2011 Vol. 32, No. 3
With the ever demanding requirements of servo mechanisms for high precision and large slew rate in sophisticated detection and targeting systems, servo error sources such as gap, backlash and friction become limiting factors for the improvement of servo performance. The requirements of the cutting edge servo mechanisms for different electro-optical targeting systems on various platforms were investigated, which include missile, warship and aircraft applications. Major problems and challenges in designing and manufacturing precise servo mechanism were studied, and several key topics were put forward for the development of the precise servo mechanism, including error budget and dynamic analysis, design and manufacture, integrated mechanicalcontrol design method. Finally, future work is suggested for developing precise servo mechanism.
In the design of infrared optical system, the impact of thermal effect on optical performance should be taken into account so as to achieve a good temperature performance and the integrated opto-mechanical-thermal analysis should be conducted. The method and flow chart of integrated optomechanical-thermal analysis were discussed. An infrared lens with a focal length of 200 mm was designed, which matched with cold shield and could operate at a wide temperature range. The finite element model of the infrared lens was established and the thermodynamic analysis was accomplished, each lens interval and surface figure changes were obtained by using processed analysis data. The interval changes, Zernike coefficients and refractive index at ambient temperature were substituted into optical design software, and the temperature effect on image quality was obtained. The analysis results show that the modulation transfer functions of infrared lens with 16 line pairs in all field of views are larger than 0.5 from -40℃ to +60℃. The design of infrared lens is easy to be implemented and meets the requirements.
Based on three-junction (InGaP/InGaAs/Ge) high efficient solar cell, the PV conversion of a high power optical system was achieved, which used high-order precision aspheric Cassegrain system. Two solar PV systems of 200-500 times concentration-ratio were obtained with Zemax and Tracepro. One of them was a monolithic system with solar condenser component. Secondary mirror of high power solar PV system was manufactured using hot-press forming. 16 sets of optical concentration elements combined with three-junction (InGaP/InGaAs/Ge) high efficient solar cells of the same volumes were used to form a complete unit of a high power solar condenser PV system. The solar concentration ratio is greatly increased, which provides a good reference for the design of solar PV power generation and high-convergence-ratio facilities.
Tracking error due to the misalignment and lag of a two axes electro-optical tracker with elevation over azimuth configuration in high elevation angle was analyzed. The mathematic method for calculating blind zone induced by this error was given. Misalignment and lag error were simulated in Matlab. The simulation and tracking data indicate that blind tracking zone increases as the elevation angle of the electro-optical tracker increases.
In order to test the information field performance of laser beam riding guidance, a simulation system based on virtual-instrument is designed. This simulation system is used in the test of information field performance and spatial matching to realize the calibration and built-in-test of testing system. The design accuracy of the information field simulation system is 0.001 unit command and the output signals have advantages of phase continuity, wide dynamic range, stable reliability, high precision and strong extendibility. After the calibration of simulator and standard photometer, the accuracy of instruction test reaches 0.01 unit command. The accuracy of irradiance measurement is 5%. The accuracy of spot size measurement is 5% and the optical axis misalignment is 0.00876. It demonstrates that this simulation is feasible and satisfies the measurement accuracy and stability for testing system. This system features modularization, generalization, intelligence and standardization.
Optical window of remote sensing system has thermal exchange with ambient environment and it causes non-uniformity thermal distribution, including system average temperature shift as well as circumferential, radial and axial temperature differences, which degrade the image quality. A new method was presented to analyze this effect on the optical system wavefront error by building segments made up of complex pupils. Each segment can be effectively analyzed because of only the radial temperature being processed by non-sequential ray trace. Then all the separate impacts of the segments were calculated on the entire optical window. An example of the optical window is given, and the result shows that the method is feasible, the optical system quality is reduced by this effect and its MTF can not be completely compensated by focus shift.
The impact of the different half-intensity light angles on the LED array maximum interval was discussed. The illumination data of LED unit was calculated and simulated using Matlab. The corresponding simulation graphics were given. The simulation results show that the maximum interval between the LED light sources is independent of the power. Since the simulation results agree with the theoretical values, the LED optical model established in the calculation has good credibility. These results are useful in the modeling and application of LED multiple arrays such as round, rectangular and oval.
