2017 Vol. 46, No. 12
column
- Invited paper
- Laser technology
- Laser technology and application
- Infrared technology and application
- Atmospheric optics
- Optical communication and optical sensing
- Photoelectric measurement
- Advanced optical materials
- Optical design and simulation
- Photoelectric device and microsystem
- Information acquisition and identification
- Scene information and processing
2017, 46(12): 1202001.
doi: 10.3788/IRLA201746.1202001
As the first spac-borne polarization lidar to observe the state of the global atmosphere, CALIOP has provided large number of first-hand data on global climate and environmental changes since being launched in 2006. It has been proved to be a promising tool in the field of atmosphere remote sensing. In this paper, the functional structure, data products, and data processing of CALIOP were introduced. Moreover, the principles and processes of layer detection, scene classification and extinction retrieval were also especially emphasized.
2017, 46(12): 1205001.
doi: 10.3788/IRLA201746.1205001
Planar laser induced fluorescence (PLIF) is a significant method to study the characteristics of flow field and combustion, owing to the advantages of non-conduction, high spatial and temporal resolutions. In comparison with existing low-speed PLIF, high-speed PLIF has a lot of advantages. High-speed PLIF with repetition rate higher than 10 kHz is necessary to study turbulent and reacting flows in order to capture the dynamics that governs the underlying physics in the fields such as supersonic and hypersonic flows, combustion and plasma physics. The lack of laser sources with high repetition rate and high pulse energy significantly limits the development of high-speed PLIF. A comprehensive overview for the development and the latest achievements of high-speed PLIF and the employed laser sources was given in this article. The characteristics of different laser sources were compared, and the pulse-burst technique was believed to be a promising source for high-speed PLIF technique. The development of pulse-burst laser used as the laser source in high-speed PLIF was predicted.
2017, 46(12): 1205002.
doi: 10.3788/IRLA201746.1205002
In order to measure the absolute spectral responsivity of long-wave infrared detectors with high accuracy, improve the long-wave infrared laser power stability and beam quality, a set of long-wave infrared laser source was developed. In this laser source, a feedback-control system, based on the electro-optics effect of CdTe crystal, was designed to improve the stability of long-wave infrared laser power and a long-wave infrared spatial filter, based on the propagation properties of laser beam, was designed to improve the long-wave infrared laser beam quality. The parameters of the spatial filter were also analyzed in this paper. Experimental result shows the laser power stability is elevated to above 0.1% and laser beam quality is improved obviously. The reliable laser source is provided to measure absolute spectral responsivity of long-wave infrared detectors with high-accuracy.
2017, 46(12): 1205003.
doi: 10.3788/IRLA201746.1205003
Thermal homogeneity and low wav-front distortion are the main problems affecting the beam quality of high power Nd:YAG thin disk laser which should be solved through packaging technique. The thermal stress of thin disk produced in the process of welding was analysed and the thermal distribution was stimulated. 80 mm YAG thin disk laser gain medium and micro channel cooler(MCC) were connected by optimized packaging technology. The disk laser was tested by scanning acoustic microscope (SAM) and laser interferometer. The results show that solder layer is homogeneous and void-free, peak-to-valley(PV) departure of optical surface is less than 1 m and root-mean-square(RMS) is less than 0.15 m in the circle diameter of 60 mm. On the basis of this packaging technique, high beam quality 2.3 kW output power was extracted with one disk laser.
2017, 46(12): 1205004.
doi: 10.3788/IRLA201746.1205004
Tapered semiconductor lasers are characterized by high brightness and high beam quality. With the help of the numerical simulation software Lastip, the structure of 976 nm tapered semiconductor laser was optimized. In the condition of low confinement factor Г, the InGaAs/AlGaAs quantum wells thickness and the asymmetric waveguide thickness ratio were determined. The inject power of master oscillator(MO) and the diffraction distribution characteristics of the fundamental lateral mode coupled tapered section were analyzed. The results show that, when the operating current is 3 A and the optical confinement factors are 2%, the simulation shows the fundamental lateral mode of the optimized design has more concentrated distribution compared with the conventional 2.67 W of the single quantum well(SQW) structure. The injected optical power was increased from 2.76 W to 3.67 W. And, the diffraction distribution of the fundamental lateral mode coupled into the tapered section was more uniform, the conversion efficiency of MO of optimized structure was more stable.
2017, 46(12): 1206001.
doi: 10.3788/IRLA201746.1206001
In order to meet output parameters, especially the stability of the laser energy requirements for the 308 nm skin therapeutic apparatus, first of all, the laser energy attenuation model and proportional integral (PI) algorithm based on energy compensation by the excitation voltage were established, its theoretical analysis and simulation were compeleted. Secondly, the experimental research on excimer laser was carried out which included high voltage excitation power supply and laser energy detection module based on fast nondestructive photoelectric diode. Meanwhile, the experimental research on the relationship between excitation voltage and output power, characteristics of laser energy attenuation and laser energy stability properties with the introduction of PI algorithm was studied. The results show that the power supply and energy detection module meet the PI algorithm control precision and response speed. Meanwhile, the excimer laser output energy can still maintain a target energy within 17.5 mJ and energy variance is slowly rising from 0.2% to 3% in the 10 million pulses after introducing the PI algorithm, which well meets the usage requirements of excimer laser skin therapeutic apparatus.
