2022 Vol. 51, No. 7
column
- Lasers & Laser optics
- Materials & Thin films
- Optical communication and sensing
- Atmospheric optics
- Photoelectric measurement
- Image processing
- Invited paper
- Optical devices
- Optical fabrication
- Special issue-Novel infrared detection technology driven by local field
- Infrared technology and application
- Optical design
- Lasers & Laser optics
- Materials & Thin films
2022, 51(7): 20210743.
doi: 10.3788/IRLA20210743
The nonmechanical servo-controlled liquid crystal spatial light modulator (LCSLM) can modulate the wavefront phase in real time to achieve beam deflection by controlling the voltage loaded on each pixel. The beam deflection control ability is verified based on the Fresnel lens model and the blazed grating model. Including the relationship between deflection distance, diffraction efficiency and different model parameters, when the incident light wavelength is 1550 nm, the maximum deflection angle that can be achieved by the x-axis or y-axis is 6.96° (±3.48°), and the beam can be aligned with the two-dimensional plane offset. Aiming at the high-speed, sensitive, precise and large-angle scanning application requirements of the beam, a light wavefront phase adjustment algorithm based on the LCSLM is proposed. The phase conversion model is established by calculating the phase that needs to be compensated, and the beam control process is satisfied. The LCSLM-based beam is designed and constructed with a deflection and scanning experimental system, and the experimental results show that the light spot at any position in the light field can be flexibly shifted and controlled within a 360° recieving field of view. This research has important application value in the fields of free-space wireless optical communication, agile beam control, nonmechanical beam capture, aiming and tracking.
2022, 51(7): 20210615.
doi: 10.3788/IRLA20210615
Transient characteristics of digital closed-loop fiber optic current sensors (FOCSs) include the frequency response and step response which are important indexs in the industrial areas such as power system relay protection and fault recording. In engineering applications, due to the complexity of the test system and the poor accuracy of a small current signal, it is not conducive to evaluating the transient characteristics of an FOCS in a traditional way. According to the closed-loop control mechanism of a digital closed-loop optical fiber current sensor, a new method of adding phase modulation excitation to the feedback loop of a digital closed-loop FOCS was researched. First, the phase modulation principle of the digital closed-loop of FOCS was analysed, and a mathematical model was established to calculate and verify the equivalence of the phase modulation excitation; Second, based on the closed-loop control algorithm of the FOCS, the frequency response and step response modulation excitation generation method were proposed; Finally, use the existing digital closed-loop FOCS product platform was used to complete the simulation and test of frequency response and step response. The results show that the maximum error between simulation data and test data is 0.12%. The modulation excitation method can realize different current simulation tests of frequency response and step response on the existing hardware platform without building a complex test system.
2022, 51(7): 20210759.
doi: 10.3788/IRLA20210759
To improve the problem of slow convergence speed and ease of falling into the local extreme value of the traditional stochastic parallel gradient descent (SPGD) algorithm, a meta-heuristic SPGD (MHSPGD) algorithm is proposed. The proposed algorithm combines the exploration and exploitation of the metaheuristic algorithm with the SPGD algorithm. First, the gradient descent search of the SPGD algorithm is used to obtain the local optimal solution, and then the neighborhood search is carried out to obtain the possible optimal solution outside the local optimal region. The new starting point of iteration is determined by comparing the performance indexes of all solutions. With the adaptive expansion of the search range, the algorithm can avoid falling into the local extremum and tends to converge to the global optimum. At the same time, to avoid repeated searches, a memory table is established to save the suboptimal solution generated in the iterative process. The model of the wavefront sensor-less adaptive optics system was established, and the proposed algorithm was used to correct the wavefront distortion under different turbulence intensities. A simulation of distortions under different Zernike orders was also carried out. Under three turbulence intensities, the Strehl ratios (SR) of the MHSPGD algorithm are 0.7621, 0.6554 and 0.3749, which are 0.1%, 2% and 18.6% higher than those of the SPGD algorithm. In addition, when the distortion contains more high-order components, compared with the traditional SPGD algorithm, the number of iterations required for SR convergence to 0.6 is reduced by approximately 47%, and the limit value of SR convergence is increased by approximately 9.4% for the proposed algorithm. The results show that compared with the three main optimization algorithms, MHSPGD can achieve a higher convergence limit under various turbulence intensities while maintaining a faster convergence rate, which means it effectively solves the problem of local convergence.
2022, 51(7): 20210645.
doi: 10.3788/IRLA20210645
The micro-vibration sensor based on cascaded grating is a typical micro-vibration signal measurement scheme. However, due to the multiple transmission and reflection of optical signal in the cascaded grating, the sensor is subject to the poor spectral signal-to-noise ratio and complex components. Based on this, a spectrum signal optimization algorithm combined with empirical mode decomposition and chebyshev filter was proposed in this paper. Firstly, the original spectrum of the sensor was decomposed into a series of intrinsic eigenmode functions by empirical mode decomposition; Secondly, the order of the intrinsic mode functions including the reflection peak component was determined by using the proposed adaptive filtering method, and the chebyshev low-pass filtering was performed on these orders; Finally, the optimized sensor spectrum was obtained by reconstructing the output of the filter. A micro-vibration excitation signal with an amplitude of ±8 mV and frequency of 500 Hz was used for experimental verification. The results show that the proposed algorithm can effectively restore the micro-vibration signal from the excitation source, and the accuracy is improved by more than 87.5% compared with the traditional methods.
2022, 51(7): 20210744.
doi: 10.3788/IRLA20210744
The performance evaluatation of ground layer adaptive opitcs (GLAO) is helpful for system design and optimization. The turbulence distribution and the layout of the guide stars (GSs) are the main factors affecting GLAO performance. Considering the impact of the turbulence distribution and the layout of GSs, the performance of GLAO was analysed and evaluated by comparing spatial frequency spectrum filtering theory and Monte Carlo simulation. The results show that the conclusions of the two methods are clearly consistent with an error margin of less than 4.6%. Spatial frequency spectrum filtering simplifies the system into a linear model and it is simpler and faster for the calculation, which is convenient for discovering the characteristic rules. However, the accuracy is slightly low if considering the noise and error in a real system. In addition, this method is suitable for analysing the system performance with a symmetrical GS layout. The Monte Carlo method is better for simulating the system running state in detail with a random GS layout. The brief results of the system performance analysis are given in the end by combining the two methods. The study will be useful for the system design and optimization of future GLAOs.
2022, 51(7): 20210499.
doi: 10.3788/IRLA20210499
The establishment of a complex error model of strapdown inertial navigation system is researched, and a new system-level calibration method isproposed, which includes the inner level arm parameters of the accelerometer and temperature error coefficients. The method is based on the 45-dimensional Kalman filter to identify and estimate the error parameters, and the temperature change in the calibration process is controlled by a temperature control test chamber. Simulation experiments show that this method can simultaneously calibrate the constant drift, scale factor error, installation error of the laser gyroscope and accelerometer, as well as the inner level arm parameters and temperature coefficients of the accelerometer. The results of the navigation experiment show that when using the calibration parameters compensated for multiple error sources, the maximum positioning error of the navigation for 10 h is 0.6 n miles. The navigation accuracy is improved by 37.5% compared to that without compensation.
2022, 51(7): 20210784.
doi: 10.3788/IRLA20210784
Regular tetrahedral Redundant Inertial Navigation System (RINS) has the characteristics of high reliability and high precision, and error calibration is a necessary means to realize high-precision navigation solution. At present, the error calibration of regular tetrahedral RINS needs to be realized by using the high-precision turntable, which not only has high calibration cost and long calibration time, but also cannot calibrate full error parameters under the condition of insufficient hardware conditions such as external field. Address this issue, a rapid field calibration method for full error parameters of regular tetrahedral RINS without high-precision turntable was proposed. Firstly, the error model of regular tetrahedral RINS was established. Then, according to the relationship between the analytic coarse alignment attitude error matrix and the bias of regular tetrahedral RINS, a bias calibration method based on six positions was proposed. Then, a three-position rotation scheme was designed to calibrate the scale factor and installation error of the gyroscope. Finally, the six-position scheme of bias calibration was used to calibrate the scale factor and installation error of the accelerometer. Simulation and experiment show that this method can effectively calibrate full error parameters. In the 1h static base navigation experiment, the north positioning accuracy are improved from 61.065 5 km to 0.476 7 km, and the east positioning accuracy are improved from 161.202 7 km to 4.842 2 km.