The display color gamut determines the range of colors that the monitor displays. Since the color CRT and LCD work differently, the same RGB values show different colors on different displays. Extensive measurements for different color specimens of different displays were carried out by experimental methods, and the characteristics and color gamut of LCD and CRT were compared. The results show that the color gamut of LCD display is smaller than that of CRT, the image colors shown on CRT can not be shown on the LCD, and the color brightness, saturation and tonal range are also different.
The high-pixel mobile phone camera is demanded with the development of mobile phone market. An 8 mega-pixel lens system with large relative aperture and large field of view (FOV) is designed with Zemax. The system includes one glass aspheric lens, three plastic aspheric lenses, an IR cut filter and a sensor cover glass. The F-number is 2.45 and FOV is 68,the effective focal length and back focal length are 4.25 mm and 0.5 mm respectively. The sensor MT9E013 have 8 mega pixels which is made by APTINA, the maximum resolution is 3264 x 2448 and the minimum pixel is 1.4 m.The design result shows that RMS spot radius at different fields are less than 1.4 m，the MTF value is more than 0.5 in most fields of view at 1/2 Nyquist sampling frequency. Distortion is less than 2%, and TV distortion is less than 0.3%.
An infrared inverted telephoto objective is designed. Based on the characteristics of infrared objective, a miniaturization design is analyzed based on Gauss optics. The parameters of the optical system are given. Its focal length is 10mm, F/# is 1.2 and field of view is 60. The system consists of 4 pieces of silicon lens and 2 second order aspheric surface, and its MTF is more than 45% at the cutoff frequency. The length of the optical system is shorter than 57 mm, and its diameter is less than 24 mm. The system is compact in size, cost effective and easy to be assembled，and it provides good performance from -40℃ to 60℃.
For the design and development of a vision sensor for the ground test, a method of 3D reconstruction of feature point on large scale object surface from a single image is proposed. By establishing the math model of the 3D coordinate of feature point on the object surface and using the spatial ray through feature point, the 3D coordinate of the feature point can be determined using sigle image. According to the characteristics, the object surface can be classified into three types, high order surface type, block plane typeand block surface type, while the corresponding location methods are introduced . Simulation experiment is conducted to compare the accuracy of three different 3D reconstruction methods, and the proposed method performs the best. By the measurement precision of 1 mm in the range of 8000mm8000mm, it is proved that the proposed method is suitable for 3D reconstruction of feature point on large scale object surface.
Super-resolution restoration is employed with image converted tube streak camera to improve time resolution of camera. The feasibility of the image of streak camera being processed by super-resolution restoring is presented. The point spread function of streak image is described and formulated. The image restoration results of X-ray streak camera of Au photocathode are obtained with Poisson-MMAP（MPMAP）algorithm. The experimental results show that the super-resolution image restoration on ultra-fast diagnosis can be used for improving time resolution of image converted tube streak camera.
In order to obtain multi-boundary of digital image quickly, a new boundary tracking algorithm based on searching direction estimation is proposed. The model of multi-boundary and the initial feature point method were studied. Four direction operation templates and a searching direction matrix were defined to estimate searching direction of next step. For enhancing the robustness of tracking algorithm, a weight matrix was defined to keep tracking algorithm out of searching trap. Tests were performed on MR images, and the results show that the tracking efficiency of new algorithm is enhanced by 21% compared to variable window reptile method or traditional tracking algorithm. According to the test results, the robustness of the new tracking algorithm is improved obviously.
A compression algorithm based on asymmetric uniform-tree 3D-DWT and modified listless 3DSPIHT in conjunction with region of interesting (ROI) is presented. It is specially developed for the large aperture static imaging spectrometer (LASIS) system according to its interference properties. Firstly, the hyperspectral interference image series with asymmetric uniform-tree 3D-DWT are decomposed. Secondly, the major hyperspectral coefficients are protected by ROI method. Finally, a modified listless 3DSPIHT algorithm to encode the transformed images is given. The numerical experiment results show that the average PNSR is more than 40dB at 8:1 compression rate, and the efficient protection of hyperspectral information is achieved.
