compares them with current specifications of AR head-mounted displays to demonstrate their current levels of development and main challenge. The basic principles and parameters of various micro-displays and optical combiners in AR head-mounted displays are introduced to explain their advantages and practicability, and their development trends are summarized.
2021, 14(3): 447-457.   doi: 10.37188/CO.2020-0199
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Intelligent manufacturing has become more precise, miniaturized and integrated. Representative integrated circuit technology and its derived miniature sensors such as Micro-Electro-Mechanical System (MEMS) have become widely used. Therefore, it is important for intelligent manufacturing development to accurately obtain the surface morphology information of micro-devices and implement rapid detection of device surface defects. Fringe Projection Profilometry (FPP) based on structural light projection has the advantages of being non-contact, highly precise, highly efficient and having full-field measurement, which plays an important role in the field of precision measurement. Microscopic Fringe Projection Profilometry (MFPP) has been developed rapidly during recent decades. In recent years, MFPP has made great progress in many aspects, including its optical system structures, corresponding system calibration methods, phase extraction algorithms, and 3D coordinate reconstruction methods. In this paper, the structure and principle of a three-dimensional measurement system of microscopic fringe projection are reviewed, and the calibration problem of a small field-of-view system that is different from the traditional projection model is analyzed. After that, the development and improvement process of the micro-projection system structure is introduced, and the reflection in the measurment caused by the system structure and metal material is analyzed. On this basis, the prospects of the development of microscopic fringe projection of 3D measurement system are discussed.
2021, 14(3): 458-469.   doi: 10.37188/CO.2020-0180
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Mid-infrared lasers with emission spectrums located in the 3~5 μm atmospheric window have a wide range of possible applications in medical treatment, industrial processing, atmospheric remote sensing, space communication, infrared countermeasures and other fields. Transition Metal (TM) doped Ⅱ~Ⅵ group sulfide crystals can be used as the gain medium to achieve mid-infrared laser output. Among them, Fe2 +:ZnSe lasers are advantageous for their high conversion efficiency, their wide tunable range in the mid-infrared band and their compact structure. They are one of the most effective ways of achieving a short pulse with high power and high energy in the mid-infrared band. With the development of material technology in recent years, Fe2 +:ZnSe lasers have begun developing rapidly and have become a heavily researched topic. This paper reviews the development of a TM2+:Ⅱ~Ⅵ laser represented by a Fe2 +:ZnSe laser. The preparation methods of a Fe2 +:ZnSe gain medium are introduced and analyzed. The pump sources and factors affecting the performance of Fe2 +:ZnSe lasers are discussed. The output characteristics of the Fe2 +:ZnSe laser are reviewed. The latest development of Fe2 +:ZnSe lasers in room temperature and ultrashort pulse directions is summarized and prospected. The possible future development direction of Fe2 +:ZnSe lasers is discussed.
2021, 14(3): 470-486.   doi: 10.37188/CO.2020-0093
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As a new rapid element analysis technique, Laser-Induced Breakdown Spectroscopy (LIBS) has proven iteself to have great potential for applications in increasingly numerous industrial fields. However, due to harsh outdoor and industrial environments, newer and higher requirements are being demanded of the LIBS system, such as the size of its instruments and the ability to resist a harsh environment. The rapid development of new laser technology promotes instrumentation for LIBS, allowing it to gradually step outside the laboratory and into the industry, and allows the LIBS system to gradually move towards instrumentation, miniaturization and portability.In this paper, the development of a portable LIBS that was developed in recent years was reviewed. The application and latest research progress of different kinds of laser source (small lamp pumped solid-state laser, diode pump solid-state laser and micro laser, fiber laser) applied to the portable LIBS system were summarized and discussed, providing insight into both the fiber optic LIBS (FO-LIBS) and the handheld LIBS. In addition, the basic problems of current portable LIBS and the prospects of its future were proposed and discussed.
