2022 Vol. 51, No. 6
column
- Optical communication and sensing
- Terahertz technology and application
- Optical imaging
- Image processing
- Infrared technology and application
- Optical design
- Photoelectric measurement
- Lasers & Laser optics
- Newsletter
- Invited paper
- Special issu
- Special issue—Single-frequency laser technology
- Lasers & Laser optics
2022, 51(6): 20220096.
doi: 10.3788/IRLA20220096
Investigation on the interactions of Airy and nonlinear accelerating beams in a biased photovoltaic-photorefractive crystal was presented theoretically by means of split-step Fourier method. The results shown that, by adjusting the initial beams interval and incident angle, two finite-energy Airy beams in the in-phase or out-of-phase case can attract or repel each other. In the in-phase case, not only single breathing solitons and soliton pairs can generate, but also splitting solitons with oscillation are obtained. While only soliton pairs can be formed in the out-of-phase case. Interaction of two in-phase nonlinear truncated accelerating beams can generate an odd number of breathing solitons, and an even number of soliton pairs can be produced in the out-of-phase case. Moreover, the peak intensity, breathing period and magnitude of the interaction force of the breathing solitons can be effectively regulated by adjusting the external bias and the incident angle. The results can provide a theoretical basis for the interaction regulation of Airy beams, and also have potential application prospects in the fields of all-optical information processing and optical network device fabrication.
2022, 51(6): 20210475.
doi: 10.3788/IRLA20210475
Laser communication, with its wide bandwidth, good confidentiality and no electromagnetic spectrum constraints, has become an effective means to construct high-speed communication in the air, space, earth and sea integrated communication networks. Compared with space-based, the air-based laser communication system, which is carried on balloon, airship, unmanned aerial vehicle aircraft and other platforms, has become the first choice for high security military network, disaster relief emergency network and commercial low-cost network due to its good flexibility, low cost and good maintainability. The latest research progress and main parameters of air-based laser communication system in USA, Germany, France and China are introduced in detail. The trend of one-to-many, lighter weight, wider bandwidth and the challenges of complex atmospheric channel and serious background noise are summarized, and key technical method, such as high dynamic capturing and tracking, high density integration and high sensitivity reception are proposed, which can provide references for air-based laser communication research.
2022, 51(6): 20210622.
doi: 10.3788/IRLA20210622
The absorption and scattering of light in seawater channel cause signal attenuation, and the turbulence of seawater causes signal amplitude fluctuation, both of which will reduce the bit error rate (BER) performance of underwater wireless optical communication (UWOC) system. The effects of the two channel characteristics on the signal performance were considered comprehensively, and a method was proposed to equate the transmission distance and turbulence probability density function to the system signal-to-noise ratio (SNR) and turbulence noise, and then the signal attenuation and turbulence noise were combined into the signal waveform to establish the underwater composite channel signal transmission model. According to the experimental system parameters, the signal transmission waveforms of Gaussian minimum frequency shift keying (GMSK) modulation under composite channel were simulated, and the one-bit difference demodulation algorithm was used to compare the demodulated waveforms with the original waveform, and the influence relationships of composite channel on the system BER performance was analyzed. The simulation experiment results show that, compared with on-off keying modulation (OOK), pulse position modulation (PPM), GMSK system can obtain the SNR gain of 3.3 dB, 4.8 dB respectively only in the attenuation channel with seawater attenuation coefficient of 0.151 m−1. Under the composite channel, GMSK modulation performance is superior to OOK modulation and PPM modulation. When the water attenuation coefficient is 0.151 m−1, and turbulence intensity variance is smaller than 0.16, GMSK modulation system has no error rate limit, the system BER is decided by signal attenuation and turbulence noise and Gaussian noise together, GMSK modulation achieves SNR gain of 4.35 dB compared with PPM modulation. Furthermore, turbulence intensity variance is greater than 0.16, system BER arrives limit, which value is determined by the turbulence intensity, and the limit value of BER increases nonlinearly with the increase of turbulence intensity.
2022, 51(6): 20210386.
doi: 10.3788/IRLA20210386
A modified feedforward common gate transimpedance amplifier circuit was designed. By using CMOS active inductor in parallel with the common source amplifier stage in the feedforward common gate transimpedance amplifier circuit, the bandwidth and gain of the transimpedance amplifier circuit can be improved effectively. Based on TSMC 60 nm CMOS process, simulation analysis and layout design of MFCG cross-resistance amplifier were carried out on Cadence software platform. The simulation results show that when the power supply voltage is 1.8 V and the photodiode junction capacitance is 200 fF, the amplifier circuit's −3 dB bandwidth is 17.2 GHz, the transimpedance gain is 55 dBΩ, the equivalent input noise current spectral density is less than 55 pA /$\sqrt {{\rm{Hz}}} $ in the bandwidth, and the circuit power consumption is 3.7 mW. The circuit layout area is 0.0029 mm2. The results show that the designed MFCG transimpedance amplifier has the advantages of high transimpedance gain, large bandwidth, small layout area and so on, and can be used in the optical receiver circuit of 20 Gb/s fiber communication system.
2022, 51(6): 20210434.
doi: 10.3788/IRLA20210434
The beaconless inter-satellite laser communication system (BILCS) does not to configure beacon light components, and directly applies signal light with small divergence angle to pointing, acquisition and tracking (PAT), which is beneficial to reduce the weight, volume, power consumption and manufacturing cost of the terminal, and meet the development requirements of commercial spaceflight and LEO satellite space laser network. To overcome the existing shortcomings of long scanning time and difficult acquisition of BILCS, satellite attitude change, measurement accuracy and terminal positioning error were taken into consideration, the scanning field of uncertainty was numerically computed, the beaconless scanning-acquisition process was designed, the coupling relationship of the control bandwidth of the coarse and refined scanning mechanism, scanning step size, planning path and the light coverage area was quantitatively analyzed, a simple and reliable coarse-refined combined spiral scanning method based on beaconless was proposed. Simulation results of typical environment demonstrate that the average acquisition time is less than 20 s, and the acquisition probability is more than 95% by this method, which effectively improves the BILCS scanning efficiency, and can satisfy the requirements of the future LEO satellite space laser network to rapidly establish laser communication link.
2022, 51(6): 20210652.
doi: 10.3788/IRLA20210652
An efficient precoding scheme combing adaptive modulation, space-time block code (STBC) and orthogonal circulant matrix transform (OCT) is proposed to improve the performance of multiple input-multiple output-orthogonal frequency division multiplexing (MIMO-OFDM) based visible light communication (VLC) systems in this work. A 2×2 MIMO-OFDM VLC system is designed and established to evaluate the performance of the proposed adaptive modulation STBC-OCT precoding scheme. The performances of bit error rate (BER), peak-to-average power ratio (PAPR) are investigated experimentally for different modulation and coding schemes. The performances of BER are studied in different direct current bias (DC) and driving peak-to-peak voltages (VPP) offsets. The experimental results show that the system using proposed adaptive modulated STBC-OCT precoding obtains a relatively flat and higher signal-to-noise ratio (SNR) values, lower PAPR compared with other precoding methods. The proposed scheme can obtain the best BER performance, and it is always lower than the 7% pre-forward error correction (pre-FEC) threshold of 3.8×10−3with the transmission distance is 0.5 m, DC is set to 2.7 V and VPP is 2.7-2.8 V, it can effectively overcome the bandwidth limitation of MIMO-OFDM VLC system and provide the best reliability.