In order to achieve real-time monitoring automatically, a controlling system of optical coherence tomography for tissue optical property testing was designed and debugged based on LabVIEW. The system included a programmable driving module for reference arm control and a data acquisition module for data acquisition card operation. The modules were independent and well coordinated. The measurement was executed using different concentrations of Intralipid tissue simulating liquid, and satisfactory results were obtained. The results show that the scattering coefficient of simulating liquid is reliable. The system is cost effective and easy to maintain.
In order to find a high speed secure encryption of image, an encryption based on bit planes division for optoelectronic devices is studied. The research focuses on the security and the ability against the invader of the encryption. The simulation results show that after encrypted, the information in the image is reduced, and the change of average gray-level of encryptedimage is larger. The results demonstrate the gray-level transform cancels the correlation among pixels of primary image, and the pixel distributes randomly, which makes invader hard to analyze correlation and find outline of the original image. Hence, this encryption has a high security, and the average gray-level of encrypted image is more suitable than the change of average gray-level.
In order to compensate the forward image motion of a mapping camera on an aircraft, a method by adjusting the relationship between the shutter exposure time of the camera and the speed-altitude ratio of the aircraft was put forward. The causes of the forward image motion were studied. Firstly, the operation principles of the color area array CCD and the camera system were introduced. Then the causes of the forward image motion were analyzed based on the imaging principle of the optical system. Finally, the errors of the speed-altitude ratio and the exposure time were analyzed. The experimental results show that the errors are controlled within allowable limit and it meets the compensation requirement of less than 1.5 pixel for the forward image motion.
Aiming at several problems of traditional infrared image enhancement algorithm, an infrared image enhancement method based on wavelet analysis and histogram was proposed. Firstly，the wavelet coefficients were obtained by performing orthogonal wavelet transformation. Then the low frequency wavelet coefficients were enhanced by the double histogram equalization method and for the high-frequency wavelet coefficients，the threshold-filtering method was utilized to enhance the details of the image. Finally, the reconstructed infrared image with enhancement was obtained by using the inverse wavelet transform. The experimental results show that the method improves the gray-scale value and dynamics, doubles the detailed information, restrains the noise, and enhances the contrast in infrared images, which is an effective method for infrared image enhancement.
In order to improve the quality of photoacoustic reconstructed image, an algorithm of filter back-projection was adopted. A Q-switched Nd∶YAG laser operating at 1 064nm was used as the light source. The laser had a pulse width of 7ns and a repetition frequency of 20Hz. A needle PVDF hydrophone with a diameter of 1mm was used to detect photoacoustic signals. The photoacoustic reconstructed images of four rounded absorbers and five hairs were obtained. The results of simulations and experiments show that the algorithm restrains noise effectively, and improves the contrast and resolution of images.
This paper proposes a new method for uncertainty evaluation of corner detection. A mathematical model which relates the uncertainty of pixel intensity with the pixel intensity and image gradient is presented. To evaluate the uncertainty of corner detection, the uncertainty associated with the intensity of each pixel, which belongs to the target to be detected, is evaluated by using the mathematical model presented in the paper. Then the uncertainties associated with the output of a corner detector are evaluated by using Monte Carlo Simulation. The method was validated by using classical SUSAN corner detector as an example. The experimental results show that the uncertainty of corner detection can be evaluated accurately using this method.
Aiming at the problem of complex Light of double CCD intersection vertical target when used indoor. a measurment principle of single linear array CCD camera vertical target was presented. Two low-power semiconductor laser with projection board were used as the lamp-house of the CCD camera. The detection light screen of the CCD camera and the laser lamp-house were adjusted to same plane. When projectile passed through the detection light screen, it block the part light of the two lasers and left two shadow on the board. The two shadow were acquired by the CCD camera and their-coordinates were cilcutated by computer, then the projectile coordinate of X and Y were obtained through further calculation. The measuring principle and the formulas were given, and the measuring error was analyzed. The results show that the coordinate error of X and Y are all less than 1.4 mm when the detection light screens is 1m1m, and this solution has advanLanges of simple,low-cost and easy to be engineering implemented.
