2015 Vol. 36, No. 2
The development of shipborne helicopter abroad was summarized. The tactics function and campaign mission of optoelectronic system in the helicopter campaign concept of United States navy were discussed in detail. According to multiple spectrum targeting system, which will be the main EO system of U.S. shipborne helicopter, the technologies status and development trend were analyzed according to the sensors, filed of views, image processing and cooperative combat.The sensor resolution reached 1 280 pixel720 pixel, the biggest field of view (FOV) was bigger than 40while the smallest FOV was smaller than 1. The common path and two-level stabilization technique were used to improve the stabilization accuracy to less than 5 rad. Image enhancement, fusion and mosaic should be provided simultaneously and the image delay was smaller than 1 Hz. The inertial measurement unit (IMU) should be integrated to improve the orientation accuracy to 5 m for the target away from 80 km. The development emphases of EO system for shipborne helicopter were also proposed.
The mechanical transmission backlash mainly generated by the transmission system gap, the elastic deformation of the transmission chain, the loadeddeformation of mechanical components and other factors, has a great influence on the control precision and stability of servo system. We analyzed the mathematical model of the mechanical transmission backlash, set up a block diagram of servo system considering the transmission backlash. Furthermore, we analyzed the modeling of mechanical transmission backlash and its influence on the servo performance in depth through a typical simulation example. The results of the analysis show that the influence of transmission backlash on servo performance mainly reflects in two aspects: first, it can cause the phase lag and affect the stability of the system; second, it can cause the limit cycle oscillating which produces self-vibration static error.
According to the problem of spatial location for the moving object, the stereo vision technique and moving object detection in a single video sequence were combined. A stereo motion analyzing system was designed to achieve the goal of spatial location. It can expend the application range for the moving object detection issue in a single video sequence. According to the problems in the course of transition from monocular to multi-view, a solution was proposed based on the hardware. Combined the stereo lens with the high-speed camera, the problems of chip consistency, camera synchronization and the motion ghost can be overcome. Because the stereo images come from the one image, the traditional moving object detection method in a single video sequence can be used directly to obtain motion mask. Two groups of real experiments were taken by the system in full bright daylight conditions, containing free fall and slope movement. The results show that the system works stably and realizes the stereo motion analyzing capabilities for object. The absolute location error is less than 0.01 m at a range of 1 m.
In order to clear the suppression ability of optical system to stray light, we designed the optical system with a improved double gauss structure, whose spectrum was 0.75 m ~1 m, focal length was 12.002 mm, F was 1.8, field of view (FOV) was 1515. We obtained a optical system whose spot of every FOV was in the airy，max shift was 4.9m, spherical aberration was about 1 m，max transverse aberration was 3 m, modulation transfer function (MTF) was closed to the diffraction limity. Furthermore ,we carried on the evaluation and suppression of stray light, got the point source transmittance (PST) of stray light. Compared with the optical system without lens hood, the value of PST decreases by 76.6%~87.5% after adding the lens hood.
In order to improve the illuminance of image plane and simplify the structure of digital high-speed multi-frame gated camera, an off-axis optical system was proposed. The system uses several same lenses, one of them lies in the center of circle and the others are equally distributed on the circumference. In order to obtain the same image with the center lens, receivers of the lens that are distributed on the circumference parallel move away from the axis of its lens. The illumination, distortion and other aberration related with field of view, were analyzed. Based on the above analyses, a five-channel off-axis optical system was given. The spatial resolution of the system is better than 30 lp/mm , distortion is less than 0.1%. and F number of the lens is 2.0. Compared with mostly used prism or pyramid to split light beams, the illumination of the new system increases more than 5 times and the structure is more simple.
In machine vision systems,lens is mainly responsible for imaging object on photosensitive surface of image sensor.Based on machine vision systems, the mechanical compensated zoom was adopted, the Zemax software was used to design a visible multifocal zoom lens system that could be applied in machine vision systems to address some specific situation while different magnification were required but working distance remained unchanged during production. The system has the working distance from 290 mm to 340 mm and the focal length changing from 10 mm to 100 mm, which makes 10 times multifocal zoom possible. The results shows that for this multifocal zoom lens,the maximum distortion is less than 1%, and it can best hold 1/3 inch CCD image sensor.The system imaging performance was assessed by modulation transfer function(MTF)，and MTF is greater than 0.3 at the frequency of 100 lp/mm, which meets the imaging demands.
