2009 Vol. 30, No. 3
A finite element model of the high-speed aerocraft infrared optical dome in the aerodynamic heating environment was established to analyze the domes physical and optical properties. The temperature filed, stress field, strain field and displacement field of the dome in the aerodynamic heating environment were computed numerically. The calculated results show that the temperature distribution of the dome in aerodynamic heating environment is non-uniform and thus the dome is deformable due to its thermal stress. Based on the theories of thermo-optical effect and elasticoptical effect, the refractive index field of the dome was numerically computed with the result of the finite element analysis. Taking the refractive index of the central point in the domes outer surface as an example, the refractive index variation caused by thermo-optical effect is 0.011 while the xdirection refractive index variation caused by elastic-optical effect is 0.000107. That is, the refractive index variation caused by elastic-optical effect is only 0.97% in the amount of the refractive index variation caused the thermo-optical effect during the domes working time. Therefore, thermo-optical effect has greater influence on the refractive index variation of the dome than elastic-optical effect.
With the development of LED technology, the trend that LED supersedes traditional lamp as the dominant light source for projectors is gradually obvious, especially for micro-projector. The TIR lens optimized in design are adopted to collect and transform the light from LED to overcome the disadvantage of big volume of an optical system using the tapered light pipe or CPC in traditional projection system. A time-sequence illumination system is designed to take RGB LED as its light source and single LCOS panel as the basic structure. Considering the effect of the time-sequence illumination way, the optical performance was evaluated by the ray tracing simulation program. The result shows the luminous efficiency of the entire system is 2.38%, the volume of the entire system is 125cm3, and the compact structure meets the requirement of illuminators.
A uniform projection system with a single LED as light source was designed for the purpose of the uniform illumination in a designated region. An optical system with refraction and total internal reflection (TIR) was proposed according to the luminous characteristic of LED and the law of energy conservation. The ordinary differential equations satisfying the spots on the contour curve of TIR refractive and reflective planes were established. The coordinates of points on profile curves were obtained by solving these ordinary differential equations using Runge-Kutta method. The profile curves were acquired by curve fitting of the coordinate spots with software UG, and then TIR model of the projector and data of the surface shape suitable for NC manufacture were obtained. The TIR model of the projector was introduced into Tracepro, and rays were traced. The results show that the illumination uniformity of the illuminated region is better than 92.6%, and the efficiency of the whole system is more than 91.8%.
A design method of an airborne stabilized-aiming system based on quantitative feedback theory (QFT) was proposed to overcome the influence of model perturbation and disturbances on the system. The method takes the azimuth loop as the discussion object and the model parameters as the parameter values of the azimuth loop. The strong robustness of the model perturbation system can be obtained in a certain range by the composite consideration to the models uncertainty range of the object control and system performance specification. The simulation results indicate the performances of the designed control system are better than the PID systems.
The common relational expression of the relief depth and substrate material of multi-layer diffractive elements in an optical system was derived on the basis of analyzing the diffractive efficiency of mono-layer and multi-layer diffractive elements, and the Abbe number of 20～80 and =0.25～0.6 were obtained by the optimization of these variances. The optical system can achieve high diffractive efficiency in broad wave band by reasonably using multi-layer diffractive elements in optical system. The variances of the relief depth and substrate material of diffractive optical elements are considered in optical system design. The ways to choose the material and relief depth of diffractive elements are described. Three pairs of different material and relief depth elements which can realize the high diffractive efficiency in the broad wave band were designed with the method.
The structure of EMCCD is introduced. The functions of signal amplification and noise restraint were realized by inserting the all-solid-state electron multiplying structure in the EMCCD chip and amplifying the charge coming out in horizontal transfer before detection according to the noise resources of EMCCD. Through a theoretical analysis of mathematical models for the main noises of EMCCD, three characteristics of EMCCD noise were-summed up:the EM gain can effectively restrain the read out noise; the noise factor generated during the EM gain process has the function of amplifying the noise produced before the multiplying structure; the effect of CIC on the EMCCD performance is serious. It is pointed out that the improvement of EM gain, aggravation of cooling and optimization of clock wave form can effectively restrain the noise.