By analyzing the optical properties of several important ocean medium, a new method for monitoring oceanic suspended particles is proposed. The method makes use of an airborne lidar and is based on a bio-optical algorithm. The detection model on the concentration of alga Chlorophyll-a and the concentration of suspended sands based on the bio-optical algorithm were proposed. By simulation and computation, it is proved that these two detection models can monitor the concentration of alga Chlorophyll-a and the concentration of suspended sands effectively and could predict the occurrence of red tide. Baed on these two models, oceanic suspended particles monitoring can be realized.
As the small targets in the eletro-optical image are composed of tiny pixels, the detection of small targets can be regarded as the singular value detection of the target signal, and the wavelet-based multi-scale analysis is an important detection method of signal singular value. This paper analyzed the principle of small target detection using the existing wavelet-based multi-scale analysis method, and its use in the estimation of the modulus maxima value line is difficult and target location accuracy is not good. Based on the symmetry of wavelet function and small target signal, a method is presented to detect the small target in electro-optical image directly based on the wavelet analysis over two different scales. Finally, experiments proved that the method can improve the detection speed and location accuracy effectively.
As one of the important components in the fire security system, flame sensors are widely used in industry and military applications. With the emerging of new technologies and devices, the test and evaluation of fire sensor becomes important in the fire security system, not only for the proper and safe operation of the system, but also for the development of new sensor. A UV-IR source and its application as fire sensor are presented, and the new technology and development of such sensor are discussed. This UV-IR source consists of two black bodies, a UV lump, filter components and a diaphragm. With the setting of wave length, the size of diaphragm and the temperature of the black body, it can produce artificial fire radiation, which is used to characterize sensors. The radiation expressions of IR source, simulations results and test results are given. Calibration techniques using standard sensor method are introduced. Experiment results show this UV-IR source can meet the need in the test of fire sensor in UV or IR applications.
A device for measuring the laser facula based on the fiber-scanning was demonstrated. The laser facula was detected by a fiber probe in a progressive scanning way. The light signal was converted, measured and transmitted to computer, then finally plotted by software. A fast scanning measuring scheme was proposed and two important parameters including measurement resolution and time were calculated and analyzed based on the large diameter pulsed laser measurement. A contrast experiment with CCD photographic method was done, and the result shows that this device avoids the effect generated by the scatter of receiving screen or imaging system deviation, it uses a directly measuring way and provides a better measurement result. This device is successfully applied to the measurement of focused beam transmission.
A spectrum measurement system was built by taking solar as light source. High precision imaging spectrometer was used to collect solar spectrum. A solar spectrum at a specific time was chosen as reference data to inverse concentration of NO2 at another time by combining the concentration of polluted air at that time and applying differential absorption theory. A new method of processing spectrum data was presented. It focuses on the application of origin 7.5 to spectrum analysis as well as the application of drawing the absorption cross section graphs according to HITRAN data base. The above-mentioned data may be used in the quantitative analysis of spectra lines with less error. The process of inversion features high accuracy of spectrum data and inversion parameter, which improves the accuracy of inversion concentration for NO2. The experimental results agree with those of other measurement equipment, which proves the inversion process is feasible.
Polarization properties of gratings are used to develop new types of fiber Bragg grating (FBG)-based sensors. The evolutions of states of polarization (SOPs) of transmitted light in linear birefringence gratings were studied based on Jones matrix and coupled mode theory, and they were plotted on Poincare sphere. The effects of transmitted length, linear birefringence value and incident SOPs on PDL, the first normalized Stokes parameter and the evolutions of SOPs were discussed. The results show that the SOPs of transmitted light change with linear birefringence value and grating length, and the SOPs relative curves of different wavelengths spread gradually with the increasing grating lengths or birefringence values. The wavelength point of maximum amplitude of the first normalized Stokes parameter is the same as that of polarization-dependent loss, both increase monotonously with birefringence value, which could be used for sensor measurement.
With the rapid development of infrared technology, the higher infrared data rate is required. Aiming at the high-speed requirement of a new infrared imaging system, a novel method for infrared image high-speed transmission was proposed, which was implemented with Peripheral Component Interconnect（PCI） Express and optical fiber. The system achieved an infrared image transmission speed of over 100 Mbyte/s. The infrared imaging experimental results show that the system meets the demand for high-speed infrared image acquisition.
