2010 Vol. 31, No. 5
For the low contrast target acquisition test of the electro-optical equipment, a new method is proposed by using a contrast adjustable infinite distance target. The design of a contrast gradient adjustable optics infinite distance target device is introduced. This equipment may simulate the sky background luminance and a weak target in this background. It uses two integration spheres to simulate the background and target brightness independently. The collimating lens is installed in background integration sphere, target and its background become an infinite source. There were inner and outer light sources for integration sphere illumination. In the outer light source, a collimator was installed. It made parallel beam incident into the integration sphere. The size of the incident parallel beam was controlled by using diaphragm adjusting lever. This method didnt change color temperature, but luminance could be different. So background and target luminance became continuously adjustable under color temperature unchanged. The target contrast could change continuously, the range of variation is 0～90%, the contrast stability is better than 1%, the biggest background luminance exceeds 60W/m2sr.
The segmented aperture optical system is widely used in the field of remote sensing for its advantages in reducing the manufacturing complexity to achieve high imaging resolution. However, the misalignments among these segments may result in phase errors, and degrade the imaging resolution of optical system. Phase diversity phase retrieval is adopted to resolve this issue, which solves the misalignment of segmented mirrors inversely and provides the basis for aligning on-orbit. The misaligned optical system mathematical model for segmented primary mirror is set up, and the difference between the model output and actual output at the known defocus is regarded as the target function of misaligned phase estimation. After being compared with other methods of resolving nonlinear equation, BFGS method is used to seek the optimum phase value. The result of the simulation experiment indicates that the method of phase diversity phase retrieval can control the phase error below 6%.
Underwater-turbulence may have an impact on the performance of underwater imaging system. The impact of underwater-turbulence on laser beam propagation is studied with wave-front test. The distortion introduced by underwater-turbulence is measured and analyzed using the Zernike polynomial. The adaptive optical system with wave-front compensation is investigated for underwater imaging. The result shows that underwater-turbulence reduces the resolution of underwater imaging system. Calibration experiment is carried out to show that adaptive optical system can improve the quality of underwater images effectively.
In order to use visible and long wave infrared information for image fusion and color display, three dual-band imaging optical systems and theirs imaging performance were analyzed. All-refractive optical system, catadioptric optical system and off-axis three-reflection dual spectrum optical system were designed. A beam splitter was adopted to reflect visible and transmit LW infrared. Its full field of view and relative aperture are up to 5 and F/1.7, and MTF is higher than 0.60 at 50lp/mm in the visible region, higher than 0.30 at 18lp/mm in the LWIR region. The construction features of the lens are discussed, the aberration curves and MTF curves of the system are presented.
This paper establishes a mathematical model based on the principle of the light-scattering dots on a circular light guide plate (LGP) and gets some parameters about the light guide plate from the simulation result using Trace-pro. The distribution rule of the network is obtained. Finally, we derive a uniform spot with the help of the optical simulation software and verify the correctness of the theory.
In order to display characters and graphs by using organic light-emitting diode (OLED) display, a display driver technique based on NiosⅡ was designed. Verilog HDL was written in FPGA development environment to design the interface to support OLED displayer, C program was written in NiosⅡIDE to control the generation and transmission of characters and graphs and coordinate the data transmission between FPGA and NiosⅡ processor. Finally, the designed driver was tested. It is shown that OLED display can operate properly.
According to the requirements for the absolute calibration of spectrometer, a diffusing source formed by integration sphere was analyzed. The theoretical model of the spectral irradiance at the exit of an integration sphere was established and analyzed with a spectrometer. The calculation and experiment results confirmed the validity of the model. In the band of 0.6m～0.85m, the calculated value obtained from the model has an error of less than 4% compared to the measured value; at the wavelength of 0.9m, the error is 8.65% due to response property of the spectrometer itself and the blackbody for calibrating the spectrometer. It is showed that the model can be used to calculate the radiation value of integration sphere source.
