2008 Vol. 29, No. 3
A measurement system of bidirectional reflectance distribution function (BRDF) was developed based on the BRDF measurement principle of single reference measurement method, and it works at up to 500℃. Different angle position transfer was realized by a turntable device. The sample was heated by a furnace and the temperature was controlled by a fuzzy PID controller. The BRDF on a Cu surface was measured at the temperature of 25℃～500℃ by using a He-Ne laser as the light source whose wavelength was 0.6328μm and power was 8 mW. The Si1336-5BK photoelectric detector was selected for the measurement. The experiment shows that the measured value of BRDF on the Cu surface changes when the temperature on the sample surface is rising, and the BRDF value on the Cu surface is different when it increases or decreases to the same temperature. The forming mechanism of the phenomenon was analyzed. The conclusions can be used for further study on spatial reflectance characteristics of material surfaces.
The spectral waveband is an important factor to be investigated in optical remote sensor design. The spectral waveband suitable for the reflective TDI CCD optical remote sensor to detect oceanic objects is analyzed. With LOWTRAN 7 software, the atmospheric transmittance in the waveband of 0.4μm～1.0μm was calculated, the spectral reflectivity and contrast of typical oceanic targets (e.g. ship hull) and seawater was analyzed, the entrance-pupil radiance and the SNR of the remote sensor were estimated, and then the optimal detection waveband was selected. The calculation result shows that it is better to select the waveband of 0.5μm～0.9μm than that of 0.5μm～0.8μm considering entrance-pupil radiation intensity and SNR of the remote sensor. This conclusion can be used to support the waveband selection for the system with similar applications.
Focal depth plays an important role in optical storage systems, and high focal depth makes the focusing servo system easy to track the disk surface. The effect of the pure-phase diaphragm on the axial light-intensity distribution and focal depth was investigated in low-and high-numerical aperture systems by means of scalar diffractive theory and vector diffractive theory, respectively. The results show that the proposed phase diaphragm affects the focal depth considerably, and the focal depth may increase by six times for certain geometrical parameters of the phase diaphragm in the systems with highnumerical aperture.
The analytic expression of the fractional Fourier transform (FRFT) based on cylindrical coordinates was derived. The transform relation between the lightintensity distribution on the fractional Fourier transform plane and the various beam parameters was discussed, and the numerical calculation was made. The transmission property of FRFT for the hollow Gaussian beam based on the on the cylindrical coordinates was obtained.
An optical cone-coupled ICCD system was developed to detect the biochips labeled with fluorescent molecules. The CCD chip and image intensifier were cooled to increase the sensitivity of the system. Based on the analyzed results of the experiment, it is determined that the major background noise comes from the stray light and the fluorescence from the substrate impurities of the biochip, and the sensitivity of the system is limited by the objective lens for imaging. The background noise can be effectively reduced and the detection sensitivity can be improved by using a substrate with less fluorescent impurities, such as a quartz substrate.
In order to design a spatially matched filter to limit the influence of background noise on correlation spot on the output correlation plane, the function of the matched filter and the Fourier spectrum of the background noise were compared, and the amplitude of the matched filter was nonlinearly modulated based on the magnitude of their difference. It enables the filter to reduce the transmittance in the area of the intense noise Fourier spectrum, while maintain the high transmittance for input image Fourier spectrum in process of the matching filtering. The signal-to-noise ratio on the output correlation plane was improved and the detection of the correlation spots was realized. The results of computer simulation and experiment show that the anti-noise capability of this spatially matched filter is better than that of the phase matched filter.
A new laser beam expander with magnification of 40× as well as on-axis and off-axis aberration corrected properly, was designed based on the third-order aberration theory. This system is realized by two-step beam expanding based on a simple Galilean structure. The beam path of the system is folded by four lenses, two second-order aspheric surfaces and two mirrors (or a prism). The optical mechanical parameters, outline drawing and image evaluation are given by the aid of optical design software CODE V. This system features simple design and structure, low cost, high image quality and good performance.
