2019 Vol. 48, No. 4
column
- Invited papers
- Infrared technology and application
- Lasers
- Laser technology and application
- Optical manufacturing and craftwork
- Optical design and simulation
- Photoelectric device and microsystem
- Photoelectric measurement
- Optical communication and optical sensing
- Information acquisition and identification
2019, 48(4): 402001.
doi: 10.3788/IRLA201948.0402001
The terahertz(THz) far-field radiation properties of a butterfly-shaped photoconductive antenna (PCA) were experimentally studied using a home-built THz time-domain spectroscopy(THz-TDS) setup. To distinguish the contribution of in-gap photocurrent and antenna structure to far-field radiation, polarization-dependent THz field was measured and quantified as the illuminating laser beam moved along the bias field within the gap region of electrodes. The result suggests that, although the far-field THz radiation originates from the in-gap photocurrent, the antenna structure of butterfly-shaped PCA dominates the overall THz radiation. In addition, to explore the impact of photoconductive material, radiation properties of butterfly-shaped PCAs fabricated on both low-temperature-grown GaAs(LT-GaAs) and semi-insulating GaAs(Si-GaAs) were characterized and compared. Consistent with previous experiments, it is observed that while Si-GaAs-based PCA can emit higher THz field than LT-GaAs-based PCA at low laser power, it would saturate more severely as laser power increased and eventually be surpassed by LT-GaAs-based PCA. Beyond that, it is found the severe saturation effect of Si-GaAs was due to the longer carrier lifetime and higher carrier mobility, which was confirmed by the numerical simulation.
2019, 48(4): 402002.
doi: 10.3788/IRLA201948.0402002
In view of many technical constraints and techcical bottlenecks in traditional gating imaging system, a novel self-triggering instantaneous gating imaging of waveguide grating microarray that considered self-triggered gating and instantaneous imaging was proposed. This article not only showed a complete self-triggered gating imaging principle and device model, but also explained the advantages of quantum dot films based on perovskite in transient gating imaging. In the end, the spatial modulation effect of waveguide gratings microarray, electron beams, electronically pumped imaging and the instantaneous luminescence effect of quantum dot film based on perovskite, were calibrated and modeled in the vacuum test system. The feasibility of the technical scheme was proved by experiments.
2019, 48(4): 402003.
doi: 10.3788/IRLA201948.0402003
With the increasing demand of infrared imaging technology for time resolution, spatial resolution, spectral resolution and optical stability, the contradiction between the four is becoming more intense. The molecular filter was a filter device with a comb-like discrete transmission spectrum type. The selective transmission was realized by the resolution of the wavelength of the light by the molecular energy level transition. The effect was optical but the mechanism was quantum. Molecular filtering provided a new way for conflict resolution. Based on the theory of molecular spectroscopy, the working mechanism and theoretical model of three types of molecular filter imaging techniques, such as differential absorption, magneto-optical rotation and Doppler modulation, were presented. Combined with the related work of the research team, the applications were introduced separately:differential absorption molecular filtering in remote sensing monitoring of vehicle exhaust, magneto-optical rotation molecular filtering in combustion diagnosis, and Doppler modulated molecular filtering in spaceborne atmospheric wind and temperature remote sensing. Finally, the technical characteristics and applicability of the three mechanism filtering methods were analyzed.
2019, 48(4): 404001.
doi: 10.3788/IRLA201948.0404001
As a fast and nondestructive detection method, near infrared detection has been widely concerned. But a lot of noises, high dimension and nonlinearity of the spectra affect the accuracy of classification model. In this study, deep belief network (DBN) theory was improved and introduced into spectral features learning to solve the difficulty of learning nonlinear relation of high dimensional data. The strategy based on layer by layer and stochastic gradient ascent algorithm were used for acquiring the network weights. Combined with the SVM method, the DBN-SVM multi classification model of tobacco leaf position was established. The proposed method, was compared with PCA-SVM method based on principal component analysis and LDA-SVM method based on linear discriminant analysis.The results show that DBN-SVM method may effectively learn the internal structure and nonlinear relationship of high dimensional data. The model constructed by this algorithm not only has excellent performance in identification and feature learning, but also is superior in robust, sensitivity and specificity.
Studying the buoyancy diffusion laws and infrared characteristics on the water surface of submarine thermal wake is of great significance for submarine infrared detection. The submarine scale-down model was taken as the research object, and the three-dimensional calculation model of submarine thermal wake was established. The numerical simulation of the buoyancy and diffusion process of submarine thermal wake was performed by using the overset grid, Volume of Fluid(VOF) model method and the flow-through method separately. The buoyancy and diffusion law and temperature field characteristics of submarine thermal wake were analyzed. Through experimentally measuring infrared thermal image on water surface and the buoyancy and diffusion images of thermal wake, the accuracy of the two simulation methods was verified. The results show that the methods based on overset grids and VOF models are more accurate, the time deviation of maximum thermal wake temperature is 0.2 s and the temperature deviation is 0.003 K. It can well simulate the buoyancy diffusion and temperature distribution characteristics of submarine thermal wake.
