2010 Vol. 31, No. 6
To design proper algorithms for ultra-wide field of view (FOV) infrared fisheye warning system, the infrared image taken by the ultra-wide FOV warning system was studied. The target in the infrared image is a point target, and its background is complicated. For the sky background, its radiance will decreases and target moving track will be bent as the elevation angle increases. Such situation is deteriorated with the increase of FOV angle. Based on the design theory of the infrared fisheye lens, the illumination of the system image plane was analyzed and calibrated with CDS100-04 black body. It is found that the relative standard deviation of the gray value in different positions is only 2.26%, which indicates good image illumination uniformity. Finally, the detection distance of this system is analyzed, which is about 9.6km.
In the final course of zoom lens design, the cam curves have to be designed. In addition, in order to balance the uniformity between imaging magnification change and cam corner, the appropriate cam curve should be chosen. So it is important to establish the relationships between imaging magnification M and cam corner . Based on the boundary conditions and the continuity of the function whcih cam curves have to meet, some functions are established and discussed. Some design examples were simulated with Matlab, which indicates that the exponential function fits well with M and . Besides, the pressure angle is less than the permitted value and the uniformity of cam curves is better and smooth without cam inflexions. Compared with other solutions used before, this method helps the designer to modify the cam curves effectively and find the best cam curves of the zoom lens.
Under paraxial approximation, the transfer matrix of left-handed slab focusing system is derived. Using ABCD law, the propagation expressions for Gaussian beam focused by a left-handed material slab are obtained. On the basis of propagation formula, the focusing properties of Gaussian beam are analyzed. The beam waist of image Gaussian beam is equal to the beam waist of object Gaussian beam under paraxial approximation, that is to say, the left-handed material slab can not focus Gaussian beam. The focusing for Gaussian beam with a left-handed material coincides with imaging rules of geometrical optics and does not have focal shift.
Since the angle and angular rate measurement of the existing helicopter-borne stabilized sight system is very accurate, a real-time target passive ranging method is put forward based on these measurements. The mathematical model for locating fixed ground target by helicopter-borne stabilized sight system was established, a rotary variable differential transformer was used to measure target angle and an inertial gyroscope was used to measure target angle variation rate. The measurement accuracy is better than 0.1mrad/s, which is ten times accurate than before. The stability and precision of ranging measurement system are improved by extend Kalman filter (EKF). The simulation and experiment results indicate, it can make real-time target range estimation, which is suitable for the real time target position of attack helicopter.
In order to change the focal length of optical zoom system without using moving parts, two or more active optics were added, which could provide variable focal length and create an imaging system with variable magnification. Based on this design concept and combined with Cassegrain reflective telescope, a zoom system was designed with active optical elements in ZEMAX. Its effective focal length is from 1600mm to 800mm, and its field of view (FOV) is 0.6～1.2. The whole system consists of 2 reflective deformable mirrors, 1 fold mirror and 1 refractive lens. In order to achieve zoom function, the entrance pupil diameter, the first and the second reflective mirrors radius are variable. Its MTF at the spatial frequency of 16lp/mm is more than 0.75, the maximum RMS spot diameter is less than detector size. The results show that the imaging quality can satisfy system requirements.
In order to obtain images with an airborne electro-optical system at the required distance, the theoretical analysis and simulation calculation of an optical dome and a mirror system were conducted, and a prototype was tested. The relationship between dome aperture and received light energy at different spectra were calculated, and the vignetting coefficient of the optical system was discussed. At the flight altitude of 8.4km, the prototype incorporated with this dome could detect a fighter aircraft at a distance of 86km with a LWIR scanning system, track the same target at a distance of 180km with a MWIR staring system, and obtain a laser ranging of 47km. An optical dome and mirror system was designed successfully based on the theoretical analysis and simulation calculation.
To study the multi-path effect of airport approaching landing system, according to the theory of electromagnetic system in scale model, a controllable laser transmitting equipment is used to simulate the function of the angle navigation antenna of airport approaching landing system based on the feature of the laser beam, which emits well directional laser scanning signal. The feasibility of this method were analyzed in wave similarity, reflex point coordinates similarity, signal arrival time similarity in time axis, model of laser obstacles, scattering characteristics, and phase accuracy similarity. Experimental results show that the laser beam can simulate the multipath effect of real airport in scaled environment, which provides a new way for studying the multipath effect of landing navigation system.
