2015 Vol. 44, No. 10
column
- Infrared technology and application
- Laser technology and application
- Photoelectric measurement
- Optoelectronic devices and materials
- Photoelectric devices and material
- Photoelectrical device and materials
- Optical design
- Micro-nano optics
- Optoelectronic guidance and control
- Space optical communication
- Advanced optical imaging
- Ultrafast optics
- Optical image identification
2015, 44(10): 2867-2873.
For tracking and recognizing a flying rocket, potassium 766.490 nm and 769.896 nm in rocket plume radiation spectrum were studied by the spatial heterodyne spectroscopy. The atmospheric molecular absorption and atmospheric scattering were considered in the atmospheric transmission model. In 763-773 nm, oxygen absorption coefficient was calculated by using line-by-line method, and atmospheric scattering coefficient was calculated by Rayleigh scattering formula and the relationship between scattering coefficient and meteorological visibility. Transmittance was calculated based on Lambert-Beer law. The analyses of solar radiation spectrum and atmospheric transmittance show that these two characteristics of potassium lines in the location which solar radiation intensity is weak and high transmission efficiency, and theoretically verify the feasibility of detection of potassium spectrum. Then, the spatial heterodyne spectrometer was used to detect potassium spectrum that K2SO4 was burned in flames. The experimental datum are accordant with the theoretical results, which demonstrate that the potassium line detection scheme is feasible using spatial heterodyne spectrometer.
2015, 44(10): 2874-2879.
Dewar vacuum failure is usually caused by IR FPA device malfunction, and the evaluation hereby used is testified as a valid method in discussing and analyzing such failure in accordance with Low Density Gas Theory of Vacuum Physics, The IR FPA Dewar device cooling time is regarded as the most direct and effective method in confirming such failure. Notice that the maximum heat loading variation between the maximum reactive power of IR FPA Dewar device and the rated capacity of the cooler should be in correspondence with its use-defined maximum cooling time. And Dewar vacuum life is considered unacceptable if the heat load variation being measured by LN Evaporation Principle is under such condition that the variation is within its specified time in the case it reaches expanded uncertainty(k=3). The value tested should be 30 mW. Within the customized vacuum service life of specified 15 years,the Dewar leakage and gas rate required must be less than 510-15 Pam3/s. As the failure of Dewar vacuum occurred, and simultaneously, the gas pressure must be greater than 110-2 Pa.
2015, 44(10): 2880-2885.
The photocurrent and dynamic output impedance of MW detectors differentiate from LW by several orders of magnitude. For the requirement in integrating time and readout SNR, a designing scheme of a highly integrated readout circuit for 320256 dual-color infrared focal plane arrays(IRFPAs) was proposed by adopting a sharing methods between pixel capacitors. In this circuit, the DI structure was chosen as the MW injection stage and the BDI structure was used for LW. The buffered amplifier had a unilateral structure which always performanced with high gain, low consumption and low noise, thus it reduced the input impedance and improved the injection efficiency. The chip was designed and manufactured based on HHNEC 0.35 m 2P4M standard CMOS process. In the testing process, this chip presented a normal operating state and was sensitive enough to the change of illumination. The total effective charge capacity reached 70 Me-/pixel. Under 2.5 MHz output speed, the output swings of MW and LW were larger than 2 V and the nonlinearity less than 1%. The total power consumption was less than 170 mW when working with the frame rate of 100 f/s.
2015, 44(10): 2886-2890.
The stripe non-uniformity of infrared focal plane array strongly impact the image quality, thus the application of infrared focal plane array is strongly restricted. A real-time FPGA-based system for correcting the stripe non-uniformity was proposed. The system was based on Midway Infrared Equalization method and it could execute the correction in a single frame. Simulation results have demonstrated its efficiency and effectiveness in correcting the stripe non-uniformity. System architecture was optimized for the algorithm so that the system had relatively low FPGA resources consumption and high speed. The system can be embedded into the infrared focal plane array imaging and processing system as an independent module to realize a real-time stripe non-uniformity correction. Due to the previous features, the system has great functionality and extensibility and has a broad prospect in practical application.
2015, 44(10): 2891-2899.
The model for infrared coded mask imaging systems was presented. It was composed with two functional components, the coded mask imaging with ideal focused lenses and the imperfection of practical lenses. The system's point spread function(PSF) can then be represented by the diffraction pattern of the mask and the PSF of the practical lenses. The imaging results with inclined plane waves were also analyzed to achieve the variation of PSF within the view field. According to indices for mask pattern evaluation and system's PSF assessment, mask pattern we proposed based on Dammann grating had a balanced performance for direct imaging and imaging reconstruction. Experiment shows that mask pattern for direct imaging should have more random structures, while more periodic structures in system with image reconstruction.
2015, 44(10): 2900-2905.