2022, 51(7): 20210756.
doi: 10.3788/IRLA20210756
Aimed at the requirements of remote observation dynamic performance evaluation of photoelectric imaging systems such as vehicle visual intelligent perception and low altitude regional defense, an indoor simulated moving target system was developed. Based on the linear space shift invariant system model, the MTF measurement principles with ''three-bar target'' and ''four-bar target'' were analysed. A measurement method of the dynamic modulation transfer function (MTF) was proposed for an optoelectronic imaging system based on a variable frequency target. A design scheme of a variable frequency target was introduced, the solution method of MTF value was proposed, and the static and dynamic MTF comparative test experiments were conducted for ''three-bar target'' and variable frequency target. The experimental results show that compared with the "three bar target" measurement method, the proposed frequency conversion target dynamic MTF measurement method has a relative maximum deviation ratio of 1.9% for static MTF measurement and 2.8% for dynamic MTF measurement. The method can solve the MTF curve from one target image and has more advantages than ''knife edge method'', ''three-bar target'', ''four-bar target'' and other methods in the field of dynamic MTF measurement technology.
2022, 51(7): 20210727.
doi: 10.3788/IRLA20210727
Changes in current and temperature can affect the spectral distribution of the LED, which in turn affects the visual and non-visual parameters of the light source. In this paper, starting from the spectral model based on the distribution of photon energy levels in the LED chip luminescent material, the current and temperature model was established for the RGBY four-color LED. The R-square of the spectral fitting could reach 0.99. On this basis, the genetic algorithm (GA) was used to optimize the circadian rhythm factor and luminous efficiency with multiple objectives. When the illuminance was 300 lx, 8 sets of visual parameters (color rendering index and blue light hazard efficiency) and non-visual parameters ( circadian rhythm stimulus) were designed to verify the feasibility of this model. Then, the relationship between two non visual parameters and temperature was explored. The results show that the circadian rhythm factors increased with the increase of temperature, but the circadian rhythm stimulus decreased with the increase of temperature. The reason for this situation was that the two parameters were differently affected by the illuminance. After compensating the illuminance of the light source, it was found that the two non-visual parameters both increased with the increase of temperature, and the two showed a certain positive correlation. This research started from the perspective of the light source spectrum and provided a reference for the consideration of non-visual effects in the design of LED lighting sources.
2022, 51(7): 20210715.
doi: 10.3788/IRLA20210715
In order to solve the problems of low accuracy, complex optical machine structure, and long detection cycle in the error detection of the photoelectric encoder, the optical small-angle measurement principle of an autocollimator and a polyhedral prism, and the continuous error detection method of the reciprocal rotation angle of the dual-axis turntable were combined to establish an error detection system for photoelectric encoder based on optical continuous closed-loop. By using the multi-body system theory and the relative pose matrix transformation method, a full error model of the dual-axis turntable was established, and the influence of the fixed error and variable error of the full error model on the system was analyzed. The detection system was calibrated with a calibrated autocollimator and a 23-sided polyhedral prism, and a high-precision photoelectric encoder was used to compare the detection accuracy with the system. The test results show that the rotation accuracy of the dual-axis had met the requirements of the numerical simulation calculations, the system detection accuracy had reached 0.38″, and the measurement uncertainty is 0.2″ (k=2). And for the encoder actually produced, the detection accuracy of the system is basically the same as the accuracy of the factory calibration. Which had been verified the feasibility of the optical continuous closed-loop system to achieve high precision and circumference continuous error detection.
2022, 51(7): 20210730.
doi: 10.3788/IRLA20210730
Accurate measurement of mechanical parts can provide a basis for parts processing and manufacturing, virtual simulation, defect detection and other applications. The binocular vision method based on fringe projection is widely used in the topography measurement of mechanical parts due to its high-precision characteristics. In this method, the quality of the absolute phase curve determines the final accuracy of the 3D reconstruction. Due to the influence of environmental noise, discontinuity of the scene, and complex surface structure of the parts, absolute phase curve often has a large number of noise points and varying degrees of deformation. In order to improve the reconstruction accuracy, a corresponding improvement method is proposed for the problems existing in the absolute phase curve. Aiming at the noise points far away from the phase curve that are difficult to remove, a region-by-region phase correction method is proposed. This method divides the phase curve of each row into several regions, and uses the median of the phase value in the region as the threshold to remove such noise points. For the deformed area of the phase curve, the curve fitting method is introduced on the basis of the point primitive-based stereo matching method, and the disparity map obtained after the matching is refined, which can improve the poor matching result in the deformed area of the phase curve and improve the robustness and accuracy of the matching method. The method is used to reconstruct complex part FSW inverter, and the standard deviation can be reduced to within 0.1 mm. Experiments have proved that the reconstruction accuracy of this method is higher. For mechanical parts with complex surface structure, the proposed method can achieve accurate measurement.
2022, 51(7): 20220050.
doi: 10.3788/IRLA20220050
Sequence of low coherence interferograms were captured during the vertical scanning of the interferometric microscope in the measurement procedure of the white light interferometric microscopy, and thus the topography of the surface under test was retrieved through determining the locations where the optical path difference (OPD) was zero in the envelope of the correlogram. The calculations of the topography for the micro-structures were composed of the vertical scanning interferometric (VSI) algorithm determining the coarse map and the phase-shifting interferometric (PSI) algorithm retrieving the fine map. Usually, the vertical scanning step was set as one eighth of the central wavelength, but the phase-shifting departures from π/2 inevitably due to the phase shifter error as well as the numerical aperture (NA) effect of the interferometric microscope. In this manuscript, the center-of-gravity solving of the visibility curves was adopted as VSI algorithm, and the 4M-frame method as well as the 7-frame method were both utilized as PSI algorithm respectively. The effect of the phase-shifting error on the topography measurement adopting the three above mentioned methods was discussed. Both theoretical derivations and simulation analysis demonstrate that the 7-frame method was insensitive to phase-shifting errors even under the low coherence illuminations. The fine phase error induced by phase-shifting error utilizing the 4M-frame method was by lucky coincides the form of the NA effect increasing the fringe spacing, and they were cancelled out during the transform from the fine phase to the topography. Therefore, adopting the center-of-gravity method as VSI algorithm and the 4M-frame method as the PSI algorithm, the phase-shifting errors arising from NA effect can be ignored, and the topography can be calibrated confronting the phase shifter error through measuring a certificated step standard in advance. A step height of 460 nm was measured utilizing the proposed method, and the topography demonstrate that it was both accurate and robustness.
2022, 51(7): 20210638.
doi: 10.3788/IRLA20210638
Deep learning-based object detection technology has recently made significant progress and has a wide range of applications in robotics, autonomous driving, traffic surveillance, etc. However, due to the distribution discrepancy between the training and testing datasets, the off-the-shelf detectors pre-trained using the data in a specific domain often show apparent performance degradation when applied in wild scenarios. To address this problem, a domain adaptation method for object detection in the frequency domain is proposed. In light of the energy concentration property of the discrete cosine transform, the proposed algorithm conducts domain adaptation for object detection by processing only a few of the most significant frequency coefficients, which reduces memory and computing resource consumption and alleviates the domain shift problem. The proposed method consists of two stages. In the first stage, it translates annotated training data from the source domain to the target domain using unsupervised image-to-image translation. Adversarial domain adaptation is then applied to the object detection model to align the features of the translated data and the real data in the target domain. The experimental results of the object detection under different weather conditions show that the proposed method ranks first among the four testing algorithms. Compared with the object detection model trained with only source domain data, it can increase the mAP value by 33.9%.
2022, 51(7): 20210611.
doi: 10.3788/IRLA20210611
Far-infrared images have problems such as low resolution, large numbers of repetitive structures and sparse structures. The stitching of this type of far-infrared image faces many challenges. Aiming at the far-infrared image stitching in aerial scenes, this paper divides the image alignment process into sequential image sequence alignment and multicolumn image alignment. Single-column images are based on nonmaximum suppression to obtain the homography matrix, and the transfer relationship is derived for splicing. The image stitching between columns is divided into grids, combined with regional similarity transformation and local homography transformation to optimize the weight of the transformation matrix grid by grid and through the recursion of grid transformation to achieve precise stitching. The methods used can avoid the problem of disappearance of splicing features of multiple consecutive far-infrared images and adapt to the problem of inconsistent overlap rate when in multicolumn image stitching, realizing the stitching of massive far-infrared images.