A short focal digital projection lens for 2.03cm DLP projectors was designed with ZEMAX. The structure is composed of ten lenses. Its production cost is low, and it is processed easily. The full FOV of the lens is 80, the aperture is about 1/2.1, E.F.L is about 12.7mm, B.F.L is about 37mm, and projection ratio is about 0.78/1. Its MTF in all fields less than 28is higher than 0.35 at the limiting spatial frequency of 35lp/mm. MTF in the most fields at half of the limiting spatial frequency is higher than 0.7. The absolute value of the full field of view distortion of the lens is less than 3%. The image quality of the lens is very good.
The effects of Ag and Fe doping contents on photocatalytic performance of the TiO2 thin film were studied. Ag and Fe doping and co-doping contents on nano-TiO2 photocatalytic bactericidal films were prepared by sol-gel method. The photocatalytic activity of TiO2 films was evaluated by the sterilizing rate of the E.coli. The microstructure and UV absorb ability of films were measured by using XRD and Uv-Vis technology so as to analyze the intrinsic mechanism of Ag and Fe doping the photocatalytic TiO2 thin films. Results show that, for fluorescent light irradiation, optimal doping amounts for Ag/TiO2 and Fe3/TiO2 are 0.05%, 0.1%, respectively. The co-doping of them shows a good photocatalytic effect on the fluorescent light irradiation. And co-doping has a good ability of photocatalytic decomposition. The as-prepared particles had content of anatase phase. By Uv-Vis, we can see co-doping in the visible area has a good absorption property. Fe3+doping expanding the scope of the absorption of TiO2 and Ag+ effecti-cnvely inhibits the photo-generated electron hole recombination. All this makes filmsphotocatalytic ability enhanced. Co-dopeds superiority over the single-doped is to be investigated in the future.
In order to convert weak optical signals into electrical signals effectively for post-processing, a weak optical signal detection circuit is designed. The circuit consists of a photoelectric conversion circuit and a preamplifier circuit. The photoelectric conversion circuit was implemented with a low input bias current operational amplifier AD549. The preamplifier circuit was implemented with a logarithmic ratio circuit using symmetric transistors, and was compared with the preamplifier composed of IC LOG100 under the same conditions. Measurement results show that the amplifier circuit can amplify weak input signals lower than 1nW and noise can also be suppressed efficiently, while the circuit composed of LOG100 has a relatively poor performance in noise suppression.
Image enhancement is important for intelligence management system. It has potential applications in many fields such as traffic management，highway toll collection station，ship, airport and etc. The adjustment ability of logarithmic function, hyperbolic tangent function and inverse hyperbolic tangent function for fog-degraded images were compared. It was proved that hyperbolic tangent function had better ability to regulate brightness than logarithmic function. Accordingly, an image enhancement algorithm based on single scale Retinex was proposed. The algorithm conversed RGB color space to HSV space. Hue was kept unchanged. The hyperbolic tangent function based on center self-adaptive adjustment was used to enhance overall brightness of image. Local non-linear transformation was adopted to improve local contrast of images. And linear stretching was used to adjust saturation. Then color compensations are achieved. Experiments show that this kind of algorithm has significant effects on defogging and making color full of nature. Combined with parameters such as variance, entropy and arithmetic, experiments were conducted to make comparisons for algorithms based on single scale Retinex and multi-scale Retinex. It is proved that algorithm based on single scale Retinex has more advantages on image contrast and detail enhancement. And it has faster arithmetic speed. Generally, the algorithm based on single scale Retinex can be applied in real-time image processing.
According to the Fresnel-Kirchhoff diffraction integral formula, numerical calculation methods for the circular aperture diffraction irradiated by a point source or a plane light or a Gauss beam are given. The analytic calculation formula for these three kinds of circular aperture Fresnel diffraction and their special circumstance Fraunhofer diffraction are deduced with correlation methods, and their paraxial zone diffraction fields are simulated with Matlab software. The simulations show that these two calculation methods for the three kinds of common and important circular aperture diffraction are effective and feasible.