Aiming at the hysteresis property of PZT under small thrust, a novel design of a white-light interference micro-displacement scanning system controlled by SPCE061A MCU is proposed. The micro-displacement scanning system taking a low-voltage error magnifier OP07 and a high-voltage power amplifier PA78 as the key elements of voltage stabilizer, made the overall bandwidth and magnification adjustable. The mathematical modeling for the hysteresis curve of micro-displacement of PZT in the scanning system was carried out with the least square fitting method. The experimental results show that the output voltage can be continuously adjustable from 0 to 200V, the maximum value of the ripple voltage is 1.06mV, the total displacement of 20and the linearity of 0.9 can be obtained when applied to the micro/nano scanning control, and the system has step-response time of 1.5s and the control accuracy of 10nm，which can realize the precise and rapid open-loop control for micro/nano scanning system.
In order to get laser incident angle from transmission of non-mechanical scanning Fabry-Perot etalon, a new Fabry-Perot etalon is designed, whose transmission is nearly linear to incident angle. The principle of thin film optics was applied, and the influence of the parameter change of antireflection coating and reflective film on transmission was investigated for oblique incident beam, especially for high incident angle. Main parameters of Fabry-Perot etalon were selected by simulating 1.06m laser wavelength. K9 glass was selected as reflection plate material. When reflection film is ZnS, its cavitylength is (4755)nm, film thickness is (655)nm and vertical reflectance ratio is 20.7%～24.0%, approximate linear relation is T=-52.23+87.92, nonlinear error is 5%. When reflection film is Ag, its cavity-length is (46010)nm, film thickness is (3.800.15)nm and vertical reflectance ratio is 22.4%～24.8%, approximate linear relation is T=-52.28+82.05, nonlinear error is 4%. Further study will be conducted for the implementation and fabrication process of this technology.
An image-rotation system which could efficiently enhance its scanning performance at a large scanning range was designed to eliminate the effect of the image rotation in a cancellation form according to the characteristics of the reflector prism that might adjust the optical axis and generate the image rotation, since the panoramic system composed of an imaging system and controllable scanning mirror usually produces the image-rotation phenomenon. The influence of prism fabrication and other factors on the clear aperture was eliminated by the arrangement of the flat reflectors instead of the reflective prism. The reason that the scanning mirror generates the image rotation was analyzed according to the image-rotation theory. The feasibility that the mirror combination can solve the problem of the image rotation was illustrated with examples.
The surface states of semi-infinite one-dimensional photonic crystal composed of positive and negative refractive materials are theoretically investigated with the method of the transmission matrix and Bloch theorem. It is found that when the photonic crystal is adjacent to a dispersive medium background and the average refractive index is equal to zero, the surface states can be sensitively changed in a large frequency range while the thickness of the cap layer is changing. The electric field distributions of two surface states with the same incident angle and different frequency are discussed. The result shows that the surface state which is far from the band edge has a smaller local length.
The modeling method of ultraviolet scattering characteristics for space satellites was studied according to background radiation environment. The target surface was divided into regions and each region was divided into grids in view of surface material characteristics and appearance respectively. The bidirectional reflection distribution function (BRDF) model was introduced to describe light scattering properties of target surface grid based on radiation theory, and a mathematical model of ultraviolet scattering properties of the target was built by superimposing scattering components of all the surface grids. The optical dynamic characteristics of the target on its orbit was achieved by using its given physical dimension and parameters. The solar sail irradiance obtained from the entrance pupil of the detector at a certain observation angle is approximately equal to that from the target body, and the maximum magnitude is 10-11W/m2. The simulation results indicate the solar sail can not be neglected when the target characteristics is analyzed.
After the gray projection analysis, an imaging CCD translation compensation method based on the movement estimation of gradation projection technology is proposed to improve the imaging quality and obtain the high resolution image. The system structure is presented. The system compensation effect of the resolution sign board moving in every status was verified. The restoration of a life-sized image was performed. The result shows that the compensation method has high restorability to the slow moving images and random vibration images. The overall performance of the system was greatly enhanced, and the imaging resolution was greatly improved.