2022, 51(6): 20210648.
doi: 10.3788/IRLA20210648
A tunable broadband, polarization insensitive and incident angle insensitive metamaterial terahertz absorber is proposed, which consists of silicon semi-ellipsoid/semi-spherical structure, graphene, dielectric layer and metal back plate. Based on the known results, the electric field results under different chemical potentials of graphene and different structural conditions were analyzed by simulation under the condition of vertical incident TE wave show that under the synergism of continuous and multimode Fabry-Perot resonances formed by silicon semi-ellipsoid/semi-spherical subwavelength structure and multiple discrete plasma resonances excited by graphene the absorption spectrum is smoothed and expanded so that the structure can achieve a wide range of adjustable absorptivity and a broadband absorption characteristic of nearly 100% absorptivity. When the chemical potential of graphene is around 0.2 eV and 0.9 eV, it can obtain about 5.7 THz and 7 THz wideband terahertz wave absorption (the absorption rate is more than 90%), respectively, and its maximum absorption rate is close to perfect absorption (about 99.8%). In addition, the structure is insensitive to 360° polarization and incident angle higher than 60°. In the above angle range, the absorptivity of the absorber can still be maintained to more than 90%. and the structure has potential applications in terahertz wave detection, spectral imaging and stealth technology.
2022, 51(6): 20210338.
doi: 10.3788/IRLA20210338
The detection of the main components in crude oil samples and the origin traceability is of great significance to the fields of national defense security and ecological environment. At this stage, the measurement of crude oil composition are complicated, high-cost, and have long detection time, which cannot meet the demands of rapid detection of crude oil composition and traceability of the origin of crude oil. Combining with a highly sensitive terahertz detection chip (Based on dual torus toroidal effect) and terahertz time-domain spectroscopy system, the terahertz spectra of crude oil samples from different origins were measured in this paper, and it was found that the frequency shift of the chip resonant peak showed different rules. For two main indicators of sulfur content and residual carbon in crude oil, quantitative analysis can be carried out according to their unique frequency shifts. The calculation of experimental data shows that the relative difference of the average resonance frequency of crude oil from the same origin is about 4.63%, and the relative difference of the average resonance frequency of crude oil from different production areas is about 56.53%, which can clearly distinguish the origin of crude oil. The designed metasurface chip can excite new electromagnetic mode, providing a highly sensitive detection technology, which can be widely used in real-time monitoring of biomolecules or detection of chemical substances (such as crude oil) composition detection, origin traceability and other fields.
2022, 51(6): 20210430.
doi: 10.3788/IRLA20210430
Multilayer bonding structure is widely used in aerospace field, and its bonding strength is the key factor to ensure engineering safety. Different terahertz time-domain spectroscopy parameters such as time-of-flight, energy and amplitude were used to characterize the uniformity of the adhesive layer of multilayer bonding structure, and then evaluate the bonding quality of multilayer bonding structure materials. The uniformity of the adhesive layer was qualitatively analyzed by the terahertz time-domain spectroscopy time-of-flight imaging method. The relative standard deviations of flight time of four experimental samples are 8.78%, 8.09%, 7.30% and 9.57% respectively; Using the energy integration information of terahertz time-domain spectroscopy, the kurtosis and skewness of the energy integration curve were used to qualitatively analyze the uniformity of the adhesive layer. The energy standard deviations of four experimental samples were 0.95, 0.9, 0.71 and 1.01, respectively; In addition, according to the amplitude characteristic information of terahertz time-domain spectroscopy, the uniformity of adhesive layer was quantitatively characterized by amplitude dispersion coefficient. The results show that the time-of-flight, energy integral and amplitude of terahertz time-domain spectroscopy can be use to quantitatively evaluate the adhesive layer uniformity of multi-layer adhesive structures. This method can provide a reliable means for evaluating the adhesive strength of multi-layer adhesive structures.
2022, 51(6): 20210438.
doi: 10.3788/IRLA20210438
Optical microscope is a vital tool to explore the microscopic world for humans, which plays an important role in the fields of biology, medicine, materials science, and precision measurement. Due to the diffraction limit, developing super-resolution optical microscopy imaging technology with higher image quality and spatial resolution has become a hot research frontier. Super-resolution imaging technology based on microspheric lens has great development potential because it's obvious advantages of being easy to implement, simple operation and label-free. However, the field of view (FOV) of a single microsphere is limited, and it is difficult to locate the microspheres accurately. Improving the maneuverability of microspheres and expanding the FOV of super-resolution imaging have become the key of this technology development. Based on the principle of microsphere super-resolution imaging technology and the main factors for imaging quality, the paper focuses on the latest research progress in expanding the FOV of microspheric lens super-resolution microscopy imaging. According to the control methods of the microsphere, these progresses are summarized into four categories: Mechanically contact control, non-contact control, microsphere assembly layer, and microsphere-objective integration. The technical characteristics of these four categories are discussed, and the image processing technologies for field expansion are also analyzed, such as large FOV and image stitching. At the end, the paper points out the key problems, existing difficulties and challenges for microspheric lens super-resolution imaging technology, as well as the breakthrough for the future research work. The development direction and application future of this technology are prospected.
2022, 51(6): 20210605.
doi: 10.3788/IRLA20210605
In image acquisition process, the image blur caused by the moving subject or the camera itself will have a negative impact on the subsequent high-level vision tasks. Aiming at the problem that the current deep learning image deblurring method cannot balance the deblurring effect and efficiency, a multi-scale recurrent attention network was proposed, which used separable convolution to reduce the amount of parameters, and improved the attention module to allocate computing resources reasonably. Layers were used for dense connection to improve parameter utilization efficiency, and edge loss was introduced to improve the edge detail information in the generated image. Experiments prove that the proposed method has good generalization performance and robustness. Compared with the typical methods in recent years, the SSIM and PSNR have increased by about 1.15%, 0.86% and 0.91%, 1.04% on the Lai dataset and Köhler dataset, respectively. The average single frame running speed on the GoPro dataset is nearly 2.5 times faster than similar methods.
2022, 51(6): 20210491.
doi: 10.3788/IRLA20210491
In order to solve the problems of long registration time and low accuracy in the case of data lossing and noise points existing in the traditional iterative closest point (ICP) algorithm, a new registration algorithm based on improved voxel cloud connectivity segmentation (IVCCS) combined with weighted nearest neighbor distance ratio was proposed. Double threshold voxel denoising was used to remove the noise voxel in the initial seed voxel, which was caused by a single constraint in the original voxel cloud connectivity segmentation algorithm (VCCS). Meanwhile, layered voxel cloud denoising was used to speed up the operation speed of registration. The feature points in the point cloud were extracted by flow constrained clustering, and whether the feature points were coincidence points was verified according to the nearest neighbor distance ratio. The minimum objective function of ICP was optimized by giving different weights, so as to accelerate the registration speed.Experimental results show that compared with the traditional ICP algorithm, the algorithm has reduced the number of iterations, and significantly improved the accuracy and speed. Compared with the ICP algorithm based on fast point feature histogram (FPFH), the algorithm has improved the registration accuracy by 8.5%-24.7%, the speed by 65.6%-92.3%, and the number of iterations decrease by 16.6%-38%.
2022, 51(6): 20210532.
doi: 10.3788/IRLA20210532
Inspired by the direction selectivity mechanism of vision system, a new image clutter modeling method was proposed and applied to the target acquisition performance evaluation of imaging system. Firstly, the gradient direction of pixels was used to simulate the response direction of neurons in the local receptive field of the visual system. By comparing the gradient direction similarity between the central pixel and the adjacent pixel, the relationship between neuron "excitation" and "inhibition" response was simulated. The visual pattern was designed based on directional selectivity. Secondly, considering the sensitivity of human visual system to brightness contrast, the brightness contrast was used as a factor to weight the visual pattern histogram. The background clutter was modeled in the weighted histogram space. Finally, the relationship between background clutter and target acquisition performance was deduced, and the target acquisition performance evaluation model of photoelectric imaging system was established. The experimental results show that the target acquisition performance evaluated by the proposed method is consistent with the actual target acquisition performance in the field, and is superior to the existing performance evaluation methods in terms of root mean square error and correlation.