In this paper, the wavefront aberration was simulated by using the phase screen set under the influence of combined oblique propagation and beam propagation. First, the phase screen of the vertical transmission path was generated by the power spectrum inversion method and the subharmonic compensation method, and the oblique atmosphere propagation theory was used to correct the phase screen, then the phase screen suitable for the simulation of the influence of the oblique atmospheric turbulence was obtained. The difference of phase structure function between oblique phase screen and vertical path phase screen was compared by numerical analysis. The space distribution of wavefront distortion corresponding to each height interval was calculated, and the phase screen group model was established. Finally, the phase distribution of each position of the received light wave plane was obtained.
2019, 48(4): 405001.
doi: 10.3788/IRLA201948.0405001
The control precision and stability of emitting wavelength of distributed feedback laser directly determines the measurement accuracy of detection system that uses infrared distributed feedback laser excitation light source as the core section. A temperature control system of distributed feedback laser was developed utilizing analog PID control. Simulated proportional-integral-differential temperature forward control module and real-time temperature backward acquisition module were adopted to control temperature. Emitting wavelength of 2 049 nm DFB laser was used in temperature control experiment. Results show that system temperature control stability is 0.05℃, and the stability time is less than 30 s. Meanwhile, spectrum test experiment was conducted using the developed temperature control system to control the proposed distributed feedback laser. The results show that the emitting wavelength of laser is linear with its working temperature while the laser drive current is fixed.
2019, 48(4): 405002.
doi: 10.3788/IRLA201948.0405002
In order to study the influence of pump bandwidth and wavelength-drift on the performance of solid-state lasers, theoretical analyses were performed on a quasi-three-level Tm:YAG laser, and the corresponding theoretical models, including both spectral and thermal models, were presented. In the Tm laser experiment, a compact and high-efficiency composite Tm laser operating at 2 013.2 nm was demonstrated, which was end-pumped by volume Bragg gratings(VBGs) locked laser diode(LD) with emission wavelength centered at 784.9 nm and bandwidth as narrow as 0.1 nm(full width at the half maximum, FWHM). A maximum output power of 7.96 W was obtained with a slope efficiency of 62.5% and optical conversion efficiency of 53.3%, respectively. The maximum laser wavelength drifted from 2 013.25 nm to 2 014.53 nm when increasing the absorbed pump power from 1.87 W to 14.93 W for the 3% output coupling. As for 5% output coupling, the drift was from 2 013.91 nm to 2 014.26 nm. It was found that a narrow LD bandwidth of 0.1 nm resulted in a more pronounced excitation efficiency and thus a higher laser efficiency, despite that the maximum temperature within the crystal was slightly higher. The present study could be extended to other solid-state lasers for the choice of pump source by comprehensively considering the pump bandwidth and wavelength-drift and the spectral profiles of gain medium, which would be helpful for an efficient laser system.
2019, 48(4): 405003.
doi: 10.3788/IRLA201948.0405003
A passively Q-switched human-eye safety micro-ranging laser with a double-end bonded composite structure was reported. The double-end bonded structure was formed by the heterogeneous material composite technology, including the gain medium Er3+/Yb3+:glass, F2 glass and passively Q-switched crystal Co2+:MgAl2O4. The output characteristics of the double-bonded composite structure and the non-composite structure were compared in the experiment. The former laser performance parameters are significantly better than the latter. The double-bonded composite structure achieved a human eye-safe laser output of pulse energy 330 J, beam quality 1.4, pulse width 5.5 ns with 10 Hz repetition frequency; the non-composite structure laser had a single pulse energy 245 J, pulse width 6.5 ns, and the beam quality 1.9. The thermal simulation of double-bonded composite structure gain media and monolithic Er3+/Yb3+:glass shows that the former has a 51.2% increase in thermal focal length relative to the latter, and the thermal effect of the double-bonded composite structure is significantly improved. The above shows that the double-bonded composite technology can reduce the temperature gradient inside the gain medium, make the thermal focal length longer, increase the volume of the mold, and improve the mode matching of the oscillating light and the pump light, so that the single pulse energy is increased.
2019, 48(4): 405004.
doi: 10.3788/IRLA201948.0405004
The operating wavelength of a semiconductor laser(LD) varies with temperature. Temperature control of a LD was a common method of extending the normal operating temperature range of an all-solid-state laser(DPSSL). However, commonly used methods have large volume, high energy consumption and low efficiency in the wide temperature range of -50℃ to 70℃. The wavelength drift coefficient of the GaAs quantum well laser is 0.25 nm/℃, and the multi-peak characteristic of the absorption spectrum of Nd:YAG crystal was analyzed. A GaAs quantum well laser with a working wavelength of 808 nm at high temperature was used as the pump source. The two absorption peaks of 795.7 nm and 808 nm of Nd:YAG crystal were used to reduce the temperature control power consumption by segment heating. The experimental results show that the output pulse characteristics of the DPSSL at the two absorption peaks are basically the same. At lower temperature, the heating power of the segmented temperature control is reduced by 4.7 W, which is close to half of the maximum heating power without segmentation.
2019, 48(4): 405005.
doi: 10.3788/IRLA201948.0405005
The high energy pulse width tuning 1 064 nm solid-state laser was developed by adopting MOPA laser source and combining the traveling wave amplification of xenon-lamp pumping. The pulse signal out of MOPA fiber laser was controlled by the method of electric modulation pulse width. Under the premise of ensuring high beam quality, a 1 064 nm laser source output with pulse width of 8.6-220.9 ns was achieved. Adopting double pass amplifier design, five-step travelling wave amplification was achieved by xenon lamp pumping Nd:YAG crystal. The technique of restraining self-oscillations and the reasons of narrowing pulse width in the process of traveling wave amplification were analyzed. When the inject energy of xenon-lamp was 60 J and the repetition rate was 10 Hz, a 1 064 nm laser output with pulse width of 4.2-173.3 ns was achieved. Single pulse energy was up to 158 mJ.