In order to accurately track highly dynamic targets with a heavy electro-optical tracking system, a coarse and fine axes driven servo system is presented, in which a fast steering mirror is used as fine control axis and conventional gimbals are used as coarse control axes. Some key technologies were discussed. Hardware-in-the-loop simulation indicates that a tacking error of less than 70rad is obtained, and the feasibility of the system is validated.
For various applications, the develoment of optical window is a multi-discipline engineering effort, which involves optics, mechanics and thermology.Under the circumstance of pressure difference, as well as axial and radial temperature difference, the finite element model (FEM) of optical window is established. The FEM was compared with the theoretical results and validated. Taking FEA data as the input at the interface of modified Zernike polynomial structural/optical analysis, the Zernike coefficients corresponding to aberrations are abtained. Using the obtained Zernike coefficients as the figure of optical window, wave aberration and MTF as measure of imaging quality, the impact of optical windows deformation on optical performance of largeaperture and long focus collimator was analyzed.The results show that the impact is negligible.
The imaging ray will have a small displacement when the space between a pair of light wedges is changed. A light wedge regulation device is added in the detector of double CCD image stitching, which includes two pairs of light wedges, one pair is used for the image regulation in horizontal direction, while the other is used for image regulation in vertical direction. A light wedge regulation device was designed and manufactured. It is incorporated in the detector for tuning double CCD image stitching. The assembly and tuning process shows that the regulation device does not have any negative impact on the original optical system, and it can realize image displacement with accuracy better than 0.001mm. It reduces the detector assembly and tuning complexity for double CCD image stitching, improves image stitching quality and saves the production cost.
Tiled displays systems built by combining the images from arrays of rear projection cubes can provide huge numbers of pixel elements to applications needing to visually represent lots of information. It is, however, puzzled by the gaps between adjacent cubes, the gaps is viewed as black lines in the displaying picture. The reason of the black lines is analyzed and the solution of eliminating the black lines is proposed. By zooming in the projection image, the edging projection rays are led into the gaps using optical wedge at screen border. The rays strike out lateral surface of screen with approaching total inner reflection angle and refractive then incident normally to the screen. The experiment indicates the picture can be displayed through the gaps without any black or gray lines.
In order to obtain the time-dependent behavior of one-dimensional two-photon screening-photovoltaic spatial solitons under low-amplitude conditions, the time-dependent behavior of one-dimensional two-photon screening-photovoltaic spatial solitons under low-amplitude conditions is presented theoretically. The time-dependent propagation equations of quasi-state bright and dark two-photon screening-photovoltaic solitons are obtained by numerical method. The results indicate that as time evolves, the intensity width of screening-photovoltaic spatial solitons decreases monotonously to a minimum value toward steady state. The higher the ratio of soliton peak intensity to the dark irradiation intensity is, the shorter the FWHM of photovoltaic solitons within propagation time will be.
Since LED lamp can not meet the practical requirements in light distribution and heat dissipation, its power saving and economic advantages are not fully utilized. Based on the existing solar LED streetlamps, technical specification and performance requirement of 90W solar LED streetlamp are established according to relevant national standards and the industry standards, and the preliminary design is made accordingly. The major components are selected and reviewed, and a design scheme is obtained. MATLAB is used to simulate LEDs illumination profile and light distribution, light distribution and heat dissipation are optimized to meet the requirements of street light.
In optical correlation recognition, the post-processing of correlation output results is one of the key steps to ensure the correctness of image recognizing. Neural network technique is usually used to post-process correlation output results and good result is obtained, however, this method needs to prepare a lot of training samples of correlation peaks and noise peaks in advance. Based on the polar coordinates transformations capability of transforming the rotation in Cartesian coordinate into translation and the translation invariant property of Fourier transformation, a post-processing method of correlation results based on Fourier-polar transformation is proposed. The verification results indicate that the similarity between the Fourier-polar transformations of target and its rotated images is greater compared to the similarity between the Fourier-polar transformations of target and disturbances. So the proposed method can effectively distinguish between targets and disturbances at the post processing stage, and it can avoid collecting training samples, which makes optical correlation recognition system convenient to be applied.
In order to study the effects of sampling point number on fitting precision when fitting curved surface by Zernike polynomials, the method of inadequate induction was used to obtain the relation between sampling point number and fitting precision. The results show that fitting precision has little change when sampling point number reaches a specific number. The relation between sampling point number and Zernike polynomials term number was obtained by calculation and proved by practical example.
The feature point extraction of calibration target during the camera calibration is crucial and may affect the precision of camera internal and external parameters. Based on several typical camera calibration targets, a spot array target is designed as required by the fringe projection 3D profile measurement system. According to the image edge processing theory, a new method for feature point extraction of the spot array target is introduced, which includes the analytical characteristic theory of circle, the coordinate transformation, the corresponding relation of spot and circle, and statistical theory. The validity of this method is verified by experiment. This work can be used to solve camera internal and external parameters.