2017, 46(12): 1206002.
doi: 10.3788/IRLA201746.1206002
Monitoring on the melt pool light intensity is one important method to process monitoring in selective laser melting(SLM). A melt pool light intensity monitoring system, consisting of hardware and software system, was established for the SLM forming process. By near infrared filter technology and photodiode detection circuit, the data of melt pool light intensity in the forming process were obtained. As the change of the melt pool light intensity in the different forming positions of laser act can't be visualized by the time domain signal, the mapping algorithm was proposed to model the data of the melt pool. Data analysis and modeling of the melt pool light intensity under the variable power were conducted, when the laser power was 120 W and the melt pool temperature was 1 404℃, the mean value of the diode signal was 0.31 V, the standard deviation was 0.04 V, the melt pool was stable; when the power increased to 220 W and the melt pool temperature was 1 727℃, the diode signal mean increased to 0.81 V, the standard deviation increased by 0.22 V, the stability of the melt pool deteriorated. The results show that the influence of different process parameters on the thermal radiation behavior of melt pool can be obtained through the melt pool light intensity monitoring system, which can be used to support the development and optimization of SLM forming process.
2017, 46(12): 1206004.
doi: 10.3788/IRLA201746.1206004
The frequency modulation continuous wave (FMCW) laser detecting technology has the advantages of high detecting precision and strong anti-interference ability by combining the ranging principle of FMCW and the advantages of laser. In order to verify the detecting principle and detecting performance of FMCW laser, the detecting system of FMCW laser fuze was designed, which included laser emission subsystem, laser receiving subsystem, and laser echo signal processing subsystem. The FMCW laser fuze detecting system can transmit and receive FMCW laser, process echo signal of FMCW laser, and output the information of detecting distance at last. The ranging performance of detecting system was tested. The experimental results show that the maximum detecting range of FMCW laser fuze detecting system is 12 m, and the ranging error is within 0.3 m. The FMCW laser fuze detecting system has the advantage of high detecting precision and can be used in FMCW laser fuze.
2017, 46(12): 1206005.
doi: 10.3788/IRLA201746.1206005
A new method, the particle swarm optimization algorithm for designing the laser beam shaping system was put forward. According to the law of conservation of energy, the transformation relation of the coordinates of two intersection points between an arbitrary ray and the input and output plane can be deduced, and the coordinates of an intersection point between a ray and the output plane achieved based on this relation will be used as the target coordinates. Absolute values of differences between the target coordinates and the corresponding coordinates obtained from the ray tracing will be used as the evaluation function of transformation of energy distribution, the absolute value of the y-component of the direction vector of outgoing ray will be used as the evaluation function of the collimation, and the sum of the evaluation function of energy distribution transformation and the evaluation function of collimation was the total evaluation function of a beam shaping system. Taking this function as the fitness function of the particle swarm optimization algorithm and manipulating it to the minimum value, an aspheric lens can be gotten, which can not only convert an Gaussian intensity distribution into a uniform distribution but also approximately r-collimate the output beam. A single aspheric concav-flat lens was designed by using this method, it can transform red laser beams with a spot radius of 30 mm and a Gaussian intensity profile into flat-topped beams with a spot radius of 36 mm, and output beams can be r-collimated.
2017, 46(12): 1206006.
doi: 10.3788/IRLA201746.1206006
Three CdTe quantum dots and CdTe/CdS quantum dots with different sizes were synthesized by hydrothermal method. The nonlinear absorption properties of CdTe quantum dots with three different sizes were investigated by the Top-hat Z-scan technique under ns, ps and fs laser pulses. The experimental results show that the nonlinear absorption properties of CdTe quantum dots with three different sizes are saturated absorption under different laser pulses, and all of them show the increasing tendency of nonlinear absorption characteristics with the decrease of quantum dots size. In order to further study the effect of quantum dots size on the nonlinear absorption properties, the nonlinear absorption properties of CdTe/CdS quantum dots were investigated under fs laser pulse. With the increase of cladding time, the thickness of shell increases, the size of quantum dots increases, and the nonlinear absorption properties decrease. And the nonlinear absorption properties of CdTe/CdS quantum dots were better than those of CdTe quantum dots. The nonlinear absorption properties and the quantum size effect mechanism of CdTe quantum dots and CdTe/CdS quantum dots were discussed, the experimental results show that the synthetic quantum dots have good quantum size effect.
2017, 46(12): 1206003.
doi: 10.3788/IRLA201746.1206003
In the process of multi-beams pulse laser synthesis, the synchronization time delay control precision and the pulse width control precision have important influence on the final distribution of the superposition beam energy. Based on the beam superposition theory, four beam pulsed laser light energy superposition model was established. Four beam shaping pulse as the incident light source, respectively, the superposition pulse energy distribution was calculated by the synchronization time delay control precision and the pulse width control precision. The results show that, with the decrease of the synchronization control precision and the pulse width control precision, pulse width of the superimposed pulse increase and the peak intensity reduce. The multi-beam beams will have greater influence on synthesis beam than single beam. In four laser synthesis system, when other pulse parameters remain unchanged and if the laser pulse peak intensity change rate is less than 5%, the single beam laser pulse time delay and pulse width change rate are kept within 3.2% and 10.9%. Therefore, the effect of pulse time delay on the synthesis intensity is even greater.