2019, 48(4): 405006.
doi: 10.3788/IRLA201948.0405006
A high power Tm:YAP laser device was reported. The laser gain medium was b-axis-cut YAP/Tm:YAP/YAP composite crystal rod. By using a LD module with a center wavelength of 795 nm for double-end pumping, when the temperature of the cooling water was set at 20℃, and the total pump power was 301.4 W, the linear polarized laser output of 1.94 m with a maximum of 109.5 W was obtained. The optical-to-optical conversion efficiency was up to 36.3% and the slope efficiency was about 45.8%, the measured beam quality of M2 factor was 3.8 at the highest output power condition.
2019, 48(4): 406001.
doi: 10.3788/IRLA201948.0406001
To study the phenomenon of interaction between laser induced plasma hot core and normal shock wave in application of laser induced drag reduction, high-precision schlieren measurement technology was used to study and analyze the flow structure characteristics of laser induced plasma hot core under the impact of normal shock wave, and the influence law of laser energy and shock speed was obtained. The experimental results show that under the impact of the normal shock wave, the width of the hot core is firstly increased and then stabilized and decreased. The higher the incident laser energy is, the larger the width of the hot core is. The length of the hot core rapidly decreases under the impact of normal shock and then grows linearly, with a growth rate of approximately 19% of the incident shock speed. A basis for effectively enhancing the drag reduction effect and prolonging the duration in practical applications can be provided by the conclusions. The relevant methods and results also have a good reference value for the study of laser plasma active flow control.
2019, 48(4): 406002.
doi: 10.3788/IRLA201948.0406002
In recent years, various nonlinear effects associated with femtosecond laser filamentation and their potential applications had become one of the important research directions in the field of ultrashort and ultraintense pulsed laser technology. Femtosecond laser filamentation-induced condensation of water vopor, snowfall and secondary ice multiplication opened up new perspective for weather modification,which was of great scientific significance and application prospects. Firstly, the research progress of the basic observation and mechanism of laser-induced hydrometeors were analyzed. Then, challenges in the mechanism research of femtosecond laser filamentation-induced hydrometeors had been discussed and prospects of the development direction of the active utilization of intense laser atmospheric effects were also summarized.
2019, 48(4): 406003.
doi: 10.3788/IRLA201948.0406003
The small number of pixels in APD array is the limitation of three dimension imaging resolution. A method based on optical phased array was proposed to improve 3D imaging resolution of APD array, the optical phased array was used to generate and scan the beam array, the number and position of the beam array were matched with the APD array. The divergence angle of the sub-beam in the beam array was smaller than the instantaneous FOV of a single pixel in the APD array, the APD array acquired multiple acquisitions of the target 3D information by scanning the sub-beam in a single pixel to improve the resolution of the APD array. The distribution of the beam array in the far field was simulated based on the two-dimensional scalar diffraction theory in Matlab, and the relationship between the divergence angle of the beam and the number of extended cycles was analyzed. Finally, the liquid crystal phase spatial light modulator was used as the optical phased array device, and the CCD was used to receive the echo signal, which further verified the feasibility of the proposed method.
2019, 48(4): 406004.
doi: 10.3788/IRLA201948.0406004
Absorption and scattering of seawater for light waves seriously restrict the performance of laser radar for underwater target detection. Quantitative analysis of laser backscattering generated by seawater shows that the laser echo signal is seriously affected by seawater backscattering. The ability of range-gated technology and intensity modulation technology to suppress backscattering of seawater was analyzed and compared. A chaotic pulse laser with high frequency intensity modulation was proposed for underwater target detection and the scheme was designed. Based on the study of the characteristics of backscattering light and echo signal with different backscattering intensity in time and frequency domain, the ability of chaotic pulse lidar to suppress backscattering from seawater was determined by using cross-correlation noise level algorithm. The theoretical analysis shows that the target signal can still be extracted when the backscattered light intensity is 36 times that of the chaotic pulse laser.
2019, 48(4): 406005.
doi: 10.3788/IRLA201948.0406005
One of the characteristics of coherent wind lidar is using narrow linewidth laser source. In order to study the influence of different line width light sources on the detection performance of lidar, the spectrum characteristics of the time current in and out of the coherent length were analyzed theoretically. Experiments show that when the detection distance was outside the coherent length, the signal amplitude of 100 kHz light source was about 30% lower than that of 1 kHz and 10 kHz light source, and the noise amplitude of some frequency bands was larger than that of the other two light sources. Therefore, in the design of short-range wind lidar, hundreds of kHz light source could be considered, while in the medium and long-range lidar with detection distance of several kilometers or more, tens of kHz light source could be considered.