2022, 51(6): 20210950.
doi: 10.3788/IRLA20210950
Aiming at the problem that the robustness and registration accuracy are difficult to be compatible in the existing image registration methods, an image registration algorithm using SURF feature and local cross-correlation information was proposed. Firstly, the SURF feature extraction method was used for preliminary rough registration to improve the robustness of registration. Then, the homography matrix was calculated by using the correlation coefficient of local key areas in the image. Finally, the homography matrix was applied to the rough registered image results for rotation transformation, so as to realize high precision and robust image registration. The experimental results show that the proposed registration method is compared with the image registration method based on SIFT, ORB, SURF and cross-correlation information on multiple groups of data, which not only shows higher registration accuracy and efficiency, but also shows better robustness.
2022, 51(6): 20210446.
doi: 10.3788/IRLA20210446
In order to improve the ability of Advanced Driving Assisted System (ADAS) to perceive vehicles in the road environment, the information fusion algorithm of machine vision and millimeter wave radar was proposed to detect front vehicles in this paper. Firstly, the camera and millimeter wave radar were jointly calibrated to determine their conversion formula using the coordinate measuring machine in the fusion system. The candidate frame of SSD for deep learning algorithm was optimized to improve the speed of vehicle detection, while long focus camera and short focus camera were selected for two front images acquisition, the overlapped images were fused to improve sharpness of small target image ahead. The appropriate threshold parameters of radar data were determined by radar simulator and the effective vehicle target was extracted. According to these effective target data, the image collected by the camera was selected and the region of interest was established. Vehicles in the selection region were detected with the improved SSD algorithm. In the test, the vehicle detection rate is 95.3%, and the total processing time for single frame image is 32 ms. It proves that the algorithm can help ADAS system to archieve vehicle detetcion with higher real-time and environmental adaptability.
2022, 51(6): 20210597.
doi: 10.3788/IRLA20210597
For the problem of infrared image target classification, a method combining multi-feature fusion and extreme learning machine (ELM) was proposed. Three types of features, i.e., principal component analysis (PCA), local binary pattern (LBP) and scale-invariant feature transform (SIFT) were used to describe the pixel distribution, local texture and feature point information of the target in the infrared image. The three types of features reflected the characteristics of infrared image targets from different aspects, so they had complementary advantages. Afterwards, the three types of features were fused based on multiset canonical correlations analysis (MCCA) to obtain a unified feature vector. The fused features not only inherited the distinguishing characteristics of the original three types of features, but also effectively removed redundant information. In the classification process, The ELM was used as a basic classifier to classify the fused feature vector. ELM had the obvious characteristics of few parameters, high efficiency, high precision and strong robustness, so it was helpful to improve the overall performance of infrared target classification. Therefore, the proposed method comprehensively improved the target recognition performance by combining the advantages of multiple features and ELM. During the experiment, the infrared images of four types of aircraft targets were used to test the performance of the proposed method. According to the comparison with several existing methods, the experimental results prove the performance advantages of the proposed method.
2022, 51(6): 20210517.
doi: 10.3788/IRLA20210517
The near-infrared optical tracking system has rapidly developed into an important part of surgical navigation because of its high precision and convenience. A high-precision and low-cost optical tracking system was designed based on binocular vision. The system used the passive marker ball (NDI passive sphere) installed on the instrument as the marker, and added a near-infrared filter in front of the binocular camera lens to eliminate the interference of ambient light. Firstly, the contour filtering algorithm was used to extract the marker contour, and the least square ellipse fitting algorithm was used to obtain the pixel coordinates of the marker projection center; Secondly, an instrument recognition algorithm was designed so that each instrument could store the central pixel coordinates of the marker ball separately and orderly for the resolution of multiple instruments; Finally, by matching the mark centers corresponding to the left and right views, the spatial coordinates were reconstructed, and then the coordinates of the instrument tip in the world coordinate system were derived. The system was used to track the instruments in the experiment, and the irregular placement of instruments was used to verify the accuracy and robustness of the instrument recognition algorithm. The accuracy rate was 95%, and the average recognition time was only 4 ms. The stability, static positioning accuracy and dynamic tracking of the system were tested. The results showed that the stability error could reach 0.13 mm, the static positioning accuracy could reach 0.373 mm. The proposed near-infrared optical tracking system has high accuracy and stability, and can meet the requirements of surgical navigation.
2022, 51(6): 20210463.
doi: 10.3788/IRLA20210463
The development of spatial spectral imaging technology makes the integration of detector array and light splitting elements become a trend. The long line array splice integrated filter (LLASIF) is the key device of spatial multispectral imager to realize concentrated light splitting at focal plane, and it has obvious demand in the spatial multispectral imaging system in China. In this paper, a 4-channel short/medim infrared LLASIF was designed. The narrow band filter of each channel was prepared by electron gun evaporation method assisted by ion beam. The splicing process was explored by using specially developed tools and the LLASIF was developed. The test results show that the average transmittance of each narrow band filter reaches 90%, the minimum bandwidth is 230 nm (central wavelength is 4.95 μm), and the spectral performance is consistent with the design results and meets the performance requirements. The minimum seam width is only 10 μm, the seam parallelism error is 1 μm. The integrated filter structure and splicing strength can withstand the vibration resistance test. The integrated filter has been successfully applied in space optical remote sensing instrument.
2022, 51(6): 20210555.
doi: 10.3788/IRLA20210555
Emissivity setting has a decisive impact on the accuracy of the measurement results of infrared thermal imager, so it must be calibrated accurately before temperature measurement. In this paper, the influence of emissivity setting on temperature measurement accuracy of infrared thermal imager was studied through thermocouple calibration test. Secondly, the influence factors of emissivity setting were analyzed by factorial experiment. Finally, the influence degree of each factor on the emissivity setting was studied by orthogonal experiment, and the empirical formula fitting and experimental verification were carried out. The results show that: for SiCp/Al composites, the emissivity setting is very different before and after the measured temperature is 500 ℃. When the measured temperature exceeds 500 ℃, using the recommended value as the setting method will produce large errors. In the range of 0°-45°, the measurement angle has no influence on the emissivity setting. However, temperature, surface roughness and observation distance all affect the emissivity setting. The maximum error of the empirical formula of the emissivity setting obtained by polynomial fitting is 2.76%.
2022, 51(6): 20210617.
doi: 10.3788/IRLA20210617
The thermal-structural-optical integrated analysis method has been widely used to evaluate the impact of environmental load on performances of opto-mechanical systems. However, for opto-mechanical systems with complex optical surface deformation mode and large rigid body motion, the results obtained by the traditional thermal-structural-optical integrated analysis method are inaccurate. A modified thermal-structural-optical integrated analysis method based on the complete equations of rigid body motion was proposed. Firstly, the deformed optical mirror was modified by bicubic spline interpolation method, then the complete equations of rigid body motion of the optical surface was established. The rigid body motion of the optical mirror was separated by a common optimization algorithm, and finally Zernike polynomial coefficients were solved by the least square method to characterize the elastic deformation of the optical mirror. Numerical and engineering cases were used to verify the effectiveness and correctness of the proposed method. The effects of key factors such as rigid body motion equation, surface correction method, node distribution and surface shape on the results were also quantitatively analyzed. The results show that the proposed method can identify the rigid body motion and elastic deformation of the optical surface more accurately than the traditional method, and does not depend on the analytical equation of the optical surface, and the shape of the mirror surface has a great influence on the analysis results.