Detailed characteristics analysis and power amplification of gain switched Febry-Prot cavity semiconductor laser at 1.06 m were reported. The gain switched laser diode, which is modulated by high frequency sinusoid electrical signal, can generate stable pulse laser trains with pulse width around 100 ps, average power around 20 mW and repetition rate adjustable from 500 MHz to 2 GHz, while injection locking is employed effectively in improving the spectral performance of output pulse by suppressing the extra longitude modes. Besides, the effects of the variations of modulation frequency, modulation power, bias current magnitude, injection power and working temperature on the output performance of the laser diode were experimentally demonstrated in detail. Furthermore, the injection locked gain switching laser diode was amplified in power with a two-stage all fiber amplifier chain as a seed source, obtaining an output power of 82 W with a pump light of 108 W and light-to-light conversion rate of 76% while retaining good power to power linearity.
2015, 44(10): 2906-2911.
The propagation characteristics of Airy beam in the far-field were detailly studied, which start with the theoretical foundation, including the evolution process of intensity distribution, spot diameter and Power in the Bucket(PIB). The change regular of intensity distribution was investigated with the truncation factor a and the arbitrary scale in the transverse x0 and how do a and x0 influence the propagation Distance with Keeping Non-diffraction(DKNd), the Distance in which the Evolution became similar Guassian(DEG) and Self-bending Degree(SbD). The research shows that in the evolution process of intensity distribution which transforms into similar Guassian, the DKNd, DEG and SbD increase with the increase of x0, the DKNd and DEG decrease with the increase of a and a has no effect on SbD. The evolution regular of spot diameter and PIB was also researched. The research shows that the spot diameter fistly remain unchanged and then increases, PIB firstly decreases, then increases and is 0.76 finally in the propagation progress under different values of a.
2015, 44(10): 2912-2917.
Differential absorption lidar is one of important tools for measurement of spatial distribution of ozone in boundary layer. A boundary layer ozone differential absorption lidar system was developed. The stimulated Raman laser in H2/D2 mixtures pumped by the frequency quadrupled Nd:YAG laser at 266 nm was adopted in lidar system. A new Newton telescope received the lidar atmospheric echo. The elastic scattering signals at 288.9 nm and 299 nm were divided into two channels and converted to electrical signals by photomultiplier. Finally the signals were collected by A/D acquisition card for inversion of atmospheric ozone distribution profile. Some ozone data results were given and comparison of ozone profiles between ozone lidar and ozonesonde was displayed. Results show that the influence of the geometrical factor is reduced greatly in the lidar system. Atmospheric ozone profiles from 0.2 km to 2 km can be provided reliably by the lidar system.
2015, 44(10): 2918-2925.
In view of the problem that the seal protection for a laser emission system with large-diameter and wide-band is very difficult, the purification positive pressure ventilation seal method has been put forward. This method was to achieve the purpose of sealing by exhausting the original air and making the pipe full of purified and dry and clean air, so the air and particles from outside will be resisted based on the positive pressure principle. For the flow field of the positive pressure ventilation in laser emission pipe, the numerical simulation of the continuous phase and discrete phase has been made by the CFD software-Fluent, found that the purified positive pressure airflow formed by the positive pressure ventilation could resist the air backflow from outside, but also made a barrier function for the dust particle with kinds of sizes in the air, when the concentration was less than 4.71E-3 kg/m3. In addition, this paper found that the positive pressure ventilation flow caused a 0.32 m optical path difference when laser's band was within 0.8 -10.6 m,based on the analysis of refractive index in the pipe. Measurement results from the positive pressure ventilation experiments show that trends of vary of particle concentration and simulation curve are basically consistent, which demonstrates the effectiveness of the method of positive pressure ventilation.
2015, 44(10): 2926-2932.
In order to decrease the residual stress and distortion of laser repairing titanium alloy substrate, the influence of different laser scanning paths on the residual stress and distortion of repairing substrate was researched by using ANSYS parameter design language, the residual stress distribution of different layers and different scanning paths was simulated. The result shows that the residual stress of both ends of repairing substrate is higher than other location, the residual stress of repairing layers is higher in both ends, and lower in the middle. The residual stress and its ranges in different repairing layers is lower by using direction orthogonal changing scanning paths, and the flatness of repairing substrate decreases. The residual stress of repairing substrates under different scanning paths was measured by indentation test, the distortion curves of different scanning paths were drawn, which was in good agreement with simulated results.
2015, 44(10): 2933-2937.
Aimming at detecting the micro-Doppler effect of target away, the mathetical model of variational Local Oscillate(LO) power influence to signal to noise ratio(SNR) of balanced heterodyne detection for coherent lidar were established. Besides, simulation analysis on this model was proceeded. The effect on feature extraction was observed through experiments. The results show that in balanced heterodyne detection, where quantum efficiency of two photo electric detectors can't match completely in reality, there will be a specific LO power making the SNR best, considering the shot noise,hot noise and LO intensity noise. While choosing the optimal LO power in detection, the micro-doppler feature extracted will be more readable and accurate.
2015, 44(10): 2938-2943.