A all fiber amplifier system was demonstrated based on large modulus area doped with Yb3+ ions, which used a 975 nm pump. The system used the interaction between the pump and Yb3+ ion active fiber to generate a signal source. Signal source was semiconductor laser amplified single-frequency seed light. The system was optimized, optical devices were reasonably designed and built, and the beam inverse transmission was controled to reduce the nonlinear optical interference. 100 W signal source acted on the system, the master oscillator power amplifier(MOPA) of multistage Yb3+ doped optical amplifier was adopted, the signal output 3.2 kW continuous laser. The average optical-to-optical conversion efficiency was about 78.26%. Output beam quality Mx21.657, My21.735. Output stability was less than 2%. The system continuous signal amplification output beam had a wide range of applications. The ytterbium doped ions all-fiber amplifier is mainly used in laser detection, industry measurement technology research, etc.
2019, 48(4): 406007.
doi: 10.3788/IRLA201948.0406007
Frequency Modulated Continuous Wave (FMCW) laser fuze has better resistance to interference than the pulse laser fuze, but it is still affected by cloud and fog. In order to study the influence of FMCW laser fuze parameters on the cloud and fog echo, the cloud and fog echo of FMCW laser fuze in the case of different transmitting-receiving distances, laser wavelengths and relative positions was simulated by using FMCW laser fuze detection model. The simulation results show that transmitting-receiving distance and laser wavelength of FMCW laser fuze have obvious effect on the cloud and fog echo, the greater of transmitting-receiving distance and the shorter of laser wavelength in the visible light and near-infrared band, the weaker of cloud and fog echo. The simulation results of this paper can be used to optimize the design of FMCW laser fuze for the improvement of anti-interference ability.
2019, 48(4): 406008.
doi: 10.3788/IRLA201948.0406008
Based on the principle of phase laser ranging, the idea of using phase laser range finder for underwater ranging was proposed, and the feasibility of underwater phase laser ranging was analyzed in principle. Through the underwater distance measurement experiments, the feasibility of underwater phase laser ranging was verified, the range calibration algorithm for underwater phase laser range finder was completed, and the effects of water turbidity on the dynamic range and distance measurement accuracy of laser ranging were explored. The experimental results show that the average ranging error of underwater laser range finder after calibration is not more than 3 mm in the range of 3.5 m, and there is an exponential decay relationship between range and water turbidity. The underwater phase laser range finder provides a new method for the detection of underwater distance, which can achieve accurate ranging at short range of underwater target.
2019, 48(4): 406009.
doi: 10.3788/IRLA201948.0406009
When a tail-leading Airy beam and a tail-trailing Airy beam with the same amplitude parallelly propagate in a Kerr medium, the evolution of shedding solitons was numerically investigated based on the split-step Fourier method. Moreover, the effect of high-order effects on rewinding solitons was further studied. It is demonstrated that rewinding solitons with the similar structure of DNA will be generated due to the interaction of a tail-leading Airy beam and a tail-trailing Airy beam. By adjusting the initial input amplitude and space interval, the characteristics of rewinding solitons can be influenced. Furthermore, considering single high-order effect (third-order dispersion, Raman, self-steeping) or multiple high-order effects, a great influence on the evolution of rewinding solitons will generate in the temporal and spectral domain. The results can provide some theoretical basis for manipulating rewinding solitons of a Airy beam, and also have potential application prospects in the generation of supercontinuum spectrum and the broadband light source.
2019, 48(4): 406010.
doi: 10.3788/IRLA201948.0406010
At present, laser interference is basically a one-to-one interference mode. With the large-scale use of photoelectric reconnaissance sensors, laser interference urgently requires many-to-many interference means for cluster targets. Based on solving the problem of effective suppression of interference in clustered photoelectric detection, a multi-source coordinated coherent laser interference method for cluster photoelectric imaging sensors was proposed, and the basic idea of multi-pair and multi-interference realization was using out-of-field speckle coherent synthetic interference. The coherent interference mechanism was used to model and analyze the effect of two-beam coherent laser interference photoelectric sensor. The simulation results show that the laser incident angle is an important influence parameter of laser coherent interference and can be used as the basis for coordinated deployment of interference stations. At the same time, the image quality evaluation results based on PSNR and MSE show that the coherent superimposed interference has obvious advantages compared with single beam interference and non-coherent superimposed interference.
2019, 48(4): 442001.
doi: 10.3788/IRLA201948.0442001
In order to improve the edge quality of the continuous phase plate in magnetorheological polishing and realize the full aperture polishing of the components, the edge extrapolation of the original error profile must be carried out. In view of the shortcoming of the existing edge extrapolation algorithm, a two-dimensional Gerchberg bandlimited extrapolation algorithm was proposed to realize the edge extrapolation technique that was frequency domain matching for continuous phase plate. Firstly, Zoom Fourier transform was applied to the original error profile to get its high and low cutoff frequencies. Then, the modified two-dimensional Gerchberg extrapolation algorithm was used to fill data in extrapolation region around the original region to get the same spectral structure as the original region. At last, an magnetorheological polishing experiment was performed on a 100 mm100 mm continuous phase plate element with complex frequency spectrum structure. The experimental results show that the edge processed by the method is more regular and the edge effect radius is reduced from 5 mm to 2 mm, and the residual error RMS is reduced from 19.3 nm to 9.7 nm. It indicates that the modified Gerchberg edge extrapolation technique can obviously improve the edge quality and the overall convergence precision of continuous phase plate.