2022, 51(7): 20210614.
doi: 10.3788/IRLA20210614
The infrared anti-interference technique of missiles under the background of complex air combat is one of the core technologies of infrared air-to-air missiles. Aiming at the fact that traditional static Bayesian networks cannot express the dynamic relationship of feature variables in sequence images in time series, this paper proposes an anti-jamming recognition algorithm for a space-time correlation inference network that conforms to the process of human visual inference and recognition. First, the proposed space-time association reasoning network takes into account the feature space constraint relationship, introduces prior knowledge of the time constraints of feature variables, and establishes a target reasoning network recognition model that expresses the characteristic spatiotemporal relationship, thereby enhancing the stability of sequence image target recognition. Second, a sample set is built through simulation data, offline training and learning the space-time correlation inference network structure and feature jump probability parameters, to determine the probabilistic inference network to identify the offline model. Finally, based on the test data, the model is combined with the inference identification network model to perform probabilistic inference to achieve recognition and classification of targets. The experimental results show that the anti-jamming recognition rate based on the spatiotemporal correlation inference network reaches 94% under the condition of the interference of the infrared decoy, which is 3% higher than the static Bayesian network anti-jamming recognition algorithm, which effectively improves the stability of target recognition.
2022, 51(7): 20210753.
doi: 10.3788/IRLA20210753
Lane line detection plays a pivotal role in autonomous driving and advanced assisted driving. However, traditional lane line detection technology was less robust, and most methods based on deep learning were more complex and difficult to embed platform real-time application. A lightweight lane line detection network for embedded platforms was proposed, which converts lane line detection into a semantic segmentation problem. The network draws on U-Net and Segnet network structures, and uses small-scale convolution and other lightweight components to design and calculate efficiently semantic segmentation network. Based on the detection of the lane line, calculate the distance between the vehicle and the lane line on both sides, as well as the curvature of the lane line, and give an early warning when the vehicle deviates from the lane line or the detection was abnormal. Finally, the entire system was transplanted to the HiSilicon platform. Experimental results show that the system has high detection accuracy and detection speed, the accuracy rate reaches 97.5%, the speed reaches 50 FPS, and meets real-time requirements.Therefore, the system can be used for real-time lane line detection, ranging, and distance measurement for embedded platforms. Curvature calculation and early warning.
2022, 51(7): 20210586.
doi: 10.3788/IRLA20210586
Aiming at the difficulty of small-scale face detection in unconstrained scenes, the proposes a scale-invariant face detection method based on enhanced convolutional neural networks. Firstly, On the two shallow feature maps of the SSD basic detection network, the discrimination and robustness of the current layer feature map was enhanced by blending the feature information of the current layer feature map and adjacent layer feature map. Then, the negative sample screening was performed on the two enhanced feature maps, and the false positive rate of face detection caused by the small-scale anchor box was reduced by increasing the difficulty of classification. Finally, two loss function based on anchor boxes size were set for the original feature map and the enhanced feature map, and they were merged by weighted summation. The test results on the FDDB and WIDER FACE datasets show that the proposed method has higher detection accuracy than the current mainstream face detection methods.
2022, 51(7): 20210829.
doi: 10.3788/IRLA20210829
To achieve intelligent control of indoor lighting, tracking lighting is performed according to the real-time position of indoor personnel, and adaptive brightness adjustment is completed through the coverage area of personnel, so as to achieve the purpose of overall energy savings and comfortable local lighting. An intelligent lighting system based on a fiber optic sensor network is designed, and a lighting adjustment algorithm based on deep learning lighting block design and real-time positioning of personnel is proposed. The block design divides the lighting area into multiple equal-sized subareas, and the division scale is determined by the light source coverage interval to realize the discrete processing of the lighting area. Then, through the state acquisition module to perform quantification analysis on each sub-region, the detection results are imported into the analysis model as the control parameters of the input layer of the convolutional network. The closed-body personnel positioning algorithm is combined to realize the positioning of the lighting subarea and the illuminance adjustment. The experiment tested four typical situations within the illumination range of 100 m2, obtained the illuminance weight value of each LED on the test location, and tested the degree of influence of the illuminance value of different heights. The maximum error of personnel positioning accuracy in the x-axis direction in the area is −96 cm, and it is 91 cm in the y-axis direction, both of which are smaller than the minimum unit of the preset lighting block. When the number of LEDs increases, the convergence time of this algorithm is slightly better than that of the ANN algorithm. Compared with the lighting space of the corresponding LED volume, the convergence time meets the application requirements, verifying its ability to intelligently adjust lighting over a large range.
2022, 51(7): 20220313.
doi: 10.3788/IRLA20220313
Aerosol deposition and diffusion mainly study the motion state, concentration migration and surface deposition process of aerosol particles in the atmosphere. The physical parameters mainly include the deposition flux, deposition velocity, concentration distribution and diffusion velocity of aerosol particles. Relevant research can provide a scientific basis for the optimization of aerosol generation and the evaluation and prediction of extinction effects. In this paper, three major methods for the generation of aerosols were summarized, the mechanism of aerosol particles settling and diffusing in the atmosphere was analysed, and the calculation, simulation and experimental measurement methods of aerosol settling and diffusing characteristic parameters were expounded. In view of the challenges in the study of aerosol deposition and diffusion, perspectives on future theoretical analyses, numerical simulations, experimental research and comprehensive applications are provided.
2022, 51(7): 20220221.
doi: 10.3788/IRLA20220221
Vortex beam is a kind of novel structured beam with helical wavefront and carries orbital angular momentum (OAM). Such structured field can find applications in many domains as large-capacity data transmission, remote detection, etc. The wavefront aberration occurs when the vortex beam propagates in a non-homogeneous medium as atmosphere turbulence, resulting in the OAM changing and go against practical applications. Therefore, it is necessary to compensate distorted vortex beams through adaptive optics. The recent advances on adaptive correction of distorted vortex beams was mainly reviewed. The current mature correction schemes were firstly introduced in brief, including wavefront sensing along with probe Gaussian beams, array detection along with phase retrieval algorithms, and so on. Then the deep-learning-based approaches were highlighted, as Zernike polynomial coefficients inversion, turbulence phase screen inversion, etc. The advantages and limitations of employing deep learning for distorted vortex beam compensation were also discussed. Finally, development trends of distortion compensation of vortex beams were prospected.
2022, 51(7): 20210866.
doi: 10.3788/IRLA20210866
Compared with the visible to short wave infrared spectrum, hyperspectral remote sensing imaging in the infrared spectrum has unique application advantages, especially in resource exploration, surface environment monitoring, atmospheric environment monitoring and military reconnaissance. Although the infrared hyperspectral imagers are mainly airborne at present, the domestic and foreign institutions have never given up promoting the spaceborne application of infrared hyperspectral remote sensing. Therefore, based on the detailed analysis of the design, implementation and specifications of the primary infrared hyperspectral imagers, this paper first summarizes the characteristics, existing problems and solutions of the current infrared hyperspectral imagers from the three key indexes of spectral resolution, spatial resolution and radiometric resolution. That is, breaking through the technologies of fine spectroscopy, high-sensitivity detectors, low-temperature optics and background radiation suppression are the main technical problems to be solved in the development of infrared hyperspectral imagers in the future. Based on the above, the application of infrared hyperspectral imaging in long distance gas detection is overviewed, and its unique advantages are also analysed. Finally, the development direction of infrared hyperspectral remote sensing imaging is depicted.
2022, 51(7): 20210587.
doi: 10.3788/IRLA20210587
The Novel Device Laboratory (NDL) of Beijing Normal University has been developing a silicon photomultiplier with an epitaxial quenching resistor (EQR SiPM), which has a compact structure and a relatively simple fabrication process. Recently, to meet the requirements of nuclear medicine imaging, NDL has successfully developed an EQR SiPM with a microcell size of 15 μm and an active area of 9 mm2 by optimizing the device structure and fabrication technology. Compared to previous devices of the same type, the dark count rate (DCR) of the EQR SiPM is further reduced while still maintaining high photon detection efficiency (PDE). At an ambient temperature of 20 ℃ and an operating overvoltage of 7 V, the typical DCR is 226 kHz/mm2, and the peak PDE is 46%. In addition, to further increase the dynamic range of the EQR SiPM, NDL has developed an EQR SiPM with a microcell size of 6 μm, an active area of 9 mm2 and a microcell number of 244720. At an ambient temperature of 20 ℃ and an operating overvoltage of 7 V, the typical DCR is 240 kHz/mm2, and the peak PDE is 28%. It has large dynamic range that is very suitable for the measurement of high-energy cosmic rays and other applications in hadron calorimeters.