Resolution and MTF are two important parameters of an image intensifier. The characteristics of the two parameters of a double-proximity focusing image intensifier were analyzed by means of several expressions based on the Fourier spectral theory of linear systems. Two theoretical limiting resolutions were obtained by calculation under a series of theoretical and technologic conditions, for both constructive modes of double-proximity focusing image tubes, in which one is a normal mode of photocathode/MCP/phosphor screen, and another is a mode of electron-internal amplification photocathode/phosphor screen. The calculated results are 96.6lp/mm and 98.1lp/mm.
As a military optoelectronic technology, the aircraft night vision imaging system (ANVIS) compatible lighting technology can guarantee the normal operation of ANVIS and plays an important part in night fighting in modern local conflict. Based on the simply introduction of the development status, key technologies and developing direction of LLL image intensifiers as well as the influence of common light source on ANVIS was analyzed, the importance of ANVIS compatible lighting technology was described. The main methods for realizing ANVIS compatible lighting, measurement methods and the development status of ANVIS compatible lighting technology were presented. The developing direction and the key technologies for domestic ANVIS compatible lighting were put forward based on the technology status at home.
To eliminate the bombardment of feedback ion to a photocarhode of a Gen. Ⅲ LLL night vision system and increase its operating lifetime，the preparation technique of depositing a Al2O3 ion-feedback barrier film on MCP was investigated by low-magnetron sputtering technique. The optimal depositon conditions for preparing the ion-feedback barrier film on MCP were obtained, such as operating voltage of 1000V, sputtering pressure of (4～5)×10-2Pa and deposition rate of 0.5nm/min. The results show that the ion-feedback barrier film deposited under this optimal conditions can meet the uniformity, compactness and less pinhole requirements.
A practical method for unattended equipments to auto-interpret IR dim and small multitargets is introduced. The automatic positioning of a target segment was performed by discriminating the cumulated target signal change in image sequences, and then the target recognization was implemented by using trace forecasting correlation in the target segments. The processing results for some target image sequences were presented. It is proved that this method can reduce the image interpretation time and ensure the target recognition speed.
The cyclic lateral inhibition network has the functions of enhancing the contrast of image edge and highlighting the image frame in infrared imaging preprocessing. Since the processing computation complexity of the cyclic lateral inhibition network, it is important to realize the real-time preprocessing of infrared video images with cyclic lateral inhibition network. The parallel processing structure suitable for the implementation of the lateral inhibition network by hardware is proposed based on the simplified processing algorithm of the lateral inhibition network and the characteristics of hardware calculation. It is realized in FPGA by the pipeline design. The results show that the algorithm has the real-time characteristic and is synchronized with the video stream in the FPGA, and the effect of enhancing the contrast of image edge and highlighting the image frame is achieved. When it is used in real time target tracking system, the target tracking accuracy and stability are greatly increased.
The test facility status for multiple optical systems is introduced, and the limitation of existing test targets is explained. The principle of the dynamic optical target simulation system is discussed. A new testing equipment is proposed to overcome the limitation. The feasibility of the new solution is analyzed theoretically. The coordinate transformation process was calculated, and the feasibility of new dual-light-source dynamic optical target was validated. The engineering design scheme for the simulation system of the dual-light-source dynamic optical target was elaborated. The error analysis was carried out. The scheme which could meet the test and calibration demands of the test facilty of the multiple optical system was proved.
A distortion measurement system, which is composed of high-precision goniometer, microscope measurement system, mini double-grating interferometer, collimator and star point, is used to measure the distortion of the NFOV long-focus lens precisely. Using third order polynomial fitting in center area of FOV, the theory focal length also can be computed. The measured deviation angle was corrected with the weighted mean of the high order of image height and the sine of the view angle at the edge field to acquire the relative and absolute distortion of each FOV. The results of the actual measurement and calculation show that the measurement accuracy of full FOV distortion can reach 0.02%.