In order to detect the imaging reliability of infrared target with difference wavelength at high low temperature,black body and IR collimator are adopted to simulate infinite target,IR aiming device is located in high low temperature and image of IR target is captured by CCD so as to judge the imaging quality of IR aiming device. The designed collimator was with wild-field and its MTF at 20 lp/mm spatial frequency was higher than 0.2 in corresponding focal plane of different wavelength. Meanwhile in order to provide an stable -55℃ -70℃ high low temperature testing condition rapidly and accurately, a self-adaption fuzzy PID temperature control technology was provided. Adaptive factor was adopted to combine fuzzy inferior and PID controller. By adjusting control parameters on-line, the performance of PID controller was further improved and system control accuracy was raised up. The experimental results show that this method not only improves the dynamic response process but also guarantee no static error. The temperature control precision is 0.05℃.
2015, 44(10): 2944-2951.
To fulfill the need of measurement on the small bore's interior features, a specially designed optical transmission component was adopted to divert exterior illumination into the interior of small bores and to export the interior image. This study surpassed the traditional mode and achieved the exterior placement of the measurement sensors to make it possible for the measurement in narrow space. To fulfill the need of measurement on small bores in different position and direction, a new flexible in-line measurement system was set up utilizing the movement platform of industrial robots. Firstly, the design of the measurement system was proposed based on analysis of preliminary method, and the flow of the work was given. Then, the question of alignment between sensor and sample was analyzed in detail, and a novel, reasonable method of aligning was given. Based on the system, the measuring experiment was carried out on 0.6 mm, 1.0 mm and 2.0 mm simulated defect points on interior wall of 10 mm diameter bore, the standard deviation is all less than 0.01 mm. The experimental result shows that the system is valid and able to accomplish the feasible, on-line measurement.
2015, 44(10): 2952-2958.
In order to solve the problems that the initial value of Brillouin peak power in laid sensing optical fibers is hard to be obtained and the measurement error of temperature and strain is large based on Brillouin frequency shift and peak power, the method of distinguish measurement of temperature and strain is proposed. The Brillouin frequency shift and relative peak power coefficients of temperature and strain, as well as initial Brillouin frequency shift, were obtained by calibration experiment. The coefficients in Brillouin power equation were obtained by heuristic method according to the reference fiber in known temperature and strain. Then the initial Brillouin power distribution along the laid fiber was obtained. The measurement error caused by multiplicative noises in sensing system was conquered by normalization. The spikes in the Brillouin peak power profiles at positions of changed temperature or strain were eliminated by using spectral width change. The simulated optical path of optical fiber composite submarine power cable in engineering field was established. The measurement experiment of temperature and strain was performed. The results indicate that the measurement accuracy are 4.3℃ and 110 at 5.6 km. The distinguish measurement of temperature and strain for laid sensing fiber can be realized. The method can provide theoretical and experimental basis for engineering applications.
2015, 44(10): 2959-2964.
Calibration to standard reference gas scale is necessary to improve the accuracy of the measurements,and ensure the compatibility of measurement values between different instruments for 13CO2 value based on Fourier Transform Infrared(FTIR) spectroscopy. Firstly, the calibration methods were put forward, the absolute calibration and empirical calibration methods were studied in detail. On the basis of these researches, the 13CO2 values were calibrated to standard reference gas scale. The calibration results show that measurements accuracy has been improved greatly, compared with measurement results of no calibration. The accuracy for absolute calibration and empirical calibration methods are improved 5.5 and 6.4 times respectively. The study is benefit to improve the accuracy of FTIR measurements and the compatibility between different instruments.
2015, 44(10): 2965-2969.
With the objective of collecting more accurate results and improving the testing accuracy during the mirror substrate manufacturing and generating phase, the adjustment theory to measure the large aperture mirror profile based on the instrument of laser tracker was adopted. Firstly, the adjustment theory was deduced and the main influence factors for the accuracy of the profile metrology was obtained, then the fitting model of profile of the large aperture mirror was established. And then a method to improve the metrology accuracy for the fitting model was proposed. Lastly, the method was applied to the two meter class in diameter substrate of SiC primary mirror, and the theory was verified from the different aspects of F number, residual error and structure function. The proposed method could be showed as a guideline to the metrology and manufacture of large aperture mirror.
2015, 44(10): 2970-2974.
To evaluate the jitter of the Thirty Meter Telescope tertiary mirror, the acceleration signal collected from the tertiary mirror should be integrated into displacement signal and to be analyzed. The first and foremost, the acceleration of the mirror along the normal line was achieved. Then, the trapezoidal, Simpson, 3/8 Simpson numerical integration method were analyzed to show the basic property of the integration method; after that, using the transfer function and spectrum method, the jitter property of a large telescope at one meter scale was analyzed in both value and frequency domain and the jitter after adaptive optical adjustment was 6 m RMS. At the same time, this verifies the testing process plan for the jitter of the TMT M3. In this paper, the basic procedure for mirror jitter analysis was presented, and the conclusion can be draw that the method is adequate to fit the requirement proposed by TMT project. This work will give guidance to the jitter testing in the similar large aperture system.
2015, 44(10): 2975-2980.