2017, 46(12): 1204001.
doi: 10.3788/IRLA201746.1204001
It is of great importance to study the infrared radiation characteristics of flow over hypersonic interceptors for the design of infrared seeker. The flow field over a hypersonic interceptor was simulated numerically by solving Navier-Stokes equations with chemical non-equilibrium terms. Based on the flow field, the infrared radiation from the flow over the optical window on the side of interceptor in 0.8-20 m range was computed using a spectral band model, and the change rules of the flow radiation versus flight parameters were researched. The research shows that the spectral radiation of the flow mainly comes from the vibration-rotation bands of CO2 and NO molecules, the change rules of spectral radiation versus flight altitude are dominated by the number densities distribution of molecules species in the flow with a constant flight Mach number, and the change rules of spectral radiation versus flight Mach number are controlled by flow temperature with a constant flight altitude, and the spectral radiation of NO molecule in the flow strengthens with increasing flight Mach number.
2017, 46(12): 1204002.
doi: 10.3788/IRLA201746.1204002
Sensing in scattering environments, such as fog, poses a serious challenge for infrared systems. Circular polarization is of increasing interest due to its potentially superior persistence in fog. Circular polarization imaging is one of the ways to avoid fog attenuation in infrared waves. Fog attenuation in infrared waves involves complicating interactions of scattering and absorption. The mechanism of circular polarization's increased persistence was theoretically expounded; it was proposed that circular polarization depolarized slowly due to the randomization of the photon's direction and the randomization of the helicity. Then, circularly polarized light was less affected by scattering. Optimal detection bands of target detection in fog were selected based on the mechanism of circular polarization's increased persistence and the atmospheric radiation spectrum. Optimal bands were selected which were 0.78-1.1 m, 1.48-1.56 m, 1.63-1.86 m, 2.03-2.18 m, 2.39-2.5 m in the SWIR and 3.6-4.15 m in the MWIR. However, the circular polarization imaging technique wasn't conducive to improve the fogging performance in the LWIR due to the optical absorption ratio increased. Finally, the characteristics and the development direction of circularly polarized imaging in complex atmosphere were summarized.
2017, 46(12): 1204003.
doi: 10.3788/IRLA201746.1204003
The In1-xAlxSb epitaxial layers of p+-p+-n-n+ barrier structure were grown on the InSb(100) substrate by molecular beam epitaxy. The crystal quality and Al composition of the material were measured and characterized by X-ray diffraction. The full width at half maximum of the InAlSb epitaxial layer was 0.05, indicating good performance monocrystalline epitaxial material. The Al content of 2.5% was calculated according to Bragg's formula and Vegard's law. When the InAlSb material was fabricated as an infrared detector diode and the spectral response curve was measured at 77 K to 210 K, it was found that the cutoff wavelength of the detector increased from 4.48 m at 77 K to 4.95 m at 210 K. By fitting the Varshni relation of In0.975Al0.025Sb with the experimental data of bandgap, the values of Eg(0), and are 0.238 6 eV, 2.8710-4 eV/K and 166.9 K, respectively. After the I-V test, the dark current density reached as low as 1.0910-5 A/cm-2 and the resistance area product is 1.40104 cm2 at 110 K, -0.1 V bias, which is equivalent to the performance of InSb detector at 77 K. Besides, the influence of the temperature on different types of dark current was analyzed, and the transition temperature between the diffusion current and G-R current was 120 K.
2017, 46(12): 1204004.
doi: 10.3788/IRLA201746.1204004
The infrared earth sensor is a pose measuring component located on man-made earth satellite for measuring the attitude deviation between the satellite body and the earth. And the collimating infrared earth simulator is the main demarcating device for testing high orbit satellite infrared earth sensor on the ground. In order to solve the practical problem, it is needed to simulate a variety of earth angles during the earth sensor ground performance test. A multi-track infrared earth simulation technology was studied deeply by using a collimating optical system to simulate the target. A general scheme of simulating variable earth angles was proposed, the optical and mechanical structure design methods of key parts on the simulator such as the germanium lens optical system and the variable earth aperture were illustrated in detail. Aiming at the requirement of detection of earth angles, a method of detecting earth angles was also proposed. A detection device was set up, and the simulated earth angles under different tracks were measured actually. The test results show that the simulation accuracy of each earth angle corresponding to orbit altitude 18 000, 35 786, 42 000 km is better than 0.05, which can be fully in line with the calibration requirements of the earth sensor.
2017, 46(12): 1211001.
doi: 10.3788/IRLA201746.1211001
The effects of reflective index and particle size parameters on optical properties of atmosphere aerosol particles were studied by using Mie scattring method at the wavelength of 0.65 m over small scales. The influence of the imaginary part of refractive index on the aerosol particle scattering phase function was analyzed. The results show that, in the small scale, the light scattering properties are sensitive to the refractive index and size parameter. The influence of the real part of refractive index and size parameter on non-scattering angle optical parameters is a degree of symmetry. It was also found that in the special position of the scattering angle, no matter the single particle or polydisperse particles, the scattering phase function are independent of the imaginary part of refractive index, scattering phase functions of different imaginary part of refractive index have an intersection point in the forward direction, the intersection point takes Gaussian distribution with the increase of particle size parameter. With the increase of particle size parameter, the intersection point would move to the small forward direction, and gradually become discrete. This work is of reference value in studying the scattering properties of aerosols and their climatic effects.