2022, 51(7): 20210511.
doi: 10.3788/IRLA20210511
To characterize the diffraction characteristics of the liquid crystal polarization grating when the beam is incident obliquely, a three-dimensional model modelling method of liquid crystal polarization grating oblique incident angle-driving voltage-diffraction efficiency was proposed. This method uses the Gibbs free energy equation to solve the director of the liquid crystal molecule, obtains the expression of the driving voltage and the tilt angle of the liquid crystal molecule, derives the relationship between the oblique incident angle and the phase retardation, and combines the extended Jones matrix to characterize different incident angles. The transmittance of the lower liquid crystal polarization grating, through the vector diffraction theory, establishes a three-dimensional model of oblique incident angle-driving voltage-diffraction efficiency. This model can not only quantitatively solve the diffraction efficiency of liquid crystal polarization gratings at different oblique incident angles, but also realize the calibration of the driving voltage when the diffraction efficiency is optimal. The effectiveness of the model was verified by simulation analysis and experiments. The results show that when the beam incident angle is tilted from 0° to 10°, the optimal driving voltage is reduced from 2.2 V to 2.0 V, and the diffraction efficiency of the liquid crystal polarization grating is reduced from 85% to 78%; when the beam incident angle is tilted from 0° to −10°, the optimal driving voltage is increased from 2.2 V to 2.4 V, and the diffraction efficiency of the liquid crystal polarization grating drops from 85% to 74%.
2022, 51(7): 20210958.
doi: 10.3788/IRLA20210958
Microlens arrays are widely used in beam homogenization, wavefront measurement, integrated imaging and other fields. A liquid tunable-focus plano-convex microlens array based on optical film (Optically Clear Adhesive, OCA) was demonstrated. A rectangular array of silicon microholes was used to control the aperture and arrangement of a single lens, and OCA optical film and deionized water were used as the shaping material of the microlens array. The focal length of the lens could be adjusted from 1.46 mm to 10.44 mm by adjusting the volume of liquid injection in the microfluidic cavity. According to the focusing and imaging experiments, it was confirmed that the microlens array had good uniformity. Finally, this microlens array was applied to laser beam homogenization and shaping. The beam homogenization and shaping were realized by a pair of microlens arrays. Furthermore, by fixing the spacing of a pair of microlens arrays, the size of the homogenized light spot can be adjusted within 7.2 mm to 8.4 mm, which provides a new idea for the adjustment of the size of the homogenized light spot.
2022, 51(7): 20210590.
doi: 10.3788/IRLA20210590
Spectral image degradation is a common problem of acousto-optic tunable filter (AOTF) imaging spectrometers, and it is difficult to quantitatively predict. To quantitatively evaluate the image quality of spectral images, a modulation transfer function (MTF) calculation method including the influence of the AOTF rear cut angle is proposed. In this method, the line spread function (LSF) of the AOTF device is obtained by establishing the spectrum-space dimension response model of the AOTF, and then the theoretical MTF is obtained by Fourier transform of the line spread function. In the validation experiment, the deviation between the measured MTF value and the theory is less than 15% within the cut-off frequency. It is a theoretical basis for image quality evaluation of the AOTF. Furthermore, the influence of different AOTF rear cut angles on spectral image quality is discussed by this quantitative method. After simulation, it is concluded that the rear cut angle of the AOTF has difficulty meeting the requirements of lateral chromatic aberration and image sharpness at the same time. The cut angle needs to be selected according to the requirements of practical application. Therefore, it is significant to evaluate the image quality of AOTFs with different rear cut angles. The method is an important theoretical basis for AOTF device design.
2022, 51(7): 2021G005.
doi: 10.3788/IRLA2021G005
The ultra-precision turning performance of electroless nickel-coated mandrels which are used for the replication of X-ray mirrors. Effects of single-point diamond turning parameters such as depth of cut, spindle speed, and feed rate on the surface roughness are studied. The experimental results show that the feed rate has a significant influence on the surface roughness, while the spindle speed and depth of cut have no obvious influence on it. The process experiment of NiP alloy ultra-precision turning was carried out, the optimized process parameters of cutting depth, spindle speed and feed rate were obtained, and the surface roughness prediction model was established. The optimized process parameters were applied on manufacturing of electroless nickel-coated mandrels with diameter of 110 mm and length of 140 mm. The mandrel has been successfully machined to about PV61.37-83.47 nm, RMS7.952-10.326 nm, Ra6.379-8.332 nm, roundness 0.39 μm, slope error of the profile 0.42 μm. The above results meet the manufacturing requirements of the X-ray mirrors, which prepares the technical storage for manufacturing of larger X-ray mirrors.
2022, 51(7): 20210688.
doi: 10.3788/IRLA20210688
An spherical cylindrical lens is an important micro-optical element that has the functions of laser collimation, focusing, homogenization, etc., and has a wide range of applications in laser communication, optical fibre sensing, lidar ranging, laser pumping and other systems. To reduce the volume of the optoelectronic system and improve the performance of the optical fiber, increasing the numerical aperture of the lens is a common solution. Proposes the use of silicon with a higher refractive index as an alternative material for the low refractive index quartz substrate, which greatly increases the numerical aperture of the lens under the same volume and at the same time reduces the amount of processing and improves the manufacturing efficiency. Aiming at the problem that traditional quartz microlens preparation methods are no longer suitable for silicon-based lenses, a mask-based moving exposure method is proposed to prepare photoresist aspheric patterns using multiple spin coating and cycle exposure methods to solve problems such as poor thick photoresist surface uniformity and obvious traces of the exposure mask. Plasma etching technology is finally used to transfer the pattern to realize the preparation of the microlens. Taking a silicon-based aspherical cylindrical microlens array with a numerical aperture of 2.9 as an example, the actual preparation process experiment was carried out.The surface precision PV of the prepare microlens array is 0.766 μm, the surface roughness Ra is 3.4 nm, and the surface finish was in line with the design value. The feasibility of the preparation method was verified. This method is expected to promote the large-scale application of aspheric cylindrical microlens array in compact infrared optoelectronic systems.
2022, 51(7): 20220277.
doi: 10.3788/IRLA20220277
Mercury cadmium telluride (HgCdTe) material is an important detection material used in third-generation infrared detection systems, and its development level can reflect the optimal performance indicators of current infrared detectors. In recent years, astronomical, remote sensing, and civil equipment have put forward higher requirements for detector performance, which has brought new challenges to the design and preparation of HgCdTe infrared detectors. The finer design and processing technology of HgCdTe infrared detectors provide solutions for improving the performance of HgCdTe infrared detectors. Suppressing the harmful local field of the device and regulating the beneficial local field of the device can achieve further breakthroughs in device performance. However, how to characterize and analyse the local field of HgCdTe optoelectronic devices and clarify the origin of dark current and related noise in HgCdTe optoelectronic devices have become key scientific and technical issues to be solved to promote device performance breakthroughs. This paper summarizes the research progress of local field characterization and analysis of HgCdTe infrared photodetectors and provides basic support for the development of a new generation of HgCdTe infrared photodetectors.
2022, 51(7): 20220288.
doi: 10.3788/IRLA20220288
Photodetectors are widely used in daily life and national security, including communication, the environment, health and national defense. With the development of time, the performance requirements of photodetectors in terms of sensitivity, response speed and wavelength range have been increasing. The unique electrical and optoelectronic properties of low-dimensional materials make them an essential application prospect in the field of optoelectronic devices. To make full use of the advantages of low-dimensional materials and overcome the shortcomings of high dark current and low absorption rate, researchers have combined ferroelectric materials with low-dimensional materials and used the remnant polarization of ferroelectric materials to form a strong localized field to modulate carriers, which improves the photodetection capability of low-dimensional materials. Recent research results of ferroelectric localized field-enhanced low-dimensional material-based photodetectors are summarized in this paper. Meanwhile, related research on the modulation and performance enhancement of ferroelectric materials in one-dimensional nanowires, two-dimensional materials and junction devices was introduced. Finally, the development trend of ferroelectric localized field-enhanced low-dimensional material-based photodetectors was briefly summarized and proposed.
