2015 Vol. 44, No. 9
2015, 44(9): 2535-2546.
High spectral resolution lidar can realize accurate measurement of atmosphere parameters, which has good development prospect in the field of atmosphere remote sensing. In this paper, the detection principles of atmosphere aerosols, temperature and wind velocity of high spectral resolution lidar and its domestic and abroad research progress were introduced. Moreover, the technologies of frequency- discriminating, laser, frequency-locking and data processing in high spectral resolution lidar were also especially emphasized.
2015, 44(9): 2547-2555.
Ghost Image via Sparsity Constraints(GISC) lidar is a novel image lidar system which combines the light field coherence theory and modern information theory. The field of view(FOV) of GISC lidar is independent from its image resolution, and can obtain high resolution image of moving targets with a large FOV. While flash imaging lidar divides the intensity of target image into many small pixels of array charge-coupled device(CCD) camera on the imaging plane, GISC lidar uses a single pixel detector without spatial resolution to collect the entire reflective light intensity, which can greatly increase its detection sensitivity. Besides, based on various sparsity constraints of the target, GISC lidar can greatly improve imaging speed with much less samples compared to Nyquist Sampling requirement. Current development of GISC lidar based on the research experience of SIOM was introduced. Finally, the topics which need further investigation to improve the performance of GISC lidar in real application were also presented.
2015, 44(9): 2556-2561.
Lidar cooperative target is one important part of lidar rendezvous and docking measuring system. According to the requirements of lidar rendezvous and docking measuring system, the optimal design for the structure of lidar cooperative targets to make laser signals return back along incoming path was performed by using the method of the far and near field cooperative targets in order to fast search for and capture to objective spacecraft in the far field and implement accurate measurement in the near field. For the far field cooperative target the multi-dimensional structure of reflector array were adopted and the minimum reflective area can be reached to more than 100 cm2 within the effective field of view of 90105 to make sure of the ability of laser signal reflection and acquisition of objective spacecraft. The designed lidar cooperative targets in this paper meet the requirement of lidar rendezvous and docking measuring system.
2015, 44(9): 2562-2568.
In the noncoherent Doppler wind lidar system, the laser line width and frequency stability are two important factors influencing the accuracy of measurement results. The injection seeding technique method was used to obtain narrow linewidth of 532 nm lidar. The iodine filters as receiv frequency discriminators and lock the transmitter laser frequency. Using VB language writing instrument control program based on PID algorithm, the frequency of seed laser locked in iodine molecular absorption lines, which was 1 109 line of high reflection on the edge. The frequency stability was better then 0.5 MHz for 4 h, the long-term frequency stability as 3.5510-9. Design the continuous light velocity measuring system, which concluded the cure about Doppler frequency shift and actual speed of chopped wave plate, the velocity error was less than 0.4 m/s. This also shows that the laser velocity measuring system can be calibrated on the lock the frequency of the whole system. This experiment also provides guidance significance for the construction of wind lidar.
2015, 44(9): 2569-2574.
A super-resolving quantum LADAR scheme based on odd coherent superposition states of light was studied. According to the theory of quantum optics, the output signal of traditional intensity detection, projection measurement and parity detection schemes were widely investigated and analyzed. Based on above analysis, the parity photon number resolved scheme was especially investigated. Meanwhile, the numerical results show two super-resolving features, i.e., multiple narrow peaks and well-define narrow peaks. Finally, the lowdown of the first super-resolving power of the odd coherent superposition states were analyzed and discussed in detail.
2015, 44(9): 2575-2582.
Synthetic aperture ladar is a generalization of the synthetic aperture technique in the field of laser coherent detection with a higher resolution compared with the conventional synthetic aperture radar. Due to the frequency modulation rate and frequency nonlinear, the traditional frequency modulated mode can't be applied on the high-speed platform. In this article, combined with optical communication modulation method, the functions of synthetic aperture ladar imaging based on the pseudo code intensity modulation were deduced in detail and the compression performances of M codes were simulated simultaneously. By analyzing the ambiguity function, it proves that the pseudo code intensity modulation signal is not affected by the multi value ambiguity or the intercoupling error. An experiment system of the pseudo code intensity modulation was set up by fiber of 2 000 m to test the range resolution with M codes in length of 1 023 and code width of 5 ns. Under consideration of intensity jitter of the signal carrier, a range resolution of 0.787 5 m with 5% accuracy error was obtained. Through the above analysis, it has been proved that synthetic aperture ladar based on the pseudo code intensity modulation is feasible in theory and experiments and it provides practical support for the project implementation.
2015, 44(9): 2583-2587.
A photon counting imaging lidar system with four Geiger-mode avalanche photodiode(Gm-APD) detectors was proposed. A 22 optical fiber array was used in the system to receive echo pulse simultaneously. The distance of the target was obtained through the signals of the four channels in real time. The detection probability, the false alarm probability and the range accuracy of the lidar system were calculated. Comparing with the single Gm-APD system, the detection performances were all significantly improved the detection probability was improved from 60.6% to 91.6%, the false alarm probability was restrained from 1.9% to 0.2%,and the range accuracy was improved from 1.771 m to 0.440 m. By mean of the 6464 pixels range imaging simulations of the single Gm-APD system and the approach in this paper, the validity of the theoretical derivation is demonstrated.
2015, 44(9): 2588-2592.
Based on the LFM(Linear Frequency Modulation) signal and the principle of the heterodyne, the expression on the output of the heterodyne detection in synthetic aperture ladar was induced in detail with the considerations of phase error. Combining with the reference channel design and phase compensation algorithm, the influence of reference channel design on single point object image had been analyzed by simulation. Some error analysis concerning the compensation algorithm with sharpen function had been given by researching the physical meaning of sharpen function. Finally, the application scope of the phase compensation algorithm with sharpening function had been given out, and some problems to realize high quality synthetic aperture laser radar imaging had been pointed out in these paper.