Since the undulate topography of the lunar surface leads to the variance of the lunar surface remote sensing image pixels with the sun relative location and geometry orientation, the shadow pixels of the lunar surface remote sensing digital images are produced. In order to solve the problem, the judgment of the shadow on remote sensing images was implemented by utilizing DEM matching with the remote sensing images and the parameters of illumination orientation. A method for shadow removal of lunar remote sensing images taken under the condition of the natural topography was developed using adjacent reflective radiation based on DEM data. The shadow pixels remote sensing value can be rectified to the horizontal remote sensing value with same solar direct radiation. The simulation experiment result shows that the method can eliminate the shadow of lunar surface images and can thoroughly recover the reflection/spectrum characteristics of lunar surface images.
Wavefront curvature sensor is used in the fields of adaptive optics and optical metrology. It is assumed that the intensity of the incident wavefront is uniform in these fields, which does not conform with the fundamental theory. The signal expression of wavefront curvature sensor under nonuniform intensity was presented by means of Fourier optics theory. The numerical analysis of signal error for Gaussian beam was conducted using the signal expression under uniform intensity and nonuniform intensity. The analysis indicates that there is an error when wavefront curvature sensor is used to detect Gaussian beam. The error reaches the maximum when the phase distribution is 4th Zernike polynomials. The error decreases as the order of Zernike polynomials increases. The error of divisional mean curvature signal is small and below 10% generally.
The principle of SPIDER signal processing is introduced. An improved SPIDER signal processing method based on discrete spectrum correction is put forward. The signal processing error caused by the inadequate velocity of signal sampling can be overcome by the method. It is found in the testing that in the case of noiselessness, as the adequate correcting points are selected, the agonic correction can be basically achieved; in the case of noise, suitable correcting points should be selected to enhance the noise immunity. The time delay can be obtained by the method while the signalto-noise ratio is inferior. Through the simulation calculation, it can conquer the limit of the spectrometer minimum resolution and measurement range to bring about hurdle effect in the time spectrum, and to improve the measuring accuracy of the time-delay parameter of SPIDER. It is easy to realize the measurement, and can improve accuracy of the system without modification of the equipment. It can be used in the technology of SPIDER.
The smoothing of images is a very important step in the stitching process of images. An improved seamless image stitching algorithm based on the wavelet direction contrast is presented by the analysis of some available smoothing algorithms. The improved algorithm makes the luminance of the two images same first, then the multiresolution decomposition of the two images is implemented by using wavelet transformation and the images are smoothed by an improved wavelet direction contrast algorithm. The simulation results were assessed with some objective evaluation standards. The results show that this algorithm can make two images smoothly in despite of a great gray difference between the two images. Therefore, it is independent of the ambient light and can make the details of images clear.
The high-density holographic recording character of a novel water-resistant photopolymer material sensitive to red light and blue light was studied. The diffraction efficiencies of the hologram are all no less than 75%, and the sensitivities are (45～65)mJ/cm2 when exposing to red light and blue light respectively. The photopolymer material consists of compound monomer, compound sensitizer, compound initiator, chain transfer agent and binder, etc. The material has properties of waterproof, simple post-treatment, high resolution and high-temperature stability, etc. The multiplexing holographic storage shows that the reconstruction images are clear and bright. And there is no crosstalk among reconstruction images. Therefore, the photopolymer is fit for high-density data holographic recording. And it also can be used to produce the wavelength-division multiplexer used in light communication and other optical elements.
To realize the visual tracking under the complicated condition, an efficient color object tracking algorithm based on the adaptive is presented in this paper. Based on an adaptive kernel model, the nonparametric statistical modeling of a moving target was carried out with the intensity difference between the target and the background. The search region is extended for searching objects with the background-weighted histogram for statistics of the target feature on the premise of taking the relevance between the target and background into account in order to realize the tracking of the moving gargets in a large area. According to the change of the object and environment, the target model is updated to improve the adaptive ability for environment variation of object tracking. Experimental results on real image sequences show that the algorithm can efficiently track the moving gargets, and the average iteration number reduces 37.28% in comparison with other method.