Monolayer SiO2 optical thin films(refractive is 1.46) and SiNx optical thin films(refractive is 1.84) with different thicknesses were prepared by the plasma enhanced chemical vapor deposition (PECVD) technology on BK7 substrates,their laser-induced damage thresholds(LIDT) were measured,and the relationship between the monolayer optical thin film and its laser-induced damage properties was analyzed.The results indicate that monolayer SiO2 thin films prepared by PECVD technology have high LIDT,when the optical thickness of films is between o/4 and o/2, LIDT has the maximum 27.9 J/cm2 when the optical thickness is 433 nm,LIDT has the minimum 21.7 J/cm2 when the optical thickness is 350 nm. The LIDT of monolayer SiNx thin films decrease with the increase OF optical thickness , LIDT has the maximum 29.3 J/cm2 when the optical thickness is o/4,LIDT has the minimum 4.9 J/cm2 when the optical thickness is o/2.
Digital shearography has broad application prospects in the field of industrial non-destructive inspection. However, the traditional Michelson-interfero-meter-based digital shearography suffers from the small angle of view due to the structure,which limits its employments in industrial application . We demonstrated a novel digital shearography system with a large angle of view by embedding a 4f optical system between the separate lens and camera, achieving the lens outside of the instrument housing. Theoretical analysis shows that the angle of view has no limit to the setup but it is based on the focus length of the imaging lens and the size of the imaging sensor inside the camera. A novel digital shearography system was built and experimental results prove that the new shearography system is a good tool to conduct the full field inspection of a big size sample at a short working distance. At a working distance of 1m, the measuring area of the novel shearography system is 800 mm 600 mm, compared with only 250 mm200 mm of the traditional one.
For expanding the scope of the key area defense reconnaissance and positioning the incoming target, on the basis of two-unit interactive measurement positioning algorithm, the relay measurement of the adjacent array units and passive measurement, coordinate transformation, data fusion were accomplished by the central processing unit. An algorithm based on array of electro-optics reconnaissance positioning system on air targeting was proposed. A model of an mn electro-optics reconnaissance array position on air target was derived, and the single target positioning simulation, verification and error analysis of 22 array element were accomplished with the help of MATLAB. Simulation results show that this algorithm can output the real-time data of the three-dimensional track and realize the positioning of the on air target. Compared with the theory of truth value, the absolute value of the average positioning error is less than 7 m.
The polarization imaging detecting can reflect more information that the traditional optics cannot reflect. On the basis of the existing methods of the polarized image fusion, an image fusing method based on comprehensive image features was proposed to overcome the shortcoming that detailed information would be lost during the calculation of polarization parameter images. By extracting the image-s gray scale, texture and shape features to determine the weight of fusion, the polarized images were fused, and the result of fusion was good, the variance and information entropy increased by 12.6% and 17.5%, respectively, the average gradient increased from 0.59 to 1.83. However, the feature of the method needed higher dimension, a simplified algorithm was provided to improve the operation efficiency which could reduce the time from 3054 to 1337.
The uniformity of illumination is the main problem in the solar simulator system. At present, theoretical calculation has been used to design a lamp array which has uniform illumination; however, this method is too complicated to execute. Aiming at the deficiency，the numerical optimization method was applied to design the halogen lamp arrays in this paper. Different from the single optimization method, the simulated annealing (SA) algorithm and particle swarm optimization algorithm (PSO) algorithm were combined to optimize the lamp arrays, breaking through the limitation of single optimization method and achieving better result . By programming to optimize the coordinates of each lamp array, the optimal results were put into the illumination optical simulation software for analysis.The experimental data show that the uniformity of 3 kinds of lamp array are 91%, 87% and 91%,respectively; under the same conditions the uniformity of hexagonal lamp array is better than that of circular lamp array; and the experimental method is simple and feasible by utilizing the optimization method.