2022, 51(6): 20210630.
doi: 10.3788/IRLA20210630
The structure of progressive addition lenses (PALs) was introduced. A method of bi-directional fitting meridians of PALs was proposed. Two polynomial curves were fitted bi-directionally from the far and near points of the PALs to obtain meridians that meet the design requirements. Based on this, the curve cluster which was orthogonal to the meridian and meeting the design requirements was selected as the contour line. The vector height data of each point on the PALs was calculated to obtain the entire surface shape. The design results show that the bi-directional fitting method of designing the PALs′ meridians provides the flexibility to adjust the rate of increase of the focal power on the meridians compared to the single higher-order polynomial curve describing the meridians. The individual needs of the wearers can be met to control the focal power and astigmatism of the PALs in the far and near vision zones as well as in the gradient channel. When the same lenses parameters and different bi-directional fitting meridians are chosen, corresponding demanded visual area can be obtained for PALs. The designed PALs were processed, and the finished PALs were measured. It is shown that the performances of the PALs obtained by processing are consistent with the performances of the designed PALs.
2022, 51(6): 20210640.
doi: 10.3788/IRLA20210640
To solve the problem that the collimating lens in the existing dot array structured light projector will result in dramatical zero-order diffraction and uneven intensity distribution of the projected dot, an on-chip dot array structured light projector based on bottom-emitting vertical-cavity surface-emitting laser was proposed as well as the design of the corresponding diffractive optical element. In the design, the target intensity distribution was firstly modified with intensity adjustment and coordinate transformation. Then, the improved Gerchberg-Saxton algorithm based on the Rayleigh-Sommerfeld diffraction integral was applied to obtain the phase distribution of the on-chip diffractive optical element of the projector without collimating lens. Eventually, evaluations of the projected dot was conducted. Simulation results show that the projector can suppress the zero-order diffraction better and obtain more uniformly-distributed intensity when the gaussian beam is used as the light source. In addition, the structure can omit the installation of the collimating lens, thus, reducing the size of the projector and realizing the integration of the light source and the diffractive optical element through chip manufacturing process.
2022, 51(6): 20210670.
doi: 10.3788/IRLA20210670
A novel mixed flexible support structure was proposed to satisfy the requirements of surface and position accuracy of a large-aperture lens. First, Castigliano’s second theorem was used to analyze the various flexible hinges and the whole flexibility model of the support component was established. Then, the objective function of the total deformation energy of the flexible support assembly was used to establish the constraint equation based on the position accuracy and the actual space requirements, and a structural optimization design model was established. It was determined that the radially flexible support structure was the most sensitive to the flexibility of the flexible support assembly, and its stiffness was verified. Finally, the finite element analysis of the optimized whole structure of the lens assembly was carried out, and the surface accuracy was obtained by using the geometric fitting method. The simulation results show that the surface shape accuracy of the new hybrid flexible support structure is better than λ/20 (λ=632.8 nm) under various conditions. The novel mixed flexible support structure and its theoretical analysis process can provide a reference for the supporting technology of high precision large-aperture lens.
2022, 51(6): 20210472.
doi: 10.3788/IRLA20210472
High performance optical imaging device is an important basis for machine vision measurement, as a compact and fast electronic controlled focusing device, liquid lens has a promising application in the field of machine vision measurement. In practical, the performance of liquid lens focusing device is easily interfered by the environment, and the intrinsic parameters are difficult to be calibrated accurately, which limits their application in machine vision measurement. The problems described above were researched, a machine vision measurement system was built based on Optotune's liquid lens. By analyzing the electronically controlled focusing mechanism of liquid lens, the model between current and focal length was proposed. Then the interaction mechanism between system parameters and temperature factor and gravity factors was studied, followed by the proposition of temperature-focal length model and gravity-main point vertical position model. By combining the system models with pin-hole imaging model, a functional expression of system intrinsic parameters was proposed, and the corresponding calibration device and calibration process to acquire all the coefficients of the expression were designed and verified through experiment. Finally, to evaluate parameter calibration accuracy, measurement test was performed using a checkerboard with sides of 30 mm. Test results show that the proposed calibration method can get more accurate intrinsic parameters, the average positional error of image corner points' world coordinate mapping result is 0.10 mm, meanwhile the maximum relative error of the length of the side of checkerboard is 0.68%, the errors are reduced by 27.2% and 54.4% respectively compared with test results using intrinsic parameters calibrated by mostly used interpolation method.
2022, 51(6): 20210503.
doi: 10.3788/IRLA20210503
The nonlinear response of digital projector is a hot issue in recent years, because although the digital projector can avoid all kinds of defects of physical grating projection, its own nonlinearity directly affects the output information, which is the main source of phase error, and then affects the measurement accuracy. Aiming at the problem that Gamma nonlinearity in 3D measurement of digital fringe projection was inconsistent with Gamma value in different regions, a method of correcting Gamma nonlinearity by precoding of subregion of orthogonal fringes was proposed. By dividing the region by orthogonal fringes, the region fringe image was corrected by polynomial fitting and precoding value calculating. The phase error was reduced by 82.24% after correction by this method. It was suitable for the position relationship between any projector and camera. Only a set of precoding coefficients of subregion need to be calculated and encoded fringe graph can be generated by this method. The method can meet the measurement requirements of the system after that. The method has strong flexibility and high accuracy.
2022, 51(6): 20210641.
doi: 10.3788/IRLA20210641
The installation error of the star sensor was one of the main factors restricting the accuracy of SINS/CNS navigation. It was necessary to calibrate it before use, especially the NFOV star sensor could not obtain the attitude information from a star map. This paper proposed a fast and high-precision calibration method for SINS/CNS integrated navigation system. The attitude and velocity output by the inertial navigation and the vector information measured by the star sensor were used to construct quantity measurements. A Kalman filter model was established to realize the ground calibration of installation error and inertial device constant error. Through global observability analysis, the observability of the system under different carrier attitudes and star points was given and verified. The simulation results show that the carrier needs to rotate in at least two axes and observe stars three times, and the star point should not be located at the star sensing measurement origin, so as to estimate the three-axis installation error of the star sensor with high precision. For a FLOV star sensor, part of the carrier attitude is not conducive to improve the observability of the system. The estimation accuracy of carrier attitude and star-sensitive installation errors is within 0.5″ and the constant errors of gyro and accelerometer are less than 0.000 7(°)/h and $0.3\;{\text{μg}}$ , respectively. This method can achieve high-precision calibration without sophisticated external equipment and manual reference. It has certain significance for the stargazing scheme design of SINS/CNS integrated navigation system.
2022, 51(6): 20210647.
doi: 10.3788/IRLA20210647
Synchronous Monitoring Atmospheric Corrector (SMAC), a support for the main camera, was one of the mayor facilities of high resolution and multi-mode imaging satellite. SMAC was designed to achieve atmospheric correction for high spatial resolution images based on radiative transfer model by getting synchronous parameters of aerosols and water vapor. SMAC had a special channel, where the radiance could be mostly absorbed by water vapor, for remote sensing of cirrus cloud. This channel was sensitive to the fluctuation of water vapor in the lab while stability measurement, thus the real performance of this channel could be covered up. The influence of water vapor fluctuation on stability test data was suppressed by controlling water vapor and setting synchronous monitoring detector. The results show that the stability error of SMAC’s channel for cirrus cloud detection decreased from 4.08% to 0.23%. It indicates that the stability measurement method of cirrus cloud diagnosing band for SMAC is reasonable and effective, which could reflect the stability performance of the product, and has important guidance significance for stability measurement of similar instruments.