A data processing program was written in MATLAB 6.5 with the simulated annealing algorithm and genetic algorithm to process the ellipsometry data detected by VASE Ellipsometer in the spectral range of 500nm～900nm. The evaluating function equation was improved according to the photometry principle of VASE Ellipsometer, and some calculations were made with some proper annealing and genetic parameters. The results of the data processing agree with those of the instrument processing. At last, the two algorithms were compared.
An optical fiber gas detection system with two gas cells was developed based on the near infrared absorption mechanism of gases. A Light emitting diode is used as a broadband light source. The wavelength of the LED is modulated by the fiber grating and piezoelectric ceramics to obtain the narrowband reflection output light corresponding to gas absorption peak, and then the high sensitivity detection of gas density can be realized by the detection of the second harmonic. The influence of the beam path interference on the detection accuracy, the variation of absorption coefficient with the environment and the fluctuation of the luminous power were eliminated by the ratio of the two secondharmonic signals from both the measurement and the reference gas cells. The detection experiment for CH4 was implemented by the system. Experiment indicates that the measurement sensitivity of the system is 0.2×10-6.
As digital binocular is the combination of digital camera and binocular, the resolution for estimating the imaging quality of digital cameras can also be used to estimate the imaging quality of digital binoculars. However, there are many problems if the international standard of resolution measurement for digital cameras is directly used on digital binoculars. A new method to measure the resolution of digital binocular by a collimator is proposed. Repetitive experiments on a certain set of digital binoculars were carried out based on the theoretical feasibility analysis. Some results were obtained by the auto reading software developed by the authors. The average value of horizontal resolution is 814LW/PH, and the standard deviation is 24LW/PH. It shows that the measurement has good reproducibility and high reliability. It is more objective and precise than traditional manual method.
With the illumination of the long pulse laser, the calorimetric laser energy obtained by the traditional data processing differs significantly from the actual laser energy due to the thermal loss. To solve this problem, the mathematic model of temperature distribution of the energy probe under laser illumination was established. Taking heat conduction and radiation into consideration, a measurement method of the thermal loss coefficient for characterizing the extent of thermal loss of the laser energy meter is proposed. The validity of the measurement method was verified by experiments. The obtained thermal loss coefficient can also be taken as an important parameter to evaluate the calorimetric laser energy meter.
The large amount of data such as the sample covariance, correlation coefficient and graded examination was analyzed in real time to implement statistics analysis of the correlated characteristics between the target detection range parameters. It is concluded that the detection range is highly dependent on parameter type and altitude of sea-air targets, less dependent on the seaair different targets, and the different equipments are uncorrelated to sea-air different targets. An analysis procedure for the test was established. Such procedure is helpful for improving the test quality and shortening the test period.
As a new method to generate underwater wave, laser-acoustics has a variety of commercial and oceanographic applications due to its merits such as high acoustic intensity, spike pulse and wide frequency spectrum. The primary model for laser-acoustic signal characteristic was established according to the linear and nonlinear theories of the laser-acoustic pulse. The characteristic that the laser may create acoustic wave in water was investigated. The research indicates that the increase of laser intensity can improve the laser-acoustic conversion efficiency in the state of the thermal expansion excitation, and when the intensity is higher than the breakdown threshold, the excitation mechanism of the laser-acoustics becomes nonlinear light breakdown mechanism. The laser-acoustics features high distance resolution and anti-interference. It has a great application prospect in underwater and airborne target detection.
he divergence angles of the single-mode Gauss beam generated by GaAlAs SDL-5400 LD laser in the perpendicular directions are not equal, and there is astigmatism in the beam. In order to obtain the circular light spot with common beam waist, a collimating and shaping module with two semi-cylinder perpendicular lenses and a pair of prisms was designed according to the complex parameterand ABCD-law. The far-field divergence angle of the collimated and shaped LD laser beam, which was calibrated with CCD, was 0.53mrad in the sagittal direction and 0.64mrad in the meridional direction.