2015, 44(9): 2638-2642.
A Nd:YVO4 laser end-pumped by laser diode was designed, when the repetition frequency of acousto-optical Q-switch was 50 kHz, LD pump power was 50 W, the output power of 26.37 W and pulse width of 26.28 ns was obtained. And with this arrangements, by pumping external cavity OPO with bonding KTP crystal, when the LD pump current was 24 W, corresponding to the 1 064 nm laser power of 7.36 W, the wavelength of 2.174 m pulse laser was achieved, the average power was 324 mW and pulse width was 17.8 ns. Meanwhile, the laser output power and pulse width of 1.064 m and 2.1 m under different output transmission and repetition frequency was analyzed in experiment. At last, by comparing the calculated date and measured date in experiment, the results show that the measured date is consistent with the calculated date, and the output power is not saturated.
2015, 44(9): 2643-2648.
Optical rectification is one of the important techniques for efficient generation of terahertz pulses. The theoretical model of the optical-to-terahertz conversion efficiency in optical rectification by tilted-pulse-front pumping was built. On the basis, the influence of the different tilted angles from tilted-pulse-front pumping on the conversion efficiency was compared. The effect of the important factors on the optical-terahertz conversion efficiency was analyzed quantitatively, and the influence of the parameters of both the crystals and the femtosecond pulses on the conversion efficiency was discussed. The results show that the influence of the titled angle on the optical-terahertz conversion efficiency was very obvious. The optical-terahertz conversion efficiency increases first and then decreases with the increasing of the pulse duration, where as it increases with the intensity pump pulses. In addition, the optical-terahertz conversion efficiency decreases rapidly with the increasing of the absorption, while increases and then remains unchanged with the increasing thickness of the crystal. Hence it is not only necessary to take measures to meet phase-matching condition as far as possible and decrease the terahertz absorption in the crystal, but also choose optimal parameters of the femtosecond pulse and the nonlinear crystal.
2015, 44(9): 2649-2654.
Along with the speediness development of laser technology, jamming problem of laser to push-broom camera is widely noticed at all times. Push-broom camera has commonly high angular resolution, big optical caliber and long focus, and its price is costly. If research on the laser jamming experiment for push-broom camera is carried through by equity request, the technology difficulty will be very big, and the experiment fare will be high too. In allusion to jamming effects evaluation difficulty problem of laser to push-broom camera, a laser jamming equivalent scaling model of push-broom camera was put forward on basis of jamming mechanism and camera imaging principle, the model was validated by experiment. The experiment shows if F number, pupil laser power and CCD integral time of push-broom cameras are same, jamming effects of laser to original camera and scaling camera are basic same, namely laser jamming area on the two cameras's imaging is basic same. This result can be used for evaluating laser jamming effects to Push-broom camera and researching camera laser protection method.
2015, 44(9): 2655-2660.
Optical parametric oscillation is the critical part in the preparation of squeezed states of light. The mode-matching and fringe locking technique should be employed to improve the stability of the optical parametric oscillator cavity. How the mode-matching efficiency influence the squeezing degree of the squeezed light and the locking accuracy of the fringe locking technique were analyzed theoretically. Then the fringe locking technique was employed to stabilize the optical parametric oscillator cavity after the mode-matching between the laser mode and the fundamental mode of the cavity. The theoretical and experimental results show that a perfect mode-matching would improve the squeezing degree and the locking accuracy of the fringe locking technique, when the mode-matching is optimized, the length variance of the cavity is 7.35 nm and the locking time is no less than 2 h, which is sufficient for the detection of the squeezed states of light.
2015, 44(9): 2661-2665.
A MARX circuit was designed by connecting the avalanche transistors serially and parallel. A high-voltage pulse driving source with low jitter was developed based on this circuit, and it was applied on a electro-optical switch clipping system of ultraviolet laser pulse. The time matching degree between high-voltage driving pulse and laser electro-optic system was regulated by synchronous regulator to get the best work state of the driving electrical pulses coupling with the electro-optical switch; work state of the electro-optical switch and shaping process of the laser were researched while matching the working time, when the amplitude and pulse width of high-voltage driving pulse was 2 690 V and 7.9 ns, the UV laser pulse with 7.1 ns in pulse width can be compressed to 2.1 ns. Then the transmittance of KDP crystal is 92.2%, and the efficiency of electro-optic switch has reached 31.7%.
Using the self-developed electromagnetic stirring device to assist titanium alloy laser deposition repair, numerical simulation was carried on by finite element software ANSYS, the interaction relations of titanium alloy in laser molten pool was studied combined with experiment. The results show that the magnetic flux intensity on liquid surface is proportional to the excitation current and inversely proportional to the current frequency in laser molten pool with the influence of rotary magnetic field; the laser molten pool is impacted by the radial force and tangential force, but the former is lesser and it can be neglected, the maximum of electromagnetic force density on liquid cross-section is proportional to the excitation current. Surface on both sides of laser deposition repair parts bulge under the effect of rotating magnetic field and length to diameter ratio of lamellar / in laser repaired zones reduced.
2015, 44(9): 2672-2678.
A multilayer transient temperature finite element model of Selective Laser Melting was established. This model took account of the temperature-material properties and the powder-to-solid transition by converting the powder thermophysical properties to the solid thermophysical properties. The FE model consisted of two layers of elements. The simulation results are in good agreement with the single track experiment result. The effects of scan speed (0.2 m/s, 0.4 m/s, 0.6 m/s) and laser power (80 W, 100 W, 120 W) on the temperature field were investigated. Simulation results show that the point of peak temperature slightly shifted toward the back of the laser beam rather than the center of laser beam when the laser beam moves. The peak temperature as well as the thermal gradient increases with increasing laser power and decreasing scan speed.