To solve the existing problems such as multi-station setting complexly and high single station accuracy demanding in pose measurement of flying targets, a new optical method for pose measurement was proposed. The method made full use of the continuous image information and the corresponding target flight trajectory position data. First, starting point of target axis vector was determined by the target location data, and also the end point was acquired by the constraint equations of target axis vector. Then, the pose angles (including the yaw angle and pitch angle) could be calculated according to the relationship between the pose angles and the axial vector. Finally, the unique pose value could be obtained by the prior information. The corresponding simulation and accuracy analysis were performed, and the results show that the attitude measurement error is less than 1, and the method proposed in this paper considering both the convenience and accuracy of measurement, has high application value.
Using the angular spectrum theory of scalar diffraction, the phase retrieval algorithm with two intensity patterns was carried out, and was used to test the optical surfaces and wavefronts. The wavefronts of the spherical wave surfaces were retrieved by the algorithm in experiment. The algorithm of wavefront fitting based on the Zernike polynomials was realized with computer programmer by calculating generalized inverse matrix of Zernike coefficients.
The attack angle of projectile,which is an important parameter to describe the flying attitude, refers to the angle between victory and axis.The measurement of three-dimensional attack angle, an important part in conventional weapon test, aims to analyze the validity and stability of the projectile and provides a vital basis for the evaluation of the weapon system performance.The traditional method is to use a slit camera on the synchronous scan mode(the speed of film is equal to the speed of target image). We proposed a measurement method of the attack angle based on scanning image of high-speed area array camera. The principle is as follows: A scan image is formed through extracting a fixed column of per frame and stitching the pixels sequentially;By interpreting the feature points, the 2D attack angle is obtained; Aiming at the problem that the scanning speed isn-t up to the film speed, the attack angle correction model and scanning image restoration method were built.Furthermore, we proposed a method of two cameras shooting from non-orthogonal directions to get the 3D attack angle, based on the surface-surface intersection theory. The experimental results show that this method can measure the attack angle of the targets under 1 000 m/s, the accuracy is better than 0.1.
In order to evaluate the integrated properties of visible photoelectric imaging system exactly and objectively, the calibration equipment was developed. The equipment was composed of integrating sphere, standard card, off-axis reflective collimator, mechanical adjustment bench, video acquisition module and comprehensive software. It could complete a measurement of resolution,contrast,optical transfer function(MTF),noise power spectrum, noise equivalent light and sensitivity.For a certain visible photoelectric imaging product, the effectiveness of the equipment was proved. The comprehensive parameter measurements are given:the cut-off frequency is 39.4 mm-1, the contrast is 76.5%,the root-mean-square (RMS) noise is 2.14 mV,the noise equivalent light(NEL) is 0.045 5 cd/m2 and the sensitivity is 47 mV（cd/m2)-1. In addition, an illuminometer and a standard video pattern generator were respectively adopted for making calibration, results show that the maximum relative measurement errors of integrating sphere and the signal acquisition system are -2.3% and 1%.
In order to accurately measure the high-precision microscopic module of optic fiber array , a method combined a dual-frequency laser interferometer with a micro-vision system was adopted. The characterized scale was extracted and located precisely from the micro-vision image by way of skeletonization, erosion algorithm and the centroid method. The spaces between 8 scales were repetitively measured, with the maximum standard deviation being no more than 0.07 m. These 8 scales were further measured through the combination method, with the maximum standard deviation being no more than 0.04 m. The configuration and principle of the measurement system were described. Accuracy analysis indicates that the limit error of the method is less than 0.10 m.
The difficulties of digitally evaluating surface defects of optics using American military standards MIL-PRF-13830B lie in judgment of surface defects concentration. For this problem, we raised a kind of judgment algorithm of surface defects concentration. The algorithm uses the method of overlap of weight region. It seeks circular area where defects are dense by means of attaching weight region for surface defects, and turns overlap of weight region into position judgment and calculation between matrixes, which makes full use of convenience of matrix operations. In experiment, using this algorithm judged quartz standard board where information of defects was known, and the circular area where defects were dense was accordant with expectation, which validated the correctness of the algorithm. At present, the algorithm have been used for precise surface defects digital evaluation using American military standards in optical workshop.