The signal-to-noise ratio (SNR) is always a key factor to limit the development of passive laser detection system. In order to improve the SNR of the system with Hadamard transform, the formation of Sn circular matrix is introduced, and SLM served as the coding templet was selected based on the calculation of the appropriate coding templet size（17.48mm×17.48mm）and code symbol number (N=255). By applying different voltages on different locations of the templet, the transmitting laser diffracted stripes are controlled by magnetic rotation effect, and coded according to if they have passed through or not. The simulated experiment for the system proved that this method is successful. The experiment result indicates that the SNR can be improved effectively without increasing the times of measurement if the Hadamard transform is applied to the measurement of the laser spectrum.
Since the interference of two laser beams propagating in opposite directions in a medium can form a 1-D periodic structure volume hologram which can be taken as 1-D photonic crystal or 1-D laser holographic photonic crystal, the dependent relationship of the forbidden band on incident angle, recording wavelength, medium refractive index as well as modulation of refractive index in the transmission spectrum of 1-D laser hologram photonic crystal was investigated with eigen matrix. The results show that the forbidden band moves towards the short wavelength and its width decreases as the incident angle increases or the laser wavelength, the refractive index of medium and the modulation of refractive index decreases.
A method is proposed to realize anti-synchronization of different chaotic systems. A controller was designed based on Lyapunov stability theory. The single-mode laser Lorenz system and Rossler system were taken as examples to verify the effectiveness of the proposed method. The anti-synchronization of uncertain chaotic systems was studied. Taking the uncertain single-mode laser Lorenz system and Rossler system as examples, the chaotic anti-synchronization control was realized, and the uncertain parameters in the systems were identified. The simulation results show that the method is effective and practical. The method is applicable to any chaotic systems, and can be used widely.
US Standard Atmospheric Model is often used to solve the aerosol extinction coefficient with echo data obtained by Raman lidar, but it may include big errors in results. A new method, which uses the temperature mode to solving the atmospheric aerosol extinction coefficient in troposphere, is presented. It was theoretically derived. It′s found that the result acquired by the new method agrees with that obtained by a radiosonde. Theory study and experiment result show that the temperature mode is feasible in solving the aerosol extinction coefficient in troposphere by Raman lidar in ordinary circumstances. The temperature mode is more suitable for the actual situation than US Standard Atmospheric Model, and can reduce the error of the inversion result since it includes the season and geographical elevation factors.
The structure and operation principle of HDMP 1022(TX)/1024(RX) made by Agilent is introduced. The interface circuits of the two chips and light emitting/receiving modules with PECL logic are presented. The circuits for point-to-point bidirectional full-duplex fiber data transmission system and onedirection transmission system were designed with the chips mentioned above. The start-up and synchronization process of the two typical systems are described. The system can be used in fiber transmission systems for high-resolution digital television signal and other high-speed data signals.
As an intelligent unit for oil leak detection, fiber grating sensor has a great potential in the oil industry. A fiber grating sensor was designed for oil leak detection. The experiment result shows that the oil leak alarm line of the fiber grating sensor is 1.0nm, and its response time is less than 3 minutes. The sensor features good performance and high reliability, and it can be used for monitoring purpose in the oil industry.
The visible radiation characteristics of midcourse targets are very important for detecting, tracking and attacking a target. A computation method is proposed for the purpose. The bidirectional reflectance was computed. The visible radiation characteristics of a midcourse target, which were observed by the synchronous satellite, low orbit satellite and mid-orbit satellite during the daytime, was also calculated considering the solar visible radiation and the solar visible radiation reflected by the cloud. The research results show that the spectral variation of visible radiation from the target observed by the synchronous satellite is the same as that of the direct sunlight radiation, the spectral radiant flux of the target observed by the low orbit satellite is three orders higher than that observed by the synchronous satellite in magnitude, and the spectral radiant flux of the target observed by the midorbit satellite is one order higher than that observed by the synchronous satellite in magnitude.