The noise signals can be compressed and the optoelectronic signals can be amplified by the applied gate voltages in field-effect transistor(FET)-based photodetector. Organic materials have been widely applied in phototransistors, it is meaningful to fabricate all-organic photodetectors for large area, low cost and flexible device applications. However, multiple polymer layers are usually fabricated through solution processing and the 'solution corrosion' should be avoided during its fabrication process. Therefore, top-gate-bottom-contact(TGBC) FET configuration and orthogonal solvent were adopted in the experiments, and the bulty acetate was used as the solvent of poly(methyl methacrylate)(PMMA) to prevent destroying the poly(3-hexylthiophene)(P3HT) active layer. In this way, the FET-based all-organic photodetectors Au(Source, Drain)/P3HT(150 nm)/PMMA(800 nm)/Al(Gate) had been successfully prepared, showing an on-off current ratio of 103 and a maximum mobility of 810-3 cm2V-1s-1. The photocurrent shown an obvious increment under illumination of a broad range of incident wavelengths from 350 nm to 650 nm, giving a maximum photo-to-dark current ratio of 75 under 0.1 mW/cm2 illumination. The largest photoresponsivity of ~0.28 A/W was obtained under the illumination of 600 nm, and the trend of photoresponsivity corresponds to that of the absorption of P3HT film.
2015, 44(10): 2981-2986.
The electrostatic distributions between Micro-channel plate(MCP) and photocathode will affect the movement locus of photogenerated electrons and the proximity image intensifier's performance. However the distributions of electrostatic fields and equipotential lines were complex due to a lot of micro-channel in the micro channel plate. So this paper simulated the electrostatic distribution of MCP input in proximity focusing low-light-level image intensifiers by the finite element simulation analysis software Ansoft Maxwell 3D. How the electrostatic distribution of MCP input were affected by micro-channel diameter, angle of micro-channel, minimum interspacing between micro-channels walls and flaring-condition of the input end of the channel were analyzed according to the simulation result. Meanwhile, the photogenerated electrons' trajectory and image intensifier's resolution affected by the change of electrostatic distribution were discussed. This study will provide a theory foundation for the fabrication of the high quality MCP.
2015, 44(10): 3015-3019.
In order to study the changing rule of single layer thin film surface roughness using light scattering, the polarized bidirectional reflectance distribution function(P-BRDF) of the single titanium dioxide thin film at fully correlated and uncorrelated model were researched respectively based on the vector scattering theory of optical thin film. The relationship of scattering azimuth angle and BRDFpp, P-polarized scattered light caused by P-polarized incident light, was researched. The theoretical results show that BRDFpp strongly depends on the correlation between interfaces roughness of thin film and substrate with azimuth angle changing. The scattering azimuth angle of BRDFpp valley value can decrease with the increase of incident angle at fully correlated model. The result is reverse to uncorrelated model. BRDFpp does not appear valley value as the change of scattering azimuth angle.
2015, 44(10): 2987-2994.
Three DOFs elastic support for fast steering mirror driven by piezoelectric is designed in order to effectively absorb the lateral deviation of driving point caused by tilting of mirror, protect the piezoelectric drivers, restrain the DOF in non-working direction and enhance the frequency resonance of system. Firstly the scheme of all-around elastic support which consists of flexure ring and flexure staff was determined according to requirements of fast steering mirror driven by piezoelectric design. Secondly flexure ring and flexure staff was designed separately based on the buckling theory and energy theory. Finally the design was analyzed with FEA software workbench. The FEA analysis shows that the sheer displacement of piezoelectric decreases 86.7% with the application of 8 mm length and 1mm diameter flexure staff. In addition, the application of flexure ring turns the axial translation vibration into the first-order mode with resonance frequency of 340 Hz,turns the swing vibration into the second and the third order mode with resonance frequency of 420 Hz and the higher-order resonance frequency is more than 1 000 Hz. The three DOFs elastic support can prevent piezoelectric from sheering damage and help to enhance the resonance frequency of fast steering mirror system, which does help to enhancing the close-loop bandwidth of the system.
2015, 44(10): 2995-2999.
A comprehensive analysis on the relationship between the barrier height and the peak wavelength of bound-to-quasi-continuum Quantum Well Infrared Photodetector(QWIP) was demonstrated, together with its effect on characterization of microstructure and macroscopic optic properties of the device-sample. The GaAs/AlxGa1-xAs infrared quantum well material was produced via the method of Metal Organic Chemical Vapor Deposition(MOVCD). Two sample devices with different Al content(0.23 and 0.32) was designed respectively and their corresponding spectral responses were measured via Fourier Transform Spectrometer at the temperature of 77 K. The experimental results shown that sample 1# and 2# are with the peak wavelengths of 8.36 m and 7.58 m, which present obvious difference to the theoretical results based on Schrodinger equation(9.672 m and 7.928 m, corresponding to errors of 15.6% and 4.6%, respectively). By analyzing the effect of Al atoms diffusion length, it is found that the decrease of Al content is the key effect which leads to sub-band narrow down and peak wavelength red shift. Meanwhile, by using the method of High Resolution Transmission Electron Microscopy(HRTEM), it is found that the strong error of sample 1# is mainly due to the crystal lattice mismatch between GaAs and AlGaAs, together with the unsatisfied precise control during the growth of quantum well material. Above analysis demonstrates that adjusting the Al content of barrier height is an effective method to turn the peak wavelength of QWIP.