2017, 46(12): 1211002.
doi: 10.3788/IRLA201746.1211002
For the study of spatial and temporal distribution of marine atmospheric aerosol number density and particle size distribution characteristics, the atmospheric aerosol particles size distribution, atmospheric temperature, humidity, pressure, wind speed etc were surveyed, from August 2014 to March 2016, by using an optical particle counter and automatic meteorological station in Maoming seaside, the East China Sea and the South China Sea, Sanya coastal waters and the Pacific and the Indian Ocean waters respectively. The aerosol spectral distribution in different areas under different meteorological conditions were statistically analyzed and fitted. The results show that the marine atmospheric aerosol particle size distribution is composed of a fine mode and a middle mode, but offshore sea particle number density is greater than that of open sea. The open sea particle size distribution keep steady, the sea surface wind is the main reason of the change of the aerosol number density. In the East China Sea and the South China Sea, the particle size distribution was divided into two sections, the exponential distribution of Junge spectrum was used to describe the section less than 0.5 micrometer, the logarithmic normal distribution was used to describe 0.5 to 4 micrometer section. The extinction coefficient of marine atmospheric aerosol increased obviously under the strong winds, and the extinction characteristics from 1 to 3 micrometer were not affected by wavelength.
2017, 46(12): 1211003.
doi: 10.3788/IRLA201746.1211003
Atmosphere turbulence wavefront distortion phase screen (PS) according with Kolmogorov statistical law was implemented in simulation using power spectrum inversion method with subharmonics, then the statistical properties of generated PS were mainly analyzed in rotation, laying the theoretical foundation for the subsequent PS rotating application experiments. Statistical properties of sub-PSs were verified by comparing the numerical simulation results of phase structure function and atmospheric coherent length with that of theoretical values, the differences between simulated results and theoretical ones were also analyzed. The experiment result shows that the random PS obtained by power spectrum inversion method is correct, when PS is used in rotating situation, the phase structure functions of sub-PSs accord with theoretical results in principle though there is still large deviation in low-frequency component, while the simulated atmospheric coherent lengths are bigger than the theoretical values.
2017, 46(12): 1222001.
doi: 10.3788/IRLA201746.1222001
The relationship of the visible light distribution and the positioning function of the indoor ID positioning system was studied. An asynchronous positioning system based on visible light communication was constructed. Through simulation and experiment, the positioning range and bit error rate of the system were measured. The result shows that, the light distribution of the actual model can be approached by the Matlab software. After that, a 50 cm50 cm50 cm prototyping was built. Inside the optical boundary, the communication and positioning function can be achieved. And around the optical boundary, the bit error rate of the system rose. When the SNR was 25 dB, an 8 cm signal blind zone was shown around the optical boundary. The zone can be reduced by improving the SNR of the positioning system.
2017, 46(12): 1222002.
doi: 10.3788/IRLA201746.1222002
A kind of ultraviolet pulse laser energy detection system based on PIN photodiode was introduced. Firstly, the light outside main optical path was used to realize nondestructive and real-time pulse energy detecting. Secondly, high-speed and high-precision integral circuit was designed to process photocurrent signal for voltage peak. Finally, the synchronous trigger signal of laser system was used for timing sequence design. Thus, the accurate voltage difference was obtained and the exact laser pulse energy can be calculated. Tested on 248 nmKrF and 308 nmXeCl excimer laser, the real-time nondestructive measuring was realized while the laser ran in a pulse repetition mode up to 200 Hz. The relevance and repeatability of the measuring data were in accordance with the results of the external energy meter of output end and the system meets the application requirements.
2017, 46(12): 1222003.
doi: 10.3788/IRLA201746.1222003
The coaxial two-mirror reflective structure has the disadvantage of small receiving field of view and low emission efficiency when being used as optical antenna in space laser communication. At the same time, the energy loss caused by central obscuration will greatly reduce the aiming and capturing probability of communication system. For this inherent defects, an off-axis two-mirror reflective structure with freeform surface was designed to improve the performance of space laser communication. The initial structure of the off-axis two-mirror reflective structure was deduced according to the basic aberration theory. Zernike polynomial freeform surface was introduced to improve the ability of designing freedom and balancing the freeform surfaces aberration. A design example was given whose coaxial and off-axis two-mirror reflective system had same pupil aperture and focal length, and the modulation transfer function, spot diagram, diffraction encircled energy and wavefront error were compared. The results show that the image quality of the off-axis two-mirror reflective antenna with freeform surface is better than that of the coaxial, thus, the structure of the off-axis two-mirror reflective antenna structure could improve entire performance of space laser communication system.