2022, 51(7): 20220065.
doi: 10.3788/IRLA20220065
Two-dimensional (2D) materials, which have a thickness on the atomic scale, have attracted wide attention due to their unique physical and chemical properties. Because of their high carrier mobility, strong light-matter interaction, and anisotropic electronic/optical properties, etc., 2D materials show promising applications in optoelectronics. Among the 2D materials, narrow band gap semiconductors, such as black phosphorus, black arsenic phosphorus, etc., have shown huge potential in infrared photodetectors and have become star materials in infrared photodetectors. In this review, recent advances in 2D materials in infrared photodetectors are introduced, with an emphasis on photodetectors depending on the inner photoelectronic effect. First, the background of 2D materials is introduced. Then, the key parameters for infrared photodetectors, such as the responsivity, quantum efficiency, specific detectivity, and response speed, are listed. This is followed by the presentation of the recent advances of 2D materials in infrared photodetectors, which is divided into three parts: single component 2D material photodetectors, heterostructure infrared photodetectors, and waveguide photodetectors. Finally, a summary and outlook are provided for a guideline. We hope the present review will show the huge potential of 2D materials in infrared photodetectors and attract more exciting work on infrared photodetectors based on 2D materials in the future.
2022, 51(7): 20211118.
doi: 10.3788/IRLA20211118
Two-dimensional materials with excellent photoresponse have presented high potential in new-type infrared photodetection technologies. Introducing a localized field into two-dimensional infrared photodetectors can greatly enhance their photodetection performance. An infrared detection technique is presented based on the photothermoelectric effect through twisted bilayer graphene Moiré superlattices. The formation of the Moire superlattice alters the Seebeck coefficient of the system and the concentration of hot carriers. Applying a high-resolution photocurrent tip is capable of detecting photoresponse of a single Moire unit cell, thereby obtaining a high-resolution photocurrent map of the whole twisted bilayer graphene system. This technique demonstrates the prospect of spintronics in the field of photodetection, and provides a novel pattern for designing future single-photon detectors.
2022, 51(7): 20220224.
doi: 10.3788/IRLA20220224
Metamaterial absorbers can confine and completely absorb incident electromagnetic waves to the subwavelength scale and have promising applications in detection, thermal emitters, energy harvesting, cooling, etc. The multiband metamaterial absorbers reported thus far are mainly the perfect absorption of multiple similar wavelengths in a specific wavelength range. Achieving multiwavelength absorption over a wide spectral range requires the combined work of multiple structures. Based on the three-layer structure of the titanium cross resonator-silicon nitride dielectric layer-titanium reflective layer, a triple-band metamaterial absorber with operating wavelengths spanning midwave infrared, longwave infrared, and very longwave infrared was designed and numerically simulated. Using the propagating surface plasmon resonance, the localized surface plasmon resonance, and the silicon nitride intrinsic absorption mode excited by the metamaterial absorber, high absorption reached 97.3%, 94.4%, and 93.6% at wavelengths of 4.8 μm, 9.1 μm and 18 μm respectively. Meanwhile, the wavelengths of the three absorption peaks can be flexibly manipulated by changing the geometric parameters of the metamaterial absorber, and the absorber exhibits insensitivity to polarization and incident angle. The materials used in this work are commonly used in existing processes and have application prospects in gas detection and infrared imaging.
2022, 51(7): 20220441.
doi: 10.3788/IRLA20220441
To study the mechanism of interaction between ions and mid-infrared crystals and explore the preparation and properties of mid-infrared crystal optical waveguides, an optical ridge waveguide with a depth of 17.5 μm and a width of 14 μm was fabricated in MgF2 crystals by ion irradiation combined with precision diamond blade dicing. The SRIM software was used to simulate the process of electronic and nuclear stopping powers of MgF2 crystal irradiated by C5+ ions, and the mechanism of waveguide formation was analysed. The refractive index variation of the waveguide was simulated, and the near-field mode of the waveguide was experimentally measured and theoretically simulated. The propagation loss of the waveguide was reduced to 0.4 dB/cm by thermal annealing. The micro-Raman spectra show that there was no significant lattice damage in the waveguide region of the MgF2 crystal during ion irradiation. The results show that ion irradiation combined with diamond dicing is a very mature method to prepare ridge waveguides, and the prepared MgF2 crystal ridge waveguides have a wide application prospects in the field of mid-infrared integrated optics and optical communication.
2022, 51(7): 20210646.
doi: 10.3788/IRLA20210646
To realize the application of light field imaging technology in the longwave infrared band, the radiation calibration and nonuniformity in infrared light field imaging were investigated. First, according to the principle of light field imaging and nonuniformity correction, a radiation calibration model for infrared light field imaging was proposed, and the relationship between response drift and nonuniformity was analysed. Next, a standard blackbody experiment was designed to record the image data within 30 hours after the two-point calibration, and the nonuniformity changes of light field data and light field imaging under the same conditions were compared. The experimental results show that within 10 minutes to 30 hours, the nonuniformity of light field data increases from 0.062% to 0.62%, while the nonuniformity of light field imaging increases from 0.024% to 0.27%. Therefore, the effect of response drift on the nonuniformity of infrared light field imaging is affected by the calculation of vignetting and refocusing of the microlens array. Refocusing can effectively suppress the increase in nonuniformity due to response drift.
2022, 51(7): 20220395.
doi: 10.3788/IRLA20220395
Radiometric calibration technology is the key link to realize quantitative remote sensing. In recent years, with the maturity of infrared telemetry technology, onboard infrared radiation calibration has become an important development direction of space quantitative remote sensing technology. Based on the background of real-time absolute radiometric calibration of infrared cameras, this paper puts forward the semioptical path on-board absolute radiometric calibration and site absolute radiometric calibration based on multitemperature field. Combined with the experimental data, three schemes of onboard calibration, site calibration and cross calibration are used to verify the on-orbit absolute radiometric calibration experiment. The applicable scenarios of onboard calibration, site calibration and cross calibration are analysed. The results show that by combining the semi and all optical calibration data processing and conversion technology, using the site absolute radiation calibration method of the water surface field and land surface field, a suitable calibration site is selected, and typical ground object scenes are added to the land surface field to realize multitemperature field calibration. The radiometric calibration method proposed in this paper realizes real-time high-precision absolute radiometric calibration, and the calibration accuracy is better than 1.5 K.
2022, 51(7): 20220286.
doi: 10.3788/IRLA20220286
The classical Malkmus statistical narrow-band model was extended with a fictitious gas method to improve the numerical accuracy of the infrared radiation signature of high-temperature gas in aeroengine exhaust systems. In this study, the accuracy of the extended model and the classical Malkmus statistical narrow-band model were evaluated. The results show that the numerical accuracy of the classical Malkmus statistical narrow-band model was improved significantly by the fictitious gas assumption, particularly for nonisothermal and nonhomogeneous gases. Compared with the line-by-line results, the root mean square error of the classical Malkmus statistical narrow-band model for the average band transmissivity of CO2-H2O-N2 mixture is 0.018, while the root mean square error of the fictitious gas-based Malkmus statistical narrow-band model is 0.012, which is reduced by 33.3% compared with the former.
2022, 51(7): 20210558.
doi: 10.3788/IRLA20210558
Aiming at the angle of attack, which is an important influencing factor of infrared guided air-to-ship missile path planning, constraint models of the attack angle were built, including the number of waypoints, distance between two adjacent waypoints, turning angle and pathway distance. An analytical calculation method of the maximum attack angle was proposed. Applying the principle of geometry, the maximum angle of attack calculation model was built, which could be used to solve the pathway with one waypoint, two waypoints and multiple points. Finally, the maximum attack angle under different conditions was simulated when the waypoint number, turning angle and missile range were changed separately. The results show that the maximum angle of attack would increase rapidly as the missile path waypoint increased; it would also increase as the turning angle decreased if the waypoint number was constant. However, the attack angle increased at the expense of the infrared guided air-to-ship missile range.