Key frame extraction plays a very important role in content-based video retrieval. Since general clustering algorithm can only predefine a threshold in key frame extraction, this paper presents an improved method of adaptive threshold based on unsupervised clustering. The video frames texture feature is extracted based on regional segmentation. The adaptive threshold is determined by video content, and then the key frames are obtained through unsupervised clustering. This algorithm is simple and effective, it extracts key frames without predefined threshold. Experimental results of some videos with different traits demonstrate the good performance of the proposed algorithm.
To overcome the limitations of traditional threshold algorithm, an algorithm for adaptive segmentation is proposed. According to the basic concept of the algorithm, a window is defined for every pixel with itself as center, the maximum and minimum value of the pixels in the window are calculated and their average is used as the threshold for image segmentation. Two different image segmentation methods are used, adaptive threshoding and iterative threshoding. The experimental results show that adaptive threshoding achieves higher performance and robustness in practical applications.
In the detection of field fire or leakage, the target signature is very weak. Analyzing statistical models of actual spectral detector output distribution is crucial for setting detection thresholds, selecting statistical classifiers and designing constant false alarm rate detectors. Multispectral image data is processed with the CEM algorithm. Statistical model of detector output is discussed based on the stochastic mixing model. It is concluded that Gaussian mixture model is suitable. This is demonstrated with the ETM Satellite date. EM algorithm is adopted to estimate parameters of Gaussian mixture model. Computer simulation results show that the probability density function of statistics derived from Gaussian mixture model agrees with that of actual data. Curves of false alarm rate also show that Gaussian mixture model is effective at the condition of Pfa＞10-4.
Fluorescence dispersion of Lu2SiO5 crystal as a -image converter was analyzed in theory and point spread function (PSF) of LSO scintillator was studied using Monte Carlo method. The simulation was divided into two processes. The energy deposition distribution of -ray was calculated with MCNP code and transferred to distribution of light photons in the scintillator. PSF was obtained through the Monte Carlo simulation of light transport, which was not available by MCNP code. The result was verified by PSF measurement in the knife-edge experiment. The FWTM (full width at tenth maximum) of PSF, which indicates spatial resolution, was calculated as a function of incident -ray energy and LSO thickness.
Frequency-sweeping interferometry can be used to measure absolute distance and phase measurement plays an important part in it, because the precision of phase directly influences the precision of distance. The paper puts forward a new phase measurement method making use of Discrete Fourier Transform of reference signal and measurement signal. It does not start to sample until each signal crosses zero negatively. After the spectrum analysis, relative errors can be eliminated if zero-crossings can be tested before sampling signals. According to the theory, the paper has made simulations in LabVIEW, and the results show that the method has the advantages of high precision and good ability to overcome the noise. When the distance is 10m, the difference between the average of the measured phase and ideal value is 0.2, and relative uncertainty is 0.105%.
A study on the radiometric calibration of large entrance pupil space telescope is made. After analyzing the difficulties on this work, a new calibration method based on the improved on-board blackbody source calibration in FY-2C is put forward. This new method overcomes the limitation in field of view and diameter of the entrance pupil; and it realizes the full light path calibration to telescope with any possible entrance pupil. Finally, based on the uncertainty analysis of the new method, the advantages of the new method are given.
The dynamic range of streak camera is measured by Fabry-Polo etalon,the definition of dynamic range of streak camera is given when the intensity saturation is taken for 120% pulse width. The control of noise are analyzed. With the laser of 531nm wavelength as input, the pulse duration is about 30ps, the sweep speed is fixed, and the dynamic range of S-1 streak camera is 102.
To develop a convenient illumination detection device with a wide dynamic range, a simple configuration, an automatic light adjustment function and a uniform light radiation distribution, this paper presents a new illumination detection device for CCD camera based on analyzing the structure and light source used by the traditional illumination testing method. This new equipment uses a curved surface reflector lamp cup with an inner-fixed lamp light source, and it is automatically controlled by a single chip processor. We introduce the research work, such as the light source design, illumination detector design, control circuit design and experiment results. The new type illumination detection device for CCD camera realizes the functions such as uniform radiation and automatic light adjustment, its detection range is from 1.010-1lx to 1.0105lx for diversified CCD camera.