2021, 14(3): 487-502.   doi: 10.37188/CO.2020-0134
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Acoustic-to-seismic coupling landmine detection technology based on the unique mechanical characteristics of landmines and the acoustic-to-seismic coupling principle has broad application prospects in safe and effective detection of landmines. However, a significant amount of work must be done to study the practical landmine detection system. Among them, the acoustic coupled surface vibration signals are very weak and complicated, which has always been a challenging problem to detect such signals accurately and quickly. In this paper, the non-contact laser measurement techniques of surface vibrations based on the principle of the acoustic-to-seismic coupling landmine detection technology were reviewed, including laser Doppler interferometry, electronic speckle pattern interferometry and laser self-mixing interferometry, etc., and the application feasibility of electronic speckle-shearing pattern interferometry in acoustic-to-seismic coupling landmine detection was analyzed.
2021, 14(3): 503-515.   doi: 10.37188/CO.2020-0039
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Polarization modulation technology based on electro-optic crystals is playing an increasingly important role in the field of three-dimensional laser imaging. Due to the low field of view and high half-wave voltage of LiNiO3 (LN) materials, it is difficult for traditional electro-optic modulation technology to further improve 3D imaging performance. As the preparation technology of perovskite-structured electro-optical materials becomes more mature, electro-optic modulation technology based on new materials will become an excellent means to create a breakthrough in the detection accuracy of laser 3D imaging. PMNT, PLZT and KTaxNb1-xO3 (KTN) three typical materials have excellent electro-optical properties and dielectric properties that might surpass the field of view and half-wave voltage limitation. However, their applications in electro-optic modulation has lead to difficulties such as a low modulation bandwidth for PMNT, poor transmission performance for PLZT, and low practical application bandwidth for KTN. Future research will focus on the practicality of this modulation technology. The electro-optic modulation performance can be improved by doping and the signal-to-noise ratio of the system can be optimized by establishing performance characterization models.
2021, 14(3): 516-527.   doi: 10.37188/CO.2020-0051
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With its unique advantages, Visible Light Communication (VLC) can compensate for limitations in radio frequency communication, allowing it to become a recent avid topic of research. Orthogonal Frequency Division Multiplexing (OFDM) has been widely used in VLC due to its high rate of data transfer and frequency selective fading resistance. We compare the performance of several OFDM modulation techniques in VLC, including unipolar schemes, enhanced schemes and hybrid schemes based on discrete Fourier transformation, as well as optical OFDM systems based on Hartley transform and LED index modulation. We perform these comparisons in terms of energy efficiency, spectral efficiency, bit error rate, and algorithm complexity. The principles of some kinds of optical OFDM systems are firstly illustrated and their spectrum efficiencies are theoretically analyzed and compared. We also research and analysis the improved design of receivers in optical OFDM systems. The challenges and upcoming research of OFDM systems in VLC are summarized. The research in this paper can provide a research reference and propose more efficient unipolar modulation schemes to further improve the spectral efficiency and reliability of optical OFDM systems.
2021, 14(2): 227-244.   doi: 10.37188/CO.2020-0126
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Optical free-form surfaces are difficult to detect due to their rich degrees of freedom. Interference detection methods are both highly precise and non-contact. However, the static compensator in a traditional interferometer faces difficulty in achieving in-situ tests of unknown surface shapes or those changing during fabrication. Therefore, programmable adaptive compensators for large dynamic ranges have become a well-researched topic in recent years. Combined with the research work in the field of freeform surface metrology, we introduce the latest research progress in adaptive interferometry for optical freeform surfaces. Adaptive interferometers based on a Deformable Mirror (DM) or Liquid Crystal Spatial Light Modulator (LC-SLM) are analyzed in detail. An adaptive controlling algorithm in the adaptive interferometer is introduced as well. Finally, the advantages and development bottleneck of the above two kinds of adaptive interferometry are summarized and the prospects for the future development of freeform surface adaptive interferometers are proposed.
2021, 14(2): 245-263.   doi: 10.37188/CO.2020-0121
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Quasi-distributed fiber sensing systems play an important role in the fields of civil engineering, energy surveying, aerospace, national defense, chemicals, etc. Interrogation technology for quasi-distributed fiber sensing systems based on microwave photonics is widely used in high-speed and high-precision signal demodulation and sensor positioning in optical fiber multiplexing systems. Compared to conventional optical wavelength interrogation, this technology greatly improves system demodulation rate and compensates for the defects of traditional sensor positioning methods. This paper introduces the recent research progress of quasi-distributed fiber sensing interrogation technology based on microwave photonics; compares and analyzes the advantages and disadvantages of several existing microwave demodulation systems from the perspective of their fiber grating quasi-distributed sensing and fiber Fabry-Perot quasi-distributed sensing systems, respectively; and provides a summary of the prospective direction of future research in quasi-distributed fiber sensing interrogation technology based on microwave photonics.