2022, 51(6): 20210375.
doi: 10.3788/IRLA20210375
In order to improve the tracking performance of the laser communication tracking system and enhance the anti-disturbance capability of the system, a single-detector composite axis control method based on Kalman filter was proposed. Firsty, the principle of the single detector composite axis system was analyzed, and the feasibility of the decoupling algorithm was verified by the error transfer function. Then in order to improve the impact of miss distance and reduce the real-time processing requirements of the detector, an adaptive Kalman filter algorithm was proposed. Finally, according to the rotation transformation relationship between the detector coordinate system and the fast steering mirror coordinate system, the decoupling matrix of the coarse and fine system was calculated, and a desktop experimental system was built to verify the principle. With the condition of 0.1 Hz low frequency disturbance, the relative displacement of the fine tracking system will not exceed the critical value of the mirror deflection angle, and the tracking error will decrease from 2.54 μrad to 0.86 μrad. The experimental results show that the decoupling control can improve the tracking accuracy and enhance the anti disturbance ability of the system. It has a certain guiding significance for the practical application in the future engineering.
2022, 51(6): 20210675.
doi: 10.3788/IRLA20210675
In response to the demand for precise attitude measurement in the production, manufacturing and assembly of large-scale equipment in modern industrial production, a laser tracking attitude angle measurement method based on weighted least squares was proposed. Firstly, the composition of the attitude measurement system was explained, and the coordinate system used in the attitude measurement system was defined; Secondly, the mathematical model of attitude measurement was established, and on this basis, the redundant angle information was data fused using the weighted least square method. The Monte Carlo method was used to simulate and analyze the fusion method; Finally, an attitude measurement experimental platform was built, and the precision of the system’s attitude angle measurement accuracy was evaluated using a precision two-dimensional turntable. The experimental results show that within the angle range of [−30°, 30°], the attitude angle measurement accuracy is 0.28° when the measurement distance is 3 m, and the attitude angle measurement accuracy is 1.76° when the measurement distance is 8 m. Compared with the monocular vision method, attitude angle measurement accuracy increased by 6.7% at 3 m and 18.8% at 8 m. The poposed data fusion method has a good effect on improving the accuracy of attitude angle measurement.
2022, 51(6): 20210629.
doi: 10.3788/IRLA20210629
In order to achieve the demand of real-time detector damage detection in the external field, a photoelectric detector surface damage state polarization imaging type detection system was developed. The expressions of the cat eye target echo polarization characteristics (DP) and the degree of polarization (DOP) were derived theoretically, the relationship curves among surface roughness, DOP and DP were simulated by MATLAB software. A simultaneous polarization imaging optical system was designed, a real-time detection outfield experiment of the Charge Coupled Devices (CCD) surface damage state by a 671 nm continuous laser was carried out and a MATLAB GUI-based echo image visualization real-time acquisition system was developed to obtain information such as echo image intensity, DP and spot size. Moreover, by analyzing the morphological images of the damaged and undamaged detector surface with optical digital microscope and white-light interferometer, it was found that the silicon substrate was visible on detector damage surface and the roughness parameter Sq was large. Clearly, the simulation results are in good agreement with the experimental test results. The results show that after the photodetector is damaged, its surface roughness increases, DP decreases, the depolarization characteristic is obvious and DOP decreases. Overall, the polarization imaging technique can effectively detect the damage state of the photodetector surface in real time, and this study provides a good method for real-time detection under external field conditions.
2022, 51(6): 20210680.
doi: 10.3788/IRLA20210680
With the rapid growth of video surveillance data, there is an increasing demand for video anomaly detection, and reconstruction error detection methods based on deep autoencoders have been widely discussed. However, the autoencoder generalizes well, can reconstruct the anomaly well and lead to missed detection. In order to solve this problem, this paper proposes to adopt a memory module to enhance the autoencoder, which is called the Memory-augmented autoencoder (Memory AE) method. Given the input, Memory AE first obtains the encoding from the encoder, and then uses it as a query to retrieve the most relevant memory items for reconstruction. In the training phase, the memory content is updated and encouraged to represent prototype elements of normal data. In the test phase, the learned memory elements are fixed, and reconstruction is obtained from several selected memory records of normal data, thus the reconstruction will tend to be close to normal samples. Therefore, the reconstruction of abnormal errors will be strengthened for abnormal detection. Experiments on two public video anomaly detection datasets, namely Avenue dataset and ShanghaiTech dataset, proves the effectiveness of the proposed method.
2022, 51(6): 20210547.
doi: 10.3788/IRLA20210547
Due to the vagueness of anomaly definition and the complexity of real data, video anomaly detection is one of the most challenging problems in intelligent video surveillance. Frame reconstruction (current or future frame) based on autoencoder (AE) is a popular video anomaly detection method. Using a model trained on normal data, the reconstruction error of abnormal scenes is usually much larger than that of normal scenes. However, these methods ignore the internal structure of the normal data and are memory-consuming. Based on this, a deep auto-encoding Gaussian mixture model (DAGMM) was proposed. Firstly, the deep autoencoder was used to obtain the low-dimensional representation of the input video segment and the reconstruction error, and then further input into a Gaussian mixture model (GMM). The energy probability was predicted through the Gaussian mixture model, and then the anomaly was judged through the energy density probability. The proposed DAGMM can simultaneously optimizes the parameters of the deep autoencoder and GMM in an end-to-end manner, and balance auto-encoding reconstruction, density estimation and regularization of low-dimensional representation, and has strong generalization ability. Experimental results on two public benchmark datasets show that DAGMM has reached the highest level of technological development, achieving 95.7% and 72.9% frame-level AUC on the UCSD Ped2 and ShanghaiTech dataset, respectively.
2022, 51(6): 20210632.
doi: 10.3788/IRLA20210632
In order to meet the needs of closed cabin and windowless driving of military vehicles such as tanks and armored vehicles, a new assisted driving system was developed. The scene around the vehicle was obtained through a multi-path optical sensors and the 360° panoramic view video of the vehicle body was obtained through the panoramic splicing algorithm. The panoramic video was displayed on the on-board display screen to assist the driver to watch the vehicle when driving in a narrow roads, an obstacles and the other special sections, or when reversing. When the vehicle driving in a standard road, the video can also provide a scene video around the vehicle according to the driver's head torsion angle, and transmit it to the driver's display helmet for the driver to use. In case of a special circumstances, the on-board display will give an alarm to driver. The driver's head position determination method used the infrared LED light source image positioning technology and the MEMS inertial device positioning technology. The vehicle modeling in the laboratory can verify the panoramic view video generation technology and the helmet free-viewpoint-observation technology. In addition, the driving experiments were carried out with a real vehicle. The experimental results show that this system can meet the requirements of vehicles with closed cabin and windowless driving with a standard road conditions, a speed of 40 km/h. It can assist in driving with a special situations such as narrow roads, obstacle detour and reversing.