Refractive index is an important parameter for optical glass and there are many methods to measure the refractive index of optical glass. In order to measure refractive index accurately and quickly, a new method is introduced to measure refractive index of optical glass based on photo-electric technology. Optical flat has the feature of deviating incident ray, we can get the function of the offset distance and the refractive index, and the displacement fluctuation of light spot image is converted to electric signal outputting by a position sensitive detector. We designed an optical system and a signal detecting and processing circuit, measured the refractive index of K9 glass, and compared the results with the data measured by the method of minimum angle of deviation. The result proves this method is feasible, the accuracy of refractive index reaches 10-4, and it can be used to measure the refractive index of glass with high accuracy demand.
The mode field of a kind of photonic crystal fiber structure with hexagon symmetry hole cladding was analyzed by multipole method, and the effective refractive indexes of base mode at different wave lengths were obtained. The characteristics of this photonic crystal fiber grating were computed and simulated by coupled-mode method and transmission matrix method, and the difference between conventional fiber grating and photonic crystal fiber grating on their reflection spectrum was compared. The paper also analyzed the changes of photonic crystal fiber grating resonant wavelength with the structural change of photonic crystal fiber. Photonic crystal fiber grating has shorter resonant wavelength with increased radius of photonic crystal fiber pillars. Photonic crystal fiber grating has longer resonant wavelength with increased layers of photonic crystal fiber pillars but same radius.
The laser communication link system between the ground station and the orbit satellite is inevitably subject to the atmospheric turbulence, which often leads to message error at receiver or communication interruption. Based on the Born approximation and the Rytov method, the characteristics of the light field on the receiver plane was derived when the laser beam propagated through the turbulent atmosphere by the slant path. At the same time, using the McGlamery algorithm, the atmosphere turbulence phase screen under the Kolmogorov power spectrum was numerically simulated. Based on the simulated phase screen and the Huygens-Fresnel principle, the McGlamery algorithm mainly used to simulate the phase screen of the plane wave was extended to the Gaussian beam propagation. Finally, it is concluded that the atmosphere turbulent channel has a significant impact on the satellite-toground laser communication link systems, and the result indirectly illustrates the McGlamery algorithm is valid to simulate the wave-front of Gauss beam.
In practical application, the light injected to polarization maintaining fiber（PMF）-is typically quasi-monochromatic. When the polarization direction of the incident light and the birefringence axes of the fiber were misaligned, the degree of polarization(DOP) would be changed in transmission process. Using partial coherence theory, the dependence of polarized and partially polarized lights DOP on the starting angle and transmission distance in PMF were analyzed theoretically. And some experiments were done to study the dependence of partially polarized light's DOP on the starting angle. The results show that, if the transmission distance is in centimeter magnitude, the influence on DOP is great. To normal long distance transmission, its influence could be neglected. Compared with the transmission distance, DOP varies greatly with the starting angle. To achieve the relative change of DOP less than 0.01%, the starting angle must be smaller than 0.405.
Polarization-maintaining fiber coupler（PMC）is widely used in military and commercial applications．However，the bandwidth of the ordinary PMC is very narrow and it could meet the requirements of the various light sources．To solve this problem，a broadband PMC shall be developed．Based on the electromagnetic theory of fibers and the principles of the fused bi-conical taper polarization-maintaining fiber couplers（FBTPMC），the tapefused process was improved．The fabrication of improved FBTPMC was realized based on years of production experience and experimental results.Meanwhile, the measurement results show that the bandwidth parameters of the products could meet the requirements of various light sources.
A tunable erbium-doped fiber laser based on acousto-optic tunable filter is introduced. According to the rate equation and transfers equations applicable to the erbium-doped fiber amplifier, the output formula of the acousto-optic tunable erbium-doped fiber laser was deduced. The dependence of the tunable range of acousto-optical tunable erbium-doped fiber ring laser on the amplification bandwidth of erbium-doped fiber amplifier was obtained. In the experiment, the tunable range from 1526.05nm to 1560.63nm was achieved. The experiments show that the tunable range obtained from acousto-optical tunable erbium-doped fiber ring laser is consistent with the theoretically calculated one.
