2007 Vol. 28, No. 6
The technical solution for electro-optical pod inertial orientation during the geographic tracking was discussed. An accelerator was added in the stabilized platform, which could rotate in azimuth and elevation. The accelerator was combined with the gyroscope on board to form an inertial measurement unit, which provided the signals to servogimbal driving system and navigation system. The attitude matrix of the moving platform could be resolved when the stabilized sight was pointing at a target. By use of the rotation angle of the gimbals, the pod attitude matrix was obtained. The component of the pod acceleration value in the navigation coordinate system was calculated, and the derivation of the flight path was realized. The theoretical analysis and verification test indicate that the orientation and attitude of the electrooptical pod can be obtained with inertial measurement unit.
Since the energy distribution of the optical spot has great impact on the imaging quality in the microimaging with the filtering method of nondiffracting beam, the energy distribution of the weak imaging spot must be measured accurately. In the experiment, the light spots were measured by the scanning method. A pinhole attached to the flexure hinge mechanism was used to implement the 2-D scanning of the imaging spot accurately with a very small step, and the sampled light signal passing through the pinhole was received by a photomultiplier tube. Then the signal was transferred to a computer for the further processing after it was processed by the low noise current-to-voltage conversion and amplification circuits. Finally the energy distribution of the spot was reconverted and obtained through computer processing of the measurement data. The result was given in three dimension energy profile after the actual weak light spots were measured by the selfmade device. This method can be used to accurately measure the energy distribution of irregular small weak spots.
The error factor of injection molding has a direct effect on the quality of a plastic freeform optics. In the process of injection molding, the combination of injection parameters and the injection process control significantly affects the error of molded plastics. In order to obtain higher precision plastic optical components, this paper focused on some key parameters such as the temperature of mold and injected material, injection pressure, holding pressure and holding time, and analyzed their effect on the quality of injected part. The theoretical research was proved by the experiments. The result indicates that, the shrinkage rate of volume is reduced, and the form and surface accuracy is improved by increasing the temperature of injection and mold, the pressure of injection and holding pressure. Thus, the precision plastic optical components can be obtained with the error of less than 0.1μm.
The design of a driver circuit for high-stability semiconductor laser is introduced. Its output current can be continuously adjusted from zero to two hundred milliamperes and its stability reaches 1.5×10-5. The variation of the output current is less than 1μA when its operation time is longer than 12h. The modulation of frequency and intensity of optical wave in the laser interferometry can be achieved by the modulated current (100kHz～300kHz) input, whose modulation depth is continuously adjustable from zero to one hundred milliampere. By applying the grating external cavity semiconductor laser and the auxiliary temperature-control current driven by the driver current to the interferometry, the laser output with stable power and single wavelength was obtained to eliminate the mode hopping phenomenon of lasers and to realize the longdistance measurement for small vibration.
To enlarge the measurement range of a potential vision meter and improve its measurement accuracy for patients with high error of refraction, the imaging characteristics of its optical system were investigated. The visual magnification equation of the system was derived. The influence of the focal length variation of the collimating lens and the imaging lens on the magnification was analyzed respectively. The focus of the collimating lens has effects on the slope of the visual magnification curve while the focus of the imaging lens affects visual magnification of the whole moving range in the same way. With ideal parameters, the visual magnification can remain constant independent of the position of the vision pad in the moving range, and the system error can be removed. The optimum parameters for the meter were found by numerical analysis and the measurement scope of the system was expanded from -7D～＋12D to -11D～＋15D.
A novel thin cloud removal method based on advanced multiscale Retinex algorithm is suggested for color remote sensing image. Typically, the image enhanced by multiscale Retinex algorithm can provide the information in the shadow area, but the cloud in remote sensing image can not be removed directly by Retinex algorithm if it is in the bright region. This new method uses two complementary color operations between which the advanced multiscale Retinex algorithm is applied. The experimental result shows that the new method can remove the thin cloud in the image effectively and provide adequate information.
On-line process monitoring is beneficial for maintaining high quality products at high production rate and low cost. The traditional off-line weld testing is costly in terms of time, material, and productivity. Real-time nondestructive testing, however, can be as accurate as off-line testing; yet faster, cheaper, and better productivity. In the field of real-time monitoring, various methods have shown their prospects in detecting gas shielded tungstens arc states. In this paper, a new technical way for real-time weld process monitoring based on image analysis with DSP is presented. The focus is on how to decrease the effect of the arc light and make the system more faster (≤50ms) and more accurate (≤10μm).