The measurement method of the bidirectional reflectance distribution function (BRDF) for a rough surface was analyzed. A method to establish the BRDF model of the target surface material by artificial neural network is proposed. The sample BRDF curves variating with the scatter angle under several incident angles are given, and some of the curves were selected and sent into the artificial neural network. The network was trained with the Bayesian regularizing method. The mapping relation model of BRDF with incident and scatter angles was obtained. The scattering distribution curves under the incident angles, which participated in or did not participate in the training, were calculated with the network model. It was compared with the measured curves, and the result shows that the model is correct and practical.
A novel method to control the photonic band gap of 2-D photonic crystal is proposed. The two-dimensional photonic crystal, which composes of triangular dielectric cylinders between which liquid crystal (phenylacetylene) is filled, is placed between two vitreosil substrates. After the liquid crystal in the isotropic arrangement is illuminated by polarized UV light, the light-induced liquid-crystal molecule arranges orientationally. Results of numerical simulation show that the structure of the forbidden band of the 2-D triangular photonic crystal can be tuned by manipulating the photoinduced direction of the nematic LC molecules by the aid of external light field. Since the selective transmission of TM- and TE- polarized modes in the waveguide can be controlled by the adjustable photonic crystal, it can be used to manufacture the alloptical switch in photonic integrated circuits.
Vibration frequency modes of quasi-one-dimensional SiO2 clusters with one chain, two chain, three- and four- membered ring structures were calculated according to the density-functional theory. The bending vibration at low frequency (less than 300cm-1) was emphatically investigated in the infrared spectrum with different conformation. This type of vibration mode shows strong size effect dependent on frequency and intensity, in which the frequency has exponential relations with the length of clusters. Furthermore, the variation of the exponent with diameter is corresponding to the geometry dimension of the clusters. It is found that such infrared vibration exists only at the length range of 0.8nm～5.5nm. The results reveal that the criterion can be used to characterize the specific length of nano-cluster in experiment and theory.
Based on physical characteristics of the fog, the attenuation feature of laser propagation in the fog was investigated theoretically. The signal model, noise model and transmittance of wireless laser communication systems were presented. Based on the relation between the attenuation ratio and the transmittance of the laser, the variation of the attenuation of 10.6μm laser traveling in advection fog or radiation fog with the visibility and the FOV of the laser receiver is given. The numerical analysis results show that the performance of the wireless laser communication systems is highly dependent on laser wavelength, visibility, range and receiver FOV.
Based on coupled-wave theory, the fundamental principle of angular multiplex in volume holographic storage is discussed. The influence of the different beam path geometric arrangements, such as symmetrical write, unsymmetrical write and near-plane write, on the angular multiplex density was analyzed. Considering the limitation of total reflection about storage material, the equation of maximum angular multiplex density was derived. The theoretical analysis and digital simulation results indicate that the unsymmetrical incident light path has a higher angular multiplex density than the symmetrical one, and the angular multiplex density of the near-plane incident beam path is the best and is directly proportional to the reference beam.
Bubble is a novel medium for potential broadband passive optoelectronic countermeasures. To investigate the principle of its attenuation, geometrical optics theory and electromagnetic wave theory were used to study the phenomenon of light refraction and absorption of discrete bubbles. The change of the propagation direction and the transmission energy were analyzed, and the model was established. It is found that the structures and materials of bubbles play an important role in attenuating light according to the calculation and infrared spectrograms as well as the thermal imaging test. It indicates that the extinction capability and concentration of bubble solvent can seriously influence the light absorption in some wavebands, bubbles can change the direction of light propagation and reduce the energy density, the transmission intensity and light energy decrease rapidly with the increase of times that the light passes through the bubbles, and bubbles′ floating nature can cause the uncertainty in the emergent ray direction and energy distribution.