The mirror transducer assembly causing light path variation of ring laser gyro is analyzed. This analysis reveals how the action mechanism of the mirror transducer assembly influences light path in ring laser gyro and to what extent it may have. The calculated results indicate that mirror tilt can induce a light path shift of about 10～20％ aperture diameter at the aperture transverse section. A test system is built to verify that it is the tilt of mirror transducer assembly which causes the light path variation at the aperture. At last, the impact of the action mechanism of light path variation on ring laser gyro performance is discussed.
Since laser micro-Doppler has important applications in detecting the complex vibration of a moving target, discrete wavelet transform multi-resolution analysis is used to represent the experimental data of laser micro-Doppler for detecting complex vibration of moving target to study the signal characteristics at different scales. Radon transforms and time-frequency analysis are combined together to analyze the experimental signal of vibrating target in time-frequency domain. Results show that this method is suitable for recognizing micro-Doppler signal, and it can suppress the cross terms interference produced by the time-frequency distribution of multi-component signals and efficiently extract features of the vibrating target for detection, identification and classification.
In order to improve the performance of Zeeman laser gyroscope, its magnetic sensitive characteristics were investigated. It was found that the gyro sensitive axis was the most bias magnetic sensitive axis, which resulted in the primary magnetic errors. Based on the low frequency magnetic shield theory and the key processes, the magnetic shield structure adapted to the laser gyro operation environment was manufactured. By testing it in the threeaxis magnetic system, it was found that the magnetic sensitivity of Zeeman laser gyro was decreased to 1/1000 of the original value. The magnetic sensitivity coefficient reached 2.0()/(hmT), which satisfied the requirements of middle precision guidance system.
Both the optical limiting mechanism of suspending liquid of multi-walled carbon nanotubes for 532nm laser and the impact of samples thickness on limiting mechanism were investigated by Z-scan test, nonlinear absorption test and nonlinear scattering test. The results show that nonlinear absorption is the main reason in optical limit for lower input energy. Nonlinear absorption of carbon nanotubes, nonlinear scattering of plasma generated by ionization and air bubble generated by solvent boiloff result in a strong limiting factor of carbon nanotubes for high input energy. With the increase of sample thickness, the limiting factor of carbon nanotubes increases, but its nonlinear scattering is reduced when the concentration of suspending liquid is fixed.
After a Galileos beam expander is designed, hundreds or thousands data of divergence angles corresponding to the displacements of lens group are calculated to ensure light spot size. Based on the Design of Experiment (DOE) module in Isight, fast calculation is implemented using codeVs command syntax. Hundreds data are obtained in 2 hours. Efficiency is greatly improved, and manual error is avoided thanks to software operation.
The influence of the aspect ratio on the scattering properties of small size hexagonal ice crystals in cirrus cloud is studied by using the discrete dipole approximation (DDA) method. The scattering properties such as phase function, extinction efficiency, asymmetrical parameter, single-scattering albedo and degree of linear polarization are computed. The results show that the influence of the aspect ratio on the scattering properties of randomly oriented hexagonal ice crystals is significant, and it varies with the size of the particles, but it is independent of the incident wavelength. In addition, there is an intersection point in the profiles of phase function of hexagonal ice crystals with the same sizes but different aspect ratios, and this point will extend forward with the increase of particle size. The result provides a theoretical basis for the object acquisition and identification.
The concept and design of infrared hybrid diffractive/refractive athermalized optical system are described. A diffractive optical element is used to athermalize and achromatize the optical system. A hybrid optical system operating at 3.5m～5.2m wave band and the temperature range of -50～80℃ is designed. The system parameters include a focal length of 100mm, F/# 2, and FOV of 3.5, and it achieves 100% cold shield efficiency. The system stray light is analyzed, and the irradiances of the desired light and the stay light are 1.5104W/m2 and 2W/m2 respectively. The image quality achieved in the temperature range of -50℃～80℃ approaches the diffraction limitation. It is applicable to a cooled FPA detector with the format of 320256 and the pixel pitch of 30m.