2021, 14(2): 264-274.   doi: 10.37188/CO.2020-0193
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Near-infrared continuous-wave fiber lasers with wavelengths of 0.9~1.0 μm have important application prospects in the fields of high-power blue and ultraviolet laser generation, high-power single-mode pump sources, biomedicine and lidars. They have thus become a heavily researched topic in recent years. At present, their gain mechanisms mainly include a rare earth ion gain or a nonlinear effect gain. In this paper, the research progress of 0.9~1.0 μm fiber lasers based on these two kinds of gain mechanisms are reviewed in detail, and the technical bottlenecks and solutions of these lasers are analyzed. Furthermore, the potential directions for the future of their research are proposed.
2021, 14(2): 275-288.   doi: 10.37188/CO.2020-0098
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The Time-delay Interferometry (TDI) technique is of important value for China’s gravitational wave detection program and other space-based laser interferometry missions. In space-based gravitational wave detection, laser interferometry is utilized to achieve ten-picometer precision in the displacement measurements between drag-free proof masses. Laser frequency noise and clock frequency noise are the two dominant noises in the measurement. In the European LISA (Laser Interferometer Space Antenna) program for gravitational wave detection, TDI technique is used to remove laser noise and displacement noise of optical platform by time-delaying and linearly combining the twelve phase measurement data of the three satellites and thus creating an interferometer with equal-length beams. For the cancellation of clock noise, the frequencies of onboard clocks are multiplied to GHz levels and then the GHz clock signals are added on inter-satellite laser links by phase modulation. Finally, the clock noise can be extracted from the generated clock-sideband beat note, eliminating the clock noise terms in the TDI data combination. For the time-delay operation in the data post-processing of the TDI, there is also a requirement for the precise measurement of the absolute distances between three satellites. Therefore, in the TDI scheme, there are three functions applicable to the inter-satellite laser links: displacement measurement, clock sideband modulation and absolute distance ranging. The latter two functions consume the power of the optical carrier by 10% and 1%, respectively. The TDI demonstration in the LISA’s ground-based testbed shows the laser noise and clock noise can be suppressed by the factor of 109 and 5.8×104, respectively.
2020, 13(6): 1171-1181.   doi: 10.37188/CO.2020-0033
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With its high speed, small size, light-weight and low power consumption, space laser communication has become an indispensable and effective means of high-speed communication between satellites, especially in micro-satellite applications, which can benefit more strongly from the advantages of laser communication. This paper provides a detailed introduction of the latest research progress in the field of micro-satellite laser communication technology. On this basis, key techniques such as light miniaturization of identical orbital terminals, light miniaturization of different orbital terminals and turbulence mitigation technologies are summarized, and the development trends of the technology’s applications, duplex communication, single-point to multi-point, localization and batch production capacity are concluded.
2020, 13(6): 1182-1193.   doi: 10.37188/CO.2020-0049
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Target detection technology based on laser speckles is a kind of laser detection technology that has been ignored for a long time. In this technology, the laser speckle, which is regarded as noise in the traditional laser detection technology, is used as a new source of information. By analyzing the formation mechanism of a laser speckle pattern, the relationship between the statistical characteristics and the physical characteristics of the target is explored, and the effective analysis and inversion methods are combined to obtain the target’s shape, size, surface roughness and dynamic parameters. Compared with traditional laser detection technology, target detection technology based on laser speckles has a simple structure, has low optical system requirements, is sensitive to the physical and fretting characteristics of the target’s surface, and has been widely used in aerospace, medicine, industry, military and other fields. This paper classifies and summarizes the various kinds of speckle-based target detection technologies from recent years, compares and analyzes their applications, advantages and disadvantages, as well as the environmental restrictions. Finally, this paper prospects the trend for the future development of target detection methods based on laser speckles.

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

ISSN 2095-1531

CN 22-1400/O4

CODEN ZGHUC8