2019, 48(4): 442002.
doi: 10.3788/IRLA201948.0442002
With the coming of 2025 in China, it is an irresistible trend to use industrial robots to process agricultural machinery online. In order to grasp workpiece intelligently, industrial robots need to identify the type of workpiece and pose of workpiece. In view of the difficulty in identifying the types of work pieces on the pipeline, an online recognition method based on the 3D point cloud of laser scanning was proposed. This method can identify which workpiece is the moving piece. First, the disordered workpiece on the assembly line was scanned, the 3D laser point cloud data of the workpiece was obtained, and the 3D laser point cloud data was initially denoised. Using MATLAB software to slice the 3D laser point cloud, the main view slicing, top view slicing, left view slicing was obtained. By using the HALCON software, the boundary information of the center slice was extracted, enhanced, segmented, and the characteristic parameters of the extracted area were extracted. Then the type of the workpiece was identified. Experimental results show that the accuracy of recognition is 96.67%. This method can be used for reference to similar problems.
2019, 48(4): 418001.
doi: 10.3788/IRLA201948.0418001
Aiming at the working conditions and working requirements of the fast steering mirrors for space cameras, a lightweight scheme for fast steering mirrors was proposed. Taking the mirror with a diameter of 100 mm as the research object, the lightweight structure based on ribs was designed, and the calculation method of the equivalent thickness of standard circular mirror was proposed. Two supporting methods of the mirror, rear support with three points or rear support with a central point, were designed separately, and the results of the contrastive analysis indicate that mirror supported with a central point can avoid mutual interference between multiple support points, which is caused by inconsistent temperature deformation of the holder and the mirror. The accuracy of the mirror surface is higher, and because of its simple structure, the total mass of the wobble assembly is lighter. In order to achieve the best overall performance of the fast steering mirror structure, a multi-objective optimization of the main structural parameters was executed, the total mass of the wobble assembly and the RMS value of the mirror surface were simultaneously used as the optimization goals. The optimization results showed that the rib height and the adapter thickness contributed the most to the overall performance of the structure. The total mass of the wobble assembly under the optimized scheme is only 95.75 g, and the first-order resonant frequency of the structure is 217 Hz, the RMS of the mirror surface is 7.26 nm under the condition of -8℃ temperature load, which meets the design requirements while achieving a 40.4% reduction in the weight of the mirror.
2019, 48(4): 418002.
doi: 10.3788/IRLA201948.0418002
In order to meet the need of measuring the train groups' three-dimensional coordinates, a 3D laser radar common path zoom optical system was designed. According to the characteristics of laser beam expender, multistage laser amplifiers were carried out by using lens chain. Based on Gauss optics and geometrical optics, the optical structure of the laser emission system based on liquid lens was fully analyzed, and the key parameters of the initial structure of optical system were calculated. Using Zemax optical design software to optimize the simulation, the 3D laser radar transmitting/receiving optical system was designed. The spot diagrams of the transmitting optical system which used a liquid lens to zoom were all less than 20 m/m within the image distance range between 2 m and 30 m, and the spot diagram decreased with the increase of the distance. By minimizing the spot size which was detected by the array detector channel of the receiving system to focus the energy in one point, then the power of liquid lens was the optimal state to make sure the spot diagram in the target was smallest. By optimizing the design, the radius of the 90% energy concentrated area were less than 1.6 m. The optical structure not only improves the system alignment, reducing the external disturbing, but also simplifies the structure of the instrument volume. Using the liquid lens focusing instead of mechanical focusing to avoid the vibration, and the positioning of the laser radar was proved.
2019, 48(4): 418003.
doi: 10.3788/IRLA201948.0418003
Aiming at the problem of small-field, central obscuration and low anergy of reflective optical system, the dual-mode beam positioner optical system of a folded/diffractive co-aperture infrared dual-band positioner was proposed. Based on achromatic theory and MRTD model, the equations of wavelength band achromaticity and action distance were deduced, respectively. With the property of a common focal length in the dual-band optical system, dual-band simultaneous detection and consistency of target information identification were achieved. The parameters of the folded/diffractive co-aperture infrared dual-band positioner optical system were as follows:wavelengths are 3.4-4.8 m and 7.7-9.5 m, pitch/yaw is -26-26. focal length is 115 mm and F number is 2. The results show that thermal difference eliminated in the temperature range of -40-60℃, the optical transfer function is close to the diffraction limit.
2019, 48(4): 418004.
doi: 10.3788/IRLA201948.0418004
In order to ensure the position accuracy and the stiffness of the support system for the 4 m SiC primary mirror, the parameters of hardpoints in a hexapod configuration were analyzed according to the optical indexes of the primary mirror support system. Using the finite element method, the hardpoint positioning mechanism was optimized. The hardpoint distribution radius, positioning angle, axial stiffness and the limit of axial tension and compression were determined by the finite element software. The analysis results show that six hardpoints should be equally distributed at 1 345 mm of the radius on the circumference in the primary mirror backface. When the axial stiffness of the hardpoint reaches 15 000 N/mm, the natural frequency of the primary mirror support system is greater than or equal to 15 Hz. It can meet the design requirements and provide the basis for the following design optimization.