2022, 51(7): 20220431.
doi: 10.3788/IRLA20220431
Spaceborne CO2 imaging spectrometer has become one of the important means to monitor global greenhouse gas changes due to its advantages of spectrum integration, high spatial resolution, high time resolution, non-contact and long-term monitoring. In order to solve the problems of large incident slit, low signal-to-noise ratio and poor imaging quality in large field of view, a new scheme was proposed for the initial structure design of the optical system of Offner imaging spectrometer. The scheme was based on the tangent of meridian ray and arc sagittal ray emitted at the 30 mm slit at the central wavelength to improve the utilization rate of incident light in the whole spectral range. Using optical design software, an imaging spectrometer with F number of 2.5 and spectral system resolution of 0.1 nm was designed in the range of 1594-1619 nm. The design results show that the root mean square (RMS) radius of the sequence diagram is less than 5 μm, and the modulation transfer function of the system at 33 lp/mm is better than 0.7. In addition, the system uses pixel merging (i.e. extended pixel) method to further improve the detection intensity of spectral signals. The design scheme satisfy remote sensing detection requirements of large field of view, high spectral resolution and high signal-to-noise ratio for spaceborne CO2 imaging spectrometer.
2022, 51(7): 20210808.
doi: 10.3788/IRLA20210808
In conventional microsurgery, the existing endoscope has the problem of a short working distance, is unable to achieve optical zoom, and is unable to obtain stereo images. Therefore, the design scheme of a two-path configuration 3D exoscope optical system with a long working distance and optical zoom features is proposed. The single optical path is composed of the front zoom system and the rear zoom system. The front zoom group system selects the three-element structure of optical compensation, and its function is to realize variable working distance and variable field of view while keeping the output light parallel. The rear zoom group system selects the four-element structure of mechanical compensation, and its function is to receive the parallel light of the front group system and keep the image plane position and image height unchanged. The combined optical system can achieve a zoom effect through the form of three moving group linkages. This solution is analogous to a microscope with infinite tube length. The parallel light path in the middle makes it easy to install and flexibly insert the beam splitter. Furthermore, the relation equation between the focal length of the front zoom system and the working distance of the object is derived. Based on the high-definition CMOS with a pixel number of 1920×1200 and a pixel size of 4.8 μm×4.8 μm, we design a six-switched 3D exoscope optical system. The object resolution of the system is 6.8-31.8 μm, the object field of view is 15-70 mm, the working distance is 180-380 mm, and the demagnification 1/β is 1.36×, 2.36×, 3.36×, 4.36×, 5.36×, 6.36×. By selecting a reasonable tolerance range, the design results show that the six-switched optical system MTF is better than 0.15 at 105 lp/mm with a probability of more than 90%, and the cam curve is smooth, which can meet the requirements of microsurgery.
2022, 51(7): 20210524.
doi: 10.3788/IRLA20210524
The illumination system is an important part of the projection lithography exposure optical system. Its function is to provide high uniformity illumination and control the exposure dose and different illumination modes for the mask surface. As an important part of the lithography lighting system, the zoom system plays a vital role in improving the performance of the entire lithography machine. According to the characteristics of the ultraviolet lithography illumination system, this paper uses CODE V software to complete the design of the zoom system in the near ultraviolet lithography illumination system with a wavelength of 365 nm, an entrance pupil diameter of Φ33 mm, an image telecentricity ≤10 mrad, and a distortion ≤±2%. The effect of the error source of the zoom system on the pupil performance of the system is analyzed, combined with the design scheme of the zoom system and the actual processing capability, gives a single-sided thickness tolerance of less than 20 μm, a moving part movement accuracy of less than 0.5 nm, and an eccentric tolerance of less than 0.02 mm for each lens. The tilt tolerance of each lens is controlled within 1′. The tolerances are reasonable and feasible, and meet the requirements of high uniformity and high energy utilization of the UV lithography illumination system.
2022, 51(7): 20220142.
doi: 10.3788/IRLA20220142
To meet the requirements of multidimensional spectral detection and visible-light imaging of flight targets, a common-aperture optical system based on the Cassegrain telescope was designed. The front end of the system was composed of bi-reflective system. The primary mirror is a paraboloid and the secondary mirror is a hyperboloid. The light beam in the back end was split by tilted flat plates and received by the following subsystems. The problem of astigmatism caused by tilted flat plates was solved successfully by utilizing two cylindrical lenses in the visible-light imaging system. The deviation of the optical axis caused by the tilted flat plate was compensated by adding reversed tilted flat plates. Visible-light imaging and mutispectrum (200-400 nm, 400-760 nm and 760-2 500 nm) reception could be realized for flying targets with diameters less than 0.5 m within 0.5-1.5 km. The MTF values of each field of view in the imaging module were all greater than 0.5 at a Nyquist frequency of 35 lp/mm. This result is extremely close to the diffraction limit curve. All coupling modules meet the coupling requirements of optical fibers. Through athermal design, the common-aperture system can work normally in the temperature range from −20 ℃ to 50 ℃. The tolerance analysis results show that the system can meet the requirements of manufacture, installation and adjustment.
2022, 51(7): 20210848.
doi: 10.3788/IRLA20210848
The conventional curved bionic compound eye relay system is required to undertake the task of converting the curved image plane caused by the splicing of large-field subeyes into a flat image field, which poses certain difficulties to the system design. A method was proposed for the splicing arrangement of the flat image plane of the large-field compound eyes, and the method was described mathematically. By constructing a balanced model between the number of subeyes, the total field of view of the system and the subsequent reasonable selection of the optical relay system parameters, the relationship between the depth of field of the relay system and the optical range difference of the spliced image plane of the compound eye was analysed, and it was concluded that the optical range difference generated by the splicing method of the compound eye flat image plane was within the acceptable depth of field of a typical optical relay system, which could effectively reduce the design pressure of the relay optical system. Based on the above theory, a compound eye optical system with a field of view of 16° for a single subeye and an overall field of view of 96° was designed for practical verification. The system finally achieves an aberration of less than 2%, the transfer function reaches the diffraction limit in the central field of view and the edge field of view is close to the diffraction limit with good image quality, which proves that splicing theory is feasible.
2022, 51(7): 20220234.
doi: 10.3788/IRLA20220234
The 1.7 μm ultrashort pulse fiber laser has received great attention for its promising applications in various fields, such as bioimaging and materials processing. We experimentally built a 1.7 μm all-fiber structure mode-locked Tm-doped fiber laser based on the nonlinear polarization rotation technique. The optical gain at the 1.7 μm waveband is effectively obtained by using a core-pumping scheme, and the ASE at long wavelengths is suppressed by a fiber-based bandpass filter in the cavity. The proposed fiber laser delivers an ultrashort pulse with a central wavelength of 1733 nm and a 3 dB bandwidth of 6.3 nm. The mode-locked pulse has a repetition frequency of 19.56 MHz and an average power of 1.4 mW. In addition, the evolution of the pulse inside the laser cavity is numerically simulated. The proposed 1.7 μm all-fiber mode-locked laser is beneficial to further improve the stability and integration of the 1.7 μm laser source, which could find important applications in fields such as bioimaging.
2022, 51(7): 20210435.
doi: 10.3788/IRLA20210435
A distributed feedback laser diode (DFB-LD) has become the key light source, in which a narrow linewidth and short-term frequency stability are highly demanded, in the far-distance coherent measurement systems due to the characteristics of high-speed direct modulation, low cost, and mass production. To improve frequency stability of a DFB-LD, a new method of frequency locking was proposed. The frequency of the DFB-LD was locked to an absorption line of H13C14N gas at the wavelength of 1548.956 nm by a photoelectric feedback loop based on the principle of side frequency locking. The photodetection module, subsequent error signal generation and processing module and the laser drive module were integrated on the same analog circuit board to minimize the noise of the system. The frequency discrimination signal was generated by using a divider instead of a subtractor to increase the system sensibility and precision of frequency stability significantly. The second-level frequency stability of the DFB-LD was improved by more than two orders of magnitude from 3.67×10−8 to 2.34×10−10 by using two techniques. The experimental results show that the frequency stability scheme of DFB-LD has high precision frequency stability, in addition to the features of simple structure, low cost, mass production and suitable for UAV applications. The DFB-LD is an ideal light source for far-distance coherent measurement.