In order to accurately evaluate the stealth performance of infrared materials and coating, the IRS400 type material emissivity measurement equipment was developed . It is mainly used in the temperature range of 50 ℃～400 ℃, spectrum range of 3 m～5 m and 8 m～12 m directional measurement for the emissivity of solid opaque material and coating sample. The importance of the material emissivity measurement for infrared stealth technology was introduced, the IRS400 type emissivity measurement equipment was described, including the technology performance and working principle. The IRS400 optic system adopted total reflection design, the detector selected the LiTaO3 pyroelectric detector, and the 50 ℃～1 000 ℃ black body radiation source standard device was utilized to calibrate the black body emissivity B（1,2）.By solving the key technology of calibration and environmental temperature compensation, the emissivity measurement uncertainty can be ensured less than 2%.
High imaging quality is required in the small-aperture high-resolution space-to-ground remote sensor of refractive system，as a result the assemblage tolerance is rigorous. The assemblage tolerance distribution rooted in optics design before, however, the strict tolerance cannot be achieved in smallaperture high-resolution space remote sensor now. An improved tolerance distribution was recommended based on the combination of optic design and assembly practice.It estimated the imaging quality through the emulation of whole process, reallocated the tolerance and adjusted it by compensation realtimely . The improved tolerance distribution was proved by a small-aperture camera lens assemblage.Results show that the control accuracy of eccentric error is 2,and that of mirror spacing is 1 m,the imaging quality is good after camera assemblage.
In solid-state laser, the processing technology of laser crystal has an important impact on the total quality of the output laser. For the defects of the deviation of the center position of spherical end face from the central axis in round rod crystal, a method for testing the center position of spherical end face was put forward. Through theoretical calculation of the transmission matrix in the optical path and solving the changes in position and angle of the reflection light, the relationship between deviation of the center position from the central axis and the distance from the spot position to the hole of the aperture was obtained. In experiment the distance from the spot position to the hole of the aperture was measured when the testing laser was debugged to the different positions on the plane surface of the crystal. And the deviation of the center position of the spherical end-face on the central axis of the crystal was calculated at last. The center positions of spherical end face were tested for two different kinds of crystals. The vertical distances of the center position of spherical to the central axis for two -3 crystals are 2.55 mm and 1.1 mm, and 3.25 mm and 0.9 mm for two -4 crystals. Moreover, the possible cause of the error was analyzed.
Through studying the theory of absolute optical encoder, we designed a macro/micro switch measurement . We used the incremental code for low precision measurement ,and the absolute code for high-precision measurement. The incremental acquisition method was used to acquire Moir fringe at a high rate of speed, which could solve the problem of low velocity when using precise absolute optical encoder, and implemented high-speed and high-precision measurement that was a combination of macro and micro. Experiment proves that the precision of high-precision low-speed measurement of absolute position can be up to 0.6 m, the used new-type model of high/low velocity switch measurement can make the comprehensive measurement speed up to 2 m/s.
Mid-spatial frequency(MSF) wavefront error leads to laser damage during the use of optics. Therefore the accurate evaluation and modification are necessary in manufacture. A unique way based on multi-sample analysis was proposed for error frequency. Several outstanding frequencies were found in every sampling direction. After eliminating with the help of these frequencies, along with certain sample direction, unqualified frequency errors in 0.041 7 mm-1, 0.085 8 mm-1,0.041 7 mm-1 were down to 23.9%, 18.3%, 29.2%,respectively, while the MSF in whole optic surface decreased to half. According to the method above, the uncertainty caused by directionality and regionality of MSF in optic surface can be restrained.
In order to validate the feasibility that the intensified charge-coupled device (ICCD) detect target by polarization laser assistant illumination, a polarization laser assistant illumination ICCD detection system was manufactured by polarization imaging detection technology. The system adopted an 808 nm semiconductor laser as illumination source to illuminate target, which wasn-t detected by human-eye, and the ICCD polarization detection system was used as electric-optic conversion module to detect target, and finally achieved the target detection on background. An experiment was designed to validate the result of the polarization imaging detection in the field environment. The result shows that the man-made-metal-target depolarization is almost 10%, and the green-background-target depolarization is 50%, and the sand-target depolarization is almost 30% 0 at 45, and 90 polarization angle. The imaging contrast for the man-made target and the natural background is improved as the polarization angle enlarging.