2019, 48(4): 418005.
doi: 10.3788/IRLA201948.0418005
Spectral image information provided by multispectral remote sensing cameras has extremely high application value. In order to break through the limitation of the number of spectral segments of CCD imaging devices and increase the number of spectral segments of a single camera, a two-channel solution was proposed. Starting from the optical system, a high-stability opto-mechanical structure was designed for a dual-channel off-axis multi-spectral remote sensing camera. Firstly, the high stability support of the large-diameter primary mirror was realized by using the four-point spherical support technology, which ensured that the mirror surface shape accuracy met the use requirements under various working conditions. Then, the camera's focal plane component, main frame and vibration isolation system were designed and optimized to ensure that the dual-channel off-axis remote sensing camera had good structural stability while providing eight multi-spectral segments. Finally, the finite element analysis and mechanical environment test of the entire camera show that the camera has high stability and meets the design expectations.
2019, 48(4): 418006.
doi: 10.3788/IRLA201948.0418006
Aiming at the difficulty of searching for physical evidence in complex environments by ordinary unmanned airborne cameras, a method using polarization imaging technology was proposed to conduct physical evidence detection and search. In order to ensure search efficiency and work under low illumination conditions, a large field-of-view and large relative aperture two-speed zoom polarization imaging optical system was designed. The system had a focal length of 11 mm and 22 mm, the F-number of 1.8 and 2.7, an angle of view of 60 and 34, and a reasonable focusing method was given, which can achieve clear imaging at 3 m and 10 m flying height. After simulation analysis, the design results show that the modulation transfers function(MTF) of short focus and long focus is better than 0.45 at 91 lp/mm, and the imaging quality is better. Tolerance analysis shows that tolerances are well designed to meet imaging quality. The system is integrated with the micro-polarizer array detector and equipped with a drone platform, which can perform real-time and efficient physical evidence search on the crime scene in a complex environment, and greatly enhance the ability of cases to crack.
2019, 48(4): 420001.
doi: 10.3788/IRLA201948.0420001
Optical interferometers are key devices in constructing aperture synthesis telescope. Compared with optical interferometers implemented with conventional discrete elements, integrated optical phase-shift interferometers possess ultra-compact structure, and thus can be applied in aperture synthesis telescope to optimize its structure and improve its stability as well. Silica based integrated optical phase-shift interferometer was studied, in aspects of its design, fabrication, as well as its characterization. Results show that the two direction couplers in interferometer chip possess well consistency in terms of their coupling efficiency, thanks to integrated optical waveguide technology itself. Excess loss of interferometer chip was measured to be as low as 1.8 dB, with uniformity of 0.1 dB. Phase shift error was estimated by measuring MZ interferometers, and results exhibit that error of 90 phase shifter is approximately 1.5 . Analysis show that silica based waveguide technology is promising in fabrication of optical phase-shift interferometers utilized in aperture synthesis telescope.
2019, 48(4): 420002.
doi: 10.3788/IRLA201948.0420002
The structural damage caused by micro-electro-mechanical system(MEMS) stress concentration in tunable vertical cavity surface emitting lasers(VCSEL) of GaAs-based and InP-based materials was studied. A bowknot MEMS cantilever structure was designed to reduce the von Mises stress at the fixed end of the cantilever and ensure the reliability of the device while ensuring the maximum displacement was invariable. The COMSOL software was used to optimize and analyze the influence of various parameters of the bowknot cantilever structure on the mechanical properties. The results show that the maximum von Mises stress at the fixed end of the optimized bowknot MEMS cantilever structure is reduced by 64% compared to the equal-section cantilever structure. The free spectral range of a bowknot MEMS wavelength-tunable VCSEL for GaAs-based materials is up to 45 nm.
2019, 48(4): 417001.
doi: 10.3788/IRLA201948.0417001
In order to solve the problem of automatic focus plane detection in aerial remote camera, a new method of automatic focus plane detection for aerial remote camera used Visibility based on SFV technique was proposed. Firstly, in the process of focusing, spatial filtering characteristic of spatial slits was simulated by doing interval sample with linear CCD image, the best focus position was found by searching maxim Visibility value of SFV signal, through used relationship between SFV signal and the Visibility value. Secondly, spatial filtering velocimetry and relationship of Visibility and defocusing error was introduced, and experiment setup was designed. Lastly, for the typical image motion velocity between 5 mm/s to 53.2 mm/s, 20 times focal plane detection tests were taken, and the experiment results show that the focusing accuracy was higher than 46.25m, which was within the tolerant defocus(76.8m) and satisfies requirement of aerial remote camera.
2019, 48(4): 417002.
doi: 10.3788/IRLA201948.0417002
A novel calibration method for multiple FOV star sensors based on three axis turntable was proposed. The method mainly took advantages of the turntable's three rotational freedom degrees to calibrate FOVs of arbitrary directions without reinstalling the sensor. Modeling for laboratory calibration was achieved through optimizing and trimming of the observation model, the structure model and the external parameter model. The observation model parameters of each FOV and the structure model parameters among distinct FOVs were solved by the Levenberg-Marquardt nonlinear least square algorithm. Without the need of outfield star observation in the calibration process of structure model parameters, huge amount of data sampling work load was saved, hence, the estimation error caused by the atmosphere refraction and disturbance phenomena was avoided. The validity of the method was demonstrated by the simulation of a triple FOV digital star sensor and the real experiment of a dual FOV star sensor. Compared to the conventional method that utilizes outfield star observation data, the average angle distance error within single FOV reduces by 20.32%, and the average angle distance error between FOVs reduces by 59.34%.