In the automated docking system for large-scale equipments, CCD camera is needed to get the circle target image of one equipment, then find the coordinates of the center of the image using for alignment of the two equipments. In order to meet real-time measurement and high-precision positioning requirements, the paper presents a CCD camera image center positioning method. Firstly, the image uses median filtering method for image enhancement, secondly, single-pixel-wide image edge of the image is fully extracted by generalized morphological structure of anti-noise in the multioperator expansion and corrosion, then a polynomial interpolation method is used for sub-pixel positioning of image edge, and finally use a radius of constrained least squares circle to fit the target image center of the circle for precise positioning. The experimental results show that it is fast, accurate, stable, its sub-pixel positioning accuracy is better than 1/20 pixel, and total standard deviation of center point is smaller than 0.01, which meets the automated docking system requirements.
Moving shadow is usually misinterpreted as part of moving object because of its similarity with the object in video target segmentation, and the processing speed of traditional shadow elimination method can not meet the requirement of real-time intelligent transportation system. A new shadow elimination method is proposed. In this method, every color image of a video is transformed into gray images; and difference image is obtained by calculating the difference between the gray image and its background; then the difference images are transformed into binary images with a positive threshold and a negative threshold. By selecting these two thresholds appropriately for both light-colored and deep-colored objects, only target object remains in the binary images. In the experiments of real-time vehicle detection, this method demonstrates a good performance of quick shadow elimination compared to traditional method. It can be applied to moving object detection, tracking and other real-time applications.
Local histogram equalization is a technique commonly used in image enhancement, and it is based on global histogram equalization. In the algorithm, the gray converting function obtained in the neighborhood of one pixel is implemented at the pixel. For increasing the speed of processing, especially for the processing of video or image, it is an optimal choice to implement FPGA because DSP based technique can not meet real-time processing requirement. For the specific implementation of this algorithm on FPGA, some improvements over the traditional algorithm are made. The RTL-level description of the algorithm by VHDL language is achieved. The result was validated on hardware.
High quality reconstruction image of particle fields digital holographic diagnosis can be obtained quickly by high performance reconstruction algorithm. The in-line digital holographic experiment of standard particle plate was designed with a large format CCD, and the large size digital hologram was obtained. The performances of the four reconstruction algorithms, such as the quality of the reconstructed image, the hologram size which can be reconstructed, calculation speed, were studied and compared. The results show that FFT-AS algorithm makes reconstruction image background uniform, without reconstruction image compression, has faster calculation speed and the ability of reconstructing large size holograms, so it is suitable to reconstruct particle fields of in-line digital hologram.
The accuracy of space-borne InSAR interferometric baseline vector azimuth angle measurement is very important for improving system mapping accuracy. To meet the measurement accuracy requirement of a space-borne InSAR interferometric baseline vector azimuth angle, an optical metrology camera based on image processing is presented, an integrity experiment system is constructed, and the system measurement accuracy is analyzed theoretically. An experiment for optical target assembly with fixed displacement is used to validate the theoretical analysis of the system. The experiment result agrees with the result in theory, the system with arc-seconds accuracy is realized. It proved this approach is feasible for the space-borne InSAR interferometric baseline vector azimuth angle measurement.
The high precision attitude measurement system is researched, which is made of a model-90 dithered ring laser gyroscope and quartz flexibility accelerometers, and a method to rotate the inertial measurement unit is developed. The hardware of the system is introduced and a mechanical design concept without damper is given. The technique of the alignment and the attitude computation are described. The alignment consists of coarse alignment and precise alignment, and system error propagation characteristics can be described by system error model. The static test and single-axial rotation test are performed. The results show that the precision of the attitude in 24 hours is better than 30 seconds, and the precision of the heading in 24 hours is less than 30 seconds.