The contrast between a ground target and its background under infrared illumination is very important for target detection, identification and tracking, as well as IR stealth and simulation of infrared signature. The theory model for a ground target irradiated by an artificial infrared illuminator is established. According to the definition of contrast, the basic calculation for the contrast between a ground target and its background under infrared illumination is derived; the factors affecting the contrast between the target and its background are calculated and analyzed. The results show that the greater effect on the contrast is observed when the target and its background are illuminate at a shorter distance with greater power and longer time. For illuminators at different distances, with the change of incident angle, the effect of the illuminator on the contrast becomes greater.
To avoid the particle swarm algorithm degradation and complicated computation, a repair particle swarm algorithm for infrared target tracking is introduced. Firstly, the algorithm uses the inertia factor of the defined particles to correct the location of the infrared target detected, so that the location of particles reaches local optimum and global optimum. Secondly, PSO constriction factor is limited to border search to eliminate the ambiguity of the target location. Results show that there is an error of 2.83% in 500 granule iterations and 100 tracks. The tracking result is closest to real target with sharp edge when the maximum inertia weight is 1.2 and the minimum inertia weight is 0.3.
Fast steering mirror (FSM) is a device used to control the direction of light beam accurately. As an accurate device, it has important applications in astronomical telescope, laser communication, tracking and targeting system, stabilized imaging system, adaptive optical system and laser weapon. Several types of FSM were introduced. Some key technologies and components of FSM were discussed, including actuator, controller and sensors. Finally, the development trend of FSM is described.
The polarization properties of thin film Fabry-Prot filter is investigated by eigen method. With the increase of incident angle, the wavelengths of the transmission modes of s-polarized light and p-polarized light separate gradually, but the separation is small. The transmittance of the transmission mode of s-polarized light vibrates greatly and the transmittance of the transmission mode of p-polarized light vibrates little with the increase of incident angle. When the incident angle changes at the separation of 1/100, the wavelengths of the transmission mode of s-polarized light and p-polarized light keep unchanged and the transmittance of the transmission mode of s-polarized light changes significantly, while the transmittance of the transmission mode of p-polarized light changes very small. The polarization properties of film Fabry-Prot filter can play an important role in angle measurement.
The optical characteristics of silicon oxide thin films deposited by the reactive magnetron (RMS) method were compared to those deposited by the reactive ion-beam sputtering (RIBS) method. Dependence of refractive index n, extinction coefficient k and deposition rate on oxygen concentration in Ar/O2 working gas mixture were determined. Silicon oxide films with the refractive index of 1.52～1.55 and extinction coefficient less 10-5 at the wavelength of 0.63m were deposited by RMS method with O2 content greater than 15% of working gas mixture. Silicon oxide films with refractive index of 1.52～1.6 and extinction coefficient less 10-5 were deposited by RIBS method with O2 content more than 80% of working gas mixture. In the case of RMS method, the SiO2 film deposition rate decreases almost 5 times when the process is switched to the reactive mode (more than 15% O2). On the contrary, in the case of RIBS, the deposition rate does not depend on the O2 concentration in the working gas mixture.
An active laser-illuminating sniper detector based on cat eye effect is developed. According to actual circumstances, some tests were conducted to verify the detection performance of the detector. Testing results show that night-vision sight and telescope sights with objective aperture diameters of 32mm, 40mm, 42mm and 50mm can be effectively detected by the detector in the range of 20m to 200m, and thermal weapon sight can not be detected either.
By analyzing the limitations of traditional birefringent crystal depolarizer, a new kind of depolarizer was designed for monochromatic pulse light. This depolarizer is made up of two quartz crystal wedges, and the angle between the two wedgesoptical axes is 45. The results of theoretical calculation show that this device can depolarize monochromatic pulse light. Software simulation based on the advanced system analysis program (ASAP) shows that emergent lights degree of polarization (DOP) is less than 0.00126. This depolarizer can depolarize mono-chromatic light with arbitrary polarization state, and it also works for quasi-monochromatic light. Besides, the depolarization results are independent of time domain.