2015, 44(10): 3000-3004.
Double-layered multimode waveguides were fabricated in optical glass substrate, each layer being formed by melt salt ion-exchange(IE), and subsequent field-assisted ion-migration(FAIM). Characterization of the double-layered waveguide chips were performed by microscopic observation of waveguide cross-section, output pattern observation, and insertion loss and crosstalk measurement. Results shows that dimensions of waveguides core at top layer and bottom layer core are respectively 29 m19 m and 31 m20 m, and output pattern of waveguide at different layers are of nearly the same dimensions. Waveguide loss characterization show that propagation loss of waveguide at top layer and bottom layer are 1.000.32 dB/cm and 0.780.35 dB/cm, and crosstalk between neighbor waveguide at different layers is approximately 17.7 dB. Analysis demonstrate that interconnection density can be doubled by adopting double-layered waveguide, thus this kind of waveguide can be expected a promising prospect in improving EOCB performance.
Design and calculation of absorption layer thickness on InP/InGaAs transferred-electron photocathode
2015, 44(10): 3010-3014.
The electonic structure and optical properties of standard InGaAs material, which formed the absorption layer of transferred-electron InP/InGaAs photocathode, were studied based on the density functional theory, the exchange and correlation potential energy was described by Heyd-Scuseria-Ernzerh(HSE06). First, the energy band structure of zinc blende GaAs was verified with this hybrid density functional, then the standard InGaAs bulk model was established, and dynamically optimized by self-consistent method before complex dielectric function was obtained, then the optical absorption coefficient was derivated from Kramers-Kronig relation. Finally, under the estimation of P-type standard InGaAs unequilibrium minority carriers effusion length were 0.8, 1.0, 1.2, 1.4, 1.6 and 2.0 m separately, combined with quantum efficiency formula of transferred-electron photocathode, the optimized absorption layer thickness of InP/InGaAs photocathode was derivated according to the photon energy between 0.780 260 eV and 0.820 273 eV with spacing 0.002 eV.
2015, 44(10): 3005-3009.
In order to design one special filter with wide-refection, ZnS and Ag film was chosen as the layers based on the induced transmission filter. The ZnS layers were deposited by Ion Beam Assisted Deposition(IBAD) and treated using ion source deposition, and the Ag layer was deposited by magnetron sputtering. The rate of Ag film with different working parameter was discussed in this paper. At last, the best working parameters were chosen and deposited the induced transmission filter. The results indicate that it has over 90 percents of transmission from 750 nm to 850 nm and more than 90 percents of reflection from 2 500 nm, and the face-resistence is less than 300 . The filter has a good reflection infrared and anlistatig character.
2015, 44(10): 3020-3024.
Along with more broad application fields of the high-resolution optical system, the high-precision assembling requirement of optical components, as same as the high-precision design requirement, has become the decisive element of the optical system resolution. Because the current Gauss optical correction method only considers the alignment of object-image location, and cannot actually meets the requirement of optical system adjustment, the alignment theory of optical instruments needs to be developed synchronously. The influence of aberration on misalignment of optical system was considered fully, a correction method for transmission-type misalignment optical system was proposed based on aberration theory. The variation regularity of single lens aberration caused by axial displacement was analyzed, and the aberration effect coefficients were defined. On this basis, through calculating the size of lens adjustment induced by the image position error and the magnifying rate error, the misalignment correction formula based on the constraints of the aberration was deduced mathematically. Taking the three lens collimation system for an example, the simulation was carried out to validate this method. It comes to the following conclusion: by introducing the aberration constraint theory into the correction method, the final correction result meets both the requirement of Gauss optical characteristic and the minimum aberration increase.
2015, 44(10): 3025-3031.
In order to make small infrared camera carried by a flight equipment can be well in a wide temperature range and bad dynamic environment, opto-mechanical structure of camera was designed. Firstly, the optical system and working environment were analyzed, according to design experience of the similar products, all-aluminum body were used for the opto-mechanical structure; Secondly, the core component-primary mirror support structure was studied in detail. By reason of limitations of traditional primary mirror support structure, integrative design was used for primary mirror support structure. this design was equally applicable to secondary mirror. Thirdly, thin-wall canister was used for the support structure between primary and secondary mirrors according to size of camera. And then,rational baffle was designed according to the optical system. Lastly, overload adaptability, temperature adaptability and modes of camera were analyzed. Results show that opto-mechanical structure of small infrared camera meets design requirements.
2015, 44(10): 3032-3036.
