2007 Vol. 28, No. 5
Display Method:
2007, 28(5): 521-525.
Abstract:
Image differencing is a widely used method in moving target detection nowadays. Since most of the work only use the absolute value of difference images and the motion of the background must be compensated, the reliability and practicality of the method are not satisfactory. A new moving target detection method that uses both the positive and negative difference images is proposed in this paper. The new method detects moving target by calculating the positive and negative difference images respectively and making use of the symmetry of amplitude, shape and motion information for a moving target area in positive and negative difference images. The detection results of aircraft tailflame sequential images are given at the end of the paper. The experiment shows that the method can improve the reliability and efficiency for the moving target detection.
Image differencing is a widely used method in moving target detection nowadays. Since most of the work only use the absolute value of difference images and the motion of the background must be compensated, the reliability and practicality of the method are not satisfactory. A new moving target detection method that uses both the positive and negative difference images is proposed in this paper. The new method detects moving target by calculating the positive and negative difference images respectively and making use of the symmetry of amplitude, shape and motion information for a moving target area in positive and negative difference images. The detection results of aircraft tailflame sequential images are given at the end of the paper. The experiment shows that the method can improve the reliability and efficiency for the moving target detection.
2007, 28(5): 526-530.
Abstract:
On the basis of the research on an ideal diffraction optical imaging system with sparse apertures, the algorithm of the imaging restoration for sparse aperture optical systems is proposed based on the improved wavelet threshold method and Wiener filtering. The improved wavelet threshold noiseblanking algorithm was designed to eliminate the imaging noise and obtain the ideal imaging result for the sparse aperture optical imaging systems in which noise jamming exists. And the imaging restoration was realized by using the Wiener filtering method. In the experiment, the optical design software ZEMAX was used to design the sparse aperture optical systems with different fill factors, and the algorithm proposed in this paper was applied to image restoration. The experimental results indicate that the algorithm is superior to the method which uses Wiener filtering only.
On the basis of the research on an ideal diffraction optical imaging system with sparse apertures, the algorithm of the imaging restoration for sparse aperture optical systems is proposed based on the improved wavelet threshold method and Wiener filtering. The improved wavelet threshold noiseblanking algorithm was designed to eliminate the imaging noise and obtain the ideal imaging result for the sparse aperture optical imaging systems in which noise jamming exists. And the imaging restoration was realized by using the Wiener filtering method. In the experiment, the optical design software ZEMAX was used to design the sparse aperture optical systems with different fill factors, and the algorithm proposed in this paper was applied to image restoration. The experimental results indicate that the algorithm is superior to the method which uses Wiener filtering only.
2007, 28(5): 531-535.
Abstract:
Proceeding from the CCD image sensing and digital image processing technologies which should be improved for the spherical-aberration automeasurement system based on Hartmann method, the target discrimination and search algorithms of the Hartmann diaphragm image in the image-reflectionarea, and the center superposition algorithm for the spot distance measurement of the Hartmann diaphragm image are proposed to solve the problems for accurately searching the two-dimensional image targets in onedimensional image memorizer and then implementing some calculations of the relative targets. The center of Hartmann diaphragm image is solved by utilizing the centers of mass of all the light spots, and then the algorithm for the center superposition of the mass center distance is confirmed by the center symmetry of the diaphragm image. The result indicates that the times of computation are cut down and the computing complexity of the algorithm is reduced.
Proceeding from the CCD image sensing and digital image processing technologies which should be improved for the spherical-aberration automeasurement system based on Hartmann method, the target discrimination and search algorithms of the Hartmann diaphragm image in the image-reflectionarea, and the center superposition algorithm for the spot distance measurement of the Hartmann diaphragm image are proposed to solve the problems for accurately searching the two-dimensional image targets in onedimensional image memorizer and then implementing some calculations of the relative targets. The center of Hartmann diaphragm image is solved by utilizing the centers of mass of all the light spots, and then the algorithm for the center superposition of the mass center distance is confirmed by the center symmetry of the diaphragm image. The result indicates that the times of computation are cut down and the computing complexity of the algorithm is reduced.
2007, 28(5): 536-540.
Abstract:
Gray correlation based minimum error and correlation coefficient algorithms were improved to eliminate the disadvantages of low matching accuracy and slow matching velocity existing in the image matching algorithms nowadays．In the improved minimum error algorithm, a new ML distance method is adopted and a threshold dynamic adjustment method is proposed to assure the matching accuracy and to avoid the influence of local noises. As for the correlation coefficient algorithm, the expression of correlation coefficient is simplified and three-step searching way is used to reduce the compexity of the calculation and to achieve the goal of the position acquisition. The experiment shows that the improved algorithms greatly increase the matching velocity without the loss of matching accuracy，and meet the requirement of real-time image matching system.