2015, 44(9): 2679-2683.
According to the measuring requirement for the performance measurement of pulse laser range finder with wide range, a new measuring method of laser echo signal simulation based on MODTRAN database was proposed. The laser atmospheric echo signal was simulated by detection system indoor to realize detecting of the two indexes which were the ranging precision detection and maximum range detection of laser range finder better than similar equipments. The MODRAN meteorological parameter database method was adopted to calculate atmospheric radiation transmittance of arbitration experimental in GJB2241A and mathematical model was established on this basis, FPGA and analog delay device were adopted to achieve presupposition time delay, this method made distance simulation and energy simulation becoming a close loop realizing realistic simulation of ranging laser echo signal. Experiments results show that designed laser echo signal simulator system can realize 50 m-22 km wide range distance simulation, echo delay precision is better than 2 ns, measurement accuracy of maximum range is 90% meeting the detecting demand of the ranging performance of laser range finder.
2015, 44(9): 2684-2689.
An improved metal-insulator-metal(MIM) waveguide structure was used to realize the potential of surface plasmon amplification by stimulated emission of radiation(SPASER) as amplification, although a major problem is that the net gain of SPASER equals zero, which makes it unsuitable for amplification. With the use of a theoretical Hamiltonian model as basis, the lasing conditions were obtained. The numerical calculations of these conditions show that overcoming the inherent feedback and eliminating the surface plasmon(SP) net gain are feasible by using the improved MIM waveguide structure, which can achieve stable SP excitons in less than 100 fs. This study shows that the improved SPASER amplifies with a response time of 100 fs, a bandwidth of 1.5-2.0 THz, and an SP gain of 30-60 dB. SPASER amplifier research provides theoretical and technological foundation for large-scale integrated photonic chips.
2015, 44(9): 2593-2597.
In order to make the infrared images of space target indicating its active state in orbit as real as possible, the contribution of the target spontaneous emission, the solar radiation, the earth radiation and the earth albedo radiation were considered. Combined with the information of the space target attitude and the detector parameters in orbit, a kind of infrared imaging simulation method was proposed in this article. Firstly, the method which is used to simulate the infrared imaging was explained in detail. Then, the method was used to simulate the infrared imaging of a simple cube satellite. The emulation results show that the method is feasible to simulate the infrared imaging of the space target, which has significant sense for the researches of target detection, recognition and tracking techniques.
In the process of high temperature field reconstruction, it still need through a plurality of single point temperature measurement combined with spatial interpolation methods appropriate to reconstruct the temperature distribution of the whole temperature field. Taking welding temperature field as an example, the spatial variability and distribution of temperature field were analyzed and forecasted by sample points through OK, IDW and spline methods, respectively. The results show that different interpolation methods do not significantly influence on reconstruction accuracy and the amount of sample points significantly affect the prediction accuracy of the spatial distribution of temperature field. In the temperature field evaluation, 25 sample points are more suitable for the sample number. Comparing with the sample number of our results with the formula, it was found that calculation sample number by optimum formula is significantly lower than our results. It show that if we do not consider the spatial variation and only use the formula will lead to uncertainty in temperature field reconstruction.
2015, 44(9): 2603-2608.
In order to propel the application of infrared up-conversion materials at long distance, the detection and recognition of the Ytterbium Erbium co-doped Yttrium Oxysulfide(Y2O2S:Yb,Er) were explored. The Y2O2S:Yb,Er material with an 1.5 m peak absorption and a 980 nm peak emission was prepared through an improved sulfur melting method, and was coated on a 900 mm900 mm aluminum plate to form a target. Due to the fact that the prepared material has a relative low conversion efficiency and a long fluorescence radiating period, which tends to broaden the exciting laser pulse, the target was then excited by a laser pulse of 1 550 nm wavelength, 8 ns pulse width and 5 mJ/pulse energy. The image of the target was collected by a BASLER camera with a 1 000 nm cutoff wavelength. A dedicated band pass filter with a 980 nm central wavelength and a 100 nm bandwidth was employed to suppress the interference caused by ambient light, realizing a higher signal to noise ratio. The excited spot was extracted from the acquired image of the target through simple frame differentiating image processing, so as to achieve far range detection and recognition. Test results obtained respectively at 50 m, 55 m, 60 m, 65 m, 70 m and 76 m indicate that the recognition rate reaches 98.3%.
2015, 44(9): 2609-2614.
Based on integral equation theory, the structure of the blackbody cavity model was established. Analyzed the length to diameter ratio of cavity, the aperture ratio, the distance between the aperture and the receiver, the cavity material itself emissivity and other factors that have influence on the cavity emissivity, and the optimization parameters of the blackbody cavity was designed, at the same time the finite element analysis method was used to analysis the influence of different shapes of blackbody cavity on the receiver steady temperature and the dynamic response time. The result shows that the change of the blackbody cavity structure parameters have direct influence on the blackbody cavity emissivity, the receiver steady temperature, and the dynamic response time, and then affects the performance of the blackbody cavity, and the method of the combination of the finite element method and integral equation method analysis provides a new idea for the study and optimization design of the blackbody cavity.
2015, 44(9): 2615-2621.
For infrared small target detection and tracking, it requires very high efficiency of both hardware and algorithm. Since the classic background prediction algorithm is a serial one, which is very time consuming. Considering that common GPUs(Graphic Processing Units) are big in size and too power consuming to be integrated into an infrared device, the implement background prediction algorithm was proposed with separable convolution template method on the embedded GPU platform, named NVIDIA Jetson TK1. Taking advantage of CUDA(Compute Unified Device Architecture) programming language to execute background prediction algorithm in parallel, an operable and high performance result on board was achieved, which gained a 15x speedup comparing to the serial way with a CPU.