2022, 51(6): 20220321.
doi: 10.3788/IRLA20220321
Sodium laser guide stars (LGS), known as artificial stars, can be used to detect and correct wavefront aberrations induced by atmospheric turbulence, which can significantly improve the adaptive-optical telescope's imaging quality. Due to the limited corrected field of view of single LGS, multiple sodium LGS, created by exciting sodium atoms in the Earth's mesosphere via multiple yellow laser beams, is developed to yield high-resolution imaging in a much larger field-of-view, which has important applications in the fields of precision astronomical observation and space target detection. The successful implementation of microsecond-pulse sodium guidestars constellation via 100 W level pulsed sodium laser was reported, based on a small angle precise polarized combining and splitting technology. At Lijiang Observatory, four-ways~20 W/beam yellow laser beam with kHz repetition-rate and hundred-μs pulse width were projected up to the sky through one launching telescope, and generated a distinctive four-point grouping on a 40" field of view with variable configurations of linear, parallelogram, rhomboid and square. The spot size of each guide star was about 3.25" and the corresponding brightness was around 8 magnitude in V band. The sodium return signal could well avoid Rayleigh light interference by the pulse synchro controlling technology to deliver higher spatial resolution. This could serve as a technical reference for multi-conjugate correction systems on large-aperture astronomical telescopes.
2022, 51(6): 20220249.
doi: 10.3788/IRLA20220249
Compared with the traditional multispectral imaging detection, polarized multispectral imaging detection can detect more information of the detected object surface such as roughness and moisture content, which brings great convenience to target detection. However, at present, it is mainly used for target detection and not widely used in target classification. BP neural network is a typical neural network commonly used at present. Neural network can establish the start-to-end mapping. On the premise that the training sample set is large enough, the trained neural network with good consequences is an efficient, accurate and high-speed tool. Firstly, the polarized multispectral images of typical ground objects were obtained by using the polarized multispectral imaging detection system based on rotating polarizer and filter, and after the images were preprocessed, the data set could be established; Secondly, the neural network was trained on this data set. The trained neural network could process the unknown polarized spectrum images and realize the classification of several typical ground objects; Finally, the effect of neural network classification was evaluated and compared with several other typical classification methods. It was found that the neural network method has better classification accuracy and effect. Compared with the typical maximum likelihood classification algorithm, its overall classification accuracy could be improved from 91.7% to 94.2%, and the Kappa coefficient could be improved from 0.851 to 0.898. The results show that the polarized multispectral image classification method based on neural network has certain research significance for improving and optimizing the existing data processing methods of polarized multispectral images.
2022, 51(6): 20220274.
doi: 10.3788/IRLA20220274
The technical bottleneck of realizing the three-dimensional optical information transmission of space-air-ground-sea is to solve the problem of laser uplink and downlink transmission under the dynamic sea surface conditions of air-sea sea-air cross-media. This paper mainly used the blue-green laser in the seawater environment as the carrier and proposed a numerical research method for the downlink transmission of the blue-green laser through the air-sea dynamic across the medium sea surface. The effects of atmospheric sea mist, sea surface wind speed, and particle distribution in seawater on the down-transmission scattering properties of blue-green lasers were discussed in detail. The variation of blue-green laser transmittance with transmission angle under different wind speeds, and the transmittance of blue-green laser downlink transmission under different atmospheric sea mist visibility, different chlorophyll concentrations, and different bubble concentrations were numerically calculated. The results showed that when the blue-green laser is transmitted in seawater, the effect of bubbles on laser attenuation increases with the increase of wind speed and decreases with the increase of transmission depth; the transmission rate of the blue-green laser through the atmospheric sea surface and seawater gradually increases with the increase of visibility of sea mist in the atmosphere at the offshore surface. With the increase of transmission distance, the influence of chlorophyll increases gradually, and the transmittance of blue-green laser decreases. The work in this paper provides theoretical and technical support for the cross-media wireless optical transmission and communication of blue-green lasers uplink and downlink across the air-sea and sea-air.
2022, 51(6): 20210949.
doi: 10.3788/IRLA20210949
The new spaceborne photon counting radar can acquire high-precision three-dimensional information of ground and ground targets, but its measurement accuracy is greatly affected by noise. Aiming at the difficulty of signal extraction of single-photon laser data in areas with inconsistent background noise and large slope area, this paper proposed a single photon point cloud denoising algorithm based on multi-feature adaptive. It was different from the traditional circular or elliptical filtering kernel, and used the parallelogram filtering kernel which was more in line with the characteristics of single photon point cloud data, and signals were adaptively identified by slope, spatial density and noise rate. The ICESat-2 single photon point cloud data located in the glacier area of Qinghai-Tibet Plateau was selected to carry out the point cloud denoising test and verification, and the study area had a large slope and broken terrain. Compared with the official denoising results of ATL03 and ATL08, the proposed algorithm has better performance in areas with inconsistent background noise level and large slope area.
2022, 51(6): 20220237.
doi: 10.3788/IRLA20220237
Single-frequency fiber laser has the merits of excellent monochromaticity and high spectral power density, and it has widespread application needs in, for example, coherent communication and sensing, lidar, gravitational wave detection and nonlinear frequency conversion. At present, single-frequency fiber laser technologies are moving towards the direction of higher output power, broader spectral range, and higher overall performance, and have become the research frontier and hotspot in the field of laser technology. This manuscript systematically combed through the important progress of single-frequency fiber lasers in recent years. Specifically, the landmark works with respect to the implementation mode of single-frequency lasing, power scaling, wavelength expanding and performance improvement were reviewed. In addition, the current challenges as well as future trends of single-frequency fiber laser technology were also discussed.
2022, 51(6): 20220400.
doi: 10.3788/IRLA20220400
An acoustic optical modulator (AOM) laser power feedback loop was used to suppress the intensity noise of the pump laser, and the intensity noise reduction of more than 5 dB (@f=1 Hz-50 kHz) was obtained. The relative intensity noise of the 2 μm single-frequency fiber laser obtained 3-15 dB suppression (@f=1 Hz-50 kHz), and the intensity noise level was close to the detector limit (@f=40-400 Hz). Meanwhile, its frequency noise is also suppressed by 3-8.4 dB. After the two-stage Thulium-doped polarization-preserving fiber amplifier, the output power of the 2 μm single-frequency laser was increased to about 5.2 W with almost no significant increase in frequency noise, and the frequency noise levels were all at 100 Hz/$\sqrt {{\rm{Hz}}} $ (f>13 Hz). The frequency response was 45 MHz/V, the frequency drift was 41.4 MHz@1 h, the power fluctuation was less than 0.4%@1 h, and the linewidth was less than 5 kHz. This kind of ultra-low noise 2 μm single-frequency fiber laser will be a candidate laser source for the next generation of gravitational wave detectors.
2022, 51(6): 20210970.
doi: 10.3788/IRLA20210970
Stimulated Raman scattering is a mature technology that provides laser outputs with flexible wavelengths. Stable single-longitudinal-mode (SLM) Stokes is able to be achieved in a simply designed oscillator due to the nature of spatial hole burning free of Raman gain. Therefore, the Raman laser is considered as an attractive and potential method to generate SLM output with a particular wavelength. As the single-crystal diamond synthetic technology matures, high-power continuous-wave SLM diamond Raman lasers have been widely investigated for the past few years. In this review, the mechanism of Raman SLM operation in Raman oscillator and the state art of the SLM diamond Raman lasers are summarized. At last, the future investigations of continuous-wave SLM diamond Raman lasers are proposed.