2022, 51(7): 20210654.
doi: 10.3788/IRLA20210654
High-power, high-conversion-efficiency and tunable continuous-wave (CW) near-infrared external-cavity pumped singly resonant optical parametric oscillator (SRO) was proposed. OPO based on a quasi-phase-matched (QPM) nonlinear crystal was a very effective technology to obtain the short-wave near-infrared tunable laser sources. CW laser at 532 nm was used as the fundamental laser source to drive the OPO in the cavity. The QPM crystal was a multi-grating MgO-doped stoichiometric periodically poled LiTaO3(MgO:sPPLT). The widely tunable SRO output signal wavelength ranging from 807 to 879 nm and idler wavelength ranging from 1352 to 1567 nm were achieved by combination of poling period tuning and temperature tuning with four different periodically poled gratings from 8.3 to 8.6 μm. By means of using single resonant of idler light, the output power of the signal (821 nm) was 3.1 W at a pump power of 5.4 W with the efficiency of 57.4% was achieved. Under an incident pump power of 13.6 W, a maximum signal output power of 6.8 W at 821 nm was obtained with the period of 8.6 μm.
2022, 51(7): 20210507.
doi: 10.3788/IRLA20210507
Raman frequency conversion based on a solid medium is an effective technical scheme to generate new wavelength laser. 1572 nm KTP optical parametric oscillator was used to pump the KGW crystal intracavity, and Raman laser output at 1616 nm (2nd-order), 1638 nm (3rd-order), 1662 nm (4th-order), 1686 nm (5th-order) and 1711 nm (6th-order) was realized, among which 1711 nm is dominant. The maximum total average output power of the laser is 1.13 W, the minimum pulse width is 20 ns. The single-order average Raman frequency shift corresponding to the multiorder cascade Raman frequency conversion is 86 cm−1, which is consistent with the low-frequency Raman mode of the KGW crystal reported in the literature. Using a 1572 nm KTP optical parametric oscillator as the intracavity pump source of the Raman laser has two advantages: On the one hand, it can effectively expand the output wavelength of Raman frequency conversion; on the other hand, it can provide high-intensity pump light for subsequent multiorder Raman conversion based on the pulse narrowing characteristics of the optical parametric oscillator. By introducing the multi-order Raman frequency conversion scheme, a new idea is provided for the effective use of the unconventional low-frequency shift Raman mode of a solid medium.
2022, 51(7): 20220035.
doi: 10.3788/IRLA20220035
When an ultrashort pulse bursts into a highly nonlinear fiber, some new frequency components are generated in the pulse spectrum under the combined action of dispersion and nonlinear effects, which makes the output spectrum much broader than the input spectrum. The spectrum is called the supercontinuum. Supercontinuum light sources have the advantages of a wide spectral range, good directivity, high brightness, and good spatial coherence. In mode-locked lasers, traditional solitons, dissipative solitons, and noise-like pulses can be used as seed sources to generate a supercontinuum spectrum. In this paper, we build an NPR passively mode-locked fiber laser to generate pulsed laser. Then, a section of DCF is added to compensate for the dispersion in the cavity to produce dissipative solitons. Meanwhile, the states of bound states and dissipative solitons can be switched by carefully adjusting the paddles of PC in the cavity. The output pulse is compressed by a 10 m single-mode fiber before being injected into a tapered highly nonlinear fiber to generate a supercontinuum. In the experiment, we obtain a dissipative soliton mode-locked pulse with a pulse duration of 5.6 ps, a repetition frequency of 32 MHz, and a signal-to-noise ratio of 52 dB. The compressed pulse duration is 808 fs, which is used as the seed to generate a supercontinuum. The cover range of the supercontinuum is approximately 1200 nm to 2200 nm, and its 20 dB spectrum width is 357 nm. By tuning the polarization controller, the switch between the dissipative soliton pulse and the bound state pulse is realized. The pulse duration of the bound state is 1.4 ps, the pulse separation is 14 ps, and the signal-to-noise ratio is 51 dB, which produces a supercontinuum spectrum of 1600-1870 nm with a 20 dB spectral width of 135 nm.
2022, 51(7): 20210618.
doi: 10.3788/IRLA20210618
Combining the split-step Fourier method with the fourth-order Runge-Kutta integration method, the manipulation and generation of supercontinuum by finite energy cosh-Airy pulses in a double-zero dispersion media was investigated. Firstly, the influences of truncation coefficient a, initial chirp C and distribution factor χ0 on the evolution of cosh-Airy pulses in double-zero dispersion medium were discussed in detail, and the influences of a, C and χ0 on the width of supercontinuum width were statistically analyzed. Then, the influences of higher-order nonlinear effects on supercontinuum generation of cosh-Airy pulse was further studied. The results show that the width of supercontinuum can be controlled by manipulating the characteristic parameters of cosh-Airy pulses. The flatness of supercontinuum is affected with consideration of high-order nonlinear effects. The results provide some theoretical basis for manipulation and generation of supercontinuum and broadband laser sources.
2022, 51(7): 20210771.
doi: 10.3788/IRLA20210771
Aiming at the deviation of the parallelism(on to one correspondence position) between the active laser field of view and the infrared passive field of view in the parallelism correction of the active and passive dual-band (laser/IR) composite system, the parallelism correction method of the active and passive dual-band (laser/IR) composite system was proposed and the theoretical research and physical simulation test were carried out. First, derived the angle correspondence between the active laser emission field of view and the fast steering mirror. Secondly, a parallelism correction method based on polynomial fitting is proposed according to the laser emission field of view and infrared detection field of view. Finally, the actual test platform is constructed to calibrate, solve and correct. The test results showed that the actual maximum deviation can be reduced from 0.8 mrad to less than 0.1 mrad in the ±1.4° indicated field of view of laser and ±1.4° infrared central field of view, which further improve the aiming accuracy of the laser.
2022, 51(7): 20210533.
doi: 10.3788/IRLA20210533
To solve the complicated operation problems of the laser ultrasonic method and the low sensitivity of electromagnetic acoustic transducers, that both have noncontact characteristics in their respective detection processes. It is difficult to observe the effects of different parameters on the relevant physical fields. In this paper, the finite element simulation method was used to analyse the influence of the matching relationship between the pulsed laser and the electromagnetic ultrasonic transducer on the detection sensitivity, and the optimal design basis of the laser sound-magnetic detection system was studied. The simulation model of the laser acoustic-magnetic detection system was established by using finite element software. The characteristics of the temperature field and displacement field of ultrasonic excitation by a Gaussian laser pulse were analysed through orthogonal numerical simulation, and the influence of the parameter change of the electromagnetic ultrasonic transducer on the detection sensitivity was observed. The results indicate that the voltage signal received by the spiral coil can correctly respond to the ultrasonic displacement field generated by the thermal expansion effect of the incident laser in the solid. When the height to width ratio of the magnet was 1.5 times, the magnetic field intensity distribution at the driving layer was optimal, and the effect of the lifting distance on the energy conversion efficiency presented the law of negative exponential. The receiving performance of the electromagnetic ultrasonic transducer at different receiving spacings was evaluated.
2022, 51(7): 20210497.
doi: 10.3788/IRLA20210497
The total impulse of a disc-type laser ablation thruster is linearly related to the number of ablation points on the target disk, and improving the utilization rate of the target disk is beneficial to obtain more ablation points on the limited target disk surface. In this paper, to optimize the utilization rate of the target disk, the structure of the laser ablation microthrusters was designed and analyzed. The distribution of the ablation point on the target disk was theoretically modelled, two analytical principles, namely, the bead principle and the collar principle, were proposed, and three actual ablation point distribution methods, namely, the circle path, the spiral path and the hexagonal pack, were designed. Through calculation, the influence law on the utilization rate of the target disk by the size of the target disk and the size of the ablation point under the three distribution methods was analyzed and compared. The results show that the target disk utilization rate of the hexagonal pack can reach up to 90.64%, and the target disk utilization rate theory of the circle path and spiral path can reach up to 78.54%. The target disk utilization rate is affected by the size of the target disk and the size of the ablation point. When the size of the target disk is small, the target disk utilization rate of the circle path is relatively large. When the size of the target is large, the target disk utilization rate of the hexagonal pack is relatively large. Each of the three distribution methods has its own characteristics and has its own emphasis on application. The research provides theoretical guidance and a design reference for the full utilization of the target disk of the disc-type laser ablation thruster, and has some reference significance to the engineering design of the thruster.