2017, 46(12): 1222004.
doi: 10.3788/IRLA201746.1222004
Carrierless amplitude and phase (CAP) modulation is a way of digital quadrature amplitude modulation (QAM). As the CAP modulation has the advantages of high spectrum efficiency, low cost, less complexity, etc, it gradually become an alternative option for the implementation of short distance high speed optical communication system. Firstly, the properties of these two kinds of modulation mode were analyzed by comparing the power spectrum of CAP modulation and QAM, then under the conditions of atmospheric channel simulation model(Gamma-Gamma distribution of light intensity fluctuation model), the influences of rolling pressure coefficient of filter, the length of filter and sampling clock precision on the performance of the CAP modulation wireless optical communication system were analyzed based on the Matlab simulation and the optimal parameter values were given. The simulation result shows that the sampling clock offset will cause the phase shift of the received signal, so it is needed to compensate the phase distortion in the receiving end. In addition, the research on the equalization algorithm needed by later was also carried out and it is hoped that it can provide some help for the design of CAP system in the future. Finally the simulation results had been verified by experiment.
2017, 46(12): 1222005.
doi: 10.3788/IRLA201746.1222005
Acoustic emission(AE) technology is an important method for structural damage detection, and AE source location is the most important part of the damage detection. The TDOA location method has the advantages of fast, high efficient and more accurate. An acoustic emission location system based on diamond Fiber Bragg Grating(FBG) sensor array was designed. Wavelet transform and traditional threshold method were used to extract feature signal, and the cross-correlation method was used to obtain the arrival time difference between different sensors. Then, the possible AE source was determined by solving nonlinear equations of the geometric model. Finally, the actual AE source was determined according to the feature of time difference. This location system can effectively avoid the pseudo AE source. The 10 groups of test data were carried out in the monitoring area with the diagonal of 48 cm48 cm of the aluminum alloy plate, and the average error was 1.29 cm.
2017, 46(12): 1222006.
doi: 10.3788/IRLA201746.1222006
In order to study the characteristics of UV communication system under the environment of haze, the physical and spectral distribution characteristics of haze particles were studied, the scattering characteristics of haze particles were analyzed in blind ultraviolet by using the theory of scattering. And by using the classical Luettgen single scattering model, the path loss characteristics of non-lin-of-sight (NLOS) solar blind UV transmission were studied in the haze environment. By analyzing simulation results of the relationship between path loss and communication distance, visibility and system angle, the theoretical characteristics of haze attenuation in NLOS UV transmission system were obtained:When the communication distance is short, the path loss of the system will be greatly affected by the weather condition (visibility). When the visibility is good, the influence of communication distance on the path loss will be prominent. In practice, it should be as far as possible to select the visibility of more than 2 km weather conditions. The work of this paper provides a theoretical reference for the design of the UV-light communication system and the optimization of the system performance in the haze environment. In addition, it also has certain guiding significance for the system engineering realization.
2017, 46(12): 1222007.
doi: 10.3788/IRLA201746.1222007
Bias current exerts influence on the LED performance parameters including the internal temperature, junction resistance, and the carrier concentration, which has an effect on frequency response. In this paper, the influence mechanism of bias current on frequency response was analyzed, and the influence trend of DC bias on modulation bandwidth was researched and tested. The results demonstrate that the bias current is basically linearly proportional to the modulation bandwidth while LED's (red, green or blue) working power is less than the rated power. When the working power is close to or exceeds the rated power, the modulation bandwidth will change slowly and eventually stabilizes. With respect to phosphor LED, the bias current has almost no effect on it. This study may provide reference for the selection of bias current and the design of equalization circuit in visible light communication system.
In order to meet the growing requirements of some national projects, such as the aerospace, monitoring of fuel liquid level, as a key parameter of the flight evaluation, directly affects the efficiency of all kinds of crafts. A liquid level sensor system, which can achieve both single-point discrete and multi-point continuous measurement, was designed based on the bending loss of the plastic optical fiber and the total internal reflection principle. After description of the theory, the actual equipment was used to test the theoretical analysis, illustrate the operating principle, systematical composition and the advantages of the technology were inustrated, simultaneously the feasibility of liquid level measuring experiments in theory was analyzed. Furthermore, both discrete and continuous liquid level sensing systems were finished. The verifying experimental system was also set up. The experimental results show the proposed liquid level sensor system not only can realize the measurement of the liquid level, but also has good consistency and simple implementation. The continuous liquid level sensing system can reach the test range of 450 mm with a sensitivity of 0.808 3 W/mm, showing a significant reference for the engineering application.
2017, 46(12): 1217002.
doi: 10.3788/IRLA201746.1217002
According to the demands of mod-locked laser weak echo signal detection, a method which combined high-speed correlation sampling and parallel accumulation based on Field-Programmable Gate Array (FPGA) was proposed. This method overcame the shortcomings of the traditional sampling integral algorithm and can work real-timely without reference signal. Besides, a mod-locked laser weak echo signal detection system based on this method was designed and implemented. This system mainly consisted of a 12 bit@900 MSPS Analog-to-Digital Converter(ADC) chip, ADS5409, which sampled the echo signal and a FPGA chip, Kintex-7, which was in charge of controlling and on-line calculation. To the signal with the repetition frequency of 8 MHz and the average power of 0.04 nW, by accumulation of 16 000 pulses, this system can realize efficient detection and the calculation latency is shorter than 100 ns. In 900 experiments, the correct rate of the detection system reaches as high as 100% without false alarm.