2015, 44(9): 2622-2626.
The reason why it is the resistor array but not the Digital Micro-mirror Device(DMD) that the widely used infrared scene projector was based on real time hardware-in-the-loop simulations(HILS) was pointed out. It was found that both image data transmission bandwidth of the interface and latency of external synchronization signal had impact on real-time performance. Analysis proved that only when the image data transfer bandwidth was 2 times higher than the effective bandwidth, it will meet the critical requirement of real-time simulation system. Dedicated Gigabit Ethernet hardware which meets this requirement was designed, and its software was compliant with UDP/IP protocol. The image transfer delay was only last for one MAC frame. The image data was reordered and stored in a particular way. Experiments proved that with great stability the speed of transferring 8-bit image data with 1 024768 resolutions was above 100 Hz and the latency between external synchronization signal and starting signal of projecting was only 70 s.
2015, 44(9): 2627-2632.
A novel high precision, low power and area economic current mode complementary metal-oxide-semiconductor(CMOS) bandgap voltage reference used in uncooled infrared focal plane array (IRFPA) systems was presented in this work. The proposed BGR contained two type of resistors with the opposite temperature coefficients(TCs), which could compensate the BGR's high order curvature error and obtain better TC. This paper illustrated a cascaded structure without a traditional op-amp, achieving low power consumption as well as excellent power supply reject ratio(PSRR). This circuit was implemented in a standard 0.18 m CMOS process. The simulation results have confirmed that the proposed BGR operates with a supply voltage of 3.3 V, consuming 6.3 A at room temperature, and the output voltage reference temperature coefficient is about 3.7 ppm/℃ from -40 ℃ to 120 ℃. The BGR can achieve a PSRR about -78 dB@ 1 kHz, consuming only 230 m100 m chip area. This proposed BGR is a low-power and area economic design.
2015, 44(9): 2633-2637.
A simple and computationally efficient method was presented for detecting visually salient objects in infrared radiation images. The proposed method can be divided into three steps. Firstly, the infrared image was pre-processed to increase the contrast between objects and background. Secondly, the spectral residual of the pre-processed image was extracted in the log spectrum, then via corresponding inverse transform and threshold segmentation we could get the rough regions of the salient objects. Finally, a sliding window was applied to acquire the explicit position of the salient objects using the probabilistic interpretation of the semi-local feature contrast which was estimated by comparing the gray level distribution of the object and the surrounding area in the original image. And changing the size of the sliding window, different size of objects could be found out. The method was tested on abundant amount of infrared radiation images, and the results show that the saliency detection based object detection method is effective and robust.
2015, 44(9): 2690-2695.
Multiple softwares were required in the traditional design process of LED free-form surface lens. It is obvious that this process is complicated and inefficient. Moreover, when the model was transferred from 3D modeling software to optical simulation software, the file format had to be changed to solve the problem of the software compatibility. Note that some subtle changes were inevitably introduced to the model by such an operation, such as the generation of cracks or tiny deformation which would seriously affect the light efficiency and the degree of illumination uniformity. A new design method was presented in this paper which was used to directly generate model in the optical simulation software by using Scheme language. In this paper, the method of mesh division was applied to design the LED free-form surface lens with rectangular lighting. After the corresponding surface configuration was obtained, 3D modeling software and the Scheme language programming were used to generate lens model respectively. With the help of optical simulation software, a light source with the size of 1 mm in diameter was used in experiment, in which total one million rays were computed. The simulated results could be acquired by both models. It can be seen that the model deformation problems caused by the process of the model transfer could be prevented by using Scheme language, and the degree of illumination uniformity was also increased from 67% to 93.5%. Meanwhile, only 5 seconds were needed in modeling process by Scheme language which was more efficient than 3D modeling software.
2015, 44(9): 2696-2701.
In order to overcome the insufficient of the light energy diffracted by common two dimension grating in dynamic interferometry, diffraction efficiency of the cross phase grating and phase chessboard were derived using scalar analysis and Fourier method, and selection scheme of optimum operation orders was studied. The analytical result of their diffraction efficiency demonstrates that if the cross phase grating is chosen, the(0, 1)th and(1,0)th orders should be selected as operation orders, and utilization rate can reach 54.4%; If the phase chessboard is chosen, (1,1)th orders is selected as operation ones, and utilization rate can reach 65%. Application effect of these two phase grating are compared in dynamic interferometer. When (1,1)th is selected as operation orders, the experimental results indicates that application effect of phase chessboard is better than that of cross phase grating. So influence of insufficient light energy on the measurement result can be eliminated by using phase chessboard and selecting (1,1)th as operation orders.
2015, 44(9): 2702-2709.
For the purpose to overcome the difficulty of testing aspheric surfaces by null lens or CGH (Computer-Generated Hologram), the non-null testing was proposed. The basic principle and theory of testing asphere by digital plane, partial compensation and subaperture stitching interferometry(SSI) were analysed and researched, and each testing model and flow chart were established. Combining examples, an asphere of little departure with the aperture of 350 mm was tested by the digital plane and SSI, respectively. As results, the difference of PV and RMS error between SSI and partial compensation is 0.015 and 0.002( is 632.8 nm), respectively. The prototype and setup for testing asphere by partial compensation were devised and developed, a precise convex asphere is measured by this method, the PV and RMS of the surface error is 0.183 and 0.018, respectively.
2015, 44(9): 2710-2715.