2022, 51(7): 20210639.
doi: 10.3788/IRLA20210639
LiDAR is a kind of active detection technology that can accurately and quickly obtain 3D information of targets. However, it is subject to intense noise from the solar background when it operates during the day. In this case, narrow line width lasers and filters are generally used to achieve the effect of suppression of background noise. When both of them are extremely narrow line widths, the SNR of the received signal will be significantly affected if the center wavelengths of the two are mismatched. Therefore, from the perspective of narrowband filtering and wavelength tracking of the transmitted signal by the received signal, a tunable filter receiver and the optical path of the transceiver system of the lidar were designed by using the volume grating, and the tracking of the received wavelength to the transmitted wavelength of the lidar was realized under the condition of narrow filtering bandwidth. Finally, the whole system was actually built in the laboratory to verify the correctness of the system design. At a fixed wavelength and tunable wavelength, the tracking accuracy is better than 2.9 pm. At this time, the received signal intensity is greater than 99.97% of the central wavelength matching condition.
2022, 51(7): 20210636.
doi: 10.3788/IRLA20210636
In view of the problems existing in the current high-speed TV rendezvous measurement of rocket drift, such as the great influence of the external environment and the inability to obtain the measurement data in real time, an active measurement method of rocket takeoff real-time drift based on lidar is proposed. First, the lidar is installed on the two-dimensional precision turntable through the installation platform. In the process of rocket launch, the two-dimensional precision turntable drives the lidar to continuously track and scan the target point position of the rocket with high precision, and obtain the lidar point cloud data corresponding to the target point position. Then, the data processing system receives the lidar point cloud data, fits the elliptical curve and the elliptical curve center point of each frame data, takes the position of the elliptical center point when the rocket is stationary as the reference position, calculates the relative difference between the elliptical center point position of each frame data and the reference position, and determines the real-time drift of the rocket in the take-off stage. Finally, the measurement system and method are verified by the rocket launch test, and the test results show that under the condition of environmental interference, the measurement accuracy of real-time drift is 3.1 cm. It is the most accurate measurement method in the rocket drift measurement at present. At the same time, it can ensure the real-time performance of the data, provide real-time discrimination data for the rocket launch security console, and ensure the safety of the launch process.
2022, 51(7): 20210572.
doi: 10.3788/IRLA20210572
the Due to the limitation of the optical-mechanical platform of the laser heterodyne interferometry system, the Doppler frequency shift cannot be simulated. Moreover, commercial signal generators cannot realize various types of high-complexity intersatellite heterodyne interference signal simulations. It is difficult to conduct ground tests of the phasemeter for space gravitational wave detection detailed. Therefore, the characteristics of heterodyne interference signals were analysed, the realization principle and method of the signal simulation system were studied, and then the simulation system of the laser heterodyne interference signal for space gravitational wave detection was designed. First, the simulation of the heterodyne interference signal was applied to the DDS. Then, the influence of the Doppler effect was simulated by offsetting the overall frequency. Next, based on the mixed congruential algorithm, shot noise was generated and modulated into the heterodyne interference signal. Finally, with the usage of FPGA, the system hardware platform was built. The time domain and frequency domain characteristics of the generated signals were analysed by an oscilloscope and a spectrum analyser. The experimental result shows that the spurious suppression of the system is −53 dBc and the harmonic suppression is −47 dBc at 2-20 MHz. The signal generated by the system is in good agreement with the expec-tations which satisfies the ground test requirements of the phasemeter for space gravitational wave detection.
2022, 51(7): 20210537.
doi: 10.3788/IRLA20210537
Lasers are an effective way to counter photoelectric reconnaissance. To improve the damage efficiency, a new idea of a composite laser damage photodetector is explored. Damage efficiency experiments of a 1064 nm and 532 nm laser with a 10 ns pulse widths and its dual wavelength composite laser, 1064 nm laser with 0.4 ms and 10 ns pulse width and its dual pulse width composite laser on a CMOS image sensor were carried out respectively. The results show that when the dual-wavelength composite laser causes complete damage to the CMOS, the fundamental frequency light energy is 77.8% of the 1064 nm laser alone and 62.5% of the 532 nm laser alone; when the dual-pulse composite laser damages, the pulse width of the 0.4 ms laser is The energy density is reduced to 1.7% of the single action, and the energy density of the 10 ns pulse width laser is reduced to 76.4% of the single action. This discovery provides a new idea and reference for high efficiency optoelectronic countermeasures of multisystem composite lasers.
2022, 51(7): 20210565.
doi: 10.3788/IRLA20210565
ZnSe has always been one of the preferred materials for optical parts due to its excellent optical and mechanical properties. The manufacturing cost of optical parts such as optical windows and optical lenses largely depends on the machinability of optical materials, and processing costs account for more than 50% of the total manufacturing costs. The machinability of optical materials is related to the grain size. In this paper, the physical vapour deposition (PVD) method was employed to prepare PVDZnSe infrared optical materials, and the influence of the PVDZnSe preparation process on its grain size and machinability was investigated from the aspects of deposition temperature and raw material properties. It was demonstrated that under the three temperature conditions of 920 ℃, 960 ℃ and 1000 ℃, with the higher deposition temperature, the grain size of the PVDZnSe material showed an increasing trend, and the size ranges were 20-180 μm, 300-2000 μm and 1200-2800 μm, respectively. Under the same process parameters, the PVDZnSe materials were prepared from three different ZnSe raw materials with particle diameters of 2 -10 μm, 10-20 μm and 300-2000 μm. With the increase in grain size of the ZnSe raw materials, the grain size also increased. The results show that the grain size of the obtained PVDZnSe increases significantly, and the brittleness index also increases, which indicates that the machinability of PVDZnSe gradually worsens. The study also found that the influence of grain size on the transmittance of the PVDZnSe material is not significant. The average transmittance of the PVDZnSe material can reach more than 70% in the wavelength range of 2-14 μm. This study provides practical experience and technical support for the application of PVDZnSe optical parts.
2022, 51(7): 20210609.
doi: 10.3788/IRLA20210609
Micronano structure films supporting local surface plasmons were prepared by vacuum thermal evaporation and annealing, and the chalcogenide glass Ge28Sb12Se60 film was evaporated on this film. The dispersion characteristics of optical nonlinear enhancement were studied by the Z-scan technique under femtosecond laser pulse excitation. Nonlinear absorption enhancement was observed at 650 nm and 850 nm. The nonlinear refractive index changes from negative to positive with increasing wavelength. The principle of nonlinear absorption enhancement of chalcogenide glass Ge28Sb12Se60 thin films was characterized and analysed by scanning electron microscopy and transmission spectroscopy. The nonlinear absorption gradually changed from single photon absorption to two-photon absorption with increasing wavelength. The resonance center frequency of chalcogenide glass films shifted due to the micro/nanostructures of silver films. The preparation of micro/nanostructures for enhancing the nonlinearity of chalcogenide glass is simple without a complex lithography process, which provides a new idea for the design of nonlinear photonic devices.
2022, 51(7): 20220211.
doi: 10.3788/IRLA20220211
Chiral two-dimensional perovskites are a class of low-dimensional perovskite materials with noncentrosymmetric structures. It combines the advantages of low-dimensional perovskites and chiral materials and thus can be used to produce nonlinear optical effects. Various optical properties of low-dimensional perovskites have been reported to be regulated by high-pressure technology. However, there are few reports on the high-pressure optical properties of chiral two-dimensional perovskites, especially the nonlinear optical effect under high pressure. The PL spectrum, absorption spectrum and second harmonic effect (SHG) of a high-pressure chiral two-dimensional perovskite material (R-, S-)ClPEA2PbI4 were studied by the diamond anvil cell technique. The results show that with increasing pressure, the PL spectral intensity of the material first increases to a peak of 1 GPa and then decreases gradually until it disappears at approximately 6 GPa, and the peak wavelength shifts from 507 nm to 568 nm. The high-pressure absorption spectra show that there is a sudden change in the absorption edge of the chiral perovskite at approximately 6 GPa, indicating the occurrence of a phase transition. Under high pressure, the intensity of the laser second harmonic signal decreases gradually with increasing pressure and significantly changes near a pressure of 6 GPa. These results show that high pressure is an effective way to regulate the optical properties of two-dimensional chiral perovskites, which provides a basis for their future applications in luminescence, near-infrared frequency conversion and other devices.