In Ritchey-Common test，the intrinsic astigmatism of the mirror plane under test and the astigmatism of the large curvature can not be distinguished in the measured system wave-front aberration. The flat is set in a divergent beam, which makes the relation between figure errors of flat and wavefront aberrations (influence function) complicate and difficult to derive. The procedure to simulate the Ritchey-Common test to derive the relationships between the figure errors of an optical flat and the wavefront aberrations, as well as the procedure to construct two set of influence functions by ray-tracing program are presented. Figure errors of the flat can be extracted from a set of over defined linear equations with the aid of least squares, using the influence functions and the measured wavefront aberrations for two different Ritchey angles. Both Ritchey-Common test and direct measurement results are presented. The comparison result proved the feasibility and reliability of this method．
A new method for in situ measurement of hemoglobin oxygen saturation (SO2) in brain tissue by the combination of the spectrometer and fiber probe is presented. In situ visible absorption spectrum measured by the fiber optical spectrometer at different SO2 and their corresponding SO2 values measured by OXI meter was collected on a kind of tissue model, which was a mixture of Intralipid and blood. The spectra were normalized and four spectra characters were obtained between 500 and 600nm. An empirical formula of the relationship between the four characters and hemoglobin oxygen saturation is derived by statistical method. SO2 values of 30 living ratsbrain cortex at different depth were obtained, and the experimental range was 64%～76%. This method can be used for monitoring hemoglobin oxygen saturation in different depth in brain Minimally Invasive Surgery.
The fiber Bragg grating (FBG) demodulation system based on the traditional matching FBG technology has the disadvantages of low wavelength matching accuracy, difficult wavelength adjustment and small dynamic measurement range. To overcome these disadvantages, a novel wavelength demodulation technology of fiber grating is proposed by using a tunable Gaussian filter instead of the conventional matching fiber grating. A vibration demodulation system using fiber grating is established based on the Gaussian filter. The vibration demodulation experiments are conducted for periodic vibration with different frequencies and amplitudes. It is found that, when the Gaussian filter with a suitable bandwidth is selected, the optical power of the light passing through the filter varies synchronously with a high fidelity as the voltage signal applied to the PZT varies. This indicates that the system demodulates the vibration signals effectively. Also, this system features high response speed,simple physical framework and large dynamic measurement range.
A 4-channel parallel optical module used for long distance transmission for high-definition multimedia interface (HDMI) signal is implemented and tested. An 850nm vertical cavity surface emitting laser (VCSEL) array is used as the light source of the transmitter, and a photodiode (PD) array is adopted as the detectors of the receiver. Connected by a multimode fiber array with maximum length of 300m, bit rate of each channel is up to 3.4Gbps. While highspeed signal can not reach far with traditional copper lines, HDMI fiber is a good solution to meet the needs for long-distance transmission of high definition video signals.
A method for desiging the software of FBG sensor network in the VB language environment was introduced to compile the software for serial communication based FBG sensor network conveniently and achieve the long-distance control of the FBG sensor network. The serial communication between PC and SCM in the environment of VB programming language, the control of the PC to the SCM, the data processing and figure drawing were implemented. The accuracy and feasibility of the FBG sensor network based on the tunable laser demodulation method and its analyzing software were verified by the calibrated FBG. The result of the experiment shows that the software is easy to design and it works reliably. A new solution for the remote control and the network control of the fiber grating sensor network is presented.
The dependence of SFS performance on the length erbium-doped fiber is important for the design and optimization of SFS. The experimental investigation on single-pass Erbium-doped superfluorescent fiber source (SP SFS) was presented. The dependence of the center wavelength, spectral line width, and output light power on the Erbium-doped fiber length was measured. It is discovered that, there is an optimal-length of Erbium-doped fiber for SPB SFS. The results of the experiment are significant for the selection of devices and the proper design of Erbium-doped super-fluorescent fiber sources.
To overcome the shortcomings of limited range and low precision in conventional absolute distance measurement, a new method is introduced by combining phase distance meter and heterodyne interferometer using He-Ne laser in dual longitudinal modes. The phase distance meter is used for coarse measurement and the heterodyne interferometer using He-Ne laser in dual longitudinal modes is used for accurate measurement. The result depends on the reliable combination of the two methods. A measurement system was built to verify the feasibility of this method and the sources of measurement error were analyzed. The comparison experiment was made against dual-frequency laser interferometer. The result shows that the system achieves the expected accuracy and its standard deviation is better than 1mm, which meets the large-scale measurement requirement.
Responsivity is an important factor for reflecting the performance of photoelectric detector and could be altered if the detector is laser-induced damaged. A system for monitoring real-time responsivity of the detector was developed. A PIN detector was irradiated by Nd∶YAG laser with energy increasing gradually, the relationship between the responsivity of detector and the power density of incident laser was obtained. The detector remained its performance when irradiated by laser with the power density of Nd: YAG laser less than 7.6105W/cm2, the responsivity of the detector was constant for 532nm reference light. When the power density of laser was more than 1.27106W/cm2, with increasing incident laser power density, the responsivity of the detector was reduced slowly. When the power density of laser was more than 1.27106W/cm2, the responsivity of the detector was reduced sharply after being irradiated. The reason for the fall of responsivity was analyzed. The conclusion was confirmed by scanning electron microscope photographs (SEM).