Athermal design is necessary to design a LWIR optical system for working under temperature range of -40-+60℃, because the infrared optical materials could transform extremely with the change of temperature. On the basis of introduction of athermal system and analysis on the effects of optical elements, an infrared telephoto objective lens was designed in the way of optical passive compensating, which working waveband was 8-12 m long wave infrared band, F# was 2, the field of view was 6.8,uncooled focal plane array was adopted. A prism was added in the system to achieve athermalization and compact structure without adding a special surface, the telephoto ratio of this system was 0.69. All of the surfaces were designed to be standard sphere, which was of benefit to processing, alignment and testing. The result of design indicates that the optical transfer functions are close to the diffraction limit in the required temperature range and the design requirement is met.
2015, 44(10): 3037-3042.
A new structure is adopted to design a visible and near infrared large aperture telescope with 1.2 m diameter, 2-6 m focal length, and 1/1.67-1/5 relative aperture. For meeting the requirement of modern ground-base large telescope, the front primary system using Cassegrain reflective form. And the back part uses three group mechanical compensation zoom refractive system, which makes the structure more simple and compact. Based on Gauss optics calculation and analysis of aberration, the initial form of each group was determined, and the whole system was optimized subsequently. The design results show that all of the optical indexes satisfy the command of the system, and the structure was compact, the compensation curve was smooth. The design demonstrates that the form is an effective optical structure for large aperture continuous zoom telescope.
2015, 44(10): 3043-3048.
In order to reduce the influence of the mass and sizes of mirrors on the quality of space camera, such as optics quality, mechanics quality and stability of thermal dimension of structure, the necessity of lightweight for mirrors was introduced. Material selection, substratum's back shape, lightweight pattern and support pattern were taken into account in the design of large-aperture mirror in space camera. A new design with open bottom, triangular aperture was proposed based on theoretical and finite element analysis. Through the rational design of support structure parameters, the surface accuracy of mirror meets the needs of the imaging quality(PV63.2 nm) under environment of gravity.
2015, 44(10): 3049-3054.
Whispering gallery modes(WGM) optical resonators is an important tool for optical research with broad application prospects. A CaF2 disk resonator was fabricated with ultra-pure single crystal of calcium fluoride characterized by the diameter of 5 mm and thickness of 1 mm. The CaF2 disk resonator was polished with chemical mechanical polishing method and nanometer-scale roughness was achieved. The coupling test platform of disk resonator and tapered fiber was set up to test the optical properties of the resonator. The test results showed that CaF2 optical resonator characterized by the quality factor Q=2.1106 at =1 550 nm. The loss mechanisms of the resonator was analyzed and the method to improve quality factor of the CaF2 resonator was proposed.
2015, 44(10): 3055-3060.
Microchannel plate is the key component of the image intensifier. Compared with traditional MCP, Si-MCP has a great improvement in performance. Before DRIE in Si, the wet etching is necessary in the Al film. As the film pattern was the big area and periodic micropore with the pore of 10 m, the pitch of 5 m, the micropore resulted in the H2 absorbing on the reaction interface easily and affecting on the reaction. Meanwhile, the arrayed micropore pattern would appear random corrosion, incomplete corrosion and over etching because of the inappropriate corrosion parameters. By adding surfactants, the surface stress can be reduced, which can promote the reaction H2 discharge. By individually controlling variable, the affects of the corrosive concentration, temperature and the etching time on the result were focused. The results shows the corrosion rate is proportional to the corrosive concentration and temperature. By optimizing parameters, the best corrosion parameter is got. The pattern is complete and the size is accurate. The pattern of the arrayed micropore is solved which has a important significance to the DRIE.
2015, 44(10): 3061-3065.
For triple-electrode carbon nanotube sensor, the electrode separation between electrodes is one of the key factors to influence the accuracy of detection. It is very difficult to decide the sensors' electrode separations when detecting the multi-component gas mixture using sensor array. A electrode separation optimization method for triple-electrode carbon nanotube gas sensor was presented. The method is based on particle swarm optimization(PSO) and includes following procedures: designing electrode separation, constructing sensor array using multi-sensor with different electrode separations, building data base including electrode separation and detection ionic current, creating quantitative analysis model of mixed gas, and optimizing electrode separation. The NO and SO2 gas mixtures were detected by multi-group sensor array, which were composed of three carbon nanotube sensors with different electrode separations. The electrode separations of three sensors was optimized using above-mentioned method. The experimental results show that the proposed method is able to select the optimal distances between electrodes effectively and the sensor with optimized electrode separation achieve higher detection accuracy.
2015, 44(10): 3066-3069.
With obvious advantages comparing to gimbaled seekers, strap-down seekers attract more and more attention from military of different countries. Since strap-down seeker can not measure the line-of-sight(LOS) angular rate directly, the problem of LOS angular rate extraction is solved firstly, which generally has two methods. One method is to get the LOS angular rate by solving the differential of LOS angle versus time, the other is to estimate the LOS angular rate by Kalman filter. The models of these two methods was built and simulations of them were made respectively. The simulation result shows that, the second method is better than the first one. The time delay of LOS angular rate estimated by Kalman filter is relatively shorter than that obtained through differential network. With the measurement noises at the same level, the output LOS angular rate noise of the second method is smaller than the first one.
2015, 44(10): 3070-3075.