2019, 48(4): 417003.
doi: 10.3788/IRLA201948.0417003
In the field of land integrated navigation, a laser Doppler velocimeter (LDV) can be used as a speed sensor to compose an integrated navigation system with a strapdown inertial navigation system (SINS). To suppress the influence of the inclination variations caused by vehicle jolts on conventional LDVs, a split-reuse LDV based on Janus configuration was presented. Aiming at the error parameters of this configuration type LDV in the integrated navigation with SINS, the velocity error model of LDV was deduced first, and then a Kalman filtering method assisted by a differential global positioning system (DGPS) to calibrate the error parameters was proposed. A simulation and a vehicle integrated navigation experiment were implemented to verify the effectiveness of the method. The experimental results show that the calibration method proposed in this paper is effective. The LDV based on Janus configuration after being compensated can greatly improve the positioning accuracy of the integrated navigation system.
2019, 48(4): 417004.
doi: 10.3788/IRLA201948.0417004
Pixel non-uniformity is an important index in the evaluation of CCD imaging performance, which reflects the difference of pixel structure itself. The traditional method of calculating DSNU and PRNU based on gray value fails to consider the temporal noise introduced by the readout circuit, and the error caused by different pixel's different exposure time isn't excluded, the calculation results were also only applicable to a specific exposure condition. Based on the analysis of CCD signal flow, the influence factors of gray value non-uniformity were clarified. Referring to the calculation method of DSNU and PRNU, combined with the working mode of frame-transfer CCD, a new method which calculated the dark current non-uniformity DCNU and the photo current non-uniformity PCNU was put forward. The method including setting multiple exposure time, and the multi-frame dark (bright) images was collected under each exposure time, then fitting for the dark current (dark current+photo current). Meanwhile, a CCD pixel non-uniformity test system was established, the stability and uniformity of the light source were verified to exclude the temporal and spatial error introduced by the test system when collecting images. On the basis of the test system, the DCNU 25.51(e-/pixels-1), PCNU 0.98% of CCD were measured using the new method. The result more accurately reflects the non-uniformity of CCD pixel structure, and was more universally applicable, compared to traditional DSNU and PRNU value.
2019, 48(4): 417005.
doi: 10.3788/IRLA201948.0417005
The optical spectrum details could be detected theoretically even as low as MHz lever based on heterodyne interference principle. A scheme design of optical spectrum detecting system based on heterodyne interference technique was introduced,in which the signal transmission principle from the 90optical mixer to the balanced detector was deduced. Moreover, the relationship between the settings of the local oscillator, as well as the filter intermediate frequency and the system resolution was concluded. The compact spectrum detecting system is built upon OptiSystem software, in which the wavelength sweep and iteration could be used to simulate actual local oscillator operating mode, thus the feasibility and superiority of the ultra-high resolution spectrum analysis function were verified. In the end, the simulation results of different linewidth and scanning step length of local oscillator, as well as the filtering parameters was given in 40 MHz frequency interval. The resolution requirement on the local oscillator and filter was concluded.
2019, 48(4): 417006.
doi: 10.3788/IRLA201948.0417006
In recent years, because solar simulator can accurately simulate the sunlight, a growing number of space experiments apply solar simulator to simulate temperature environment on the ground. A large solar simulator with 2 m-diameter effective beam was introduced, and the collimator was made up of 19 unit spherical mirrors. Common alignment methods of spherical mirror were analyzed, and on the basis of spherical center self-collimated method, an alignment method of segmented collimating mirror was given. Alignment process was explained in detail and effective aperture was 2 710 millimeters and radius was 13 280 millimeters. In addition, radiation characteristics test methods and devices of the large solar simulator were also introduced, under atmospheric environment and in vacuum cryogenic environment and in vacuum thermal test, which provided reference for the better use of solar simulator in engineering.
2019, 48(4): 417007.
doi: 10.3788/IRLA201948.0417007
The conventional axis test adopted the position mode that uses a single theodolite to read the pitch absolute value. In this conventional axis test case, the line array and the axis of the detector are parallel to the +Y direction and +Z direction of the global coordinate system. The off-axis camera axis test, different from conventional axis test, did not follow the principle that the detector axis was parallel to the camera cube mirror. It is separated from the global coordinate system, the camera cube mirror coordinates and optical axis array. So a new axis test is proposed. It is need to adjust the optical axis to theory position of the camera coordinate system, and the four-colored line array should be parallel with five-colored line array before the experiment. With the aid of bracket, the camera axis was extract to camera cube mirror a and drilling cube mirror b using theodolite. Respectively, the direction cosine matrix was used to reduce error of camera axis. The accuracy and the multi-dimensional positioning of nine-band linear array were analyzed, and also the experiment image was obtained. The results show that the optical axis matrix meets the requirements and the location extraction method is reasonable and feasible.