Based on ANSYS finite-element software, internal distribution of thermal fields and heat flow vector distribution of high power VCSE in AlN film passivation layer and SiO2 film passivation layer were analyzed. According to modeling, the Rthjc of VCSEL in AlN film is 3.123℃/W and the Rthjc of VCSEL in SiO2 film is 4.377℃/W. Experiment indicates that the Rthjc of VCSEL in AlN film is 3.54℃/W and the Rthjc of VCSEL in SiO2 film is 4.75℃/W.
According to the transmission matrix theory, the resonator stability of end-pumped U-folded cavity Nd∶YVO4 solid-state laser was theoretical analyzed and numerically simulated. The stable region range of different cavity arm length and the oscillation spot at the center of crystal were obtained by changing several arm length of U cavity resonator and making comparison. A group of cavity parameters were obtained, which could keep the cavity steady at the high pump power and make oscillation spot perfect. Experiment was conducted with a group of cavity parameters. The experiment result shows that, resonator cavity work steadily and 21.6W output power is obtained under 100kHz repetition frequency and 60W pumped power. The results agree with the theoretical analysis.
In order to obtain a reasonable He-Ne laser beam focusing lens, the high refractive index double pieces with front convex is used and Zemax is adopted for optimization and design. A He-Ne laser beam focusing lens with dispersion speckle diameter of 0.002mm was obtained. Spherical aberration of the axial point was modified. The diameter of the dispersion speckle of the lens is smaller than that of single piece, which is 0.0019mm. The spherical aberration is modified to -0.05mm～+0.05mm. The area compassed by MTF curves increases. So the brightness of the center is increased, which meets practical needs.
Taking the frictional units of cylinder liner/pistol ring as research subject, a new laser surface honing machine is designed. For processing heavy cylinders with irregular shapes, the laser head of the machine was designed to make rotation and linear motion. Three high accuracy optical gratings are installed on the linear shaft and a high accuracy incremental rotary encoder is installed on the rotation shaft to improve the accuracy of motion control system. In order to make micro cavity evenly distributed along the circumference, the method of decimal divider is adopted. The motion control system and laser system are coordinated by programming the two cards. Processing method is so-called Single pulse interval at the point many times. It can process micro or macro morphology structure and decrease negative thermal effects of laser processing.
In order to obtain ultra-smooth optical surface in ion beam process, the process methods for reducing surface roughness are introduced and validated by experiments. Optical material is typical hard and brittle material, whose surface roughness evolves complicated variation in process. As the final precision machining, ion beam figuring can correct figure error and improve optical surface roughness. Based on the evolvement mechanism of surface roughness in ion beam process, the methods of obliquely incidence figuring and coating sacrificial layer technology were investigated. The surface roughness was measured by atomic force microscope (AFM). Experimental results indicate that the surface roughness was reduced from 0.67nm RMS to 0.38nm RMS when figuring fused silica sample was processed at oblique incidence angle of 45. Similarly, the surface roughness was reduced from 0.81nm RMS to 0.28nm RMS after removing sacrificial layer. The methods of obliquely incidence figuring and sacrificial layer figuring technology can effectively improve surface roughness in ion beam figuring.
Peak-to-Valley departure (PV) is a widely used parameter in evaluating the quality of optical surface and wavefront. However, there is great uncertainty in optical surface testing using high resolution interferometer. In order to evaluate the quality of optical surface and wavefront more precisely, PV20, PVr and PVq are discussed. Through numerical simulation and experiment, it is proved that these three parameters can not only represent the real optical surface, but also be insensitive to interferometer spatial resolution. In addition, they have great advantage in metrology repeatability, hence, PV20, PVr and PVq are better than PV for characterizing optical surface.
Beam sampling grating is an important diffraction optical element for beam sampling diagnosis. Using two gratings as initial optical structure instead of single grating, an aberration-free structure was designed by using Zemax optical design software, which is a faster and more flexible tool for designing aberration-free grating-pair than Matlab. The method can verify the calculation result of the program. Design results show that the RMS radius of the converging light diffracted by two gratings is only 0.506m in spot pattern image, compared to 7.284m for the single grating, which indicates that two gratings can reduce aberration and improve image quality. Besides, the optical system can be used to detect far field beam, which provides effective technical support for online diagnosis for laser beam characteristics.