The curvature radius of optical sphere is an important parameter to determine the properties of an optical sphere. The measurement result of the spherical curvature radius can be used to assess the quality of an optical component. Based on the theory of white light interference, a Moire raster displacement measurement system and a CCD digital image acquisition system are integrated into Michelson interferometer to form a semi-automatic measurement system for measuring the curvature radii of optical spheres. The system is accurate in measuring big curvature radii. As for the spherical radius of 71.2037mm, the standard error of 472.3μm can be obtained. The experiment result shows that the system can realize high precision measurement for big curvature radii of optical spheres.
Since all kinds of noises introduced in the process of the video forming and sampling inevitably lead to a bad quality of video images, the basic principle and algorithm of the median filter are presented to realize the real-time image pre-processing for succeeding processing. The rapid real-time median filter was designed with "flowing technology" according to an algorithm in the fieldprogrammable gate array (FPGA). The method to store the first two lines of the image data in the line output based image processing is given. The simulation result shows that the median filter can implement the real-time pre-processing of CCD output images, and achieve the goal of noise suppression and image details keeping.
Sun sensor is an important attitude control and azimuth measurement device for spacecrafts. The operation principle of the micro sun sensor based on CMOS APS detector is introduced. The calculation method of photoelectron generated on the surface of CMOS APS is analyzed. The amount of the photoelectrons was calculated when the sunlight incidence was vertical to the surface of the earth. The composition of the optical films on the surface of the mask for the micro sun sensor was designed and the transmittance spectrum characteristic of every layer was figured out. An optical film design method of the mask for a micro sun sensor based on the CMOS APS is presented.
In order to detect ［Ca2＋］i, a novel monochromatic source for the fluorescent microscope was designed. The system uses a short-arc Xenon lamp as light source. All the light is converged to a point source by the elliptical mirror. The point source is coupled into an optical fiber to form the monochromatic light output after collimating, light splitting and focusing by the blazed grating. In the illumination and excitation system of the fluorescence microscope, the light power and spectral purity of a monochromatic source are the two technical essentials，in which the aspherical reflector is the priority in design. The energy efficiency of the whole system was analyzed and calculated according to the optimization algorithm and the optical simulation. The elliptical reflector for the monochromatic source system was designed, and the complete equipment was developed. The experiment result shows that the elliptical mirror works in the whole system perfectly.
The development of aerospace science paves the way for improving earth observation and the optical imaging remote sensing technology is developing rapidly. The imaging quality can be improved by improving remote sensor quality, enlarging focal length, increasing record medium resolution, and improving optical system transfer function. A threemirror anastigmatic optical system, whose focal length is 36m and field angle is 0.75°, is introduced. The system can realize instantaneous space-to-ground scanning for a range of 90km×90km, and staring imaging over an area of 900km×450km when the system is swinging. The result of the system design is given.
Carbon fiber composite (CFC) is widely used in structure design of space systems. Its stiffness design with little distortion is still a vital problem in the structure design of aerospace cameras. The design requirement of 2μm maximum distortion for CFC was achieved by the tolerance analysis of mechanical parts in a coaxial 3R optical system of space telescope. The physical model was established according to the force distribution of the whole structure. The CFC layer sequence was reasonably simplified based on the paprag theory for composite materials. MSC.Nastran was used to improve and verify the design. The result of the Finite Element Analysis (FEA) shows that the design of the CFC lens barrel meets the requirement of structure stiffness with maximum distortion of less than 2μm.
The resistance variations of the high-performance microchannel plate and the standard microchannel plate processed by the same or similar image intensifier technique were compared before and after tube process. The variation of the resistance with voltage and temperature was tested after the high-performance microchannel plate was baked in vacuum and scrubbed by electrons in two different phases. The results indicate that the thermal stability of the highperformance microchannel plate is superior to that of the standard one, and its resistance temperature coefficient is -0.007/℃.The change of resistance with voltage is slow after the electron scrubbing in the second phase, and then the voltage coefficient is -1.11×10-4V-1. The MCP made with this material and technology has lower resistance, larger dynamic range and higher stability, which can meet the requirement of the special detectors.
In order to meet the real-time requirement of the video sequence fusion in visible and infrared target tracking, region growing method, a frequently used method in target segmentation during target tracking; was used to extract the target regions from IR image through the gray difference between IR targets and its backgrounds. The extracted target regions of IR image are fused with background regions of visible image. The fused mosaic image has good IR target features as well as clear visible background. Experiment shows that the method is simple and effective.