2019, 48(4): 422001.
doi: 10.3788/IRLA201948.0422001
In order to realize the coupling and steering of polysiloxane polymer optical waveguides with a cross-sectional dimension of 50 m50 m, a multilayer etched grating coupler with high refractive index cladding was designed. Firstly, the structural factors affecting coupling efficiency of polymer waveguide grating couplers were analyzed. Then, the coupling efficiency of polymer waveguide grating coupler was improved by etching the high refractive index layer on the grating surface. Next, different grating structures were formed by arranging and combining different periods (range:100-4 000 nm) and different etching depths (range:0-50 000 nm), where all cases were traversed to obtain the diffraction field distribution and its coupling efficiency of different grating structure based on finite-difference time-domain (FDTD) method. Beyond that, the optimization of period and etch depth were found to maximize coupling efficiency. Finally, a multilayer etched grating coupler was designed to further improve the coupling efficiency. The coupling efficiency of the uniform grating coupler with high refractive index layer was approximately 17.2% with 5 000 nm etching depth and the 2 600 nm grating period. The coupling efficiency is approximately 37.4% with multilayer etching and optimized structure. It provides a theoretical reference for the practical application of polysiloxane polymer optical waveguide in optical interconnection.
2019, 48(4): 422002.
doi: 10.3788/IRLA201948.0422002
A graded-index multimode fiber (GI-MMF) with reduced core size was designed and fabricated with large effective mode area and low intermodal dispersion for Raman distribution temperature sensor (RDTS) to simultaneously achieve high spatial and temperature resolution. In experiment, the temperature and spatial resolution of the RDTS was measured using different types of fibers under different launch conditions based on a commercially available RDTS system. By using the GI-MMF under the overfilled launch condition, a 1℃ temperature resolution was achieved with a spatial resolution degradation of 0.13 m at the distance of 25 km. The spatial resolution degradation using the standard MMF is 1.58 m in comparison. Moreover, the RDTS using the proposed GI-MMF under the single mode launch condition achieved a temperature resolution of 4.7℃ temperature resolution at the distance of 25 km with a 2.2℃ improvement and no degradation on spatial resolution compared with that using the standard SMF.
2019, 48(4): 422003.
doi: 10.3788/IRLA201948.0422003
Fourier ptychography (FP) is an effective approach capable of imaging with both large field-of-view (FOV) and high resolution, the published works have proven that the resolution is limited by the sum of the illumination numerical aperture (NA) and the NA of the objective lens used. A spatial-and spectral-constrained FP (spFP) reconstruction algorithm was introduced to improve the spatial resolution. Unlike the typical unconstrained algorithm, the proposed algorithm incorporated both spatial-and spectral-constraints based on the additional prior information extracted from the typical FP reconstruction, and it did not need any additional hardware or captured images. The proposed approach was based on an assumption that the image was known to be sparse. Both simulation and experimental results show that the spFP reconstruction improves the spatial resolution by~26%, and also improves the contrast and general quality of the reconstructed image.
2019, 48(4): 426001.
doi: 10.3788/IRLA201948.0426001
The purpose of image blind deconvolution is to estimate the unknown blur kernel from an observed blurred image and recover the original sharp image. Conventional methods used simple models to estimate blur kernel, meaning mistakes were inevitable between estimated blur kernel and the real one. It would cause the final deblurred image unpredictable. A multi-scale convolutional neural network was presented based on the novel residual network. And it restored sharp images in an end-to-end manner without estimating blur kernel. Domain constraint layer was designed to the WGAN, it could restrict parameters initial values and accelerate convergence. A total loss function was designed including perception loss which was based on the multi-scale network and adversarial loss which was based on conditional GAN. Extensive experiments show the superiority of the proposed method over other representative methods in terms of quality and quantity. The method is 4 times faster than the similar methods.
2019, 48(4): 426002.
doi: 10.3788/IRLA201948.0426002
The multifractal characteristics of thyroid dynamic infrared images of healthy subjects were studied in this paper, and the statistical analysis and differential test of thyroid multifractal characteristics of different individuals were performed. Firstly, in the constant temperature and humidity experiment environment, multiple frames of human thyroid infrared images were acquired and meshed to form a temperature-time series. Then, the original signal length, wavelet transformed scale factor and statistical moment order of the multi-fractal analysis of human thyroid were discussed. After determining the above parameters, the multi-scale wavelet transform of the temperature-time series was performed to solve the Wavelet Transform Modulus Maximal, and then the distribution characteristics of multi-fractal characteristics of the left and right thyroid lobe of different healthy subjects were solved. The results show that the singularity index c1 of the thyroid multi-fractal characteristic line dimension of healthy subjects concentrates in the range of 1.1-1.3, and the gap coefficient c2 concentrates in the range of 0.002-0.005. The test level of individual differences is =0.01; the half-width of the multi-fractal line concentrates in the range of 0.164-0.166 and the test level of no individual difference is 0.05.
2019, 48(4): 426003.
doi: 10.3788/IRLA201948.0426003
For the finger-vein is under the skin, there are many inherent disadvantages for its imaging, such as biological tissues in the finger, anatomical structure, and the imaging character of skin. A novel method was proposed to solve the problem of vascular network coloboma in finger-vein IR images. Firstly, the finger-vein images were enhanced by multi-scale Gabor filter to reduce the overall image blurring. Then, the vascular skeleton network was extracted based on binarized images so as to locate the coloboma position accurately. Thirdly, the end point and the bifurcation point were extracted from the vascular skeleton network as the original point of restoration. The coloboma of the vascular skeleton network was reconstructed according to minimal path principle. Finally, the diameter of vascular network was recovered by using the Gabor directional image as a constraint. The experimental results show that this method can be used to restore local lost of vascular network and a more complete and more stable vascular network. The recognition accuracy of finger-vein images can be further improved by using the reconstructed image.