2022, 51(6): 20220133.
doi: 10.3788/IRLA20220133
Re:YAG-SiO2 multicomponent glass fiber is fabricated by a molten core method, in which a Re:YAG is used as the core material and a quartz tube is used as the cladding material. It has the advantages of high doping concentration, high mechanical strength, and is easy to fuse with quartz fiber. Recently, the single-frequency fiber laser has been studied extensively based on the Re:YAG-SiO2 fiber. In this paper, the development of the Re:YAG-SiO2 fiber fabrication and the single-frequency laser technology based on Re:YAG-SiO2 fiber in 1.0 μm, 1.5 μm and 2.0 μm were reviewed. The difficulties and challenges of Re:YAG-SiO2 fiber fabrication and single-frequency laser based on this type of fiber were also given.
2022, 51(6): 20220119.
doi: 10.3788/IRLA20220119
Tunable single-frequency fiber lasers (TSFFLs) possess the characteristics of wide tuning range, high optical signal-to-noise ratio (OSNR), narrow linewidth, low noise, and excellent compatibility. They also have attracted extensive attention from researchers at home and abroad because of their important application value in the spectroscopy, optical detection, optical sensing, fiber communication and so on. In this paper, the tuning and longitudinal-mode selection key techniques of TSFFLs were introduced briefly. The TSFFLs with different wavelengths of 1.0 μm, 1.5 μm, 2.0 μm, and mid-infrared were summarized and their research status at home and abroad was reviewed. The results obtained in tuning range, laser linewidth, OSNR, power scaling, flatness of output power, and other output performances were also shown. In addition, combined with our new progress, the recent development of TSFFLs based on compound cavity structure was introduced. Furthermore, the future development trend of TSFFLs was also forecasted.
2022, 51(6): 20220127.
doi: 10.3788/IRLA20220127
In recent years, high-power single-frequency (SF) erbium-doped fiber lasers with narrow linewidth and low noise have been intensively studied, driven by application requirements in the fields of coherent detection, lidar, laser cooling and gravitational wave detection. The research progresses of high-power SF erbium-doped fiber lasers were reviewed in this paper, including SF erbium-doped fiber lasers and high-power SF erbium-doped fiber amplifiers. The development trend and challenges of the high-power SF erbium-doped fiber lasers were analyzed, and the next development direction was prospected.
2022, 51(6): 20220300.
doi: 10.3788/IRLA20220300
The space-based gravitational wave detection frequency band is located in the range of 0.1 mHz-1 Hz, because the gravitational wave source information with larger characteristic quality and scale is contained in the aforementioned frequency band. At present, large-scale laser interferometer space-based gravitational wave detection projects based on different sizes and space orbits have been gradually implemented. It should be emphasized that the laser intensity noise and frequency noise should be suppressed in the laser source system of the interferometer. Moreover, as the first level device of laser noise characterization and suppression, the performance of photoelectric detection will directly affect the effect of laser noise suppression. First of all, on the basis of selecting low noise chip and high stable bias system, the whole circuit was designed by self-reducing circuit and transimpedance-amplifying circuit. In addition, in electromagnetic shielding, low temperature drift factor element, low noise power supply and active temperature control and other technical means, realize the development of high gain and low noise balanced homodyne detection system. Finally, the gain and bandwidth of the photodetector were evaluated and tested by combining the fast Fourier transform method and the number line power spectral density algorithm, and the intensity noise of the laser was detected and characterized in the 0.05 mHz-1 Hz band by using the detector. The experimental results show that the electronic noise spectral density of the balanced homodyne detector is less than 3.6×10−5 V/ Hz1/2 in the frequency range of 1 mHz-1 Hz, which is less than the noise requirement of the laser source for space-based gravitational wave detection. When the incident light power is 400 μW, the gain of the balanced homodyne detection system is measured to be more than 40 dB in the frequency range of 0.1 mHz-1 Hz. What’s more, the spectral density of laser intensity noise is 3.6×10−2 V/ Hz1/2 at 1 mHz. Low noise photoelectric detection and laser intensity noise characterization are achieved, which provide key device support for laser intensity noise characterization and suppression in space-based gravitational wave detection.
2022, 51(6): 20220325.
doi: 10.3788/IRLA20220325
Based on fiber ring lasers, we designed a single-wavelength and dual-wavelength switchable single-frequency ytterbium-doped fiber laser. A high-finesse filter was composed of a three-port circulator, an unpumped ytterbium-doped fiber and a fiber Bragg grating, which was used to suppress the number of modes in the resonator. By tuning polarization controller, comb spectra and dynamic gratings were formed within Polarization Maintaining Ytterbium Doped Fiber(PM-YDF) and realized the output of a single-frequency fiber laser with narrow linewidth. The output linewidth of the laser was 346 Hz at 1064.37 nm, and the optical signal-to-noise ratio was greater than 50 dB. The instability of wavelength and power was within 0.01 nm and 0.2 dB in 30 min. By adjusting the polarization controller, the single and dual wavelengths could be switched to each other, and the dual wavelengths were located at 1064.156 nm and 1065.236 nm, respectively. This technology provides a new way for dual wavelength output of ultra-narrow linewidth lasers.
2022, 51(6): 20220401.
doi: 10.3788/IRLA20220401
Our self-built dual-wavelength single-frequency fiber laser was used as a seed, and after being amplified by an acousto-optic modulator and multi-stage fiber, the laser was injected into a 100-meter long high nonlinear fiber with the zero-dispersion point of at 1550 nm. With the help of the four-wave mixing effect of the highly nonlinear fiber, a series of new spectral components were finally obtained under the pumping of the peak power of 13 W, and a total of 46 new spectra were generated in the range of 20 dB. These spectra spanned 1.337 THz and contained only one longitudinal mode in each spectrum. Since the new spectrum was generated based on the four-wave mixing effect, there was no gain competition between different spectra, so the multi-wavelength single- frequency of the laser can exist stably, and the spectral intensity was close to each other. The multi-wavelength single-frequency fiber laser not only has the advantages of a single-frequency fiber laser such as narrow linewidth, high coherence, and low noise, but also can simultaneously output multiple wavelengths of single-frequency lasers in an all-fiber structure, which makes it possible to have very important applications in the fields of multiplexing optical communication, optical frequency conversion, lidar, microwave photonics and so on.
2022, 51(6): 20210879.
doi: 10.3788/IRLA20210879
Narrow linewidth fiber lasers can be used in applications such as remote sensing, nonlinear frequency conversion and beam combination. In this paper, the typical structures and corresponding working principles of narrow linewidth fiber laser oscillator were introduced. The single-frequency mode selecting technologies were summarized from the perspective of obtaining narrower linewidth, and the power scaling technologies were summarized from the perspective of generating higher power. The current status of narrow linewidth fiber laser oscillator was reviewed, and the development of narrow linewidth fiber laser technologies was prospected.
2022, 51(6): 20210980.
doi: 10.3788/IRLA20210980
Mid-infrared quantum cascade laser has various application prospects in infrared countermeasures, trace gas detection, free space optical communication and other fields. The method of using MOCVD to grow quantum cascade lasers has the advantages of high production efficiency, convenience for regrowth and multi-components growth. This paper reported a mid-infrared quantum cascade laser capable of continuous-wave operation at room temperature, with a wavelength of 4.6 μm, using MOCVD to grow strain-compensated InGaAs/InAlAs materials. The experiment explored the impact of different doping on chip performance, and determined that the device performance can be improved by optimizing the doping concentration. The maximum peak power of the chip with a cavity length of 3 mm and a ridge width of 13 μm in pulse mode was 722 mW at a temperature of 288K, the wall-plug efficiency and threshold current density were 6.3% and 1.04 kA/cm2, respectively, and the power output reached 364 mW in continuous-wave operation. This article has successfully realized the growth of mid-infrared quantum cascade laser by MOCVD, which provides technical support for laser applications in the mid-infrared band.