2017, 46(12): 1217003.
doi: 10.3788/IRLA201746.1217003
The slope and curvature hybrid wavefront sensing technique can realize the precision measurement of high-order aberration by using all the first and second derivative information of the wavefront in the subaperture. And it is an important development direction of zonal wavefront sensing technology. Based on the slope and curvature hybrid wavefront sensor used subaperture amplitude modulation, a slope and curvature signal extraction algorithm was proposed. The centroid detection algorithm was utilized to realize the direct measurement of wavefront slope, Laplacian curvature and twist curvature in each subaperture. The simulation results show that the detection accuracy of the slope and curvature signals are all within 0.02(=632.8 nm) under the ideal condition. In the case where the noise level is less than 10%, the detection accuracy of the slope and curvature signals are all within 0.08. The algorithm has high detection precision and good noise immunity.
2017, 46(12): 1217004.
doi: 10.3788/IRLA201746.1217004
The angle of the image rotation was studied which was caused by the movements of two frames of polar coordinates direct stable platform and indirect stable platform with four reflected mirrors. The result shows that both the movements of pitching-frame and rolling-frame cause the image rotation. The angle of image rotation of indirect stable platform which was caused by rolling-frames increased when the abaxial angle increased. When the abaxial angle was small, the angle of image rotation of indirect stable platform which was caused by rolling-frames was also small. The angle of image rotation of direct platform was direct ratio with the tangent of the angle of rolling-frame and was inverse ratio with the cosine of the angle of pitching-frame. The result of simulation shows that the angle of image rotation of indirect stable platform with four reflected mirrors was smaller than the direct stable platform and has lower influence on imaging.
2017, 46(12): 1217005.
doi: 10.3788/IRLA201746.1217005
A response function model for the XCounter Flite X1 photon counting detector was built. Using X-ray fluorescence as ray-source, the incident spectrum and the deposited spectrum were simulated by Monte Carlo method. Gaussian model and phenomenological model were used in the response function, while the parameters were determined by the least square method correspondingly. The inconsistency correction of the detector consisted of the threshold correction and the function correction. So that the error between the simulation result and experiment data was less than 2.5% in each energy bin. The spectral restoration and material decomposition result with the response function get much closer to the ground-truth, which shows the effectiveness and accuracy of the proposed method.
2017, 46(12): 1217006.
doi: 10.3788/IRLA201746.1217006
In allusion to the situation in which optic-electric tracking system tracking targets with intermittent observations, cooperative tracking with radar was proposed to ensure the constant of measurements. Firstly, the intermittent measurement model of optic-electric tracking system and the cross cueing model in cooperation between optic-electric tracking system and radar were established, multi-sensor sequence fusion algorithm based on particle filter was proposed. Secondly, Renyi information gain at each time was acquired by particle filter to be cross cueing criterions which determine the triggering time and ensure the autonomous cooperation. Simulation results show that this method can achieve a desired and stable tracking performance through selecting a suitable cross cueing threshold, under the condition of minimum radar radiation time.
2017, 46(12): 1217007.
doi: 10.3788/IRLA201746.1217007
The core component of the polarization measurement of the channel-type remote sensor is usually the similar, that is, the polarization detection is carried out by using the analyzer in different polarization direction. The relative angular error of different polarizers is an important element affecting the measurement accuracy of polarization. Firstly, the influence of relative angle error among the angle of polarizer on the accuracy of polarization measurement was analyzed. Secondly, the error sources in the measurement process were simulated and analyzed. According to the simulation results, the specific experimental parameters and methods were designed to verify the simulation results. Finally, the comparison of experiment results, which validated the measurement reliability, show that the maximum average deviation between the measured polarization degree of the system and the reference value of the reference source with variable polarization degree (VPOLS-Ⅱ) is 0.735 3%, and the maximum average deviation from the CE318 measurement is 0.036. The experimental results satisfy the real polarization measurement accuracy requirement, which indicates the method of polarization analysis direction measurement is reasonable and provides a powerful support for the high precision calibration of the polarization sensor.
2017, 46(12): 1217008.
doi: 10.3788/IRLA201746.1217008
To achieve the high precision measurement of the complicated deep-hole profile geometric parameters, the detection system for the profile based on the structured light was established. However the images collected by the camera had larger geometric distortion compared with the plane images from the profile because of the curvy surface features of the deep-hole profile. The geometric distortion affected the calculation accuracy of the geometric parameters directly. Firstly, the models were established indiscriminately for the deep-hole profile and its plane structure to analyze the space coordinate transformation between each other. Then, the ideas of the cubic spline interpolation and discrete mapping were referred to propose the deep-hole profile correction algorithm based on the discrete mapping considering the precision and speed of the distortion correction comprehensively. The purpose of correcting the deep-hole profile distortion online was achieved through the algorithm. The test precision reached the sub pixel level and the error was less than 0.1 mm.