Multiple-feedback phenomena and generation mechanism were studied systematically based on asymmetric external cavity. When the reflectivity of feedback mirror was higher than 90%, the multiple high order feedback fringes were obtained owing to the stacking effect of many high order feedback beams going back to laser resonator. These feedback fringes have the features of unevenness and high resolution. Furthermore, the single high order feedback effects were discovered, and according to this ,the light-path-blocking method was presented . The fringes of single high order feedback have the advantages of both evenness and high resolution of /10, which is important for developing high accuracy measurement system.
The wave front phase aberrations can be corrected by deformable mirror in real time, which is the key element of adaptive optics system for reducing the effect of atmospheric turbulence. The wave front error can be compensated by deformable mirror with single actuator: one optical mode is generated with one actuator. Finite element analysis was employed to research the compensation capacity for the low order aberration of single actuator deformable mirror. The simulation results show that the wave front error of defocus, astigmatism and coma can be effectively corrected using single actuator deformable mirror by controlling the displacement of actuator. The peak valley (PV) values of fitting errors of defocus, astigmatism and coma are 1.5 m, 1.6 m and 1.2 m, respectively, comparing to the initial PV value of 5 m. The root-mean-square (RMS) values of fitting errors are 0.99 m, 0.63 m and 0.59 m,respectively.
The absorption is a main cause of laser damage in optical coatings. A group of HfO2 films were deposited under the oxygen pressure of 5 mPa~43 mPa. When pressure was less than 20 mPa, the films with higher absorptance had lower laser-induced damage threshold (LIDT); however, when pressure was larger than 20 mPa, this correlation did not exist anymore. Defects might be the cause of such phenomenon. Defect models were established to mimic the absorptance test and the LIDT test. The influence of defect size, defect density, defect absorptive coefficient on absorptance and LIDT was studied, and the mechanism was analyzed. It is found that those defects with 1 000 times higher absorptive coefficient can significantly decrease LIDT to as large as 1 000 times, but do not influence the absorptance test at all. This might explain that some films with high absorptance have even higher LIDT, and some films with low absorptance have even lower LIDT.
In order to improve the recognizability of ship lights in the complex light environment to better protect the navigation safety of the ship at night, a new type of ship lights was designed according to the colorimetry and the emitting principle of semiconductor laser. Starboard light and masthead light of power-driven vessel with the length of no less than 50 m were selected as experimental objects. Starboard light and masthead light solid models were established in the three-dimensional solid modeling software (Lighttools) environment. Both of the lights- semiconductor laser spectral region, spectral weight, power, rays to trace, relative ray power threshold and other parameters were set to simulate the color properties at different reception distances. The simulation results show that: the color stimuli purity value of semiconductor laser starboard light is 1; the chromaticity coordinates of the semiconductor laser masthead light are close to the reference white (the chromaticity coordinates is (1/3, 1/3)); both of them meet the requirements of the International Regulations for Preventing Collisions at Sea for lights color properties.
To investigate the response of fiber probe on explosion loading and the response character under impacting action, the detonation experiments of the TNTRDX-Al explosive and the composite B explosive were developed. The 0.063 5 mm fiber probe with concentrating collimation convex in the front-end and the 1 mm fiber probe without concentrating collimation convex were adopted separately to determinate the transmission velocity of the chemical propagating reaction. Both of them could determine the detonation velocity of explosives ～7 000 m/s and the uncertainty of measurement 2%. The fiber reaction signals under shock were recorded using the fiber probe without concentrating collimation convex. And the black-body radiation phenomenon was validated under the high temperature and high pressure produced by strong impact.
In order to suppress the influence of the power variation which caused by the polarization drift brought to the stability of the transmission, a frequency transmission system which could quickly compensate the change of polarization was designed. The system which used a mode-locked laser as the light source, combining with the principles of feedback regulation of the proportional-integral-derivative (PID) control, employed the erbium-doped fiber amplifier (EDFA), polarizer, variable power optical attenuator (VOA) and single ship microcomputer. Experimental results show that the system can effectively suppress the polarization drift which changes with the environment, to make the output optical power stability reach 110-5 that increases 200 times when comparing with the free float after a transmission of 10 km. The design applied in the optical frequency comb transmission system, can detect the phase more accuracy, and effectively eliminate ~ 50 fs phase jitter introduced by the polarization drift on the 5 GHz transmission frequency.