2022, 51(6): 20210444.
doi: 10.3788/IRLA20210444
In recent years, ultra-fast ytterbium doped mode-locked fiber lasers have been widely used in industrial processing, medical surgery, multiphoton imaging and other fields due to their high conversion efficiency, convenient operation, free maintenance and compact size. Compensation of group velocity dispersion in lasers was an effective method to obtain picosecond or femtosecond pulses. A grating pair and a spectral filter were used to adjust the dispersion and spectral width of laser wavelength in cavity flexibly, the laser can output stable mode-locked pulses with the corresponding fundamental repetition frequency of 19.41 MHz. The central wavelength can be adjusted from 1015 nm to 1037 nm when the net cavity dispersion was +0.0127 ps2. In the case of +0.007 ps2 dispersion, the central wavelength can be adjusted from 1015 nm to 1045 nm and when the net cavity dispersion was −0.0127 ps2, the central wavelength can be adjusted from 1020 nm to 1046 nm. Meanwhile, when the net cavity dispersion changed from abnormal to nearly zero dispersion, the spectral bandwidth can be adjusted from 1.40 nm to 19.38 nm, and the corresponding pulse width after compression can be adjusted from 1.03 ps to 175.9 fs. The proposed and demonstrated scheme is capable of continuously adjusting the state of the laser, and is expected to be used in the development of a femtosecond laser front-end with high power and high energy, which can meet the application requirements of lasers with a alterable of spectrum widths and wavelengths.
2022, 51(6): 20210442.
doi: 10.3788/IRLA20210442
Fiber-bulk hybrid amplification technology combines the advantages of fiber lasers and bulk amplifiers to obtain a compact and low-cost high power ultrashort pulse laser. Therefore, a high average power ultrashort pulse laser was designed based on Yb-doped fiber-bulk hybrid amplification technology. The laser was consisted of an Yb-doped all-fiber laser and two-stage bulk amplifiers. The first bulk amplifier was based on Yb: YAG single crystal fiber, and the second bulk amplifier was based on Yb: YAG rod with unpolished barrel. The all-fiber front end delivered 6.5 W average power, 52.9 MHz repetition rate and 47.5 ps pulse duration. The single crystal fiber amplifier obtained an average power of 40 W at the backward pump power of 182 W through a single-pass amplification. The Yb: YAG rod amplifier outputted an average output power of 122.9 W at the backward pump power of 307 W in single-pass configuration. After removing the depolarization part introduced by thermal effect, an average output power of 107.3 W with linear polarization state was obtained, and the corresponding slope efficiency was 26.1%. The pulse width of 12.1 ps and center wavelength of 1030.6 nm with spectral width of 2.4 nm were achieved. At the maximum output power of 107.3 W, a beam quality factor of 1.45 and 1.20 were measured along the vertical and horizontal direction, respectively.
2022, 51(6): 20220055.
doi: 10.3788/IRLA20220055
Ytterbium-doped all-fiber nanosecond-pulsed lasers have developed rapidly in recent years and have opened up new horizons in many fields. Especially in the field of laser cleaning, there is a strong demand for nanosecond pulsed fiber laser with high-power and high-energy. Multi-channel fiber laser beam combining is the main means to achieve high-power and high-energy laser output. The complexity of the structure depends on the output characteristics of a monolithic laser. Improving the output characteristics of monolithic nanosecond pulsed all-fiber laser is very important for laser cleaning and other applications. In this paper, the research progress of monolithic Ytterbium-doped all-fiber nanosecond pulsed lasers is summarized, and the main factors that limit its power and energy expansion are analyzed. Firstly, the recent advances of nanosecond pulsed Ytterbium-doped all-fiber oscillator is reviewed with active Q-switching, passive Q-switching and gain-switching technology. Then, the research status of nanosecond pulse Ytterbium-doped all-fiber amplifiers is summarized with large pulse energy, high average power and collaborative development of the two. In the end, the development trend of Ytterbium-doped all-fiber laser in scaling of power and energy is prospected from the factors limiting the output characteristics.
2022, 51(6): 20210422.
doi: 10.3788/IRLA20210422
With the rapid development of micro-nano satellites, the performance of micro-thrusters is required to be higher. Because of its high specific impulse, precise thrust control and low energy consumption, the laser-propelled micro-thruster provides an excellent micro-thruster choice scheme for micro-nano satellite. In this paper, the influence of power density and pulse width of semiconductor laser on the performance of laser propulsion was studied in transmission ablation mode. The results show that when the thickness of the working medium layer is 200 μm, with the increase of the laser power density, the single pulse impulse and specific impulse gradually increase. And there is an optimal power density value to the impulse coupling coefficient and ablation efficiency. As the pulse width of the laser increases, the impulse of the single pulse gradually increases, and the specific impulse first increases and then decreases. At 250 μs, the specific impulse reaches its maximum value, which is about 221.8 s. The impulse coupling coefficient and ablation efficiency decrease with the increase of pulse width. When the pulse width exceeds a certain critical value, it will have a bad effect on the target pit of the laser ablation working medium, resulting in a serious waste of laser energy and working medium. The optimizing of laser parameters provides a reference for the engineering application of laser propelled micro-thruster.
2022, 51(6): 20210458.
doi: 10.3788/IRLA20210458
The GF-7 satellite is the first sub-meter two-line-array stereo imaging satellite of China. It is equipped with two sets of laser altimeters and laser footprint cameras to capture multi-source remote sensing data simultaneously. In this paper, the multi-source remote sensing data of GF-7 satellite were used to promote the horizontal and vertical accuracy, which used laser altimetry data to optimize the vertical accuracy by skewness, median, linear polynomial and quadratic polynomial model, and the footprint image was used to optimize the horizontal accuracy in the first-order affine transformation method. Moreover, the accuracy of uncontrolled plane-elevation, laser elevation optimization, footprint-laser plane-elevation optimization and field-laser plane-elevation optimization were evaluated through the field control points. The experimental results show that the vertical accuracy of DSM can be improved significantly with the support of laser altimetry data. The mean vertical error of the DSM produced without GCPs is −4.268 m and the mean square error is 4.518 m. While the mean vertical error and mean square error of the DSM optimized by the median model are improved to −0.272 m and 1.508 m, and the mean vertical error and mean square error of the DSM optimized by linear model reach −0.320 m and 1.351 m. The horizontal accuracy of DOM can be improved by the footprint image. The mean horizontal error is optimized from 13.606 m to 5.341 m, and the mean square error is optimized from 13.626 m to 5.495 m.
2022, 51(6): 20210601.
doi: 10.3788/IRLA20210601
The fluorescence spectra and laser operation of Nd:Y2O3 transparent ceramic fabricated by the vacuum sintering plus hot isostatic pressing method were reported. By comparing with the fluorescence spectra of Nd:YAG transparent ceramics, it is shown that the 4F3/2-4I11/2 transition spectra of Nd:Y2O3 transparent ceramic have multiple spectral lines with similar gain, which is more beneficial to realize simultaneous dual-wavelength laser oscillation. The spectra discrete characteristic among different Stark transitions of Nd:Y2O3 transparent ceramic was beneficial to obtain abundant wavelength lasers around 1.0-1.1 μm through the cavity mirror coating to control the loss of different wavelengths. Furthermore, a simple plane-plane cavity was used, and the output coupler with reasonable coating design was selected for different wavelength laser output. The maximum output power of 3.62 W and the conversion efficiency of 40.4% were obtained for the 1074.6 nm and 1078.8 nm dual-wavelength laser output. The output power of 1.7 W and the conversion efficiency of 19.4% were achieved for 1130.3 nm laser output.