A method for measuring the size of the dispersed spot of star sensor optical lens is presented. A measurement system consisting of a collimator, a rotary table and a CCD cameral was implemented to measure dispersed spot. After a image is acquired, a method of bibubic interpolation pixel subdivision is used to pick up the gray value of the image, and the size of dispersed spot is calculated by Rayleigh criterion. The actual measurement and verification test show that the measurement accuracy of the dispersed spot in 0.8 FOV reaches 0.5m,repeat measurement accuracy can reach 0.2m.
Based on the Kurtz theory, a measurement system of powder second-harmonic (SHG) using fiber spectrometer was designed. The test system can measure SHG in different directions by rotating the arm and not changing-direction of incident fundamental light. It has good accuracy and sensitivity. It enlarges phase-matching particles from 46m to 250m. The fundamental wavelength of 1.064m was used to measure KIO3 crystal powder SHG. The test result shows that KIO3 crystal powder has the phase-matching characteristics, which is consistent with the previous reports. The nonlinear coefficient d2 of KIO3 crystal powder obtained by simulating the experimental curve is 9.710-12m/V. The simulation value agrees with d32 of KIO3 crystal reported previously. This method is proved feasible and could be used in the study of nonlinear characteristics for other crystal materials.
A new testing method for LEDs spatial intensity distribution based on the high-level image programme language (LabVIEW) was introduced to overcome the shortcomings of the conventional method, whose light distribution curve can only reflect the two-dimensional light-emitting characteristics of LED and the third dimension is difficult to be observed and compared by human eyes. It incorporated synchronized multipath photometric detection in the traditional method, with 31 detection units to measure two-dimensional spatial intensity distribution (lighting distribution curve) of the LED source synchronously within 0.2s. By rotating LED test sample, i(i=180/) items of the lighting distribution curve were measured one by one. All the lighting distribution curves were collected and processed by the custom software, and three-dimensional solid map of the LEDs spatial intensity distribution was obtained. The method has the real time and high throughput features, and it is fast, accurate and straightforward.
Defect detection and elimination inside the wall of metal pipeline is very important for efficient transportation. The ultrasonic infrared thermal wave nondestructive test technology was employed to detect defects in metal pipeline. It adopted ultrasonic as a heat source to excite the sample and a high frequency infrared camera as a detector to capture the surface temperature, which combined the advantages of ultrasonic heating and infrared thermal technology. The pipeline with wall thickness of 3.33mm was inspected by this technology. By analyzing the temperature signal and typical time thermograph, the effective flaw information was obtained. Experiment conclusively indicates that the position of the defects on the inner wall can be accurately detected by the ultrasonic infrared nondestructive test technology.
A novel angle measurement method was introduced for measuring the deformation angle of large buildings and a photoelectric planar obliquity instrument was made. The speckle of laser was tested with a position sensitive device (PSD). In order to avoid environmental impact, magnetic fluid was utilized in the instrument. The viscosity of the special fluid could be adjusted by applying different magnetic field. Being reflected many times, the final angle of the laser beam was enlarged, which improved measurement precision. The design is simple, low cost, precise and robust to environment. The experimental resolution reaches 0.1 arc second and the repetition accuracy is better than 1 arc-second.
Based on the basic principle of the shape measurement by carrier modulation in electronic speckle pattern interferometry (ESPI) , a carrier pattern containing altitude information is formed on the object surface when the test object is tilted a small angle. The points on the surface of the object are displaced a distance when the test object is rotated. The phase difference introduced by the deformation and the phase difference introduced by the deflection of the object were compared. It is found that the carrier is introduced by the out-plane displacement and the phase containing altitude information is contributed by the in-plane displacement. Several ESPI methods for shape measurement by using carrier modulation are discussed. The typical ESPI system is effective in shape measurement because the carrier pattern containing altitude information is distinct and the phase of the object can be derived by Fourier transform easily.
Since the proximity distance, especially the 1st proximity distance (d1) is the most important factor to influence the resolution, a new on-line testing method of proximity distance for the image intensifier is put forward. According to the principle of the parallel plate capacitor, the 1st proximity distance can be obtained by measuring the capacitance value C1 between the cathode surface and the input side of microchannel plate. The functional relation between C1 and d1 was fitted by the tested data. The function formula was modified and verified by the accuracy analysis. It is shown that the maximum error is 11.9% and the tested results meet the precision requirement. The process of press seal and the proximity distance of an image intensifier can be controlled precisely by this method. Therefore, the resolution is increased. The method is simple and could be used in other online testing of short distance.