A laser direct writing way of micro-optical variable device with low frequency templates is proposed. The template is composed of 6×6 unit figures. The unit structure on the template is inputted by the spatial light modulator (SLM), exposed on photo-resist plate through the projection optical system section by section. micro-OVD with various complicated design and characteristics can be made by controlling the direction of the unit structure on the template. In order to achieve the achromatic effect of micro-OVD, a directional random speckle structure template base on the low frequency template was designed. The SVG-LDW04 laser direct writing system, whose typical phase structure is (4～100) microns, is adopted to fabricate the micro-OVD. The mentioned method does not use mechanical rotation device to change the direction of unit template, provides a novel and convenient way to fabricate the micro-OVD′s.
According to semi-classical theory for random laser, the Maxwell equations with the rate equations of electronic population can be solved by Finite difference time domain method (FDTD). The saturation effects of quasi-state modes in 1-dimension random lasers were numerically investigated based on this theory. The spatial and frequency distributions of different quasi-state modes were obtained. The results show that some properties of quasi-state modes, such as localization, will influence the saturation effects of the random laser system. By investigating these effects, the best quasi-state mode with low threshold and high saturation intensity can be achieved as a steady system output through one single frequency pump.
In order to study the influence of flight parameters on laser-induced plasma when the pulse CO2 laser is used for the air-breathing mode, the experiment of laserinduced plasma using the UV-preionized TEA CO2 laser made in our laboratory is discussed. A cylinder with a parabolic inner surface was used in this experiment, whose aperture diameter was 60mm, and the focal lengths were 5mm and 10mm. The spectrum of laser-induced plasma, the distribution of characteristic lines, and the temporal behaviors of plasma in air-breathing mode were introduced in detail. The results show that the evolution of laser-induced plasma with air-breathing mode may last 20μs, and the signal intensity reaches maximum at 6μs. When the laser pulse has a complete effect, the signal begins to decay rapidly. In addition, the signal peak value and the persistence time of laser plasma produced by 10 mm parabolic inner surface are higher and longer than those by the short focal length flight.
The feasibility of rapid quantitative analysis of coal by Laser-Induced Breakdown Spectroscopy technique was studied. The calibration curve method for LIBS quantitative analysis is introduced. Five coal samples were selected as investigation subjects, the carbon plasma line of 505.2nm was chosen as analysis spectrum line, and the carbon content of coal was analyzed quantitatively with delay of 0.8μs, 1.2μs, 1.6μs, 2.0μs and 2.4μs. The results were compared with the results measured with Element Analysis Instrument. The error measured in 1.6μs delay was the minimum, the effect of delay time on the quantitative analysis was analyzed. The results indicate that LIBS has a great potential in fast analysis of coal content.
In order to boresight the sensors in a multi-spectral electro-optical tracker, three methods for measuring the optical parallelism between laser and infrared sensor were introduced and compared. The boresight method using the thermal target to transform laser wavelength into infrared wavelength were investigated. The investigation shows that the selection of the thermal target and the measurement of laser transmittance are the most important steps. Based on the experiment result, the phenolics was selected as the material for thermal target. Its laser transmittance is only 0.5%.The result obtained by this method conforms with the result obtained by long range target method, its feasibility and validity are proved.
The features of laser ultrasonic technique and its surface acoustical wave are introduced. The principle of laser ultrasonic generation and reception as well as the application of laser ultrasonic technology are presented. The structure, properties and applications of polyvinylidene fluoride (PVDF) piezoelectric film are briefly described. The design concept and experiment methods of the PVDF transducer are discussed. With the experimental setup, the surface acoustic waves generated by pulse laser were received by the PVDF transducer. The signals generated in experiment were analyzed. The results show that this setup is reliable and can be used as a nondestructive detection solution.
Ultrathin LiTaO3 wafer is needed as a sensitive lay for fabricating high performance pyroelectric infrared sensor array. Since the thickness of LiTaO3 wafer was thicker than the required thickness, the LiTaO3 wafer was processed by the novel wafer bonding and mechanical thinning processes, i.e. benzocyclobutene (BCB) bonding, grinding, polishing, heating stripping and BCB etching. The ultrathin single crystal LiTaO3 wafer with dimensions of 10mm10mm25m was prepared with the thinning processes. The pyroelectric coefficient of the thinned LiTaO3 wafer is 1.610-4Cm-2K-1. The measured results of the thinned LiTaO3 wafer show that the thickness uniformity, surface roughness and surface profile accuracy can meet the requirement of the application.