According to the characteristics of the line-of-sight kinematics in mirror stabilization platform, a general method based on the artificial mass stabilization platform was used to reconstruct LOS angle rate by utilizing the basic mirror kinematics equations. Then the relation between mirror rotation and the field-of-view was figured out. Due to the law of reflection, an auxiliary shaft must be made for mechanical mass stabilization or semi-strapdown stabilization. Analyzing this two methods deeply show that the methods are both feasible for mirror LOS stabilization control, but semi-strapdown stabilization would accord with the future needs.
2015, 44(10): 3076-3083.
Firstly, to solve the nonlinear problem in the field of passive tracking, Gauss-Hermite quadrature is used to Gaussian mixture probability hypothesis density filter, and the quadrature Kalman probability hypothesis density filter was proposed. Then under the condition of unknown and time-varying process noise statistic, a noise statistic estimator based on maximum a posterior estimation was used in probability hypothesis density filter. According to the residual between predicted state and estimated state, an algorithm to judge and restrain filter divergence was proposed. Finally, simulations under the condition that two passive sensors tracking multiple targets show that:the proposed algorithm has better accuracy than existing algorithms, and achieve good effect when process noise statistic is unknown and time-varying.
2015, 44(10): 3084-3091.
Circular polarization control error caused by system design and intensity fluctuation as well as phase noise induced during the transmission of optical signal in atmospheric turbulence will directly lead to performance impairments of circular polarization shift keying(CPolSK) system in FSO. Therefore, on the basis of roundly considering the three parameters, which are the intensity scintillation, the phase noise and the circular polarization control error, the mathematical statistical model of the CPolSK system channel was established based on the Gamma-Gamma atmospheric channel model, and the closed expression of the average channel capacity was derived. Simulations were given to analyze the effects of intensity scintillation, phase fluctuation and circular polarization control error on channel capacity of CPolSK system. Results show that the increase of both intensity fluctuation and phase noise will cause the degradation of the channel capacity, while raising the average SNR can improve the channel capacity in a certain degree. It is also noted that the average channel capacity will significantly decrease when the circular polarization control error is larger than 8.
2015, 44(10): 3092-3097.
Because of the scattering and absorption of raindrops, laser power attenuates when travelling through the rain. Firstly, according to the Mie theory, the method of calculation of the extinction factor in the rain was presented. Secondly, Joss and Weibull raindrop size distributions were introduced, and the comparative analysis was shown that Joss raindrop size distribution was more precise. At last, the extinction factor and link loss of long wavelength infrared laser in the rain were analyzed by using Matlab. From the analytical results, it is cocluded that the value of the extinction factor becomes larger with rainrate increasing; Considering beam divergence, field of view and scattering energy, the link loss calculated by photon tracing method is more accurate compared with Lamber-Beer Law.
Adaptive parameter identification tracking based on particle filter for airborne laser communication
2015, 44(10): 3098-3102.
Airborne laser communication has became the main way of large capacity space communication for the future, high precision dynamic tracking system of airborne platform has already been one of the most difficult problem. In order to resolve the diversity of maneuvering forms for airborne platform, adaptive parameter identification with particle filter was put forward in the paper, in the continuous time domain, parameter identification model based on three order linear differential equation was applied to describe the motion of airborne laser platform, which can cover a wide variety of motion modes, the particle filter can deal with nonlinear/non-Gaussian problems, it can be introduced into parameter identification model. The results show that this algorithm can improve the convergence precison, which have some significance in engineering application.
2015, 44(10): 3103-3109.
Numerical simulations for static turbulent phase screens are presented with power spectrum method(FFT). Also simulation methods for dynamic phase screen were presented by using traditional turbulence frozen method. An indoor atmospheric turbulence simulator was designed based on LC-SLM, and a simulation test bed was built. In the Kolmogorov turbulence laser propagation characteristic in different turbulent atmosphere was simulated. The experiments results were analyzed and showed the agreement with the theory. The response of bit error to intensity of turbulence were investigated, it is meaningful for value the laser communication system indoor test.
2015, 44(10): 3110-3116.
Balanced photodetectors can suppress effectively common-mode noise produced by laser and atmospheric channel in the space coherence optical communication. The sensitivity of balanced detectors are obviously improved in the coherent detection. In order to explore the performance of balanced detector, noise mechanism of balanced photodetector was analyzed. The 2.5 Gbps and 5 Gbps theoretical limit of sensitivity was presented in the condition of incoherent and coherent detection. Balanced photodetectors were designed and test system was built for the mesaurement of sensitivity. In 2.5 Gbps communication rate, incoherent detection sensitivity reached -21.1 dBm, and coherent detection sensitivity reached -41.2 dBm. Test results roughly coincide with theoretical analysis. The reason that test results deviates from the theoretical value was analyzed. Sensitivity analysis and design of balanced photodetectors provide a theoretical basis for the realization of the space coherent optical communication system.
2015, 44(10): 3117-3123.