Double-clad doped optical fiber is used in high-power fiber lasers and fiber amplifiers. Compared to the large divergence angle of the multimode pump beam emitted by the semiconductor pump laser, its inner cladding diameter is small, which makes effectively coupling pump beam to the inner cladding of the double-clad doped optical fiber difficult. A kind of fused side-pumped coupler is developed, which enhances the pump power and realizes multi-point pump to the gain fiber. It is used in the double-clad fiber amplifier. It has good security and stability, a coupling efficiency of 70%, a ratio of 98% coupled signal light, and over 50dB isolation of the signal input and pump beam input, and 27dB isolation of the pump beam to the counter -propagation beam are achieved. The fused biconical taper side-pumped coupler has compact structure, good coupling efficiency and system stability, which meets the requirements of the high power fiber lasers and fiber amplifiers.
According to the characteristics of quartz micro-electro-mechanical systems (QMEMS) gyro, adaptive filtering and UD decomposition theories, an improved adaptive method based on Kalman filtering method is proposed. This method removes the error data during sampling and enhances the real-time performance and stability of inertial navigation system. The simulation results of QMEMS gyro output show that the improved adaptive filtering is much better than Kalman filtering on de-noise effect. The improved adaptive filter provides more accurate data for inertial navigation system, and the precision of inertial navigation is improved.
Based on transfer matrix method, the effects of doping on one-dimensional photonic crystal are researched numerically. It is shown that in doped photonic crystal, there is a conduction band in the center of band gap, and the depth of conduction band varies gradually with the doping position and refractive index. When the crystal structure is given, there is always a doping position which makes the conduction band depth maximal in the center of band gap. When the doping position is given, there is always a specific value of impurity refractive index which makes the conduction band depth maximal in the center of band gap. These characteristics of one-dimensional photonic crystals are applied for the design of filters and optical resonators.
In order to reduce the bit rate of the high speed signal for further processing, a high speed all-optical serial-to-parallel conversion system was designed and demonstrated. The characteristics of the spectral width of the clock pulse and the high speed response of four-wave mixing (FWM) in optical fiber were utilized. A narrow optical division clock pulse stream with repetition frequency of 10GHz was expanded in the time domain by using group velocity dispersion (GVD) effect in optical fiber. Moreover, an all-optical serial-to-parallel conversion function from a 40Gb/s return-to-zero (RZ) format signal to 410Gb/s signals was realized by utilizing four wave mixing process in optical fiber. This scheme is fast in response, transparent in wavelength and bit rate, and capable of increasing channels significantly.
In order to realize the precise alignment of a two mirror optical system, a method using wavefront aberration measurement technique is introduced to accurately measure misalignment. The equations between the designed optical parameters, misalignment values and the wavefront aberration of misaligned optical system were established using vector wavefront aberration theory. The interferogram of a field of view was obtained through interferometry, and Zernike coefficients representing third-order coma and third-order astigmatism of misaligned system were obtained using fringe analysis software. Finally, Zernike coefficients were substituted into the equations to solve the misalignment values. The alignment of a 4 meter aperture RITCHEY-CHR-TIEN astronomical telescope was simulated. The solved misalignment values were fitted to the introduced misalignment values, and the accuracy of the method was proved.
To improve wavefront quality in large scale laser, the residual stress in multi-layer films was controlled precisely by ion-assisted e-beam evaporation. Based on the analysis of the residual stress variation in single HfO2 layer and SiO2 layer, the effects of ion-source beam voltage and beam current on refractive index and residual stress in films were studied. The PV value of 540 mm340 mm60 mm reflective mirror was controlled below 0.5 (=632 nm). The damage threshold of the specimen tested with small-size beam was higher than 30 J/cm2 (N-on-1,1 064 nm, 5 ns). The large-size reflective mirror manufactured with this technology is applied successfully in a large aperture prototype device.