In the application of the modern laser technology, subsurface damage (SSD) on optical components generated in the manufacture process is one of major sources for laser damage. Subsurface damage detection is becoming a hot topic in optical manufacture society. With the apparatus in the lab, non-contact white light interference theory was used to detect subsurface damage of K9 optics. 3D map and portrait slice diagram were obtained to precisely determine the depth of subsurface damage and damage density at different depths. This method is nondestructive, accurate and convenient to use.
In the field of smoke screen technology, the total obscure power (TOP) is a characterization parameter of smokescreen obscure power for human visual. A smokescreen TOP testing system, which can implement the automatic TOP measurement, was developed based on the irradiance measurement technology. This system is stable, efficient, real-time and reconfigurable. Under the conditions of 26℃ and 80% relative humidity, a test for yellow phosphorus-derived smoke TOP was performed. It was verified that the test result conformed with the empirical value.
Since the traditional manual method to detect the scratches of small size pipe is complicated and may produce big human errors, a computer vision technology is adopted for the analysis and recognition of the scratches on the small size pipe surface, which uses the contour extraction of binary image to get the feature parameters of the scratches and analyzes them based on morphology. This method enables the features parameters, such as the area and the shortlong diameter ratio, to be extracted for identifying the scratches. It can effectively overcome the shortcomings of the traditional method, improve the stability and accuracy of the detection.
In order to control the light propagation with high diffraction efficiency in 3-D space, a new phase weighted iterative optimum algorithm based on GS iterative algorithm is proposed to improve 3-D phase-only diffractive optical element (DOE) design. A weighted iterative algorithm model based on multi-diffractive output planes was established. In this algorithm, a dynamic phase weighted adjustment strategy based on the feedback of design error on each output plane is performed to optimize the conventional algorithm. A designing experiment was carried out to validate the effect of this algorithm. In this designing experiment, a phase-only diffractive element was designed to transfer the incident Gauss beam into 2×2 beam arrays in every plane, which occurred at 300mm ～ 400mm to the incident plane. It is found that this method can improve the convergent effect of the algorithm on the basis of the previous algorithm and achieve the better design quality.
The hard-edge aperture is “moved out” in an complicated optical system, which means to transfer the system with such hard-edge aperture into an optical system with entrance and exit pupils, and the hardedge aperture is taken as an exit pupil so as to find the analytical solution of a light beam. The intensity distribution of the Hermite-Gaussian beam at the output plane can be characterized by the Collins formula and the relation between aperture and exit pupil, and the analytical expression of the beam at the output plane is obtained directly. Taking an optical system with a hard-edge aperture as an example, the intensity distributions of two low modes of Hermite-Gaussian beam were simulated and numerically calculated with the mathematical software. The analytical results show that the effect of hard-edge aperture can be replaced by the effect of exit pupil for any complicated optical system with a hardedge aperture and the calculation process is simplified.
A new way to make wavelength-division multiplexer using the volume holography technology is proposed to expand the communication capacity of the fiber and separate the light of multi-wavelengths effectively. The properties of wavelength-division demultiplexer were investigated. The holographic gratings were superimposed in 10×10×10 mm3 double-doped LiNbO3 crystals (mixing into Fe and Zn) to separate the multi-wavelengths light transmitting in the same direction. Some theoretical and experimental results on the properties of wavelength-division demultiplexer in double-doped LiNbO3 crystals were given. The experiment result proves that this method is feasible. The multi-channel wavelength-division demultiplexing was realized.
3dB wide band coupler is a passive device widely used in optical fiber communication system, optical fiber sensor, optical fiber measurement technology and signal processing system. A fiber fused biconical taper (FBT) 3dB wide band coupler was designed and some samples were manufactured. The bandwidth characteristics of asymmetric FBT coupler were analyzed by coupledmode equation. The bandwidth of the wide band coupler is about 300nm (between 1300nm and 1600nm), while its excess loss is less than 0.5dB.
Calibration specification is the base for carrying out the calibration. Drafting the calibration specification of IR optical focal length measuring equipment is a very important object, it is the basic requirement for metrological assurance. The calibration specification of IR optical focal length measuring equipment not only applying to metrological service, to guarantee the accuracy, compatibility and traceability of daily calibration works, but provided the technology basis for the branch that produces infrared optics system focal distance measuring device, at the same time satisfies request of the consumer who use the infrared optics system focal distance measuring systematic in the process applying for various attestation. In this paper, construction, methods of calibration, and evaluation of uncertainty of the calibration specification for IR optical focal length measuring equipment are described.