With the rapid development of LED industry, its share in the automotive lighting market is also growing very fast year by year. At present, there are mainly two design methods of LED-based headlamp which are single-moduled and multi-moduled, what's more, most of the headlamp system are composed of several modules which can just be used by specific cars. This kind of headlamp system has large volume, high power consumption, high cost and narrow application range. The main research of the article was the optical design method of the single-moduled LED headlamp with small volume and outstanding lighting effect. A brand-new design method of LED-based integrated headlamp optical system was proposed, which used only one group of reflectors and one LED module to meet the lighting needs of high beam and low beam using a baffle. The final design method was determined through software simulation and contrast of different design methods to pick up a best one. Finally, it puts forward a new design method of LED-based integrated headlamp system with high efficiency, small volume and excellent lighting effect which can be used by different kinds of cars.
Existing static wedge interferometer can not achieve zero optical path difference, and it requires a strict spatial coherence of light, thereby affecting the accuracy and complexity of spectral inversion. Therefore, a novel equivalent static wedge was proposed. It consists of two different refractive index material, and two reflective surfaces perfectly vertical. Because interference of two beams of light is derived from a beam of light, it is not strictly required about spatial coherence. Moreover, it contains zero optical path difference. By deducing and analyzing the optical path difference of the arbitrary wedge position, the formula of spectral inversion was deduced. Then the wedge was designed and processed by using two materials which were different refractive index, and its maximum optical path difference could reach 168.3 m. And the process of spectral inversion was simulated. Combining maximum optical path difference with the measured spectral band, the requirement of the linear CCD pixel count was analyzed. The wedge was analyzed by experiments which use 532 nm and 632.8 nm lasers. The results show that the spectral inversion center wavelength error is less than 0.2%.
2015, 44(9): 2721-2725.
Atmospheric turbulence is a mainly factor which restricts space laser communication. In this paper, a new turbulence simulation method was proposed. At the receiving position, a pair of correlated amplitude and phase screens was used to simulate the turbulent effects. For the situation of satellite to ground laser communication, firstly, the double infinite integral forms of the amplitude autocorrelation, phase autocorrelation and amplitude-phase cross-correlation functions were reduced to the forms of single integral; and then, according to these correlation functions, a pair of correlated amplitude and phase screens was simulated by using the covariance-based random screen simulation method. The conformities between the simulated structure functions and the theoretical ones were compared. The outer scale and inner scale of atmospheric can be considered in this simulation method.
2015, 44(9): 2726-2733.
The generalized Huygens-Fresnel principle and the cross-spectral density function were used to derive the expressions of beam width and angular spread of partially coherent Gaussian-Schell beam when it was propagating in the atmosphere on the basis of the model of the modified Von Karmon spectrum and the atmospheric refractive-index structure constant issued by ITU-R. And then, the impact on the beam propagating in the slant and horizontal ways, caused by the zenith, the transmission distance, the turbulent intensity, the coherent length of the beam and other parameters, were discussed and compared. The impact of the parameters on the ability of anti-turbulence of the beam was analyzed from the perspective of the relative expansion and the relative angular spread respectively and a series of concrete explanations were given. The research results demonstrate that the expansion and the angular spread of the beam suffer little effect from the turbulence during slant path when the zenith is less than /3, which is close to vertical transmission. The beam width and the relative beam width of the beam increase with the increasing transmission distance significantly when the distance is greater than 1 km. The larger the coherent length of the beam is, the greater the impact of the turbulence suffers, while the expansion and the angular spread decrease.
2015, 44(9): 2734-2741.
The geometrical and optical properties of cirrus cloud with multiple scattering were studied and the retrieval methods of cirrus height and lidar ratio were improved. An approach was proposed for determining cirrus height based on multiple scattering factors and the extinction coefficients of cirrus were corrected by the factors. With multiple scattering factors and the extinction coefficients, the error of the cirrus-height was computed. Finally, the precise lidar cloud detection retrieval was achieved preliminarily. In the improved method of retrieving the lidar ratio with multiple scattering, the nonlinear equations with cirrus lidar ratio and cirrus extinction coefficient as variables were constructed, and the particle swarm optimization algorithm was used to solve the equations, the extinction coefficient of the cirrus's top and the lidar ratio of cirrus clouds were acquired. Then, through the PLATT's multiple scattering equation and the ratio of total scattering and signal scattering calculated by semi-analytic Monte Carlo method, the lidar ratio was obtained. The experiment was carried on based on the proposed method, using the real return signals of the ground-based lidar. It is turned out that the proposed technique has the advantages of high accuracy. Therefore, it has a promise future.
2015, 44(9): 2742-2746.
Joint observation using Lidar and millimeter wave cloud radar(MWCR) from which more comprehensive properties of cirrus can be retrieved is the main trend of cirrus observation. Combining the information of cirrus boundary from Lidar and MWCR of ARM project, more accurate boundary of cirrus was obtained. Joint inversion method for retrieving cirrus microphysical properties was presented. Both ice water content and optical depth can be inverted accurately even in cases when the cirrus can't be penetrated by Lidar or can't be sensed by the MWCR through this method. The joint method was applied to a cirrus case, the results showed the accuracy of ice path content increased by 24% when the Lidar can't penetrate the cirrus and 48% when the MWCR can't sense the cirrus. Based on the accurate inversion of ice water content, the optical depth of cirrus was obtained using the relationship between ice water content, size distribution and optical depth. The inversion method of optical depth can overcome the difficulty arise from the attenuation of cirrus to Lidar.
2015, 44(9): 2747-2751.
The surface profile is of importance to the output characteristics of the waveguide optical phased array. The far field diffraction model of the array with an uneven surface was established based on the coherent superposition principle. The general formulas of the far optical field distribution were derived using the model. The effects of the surface profile on the output wave phase and the phase on the far optical field distribution were analyzed. When the surface profile was a inclined surface, a concave one, the single depression and the random fluctuation, the output light intensity was researched respectively. The results show that the surface profile has a great influence on the output far optical field and the position and intensity of the main lobe will be changed partly. These will affect the accuracy and power of the scanning beam and is of importance to the application of the waveguide optical phased array.