2017, 46(12): 1217009.
doi: 10.3788/IRLA201746.1217009
In order to detect the thickness of ink coated on the glass, a nondestructive and on-line measurement system was proposed, which can be used in industrial measurement. Firstly, the structure light principle was presented, and a model based on the adaptive extraction algorithm, called digital quantitative calculation model for the thickness of glass printing ink was creatively put forward to process the bright-line images of printing ink. It was extremely suitable for non-contact digital detection. Secondly, a standard glass with printing ink film was chosen as the accurate evaluation basis, managed to obtain a ratio which was related to the thickness of printing ink from multiple measurements and fitting. Finally, the maximum detection thickness was 23 mm and the precision of the nondestructive and on-line measurement system can reach 4 m. As a result, by measuring the thickness of glass printing ink, this instrument can complete a high-precision, fast and nondestructive detection, which offers a broad application prospect.
Carbon nanotubes film has attracted significant attention and has the potential application in photo-electrical devices because of its outstanding electrical, optical and mechanical properties in the wide frequency range from microwave to visible light. The active and passive terahertz devices are progressing at a rapid rate. The highly quality carbon nanotubes film offers an alternative to generation, detection, and polarization of terahertz wave. The vertically aligned multi-walled carbon nanotubes film was grown by low pressure chemical vapor deposition. The drawing method was employed to fabricate the super-aligned carbon nanotubes film. The transmission and polarization properties of the carbon nanotubes film (three kinds of film:one is carbon nanotubes film with gratings on Si substrate; another is carbon nanotubes film without gratings on Si substrate, and last is a freestanding carbon nanotubes film) had been investigated by terahertz time-domain spectroscopy. The results show that the anisotropic properties of the complex refraction index and permittivity of carbon nanotubes film were observed. The transmittance in the case of the terahertz polarization perpendicular to the axis of carbon nanotubes is more than that of the terahertz polarization parallel to the axis of carbon nanotubes. The degree of polarization and extinction ratio of film increases with increasing film thickness. The degree of polarization is up to 99% and keeps constant for 9 m-thick multi-walled carbon nanotubes film. This research provides basic knowledge useful for emerging applications of multi-walled carbon nanotubes in optoelectronics and plasmonics in the technologically important terahertz frequency range.
2017, 46(12): 1221002.
doi: 10.3788/IRLA201746.1221002
A nonamer metamaterial composed of nine split ring resonators with different orientations was experimentally and numerically researched in terahertz band. The nine split rings were arranged spirally. From the first split ring, the subsequent split rings were rotated anti-clockwise by 40. Generally, the split ring resonator was polarization-dependent. It was found that split rings oligomer, which can produce multiple resonance modes, was polarization-independent owing to the near-field energy coupling. The split rings oligomer composed of polarization-dependent resonators exhibited a polarization-independent effect, which enriched the design idea of traditionally uncoupled metamaterial composed of disperse resonators, and induced a new path for terahertz functional devices, like optical switch, modulator, filter and so on.
2017, 46(12): 1218001.
doi: 10.3788/IRLA201746.1218001
In order to satisfy the demand for the space diffraction telescope in space exploration, a new deployable space diffractive telescope was designed, which aimed at one diffraction optical system. Firstly, the structural form and geometrical sizes of the spontaneous deployable structure used in this article were preliminarily designated through the Serrurier truss theory and the optimization design theory, and a new spontaneous deployable structure was designed aiming at one diffractive optical system. Secondly, the finite element model of the deployable structure was built, and its deployment characters were analyzed. Finally, the prototype of the spontaneous deployable structure was built up and the experiment was carried out to study its characteristics. Experimental results indicate that the deployable structure is 2.9 m in length, its repetitive deploy accuracy can reach less than 2 mm, the decentration is less than 0.3 mm. Besides, the deploy accuracy can be adjusted to micrometer level by actuators when it has deployed. It can satisfy the deployment structure's requirements of simple mechanics, low mass,steady and reliable deployment, as well as higher precision for the space diffractive telescope.
2017, 46(12): 1218002.
doi: 10.3788/IRLA201746.1218002
Aiming at the TG-02 accompanying satellite's observation mission, the imaging simulation method of visible camera based on OpenGL was introduced. Based on the ephemeris and attitude data of the complex and the accompanying satellite, and 3 ds format of the complex 3D model, the parameters of OpenGL perspective projection model were set properly. Combined with the complex surface material properties and the visible camera imaging performance model, the complex's visible image sequences were simulated. By being compared with actual observation images, the simulation method was proved to be effective and credible. This research can provide references for design and system simulation of spac-based optical imaging payload, as well as the flight control task arrangement.
In order to reduce the effect of in-orbit space environment on the optical system of a laser communication terminal, improve communication quality and tracking accuracy, high-volume fraction SiC/Al that has better overall performance was used as the material of the primary mirror. Several important optimization parameters of the primary mirror structure were determined by the use of finite-element analysis. An integrated flexible support for primary mirror was proposed. The problem of stress concentration was solved because of using mismatch expansion coefficient materials for support assembly. The temperature stability of primary mirror surface shape was also improved. On the basis of this work, the weight of primary mirror and its support were reduced, a lightweight optical system was achieved. Simulation analysis shows that the PV of wavefront aberrations is /52 and the RMS of wavefront aberrations is /275, when the primary mirror under condition of gravity release. When the working environment temperature changes 4℃, the PV of wavefront aberrations is /11 and the RMS of wavefront aberrations is /71. The base frequency of primary mirror and its support is 208 Hz. The lightweight rate of primary mirror is 55.3%. After integrated design, the lightweight rate of primary mirror and its support is 19.87% compared to conventional design. In summary, system overall specifications requirements can be met.