Since there are through-holes on the ion barrier film prepared with the normal technique, a method to measure the quality of ion barrier film is put forward to test the quantity and size of the regular or irregular apertures which cause the bright apertures on the screen by MCP electron multiplication when the low voltage is supplied to the cathode. Under the condition of assigned voltage and illumination of cathode, about 2lx light is illuminated on the photocathode, the voltage is exerted on each pole of the image intensifier to make the bright apertures on the screen to be seen distinctly, and then 10 microscope or camera is used to take pictures of the through-holes on the ion barrier film, which images on the screen. The experiment results show that under the same condition of testing, the quality of the ion barrier film is different if the craftwork of facture is different.
According to the algorithm principle of wavefront fitting and computer-aided alignment, the computer-aided alignment was realized with the damping least square method based on DDE interface technique and Zernike polynomials fitting, in which the joint calculation of MATLAB and ZEMAX is adopted. The communication between ZEMAX and MATLAB was performed through DDE interface. The visual graphical interface of basis matrix function which can generate the Zernike polynomial was written by MATLAB. The versatility and easy-to-handle characteristic of the program were implemented. The validity of the program was verified by the simulated alignment of an optical system with big obscuration ratio by using the program. In order to confirm the influence of the correlation of the Zernike circular polynomials at the annular aperture on the result of computer-aided alignment, the simulated alignment was performed by using Zernike circular polynomials and Zernike annular polynomials respectively. The simulated result shows that the two Zernike polynomials are all feasible.
A calculation method to calculate the surface shape error of rhombic prism according to parallelism demand of emergent beam is introduced. The relation of the surface shape error to f-number and relevant spherical radius was achieved according to the reducing analysis model ignoring the local f-number. Two kinds of rhombic prism model are established by ZEMAX. According to the simulation results from ZEMAX, the correctness and limitation of the former methods are proved and analyzed. The results are used to analyze the effect of the surface shape error of the rhombic prism on parallelism of the emergent beam. The assignation plan of the surface shape error for each working surface is presented. A conclusion that the effects of surface shape errors of the refractive and reflective surfaces on the deviation angle of the emergent beam are different with the increase of the incident beam diameter is achieved.
Based on the stress optics law and the theory of elasticity thermal stress, the relation between optic path difference of double refraction and main stress difference is derived. The effect of the stress on the imaging quality of optic colophony lens was examined in changing temperature environment with a photoelasticimeter. At 28℃～68℃, the isochromatic line of optic colophony lens of thermal stress was determined, and the interference fringe patterns were obtained at different temperatures and main stress differences. It is concluded that the thermal stress produced by temperature change does not converge, and no residual stress exists when temperature recovers. The image quality of the optic lens is not affected in 40℃ temperature variation range.
A method of magnetorheological finishing (MRF) was discussed. The relative velocity and dwell time of magnetorheological finishing process were calculated, and the relation curve between relative velocity and part diameter as well as the relation curve between the product of relative velocity and dwell time and part diameter were simulated. The process experiment of MRF optic parts was carried out based on theoretical analysis, and the removal characteristics of this magnetorheological finishing process were analyzed. The reasons of different removal characteristics in center area were explored. The process experiment of MRF optic parts shows that uniform removal could be achieved in optical part except the center area.
This paper proposes a security monitoring system based on fiber Bragg grating sensors for pipelines in landslide area and presents the method on how to obtain maximum stress if stress values of three points on the pipeline are available. Based upon this method, this system applies FBG sensors developed by ourselves to monitor stress of the pipeline. With the good immunity to electromagnetic interference, corrosion resistance and good stability, such FBG sensors can realize temperature compensation, eliminate impact of temperature on measuring results and measure ambient temperature. This system implements automatic measurement and data storage by optical switch and optical sensing interrogator and transfers data by GPRS. According to field results, this system is capable of realizing real time monitoring and stable in performance.