2015, 44(9): 2752-2756.
Using the projected augmented wave potential based upon the density functional theory within the gradual gradient approximation approach, after the optimization of wurtzite structure GaN, the affinity variation of Cs atoms adsorbed on GaN(0001)A surface was calculated, which proving that an effective GaN-Cs dipole layer was formed, and be good for electrons escaping form the substrate. The electronic structure of adsorbed Cs and O on GaN(0001)A surface was also calculated, which pointed out the bonding of Cs and GaN substrate. Furthermore, the internal quantum efficiency of reflect photocathode of GaN material on various minority carrier diffusion length were derived from dielectric functions theoretically. The calculated results demonstrate that GaN(0001)A surface is an excellent emitter for visible-blind photocathode, and the efficiency at 254nm can reach up to 60%, far more than other alkali halide UV photocathodes.
2015, 44(9): 2757-2760.
First, the thiol modification of Au nanoparticles was carried out, then two grade modification was carried out with sixteen alkyl three methyl bromide(CTAB), and its self assembly load on grapheme nano blanket(GNSs). The successful loading of Au nanoparticles on grapheme sheets(GNSs) was demonstrated by UV Vis absorption spectra. The microstructure was proved by transmission electron microscopy. It showed that the Au nanoparticles were arranged in the grapheme nano blanket, because of its structure of grapheme nano blanket. The nonlinear optical limiting properties of grapheme nano particles with load Au nanoparticles were studied by using the Z-scanning technique. The resuls show that the threshold of optical limiting threshold is significantly decreased. The optical limiting characteristic is produced while in the low incident energy, and the nonlinear scattering enhancement is found when the incident light intensity increases. So nonlinear scattering is an important mechanism of nonlinear optical limiting effect in composite systems.
2015, 44(9): 2761-2766.
To study the evolution of refractive inhomogeneity in hafnia thin films, single layers with different thickness were prepared on BK7 substrates by Electron Beam(EB) evaporation process. The spectral measurements showed that the inhomogeneity of HfO2 thin films was significantly affected by the layer thickness. X-ray diffraction(XRD) measurements showed that the crystalline microstructure of HfO2 thin films had direct influence on their inhomogeneity and the microstructure was determined by thin film growth mechanism. Due to amophous surface of BK7, thinner films are hard to crystallize and the refractive index of the HfO2 thin films are prone to the positive inhomogeneity. If the deposition temperature is high enough, films reaching a certain thickness begin to crystallize, which causes more and bigger voids in the film and results in negative inhomogeneity. When film grows thick engough, the microstructure tends to being stable, and the layer inhomogeneity is independent of thickness and fixed to a certain value.
2015, 44(9): 2767-2773.
In order to quantitatively investigate image quality improvement of area CCD subpixel imaging and influence of fill factor on image quality, a mathematical model was established to simulate subpixel imaging of array CCD with different fill factors. Without consideration of noise influence, simulation experiment for a sub-image of ISO12233 standard resolution card was performed on Matlab. Experiment results illustrate that, when fill factor is 100%, compared with common imaging mode of array CCD, gray mean gradient (GMG) of diagonal subpixel and four-point subpixel imaging mode was increased by 2.997 0, 3.413 6 respectively, and energy of Laplacian(EOL) is enhanced by 0.567 6, 0.747 8 respectively. With the same fill factor other than 100%, GMGs and EOLs of common imaging mode, diagonal subpixel imaging mode, and four-point subpixel mode are increasing in that order too. For four-point subpixel imaging mode, GMG of 69%, 44%, 25% fill factor is improved by 1.433 0, 3.337 3, 5.153 2 respectively compared with that of 100% fill factor, and EOL increased by 0.638 0, 1.704 4, 3.196 8 respectively. With the same imaging mode other than four-point subpixel, GMGs and EOLs of images obtained with CCDs whose fill factor is 100%, 69%, 44%, 25% increase too. Research shows that subpixel technique of array CCD can improve image quality, and four-point subpixel imaging mode provides more improvement on image quality than diagonal subpixel imaging mode. In the condition of signal-to-noise ratio is met, the image quality performance becomes better when fill factor decrease for the same CCD imaging mode.
2015, 44(9): 2774-2777.
It is widely acknowledged that the temperature plays a crucial role in the process of electrochemical etching Si microchannel. Therefore, by studying the influences of temperature on the hole transportation during the electrochemical corrosion process, better understanding about the process of electrochemical etching Si microchannel can be expected. Using n-type monocrystalline silicon with (100) crystallographic orientation as the research subject, an electrochemical light assisted anode oxidation method was devised for getting the I-V curves, the morphology and the depth of microchannel at the different temperature. According to the relevant principles of the scattering mechanism in the crystal, the relationships between the temperature and the carrier mobility and the diffusion coefficient were also studied and the relationship between the temperature and the dark current was finally found. Based on the further analysis regarding to the above results, it is concluded that the lower temperature caused the less current density produced by the hole transportation and the lower value of dark current. Thus, the well-defined microchannels can be achieved by using the electrochemical corrosion method at low temperature.
2015, 44(9): 2778-2782.
With the development of satellite laser communication technology, data-relay satellite system using optical links will become the backbone of space-based information system in the future. At first, a network architecture of 2 territorial stars +2 overseas stars was designed, then the optical satellite network performance indexes were defined based on the analysis method of SPC exchange(stored program control exchange), and lastly the performance of data-relay satellite system using optical links was simulated. The simulation results show that data-relay satellite system using 12 optical links can support 50 user satellites, when each user satellite communication traffic is 0.2 Erl, access loss probability is greater than 0.2, and link utilization is greater than 0.6.