2017, 46(12): 1218004.
doi: 10.3788/IRLA201746.1218004
In order to reduce the random vibration response of the secondary mirror of the optical camera, a new method was presented to optimize the honeycomb sandwich plate. With this method, the structure parameters on the honeycomb core and the panels of bearing honeycomb plate of the optical payload of the satellite were optimized. Firstly, the satellite's fundamental frequency was greater than 40 Hz as the optimization goal, optimization design of the honeycomb core density was carried out. Besides, the equivalent mechanical parameters of the honeycomb core were calculated based on the sandwich plate theory. Secondly, taking the random response of the secondary mirror as the goal, the design of laminate of carbon fiber panel honeycomb sandwich plate was optimized, optimum laminate sequency was[0/45/90/-45]S with the total thickness of 0.8 mm. Based on the equivalent mechanical parameters of the honeycomb core and panel, the finite element model of the entire satellite was analyzed. Finally, the vibration test was carried out, in which the fundamental frequency and random response were collected. The test results shows that the fundamental frequency is 42.2 Hz and the RMS of the secondary mirror is 11.1g, which are both within a reasonable range and can meet the design requirements.
2017, 46(12): 1220001.
doi: 10.3788/IRLA201746.1220001
The relationship among the characteristics of InGaAsP/InP SPAD, such as photon detection efficiency(PDE) and dark count rate(DCR), and the parameters of the SPAD, like InGaAsP band gap,electric field distribution, avalanche length and operating temperature, was analyzed. The DCR of the SPAD was effectively decreased by using the InxGa1-xAsyP1-y(x=0.78, y=0.47) as photon absorption layer instead of the InxGaAs(x=0.53) and controlling avalanche length of InP multiplication region precisely. According to good lattice matching of InGaAsP and InP, high quality InGaAsP/InP heterojunction was epitaxially grown on InP substrate to detect single photon of 1.06 m, with 1.03 eV band gap and 1.2 m cutoff wavelength. InGaAsP/InP SPAD was designed and manufactured for 1.06 m detection. And measurement results show that DCR is about 20 kHz under 20% PDE on 270 K. The device can detect random arrival photons based on time correlated single photon counting technique under active quenching mode.
2017, 46(12): 1220002.
doi: 10.3788/IRLA201746.1220002
According to the Fresnel diffraction theory, a simulation model of grating-based X-ray differential phase contrast imaging system was established. A PMMA sphere was the image object and the level of X-ray was 30 keV. Through the simulation, the change of the wave front of the X-ray passing through the sphere and phase grating was gotten. In addition, the image of first-order derivative of object phase was extracted by the method of phase-stepping. Furthermore, the influence of Moire fringe contrast on image quality was analyzed. The optimization design of the parameters of the grating was discussed. The simulation results are helpful to optimize the experimental platform, and analyze the factors that affecting the image quality.
2017, 46(12): 1226001.
doi: 10.3788/IRLA201746.1226001
To overcome the problems of X-ray image's vertical stripes caused by uneven response of X-ray linear detector's pixels and the noise interference produced by detector and outside, a new calibration and filtering model was proposed. It solved the problem that traditional calibration result was very volatile with ignoring noise. By combining X-ray's features and X-ray linear array detector's imaging principle, the output characteristic and noise were analyzed when the pixel responded unevenly. Besides, the calibration and filtering model was built. Improved-two-point calibration algorithm was used to calibrate the image and semi implicit difference method based on partial differential equation was used to smooth the noise. Experiment results show that the unevenly response of X-ray linear array detector with a resolution of 19 216 was eliminated, and the influence of noise was suppressed. In the case of 16 bit per pixel,the mean square error was below five gray level, it improves the quality of X-ray image detection.
2017, 46(12): 1228001.
doi: 10.3788/IRLA201746.1228001
Hyperspectral remote sensing image contains the properties of much features(bands) and high redundancy, and the research of hyperspectral image classification focuses on feature selection. To overcome this problem, a hyperspectral image classification algorithm based on spatial and spectral structure preserving was proposed. Considering the physical characteristics of hyperspectral image, the weighted spatial and spectral reconstruction of the image was conducted firstly, in order to incorporate spatial structure information into the spectral feature set automatically, resulting in the spatial-spectral feature set. On the basis that the least square regression model uncovered the global similarity structure and the regularization term revealed the local manifold structure, the intrinsic structure of the spatial-spectral feature set was well preserved by the selected feature subset. The influence of window size and regularization parameter was also analyzed. The experiments on Indian Pines, PaviaU and Salinas datasets show that the classification accuracy of the proposed algorithm reaches 93.22%, 96.01% and 95.90% respectively. The proposed method not only makes full use of the spatial structure information of the hyperspectral image but also uncovers the intrinsic structure of the dataset, which contribute to select more discriminant feature subset and obtain higher classification accuracy compared with conventional methods.