The mathematical model of the hyperbolic cylinder transmission grating was established. The complex amplitude transmittance was derived from the definition of an optical path when a parallel light passes through a singular hyperbolic cylinder. The expression of light intensity distribution for a hyperbolic cylinder transmission grating on the frequency plane was obtained by means of Fourier transform method. The variation of diffractive light intensity distribution with the hyperbola semi-real axis were simulated with MATLAB. The diffraction fringe agrees with the result of theoretical analysis. The potential application of the hyperbolic cylinder transmission grating in the field of optics is pointed out.
Proceeding from the propagating Jones matrix of laser, the relation between the eigenpolarization and the temperature in the four-frequency differential laser gyro was obtained in combination with the empirical formula of quartz crystal rotatory power versus temperature and the method of calculating eigenvectors, for the research on the influence of the quartz crystal temperature effect on the four-frequency differential laser gyro. The variation curves of the light ellipticity and the differential loss with the temperature were acquired by the numerical analysis. The result shows that the influence of quartz crystal temperature effect on the optical polarization characteristics is closely related to the amplitude reflectivity and the phase shift of the mirror. For typical gyro parameters, the differential loss and the ellipticity increase respectively from 0 to 10-6 and from 0.122 to 0.138 when the quartz crystal temperature is in the range of -60℃ to 60℃.
The method of the traditional optical axis correction for laser-range-finder was improved. The angle which the eccentric ring（or eccentric frame）needs to adjust was calculated by the mathematical model of the optical axis parallel deviation and the eccentric ring（or eccentric frame）rotary angle. The correction of optic-axes parallel was realized by the optical axis correcting device. Two correcting methods (semiautomatic and fully automatic corrections) are presented. In the semiautomatic correcting method, a scale ring is attached to the lateral portion of the double eccentric structure, and the optical axis correction is realized by rotating the eccentric structure to a certain angle by the two eccentric sleeves. In the fully automatic correcting method, the double eccentric structures are controlled by two stepping motors to adjust the optical axes. The experimental research on a certain laser rangefinder is conducted. The results show that the optical axis error corrected by the method is within the maximal permitted range（0.25mrad）, the efficiency is increased by the improved method, and this method can meet the requirement of the practical need.
A new method using a cylindrical lens with two wedges to improve the uniformity of the line laser is provided to solve the problem of laser beam uniformly transmitting in the laser communication. The theory model of the optical system for the beam shaping was built with ZEMAX. The uniformity of the beam through the cylindrical lens is analyzed with the model at the different parameters (radius, angle between two slopes and the refractive index of lens medium). The result shows that the line laser with the uniform intensity distribution can be obtained by changing the cylindrical lens parameters under the condition of far field.
The frequency-offset-lock control system which is applied to the heterodyne signal of narrow pulse laser is designed based on the programmable logic device since the frequency-offset-lock technology is widely used in laser heterodyne detection and laser radar. In the design, ultrahigh-speed comparator was applied for the waveform conversion, the multi-pulse frequency discrimination and maximum probability median filtering were adopted for the digital frequency discrimination, the fast control by small step was used for the frequency modulation, and the D/A convertor and linear magnification circuit were used to output the frequency modulated signal. The simulated heterodyne signals with the 40ns pulse width generated by the signal generator were employed to simulate the whole system, and the design function was realized. The simulation experiments show that the error range of the frequency discrimination gained by the designed frequency discriminator and modulator is -7.5MHz～+7.7MHz when the pulse width is 40ns.
In order to establish a LD-pumped Nd∶GdVO4/KTP laser system and improve the thermal stability of the green laser, the relation that the spot radii w2 and w3 vary with the thermodynamic parameter 1/ft were investigated with the graphic analysis method, and the parameters of three-mirror Z-type folded cavity insensitive to the variation of thermal lens effect of laser crystal were acquired by the calculation with Mathematics software. The continuous output green laser whose wavelength is 531.5nm and power is 2.72W was obtained at 20.3W end-pumping power when l1=170mm, l2=523mm and l3=152mm. The optical-optical conversion efficiency of 13% was realized with the all-solid-state laser. It is found that the laser system is insensitive to the variation of thermal lens effect when 1/ft＜0.25cm-1.