Indoor visible light communication is a burgeoning technology that uses white light-emitting diodes(LED) for illumination to realize high rate communication. The receiving power of photodetector is limited when receiver is in the corners of the room due to the larger receiving angle, thus the signal to noise ratio(SNR) is decreased. The design method of tilting receiver plane was proposed to obtain the maximum in each place of the room including the Non-Line-of-Sight(NLOS) link. In this paper, the Line-of-Sight(LOS) was not only considered, but also the NLOS link was considered for the method of tilting the receiving plane. Newton method was employed to find the optimal tilting angle of receiver in each positon of the room and the iteration numbers of this algorithm were about three or four steps which was very fast. The simulation results show that the minimum SNR is increased 5 dB and the maximum and average SNR are both increased 2 dB. Especially, the SNR in the corners of the room is obviously increased.
2015, 44(9): 2789-2794.
Compensation characteristic of coupling efficiency in process of coupling space light into single-mode fiber was studied in the satellite-to-ground link. According to satellite-to-ground link feature, coupling efficiency model was analyzed. Wavefront phase modal compensation model using orthonormal polynomials on pupil weighted by the backpropagated fiber mode field was built. Based on this model, the relation between average fiber coupling efficiency and received aperture diameter or phase modal term compensated was obtained by numerical simulation. The probability distribution of coupling efficiency was given for typical received aperture by using different term modal compensation. The research work can offer a useful reference for compensation system design of satellite-to-ground optical communication based fiber coupling way.
2015, 44(9): 2795-2799.
Based on the full vector wave equations, the dispersion formulas of vetorial modes were accurately established, and the expressions of field components were deduced in the hollow region,core region and cladding region. Then, the transverse electric field of the fundamental mode and the propagation constant were investigated. Based on the above analysis, the characteristics of mode were analyzed in detail by changing the main parameters of HOF, such as, the relationship between nneff and wavelength, radius of air hole, thickness of core. The raw of mode characteristics based on the varying number of cladding provides a basis for further research and application of hollow fiber.
2015, 44(9): 2800-2804.
Aimed at the phase ambiguity phenomenon existing in the -OTDR based vibration sensing system, the expression to describe the relationship between the Rayleigh backscattering power and the phase difference of optical interference fields, and the expression to describe the relationship between the phase difference of optical interference fields and the strain of optical fiber induced by vibration were derived. The cause and manifestation of the phase ambiguity phenomenon and the influence of the phase ambiguity phenomenon on system performance as well as the relationship between the maximum detectable strain and the spatial resolution of the sensing system were studied theoretically, and demonstrated by Matlab simulation. The results show that the phase ambiguity phenomenon is the main factor that limits the strain measurement range of the -OTDR based vibration sensing system, and it may cause mistakes in the measurement of vibration frequency and amplitude, and a failure in reporting large strain information. And the higher the spatial resolution, the larger the detectable strain range, which indicates that the -OTDR based vibration sensing system is very suitable for applications in the measurement with high spatial resolution. This study provides a theoretical support for the parameter design and optimization of the sensing system.
2015, 44(9): 2805-2812.
As the measuring accuracy of traditional robot visual measurement system is limited by the robot absolute positioning accuracy, a new high-precision robot vision measurement system based on the workspace Measurement and Positioning System was developed and its calibration technology was researched. In this system, the robot end-effector can be positioned precisely by the workspace Measurement and Positioning System in real time, freeing its positioning accuracy from the robot accuracy. The system only makes use of the high flexibility and automation of the robot. In order to realize the high-precision measurement, a new calibration method of calibrating the exterior parameters of the visual sensor based on the homography matrix was proposed. In this method, a calibration target was designed and imaged by the visual sensor. With the aid of laser tracker for coordinate transformation, the external parameters can be easily determined with only one image of the calibration target. The verified experiment shows that the distance measuring accuracy over the robot working volume is superior to 0.2/mm, which has been improved significantly compared with the traditional robot visual system.
2015, 44(9): 2813-2818.
The Hartmann-Shack sensor is mainly affected by the dimension and the number of lenticule. Thus the measured wavefront has been inadequate sampled and affected the precision of wavefront. The wavefront reproduction principle of Hartmann sensor and dual-wedges micro-scanning technology were analyzed and disscussed. A new detected method was proposed, which added the structure of dual-wedges micro-scanning. The method can compensate the shortcoming of lacking sample with measured wavefront in the traditional Hartmann sensor. By utilizing Zemax and Lighttools software, spot distribution was simulated by Hartmann sensor of adding dual-wedge micro-scanning structure. Combined with micro-scanning image of reconfiguration algorithm with the wavefront reconstruction algorithm, the principle was verified. The wavefront reconstruction of large aberration by simulation was improved 53.53% in the optical system. Conclusions show that the method can effectively increase the accuracy of wavefront detection by Hartmann sensor with dual-wedge.
2015, 44(9): 2819-2824.
To solve the problems that extended Kalman filter is difficult to obtain the optimal state estimation of complex nonlinear system with fast convergence speed and high estimate accuracy, an improved square root Cubature Kalman Filtering algorithm was proposed by introducing the matrix QR decomposition and Cholesky factorization updating technology to traditional Cubature Kalman Filter, via it can validly avoid the complicated calculating of matrix decomposition and inverse. Moreover, aiming at the uncertainty of system's variable and statistical properties, a weighted adaptive noise covariance matrix estimator was constructed, through integrating the adaptive noise estimator under wavelet Kalman Filtering ideology. A-SRCKF was applied to airborne positioning and orientation system, the simulation results demonstrate that the proposed method can effectively improve the accuracy of POS outputs as well as enhance the efficiency.
2015, 44(9): 2825-2830.