The method for preparing solid thin films with high-order nonlinear effects was explored, and the optical properties of the materials were investigated to obtain an ideal nonli-near optical device. The MB/HTO nanohybrid thin film was prepared by intercalating reaction between the dye and titanate nanosheets. The spectral characteristics of methylene blue dye before and after intercalating into layered titanate nanosheets and forming a nanohybrid thin film were investigated by measuring absorption and fluorescence spectra. It was found that the absorption peak of the film generated a more obvious blue shift than that of the solution, which indicated the formation of H-aggregates of the dye in the interlayer space of nanosheets. In addition, the nonlinear optical properties were studied using single beam Z-scan technique under irradiation of low power continuous wave (CW) produced by He-Ne laser with a wavelength of 632.8 nm. The sample exhibited a negative (self-defocusing) nonlinearity and large nonlinear refractive index with an order of 10-10 m2/W.
A filter for producing the standard spectrum band in photorejuvvenation device was developed. Quartz was selected as the substrate, TiO2 and SiO2 were chosen as high and low refractive index film materials. The needle optimizing method was used to eliminate the ripple. By using vacuum depositing method with ion-assisted deposition system, the filter with average transmittance less than 0.3% in 200 nm~550 nm and over 95% in 570 nm~1200 nm was achieved. In the process of evaporating, an improved monitoring method was used to reduce the absorption of TiO2 and the film thickness error. Based on repeated experiments, the reason of wavelength shift was analyzed and the feasible method for solving the problem was put forward.
The layout and operation principle of multi-spectrum laser composite point target simulation dome is given, which is used for research, development and validation of fire control and electro-optical seeker systems. Three laser wavelengths(0.65 m, 0.808 m and 10.6 m) meet the dynamic simulation test requirements of TV (0.4 m～1.1 m) and long-wavelength infrared imaging (8 m～11.5 m) electro-optical tracking system. The diffuse reflectivity of 12m radius dome screen is greater than 0.7 (0.4 m～12 m), target motion range is 0 ~ + 90 in azimuth, and -90 ~+9 0 in elevation. This technology is developed for the hardware-in-the-loop simulation of vehicle borne air-defense electro-optical fire control system and the tracking precision is increased from 0.4 mrad to 0.2 mrad.
A data acquisition and processing method is reported for correlation ranging with chaotic laser, which can be used for automotive collision avoidance, fiber or cable fault inspection. We used a data acquisition card with 125 MHz bandwidth and 2ms memory depth as platform to design acquisition and processing. The acquisition and storage were programmed by using Visual Basic, and an average discrete-component elimination algorithm was proposed and programmed to caculate real-time correlation with high signal-to-noise ratio. In the demonstration, we utilized this acquisition and processing system to locate fiber fault with chaotic light, and experimentally obtained an accuracy below 0.25 m.
In order to obtain a semiconductor laser source with higher output power and good spot uniformity, two semiconductor laser beams are combined into one laser beam of higher power by using a polarizing beam splitter and transmitting through one optical channel according to the polarization characteristic of the semiconductor laser. The divergence angle of beam along the slow axis direction of each laser is expanded before combined by an aspheric lens so as to be consistent with the divergence angle along the fast axis direction. The experiment results show that this combined semiconductor laser source has good spot uniformity and its output power is the sum of two laser output powers, which meets the laser power and spot uniformity requirements for laser guidance in military applications.
The phase-matching mode of KTP-OPO was theoretically analyzed and calculated, and the angle-tuning curve of KTP-OPO was given. A 1.57 m eye-safe laser based on optical parametric oscillator was experimentally studied, which adopted KTP nonlinear optical crystal. Using a xeno-flash-lamp-pumped 1.064 m Nd∶YAG laser in intracavity KTP-OPO，under the repetition rate of 5 Hz, a laser output with the energy of 32 mJ and the pulse width of 7.22 ns was obtained. The optical-to-optical conversion efficiency was 41%, which makes long range laser range finding possible.
The invention background of alkali laser and its unique advantages are briefly introduced. Based on recent achievements of diode-pumped alkali laser (DPAL), the key technologies that includes line width matching, continuously stable operation and power enhancement are analyzed to meet the application demands. The basic principle of a novel exciplex pumped alkali laser (XPAL), as well as its advantages and disadvantages are explained. By discussing problems existing in this field, potential research work on energy level theory, pump mechanism, buffer gas effect, cavity structure optimization and highpower scaling is proposed to improve output characteristics of DPAL.