Micro-polarizer array(MPA) imaging technology has special advantage in equipment volume, weight, real-time imaging etc. All these advantages expand the application of polarization imaging. But little research has been done on how to design MPA parameters, and how to arrange MPA cells, and how to calculate polarization parameters from acquired images. In order to solve this problem, the study of micro-polarizer array(MPA) imaging was carried out in this paper, the grating diffraction and equivalent medium theory were utilized in the design of the relevant parameters for MPA, and a joint coding and decoding design method in frequency domain for MPA was also put forward. The simulation results reveal that the choice of the design method for joint coding and decoding of MPA will have a significant impact on the acquisition performance of polarization information.
2015, 44(10): 3124-3129.
Temporal-spatial Oversampling(TSO) system has unique advantage for infrared point target detection. Infrared point target imaging simulations and experiments were designed. The shapes and energy distribution of point target in infrared image which were taken by TSO and ordinary sampling systems were researched. The point target imaging features were verified by the simulations and experiment results. First, principle of TSO system for point target imaging was compared with principle of ordinary sampling system, the main difference of the two sampling system was the arrangement of infrared detector's pixels. The arrangement of pixels in TSO system used half-sensor-alignment to improve the efficiency of point target energy collection. Then, imaging models of TSO and ordinary sampling system were built for simulations of point target imaging by two systems. The two systems characteristics were researched by simulations. And also the statistical characteristics of maximum pixels were analyzed. Simulation results show TSO system can get more stable point target imaging. Finally, infrared point target imaging experiments of two system were designed. The experiment results show that the temporal-spatial oversampling system can overcome the bad influence by phase noise. And the target images also have special characteristics in temporal-spatial oversampling system. These characteristics can make the infrared point target detection more effectively.
2015, 44(10): 3130-3133.
The optical index modulation was theoretically estimated and demonstrated under short X-ray excitation in low-temperature-grown GaAs(LT_GaAs). Hot-electron thermalization time 1 ps, carrier recombination time 2 ps and the duration of the index perturbation was determined by the carrier recombination time which was of order -2 ps in LT_GaAs with a high density of recombination defects. Predictions of radiation-induced changed in the optical refractive index were in reasonably good agreement with the limited experimental data available, suggesting that LT_GaAs was a highly promising material for high speed single transient ionizing radiation detector.
2015, 44(10): 3134-3140.
With the development of wide-field detection technique, the super-wide Field of View(FOV) imaging system has been used in many advanced fields, such as missile pre-warning, extravehicular observation, airborne warning, and so on. The space application of super-wide FOV imaging system was discussed, and the advantages of space application were analyzed. The system detection performance was deduced theoretically and calculated numerically from five aspects. The results show that, compared with the small-field imaging systems, the super-wide FOV system has lower space false dismissal probability, which makes the system have less detection blind zone; the system has larger spatial resolution, which makes the target have a longer imaging time and benefits the target extraction; however, other performances of super-wide FOV system are relatively weaker. Considering all the performances, the super-wide FOV imaging system may not suitable for long-range space target detection, but can be used in omnidirectional Space Situation Awareness(SSA) and real-time threat warning of long-range strong radiation for the host satellite.
2015, 44(10): 3141-3147.
A hyperspectral subpixel target detection algorithm was proposed based on extended mathematical morphology and spectral angle mapping. The spectral and spatial information had been used to locate and detect targets under the condition that prior knowledge of targets and background was unknown. Then hyperspectral subpixel targets was detected and recognized. The extended mathematical morphological erosion and dilation operations were performed respectively to extract endmembers. The spectral angle mapping method was used to detect and recognize interested targets. The hyperspectral image collected by AVIRIS was applied to evaluate the proposed algorithm. The proposed algorithm was compared with SAM algorithm and RX algorithm by a specifically designed experiment. From the results of the experiments, it is illuminated that the proposed algorithm can detect subpixel targets with low false alarm rate and its performance is better than that of the other algorithms under the same condition.
2015, 44(10): 3148-3154.
Stripe noise is one of the important factors affecting the quality of multispectral remote sensing image, seriously influencing the interpretation of remote sensing data and information extraction. A multispectral remote sensing image quality assessment method aimed at stripe noise based on phase congruency was proposed. This method, which extracts phase congruency point in the frequency domain as the image feature, is not affected by image brightness or contrast, and can objectively evaluate the stripe noise existing in the multispectral remote sensing image by considering the number, length, width, and the intensity of the stripe noise in the image. The experiments show that the proposed algorithm correlates well with subjective quality evaluations.
2015, 44(10): 3155-3160.
Hyperspectral image has hundreds of successively narrow bands, which brings serious problems such as large correlation and redundant information. The selection of the optimal bands, which are suited for classification or recognition, has become a difficult work that needs to be overcome. In order to solve the problem of the large correlation among bands, a band selection method based on improved subspace partition through global search on correlation matrix was proposed. Through a global search, the band correlation matrix was divided into a series of subspace, from which the optimal bands were finally selected. The proposed method provides a band selection which has small correlation between each other. The result of an experiment which used Support Vector Machine(SVM) on an AVIRIS image shows that the proposed method is valid.