A high-accuracy calibration method for angular measurement of deformed and curved Moir patterns, based on template matching algorithm, was presented. It was feasible and accurate method, based on Talbot interferometry and Moir deflectometry, to measure long focal-length lenses. Theoretical analysis indicated that the precision of this method was mainly influenced by the angle of Moir patterns. However, it was difficult to obtain high-accuracy angle of Moir patterns, since the Moir patterns derived from experiment were constantly deformed or curved. A method based on template matching algorithm, was demontrated to calibrate deformed and curved Moir patterns, thus their angle can be calculated fast and accurately in sub-pixel domain. Numerical analysis and simulation prove that the method mentioned above demonstrates high precision and stability, and experiment results show that the accuracy of the long focal lengths measurement is improved obviously.
2015, 44(9): 2831-2836.
A new algorithm of system calibration based on depth constraint was presented to improve the calibration accuracy of large scale planar part vision measurement system. Firstly, an algorithm of extracting the round marks of calibration plate was proposed. Sub-pixel contours of marks were extracted by edge detection algorithm based on adaptive threshold and polynomial fitting, then the center coordinates can be computed by ellipse fitting method. Then, on the basis of analyzing camera distortion model, the optimal solution of internal parameters and plate poses were obtained using least square method. Finally, the pose of measuring plane was transformed by depth information as a correction term between parts surface and calibration plate. The dimensions could be calculated using imaging principle and the intersection point of the line and the part surface. Measurement system was designed and experiments were carried out. The result shows that the calibration back-projection error is less than 0.02 pixel and the precision of the system is up to 0.05 mm in the range of 10.75 m2.
2015, 44(9): 2837-2843.
The speed, precision and stability of inversion algorithm are research emphasis in the field of particle measurement. To counter the problems such as burrs, false peaks and concussion etc. in the process of inversion with traditional Chahine algorithm, an improved algorithm that combines regularization theory with Chahine algorithm was used to reconstruct particle size distribution. A new linear equation was constructed by introducing the regularization theory, the regularization parameter was determined by using L-curve, and Chahine algorithm was used to solve the linear equations. Simulation and experiment results show that the improved algorithm overcomes the disadvantages of traditional Chahine algorithm and improves the stability and gliding property of inversion results. Measured results of standardized polystyrene microsphere is measured by using the improved algorithm, which shows that the relative errors for median diameter D50 is within 2%, and D10, D90(characterize broadening of distribution curve) are both within 5% when the number of inversion is 15 000. In addition, the inversion time is less than 1 minute, which meets online particle size measurement.
2015, 44(9): 2844-2848.
As a new type of ultraviolet-visible linear array image sensor, NMOS has been applied to ultraviolet remote sensing abroad, but its research is still less domestically at present. This thesis aims at calibrating quantum efficiency of NMOS liner image sensor, which permits further application at space ultraviolet remote sensing. On the basis of standard detector provided by NIST, a high-accuracy calibration system was established to research quantum efficiency of NMOS linear image sensor. The number of photos, received by NMOS linear image sensor, was calibrated directly in this paper. And the number of electrons was calculated according to the signal processor and signal readout circuit of NMOS linear array image sensor. Then quantum efficiency of NMOS liner image sensor in 250-700 nm spectral range was calibrated. The result shows that quantum efficiency of NMOS liner image sensor reaches 34%@275 nm and 80%@550 nm. Through uncertainty analysis of quantum efficiency, the combined uncertainty is determined as 2.5%.
Generation method of piecewise-uneven fringes and its applications in two-frequency phase unwrapping
2015, 44(9): 2849-2853,2857.
A novel method of generating piecewise-uneven fringes was proposed in order to get even fringes on the reference plane in oblique projection grating measuring system. The relationship between image pixels and phase was described by a piecewise function. To apply the fringes in double-frequency unwrapping, the method was further improved. Continuous unwrapping image series were obtained by left/right phase shifting which is a multiple of . Double-frequency piecewise-uneven fringes method can be used for double-frequency unwrapping. The applications in piecewise-uneven fringes generation shows simplicity and good performance than conventional solutions. Contrast tests on arch profilmetry were taken herein. The results indicate that the measurement precision of piecewise-uneven fringes can get effectively improved compared with the method of even fringes.
2015, 44(9): 2854-2857.
The disturbance rejection rate problem caused by strap-down seeker was studied, the parasitical loop model induced by strap-down seeker time delay was established, the principium of how time delay causes disturbance rejection was analyzed, and the function of disturbance rejection rate induced by strap-down seeker time delay was deduced. Moreover, stability of the parasitical loop caused by time delay was investigated and of the parasitical loop with different guidance parameters was illustrated. The simulation result shows that, if the guidance system lag increases relatively to the missile aerodynamic time constant, the system can overcome larger seeker time delay; if the missile aerodynamic time constant is reduced, the guidance can tolerate larger seeker time delay. Disturbance rejection rate problem discussed in the paper is significant in the practical utilization.
2015, 44(9): 2858-2862,2866.
Optical glass is the foundation and an important part of photovoltaic technology industry, and the dispersion coefficient is an important constant which responses performance. The novel mathematical model was reestablished instead of the traditional dispersion coefficient measurement formula based on CCD imaging and automatic alignment technique of machine vision in this system. The influence of refractive index of air was considered for dispersion coefficient measurement accuracy. In the design process of small multiband collimator, on the basis of adjusting the aberration related to aperture, the optical path of the light was calculated, which was characteristic sense for aberration in meridian inner surface, the location aberration was obtained between the ideal image and the actual image, the simulation of infinity goals was achieved by a small band collimator. Finally, the technique of multiband small parallel light pipe, automatic imaging processing and grating angular displacement measurement were applied in this system. The automatic image alignment of dispersion coefficient measurement system was designed and high precision measurement was realized. It can know from the accuracy of analysis that the measurement system is calibrated with the known dispersion coefficient of optical glass, and the results show that the absolute errors is less than 2.309 310-6.