Gray correlation based minimum error and correlation coefficient algorithms were improved to eliminate the disadvantages of low matching accuracy and slow matching velocity existing in the image matching algorithms nowadays．In the improved minimum error algorithm, a new ML distance method is adopted and a threshold dynamic adjustment method is proposed to assure the matching accuracy and to avoid the influence of local noises. As for the correlation coefficient algorithm, the expression of correlation coefficient is simplified and three-step searching way is used to reduce the compexity of the calculation and to achieve the goal of the position acquisition. The experiment shows that the improved algorithms greatly increase the matching velocity without the loss of matching accuracy，and meet the requirement of real-time image matching system.
2007, 28(5): 541-547.
Abstract:
The optical system for OPU(optical pick-up) is a uncoaxial optical system. The design position of optical element and its accurate assembly are critical for the proper operation of the system. Quarternion is a convenient mathematical method to describe the spatial lightbeam propagation and dimensional coordinate transfer. Three types of light-beam propagation in the uncoaxial optical system of OPU were characterized with quarternion, and the arithmetic method of the light propagation for the system was established. With the model, the flow chart for describing the relationship between optical component design, assembly parameter, foucsing spot and readout spot is obtained. This model can be used for analyzing optical assembly error, instructing assembly technicians, simulating the focusing of objective lens or tracking the displacment of objective lens.
The optical system for OPU(optical pick-up) is a uncoaxial optical system. The design position of optical element and its accurate assembly are critical for the proper operation of the system. Quarternion is a convenient mathematical method to describe the spatial lightbeam propagation and dimensional coordinate transfer. Three types of light-beam propagation in the uncoaxial optical system of OPU were characterized with quarternion, and the arithmetic method of the light propagation for the system was established. With the model, the flow chart for describing the relationship between optical component design, assembly parameter, foucsing spot and readout spot is obtained. This model can be used for analyzing optical assembly error, instructing assembly technicians, simulating the focusing of objective lens or tracking the displacment of objective lens.
2007, 28(5): 548-552.
Abstract:
A new sighting telescope with an electromechanical hand wheel and a microprocessor for accurate ranging and automatic firing table set-up is proposed. Its function, concept and target ranging method based on an electromechanical hand wheel are introduced. The ranging error and the feasibility of this method were analyzed. The method of the elevation angle calculation and the mode of the firing table set-up are also discussed. The merits of traditional optical sighting telescopes and electro-optical sighting systems with laser range finders are retained in this design scheme. It integrates ranging, resolving and set-up functions in one unit, and can adopt several kinds of resolving and set-up modes for different situations. It is small, convenient, reliable and low cost.
A new sighting telescope with an electromechanical hand wheel and a microprocessor for accurate ranging and automatic firing table set-up is proposed. Its function, concept and target ranging method based on an electromechanical hand wheel are introduced. The ranging error and the feasibility of this method were analyzed. The method of the elevation angle calculation and the mode of the firing table set-up are also discussed. The merits of traditional optical sighting telescopes and electro-optical sighting systems with laser range finders are retained in this design scheme. It integrates ranging, resolving and set-up functions in one unit, and can adopt several kinds of resolving and set-up modes for different situations. It is small, convenient, reliable and low cost.
2007, 28(5): 553-558.
Abstract:
Zernike polynomial is an important data transmission tool for thermal/mechanical/optical integrated analysis, which can be used to implement data transmission between optical, structural and thermal analysis program effectively. However, for many optical surfaces, finite element analysis(FEA) is unable to accurately fit their surface distortion and the various aberrations generated by such distortions because they could not meet the orthogonality condition required by Zernike polynomial, such as a mirror with a central hole. The factors effecting orthogonality of Zernike polynomial were discussed. A new method for importing FEA deformation data of optical surface into optical analysis software, interferogram interpolation, was presented. This method transforms the surface distortion data into the interferogram data accurately after removing the displacement of the mirror body and directly implements them into the optical software.
Zernike polynomial is an important data transmission tool for thermal/mechanical/optical integrated analysis, which can be used to implement data transmission between optical, structural and thermal analysis program effectively. However, for many optical surfaces, finite element analysis(FEA) is unable to accurately fit their surface distortion and the various aberrations generated by such distortions because they could not meet the orthogonality condition required by Zernike polynomial, such as a mirror with a central hole. The factors effecting orthogonality of Zernike polynomial were discussed. A new method for importing FEA deformation data of optical surface into optical analysis software, interferogram interpolation, was presented. This method transforms the surface distortion data into the interferogram data accurately after removing the displacement of the mirror body and directly implements them into the optical software.
2007, 28(5): 559-563.
Abstract:
Since the shape, size, material and defect of UUT in the infrared thermal wave nondestructive detection are different, three types of uniformity materials with different characteristics were selected by means of the finite element analyze software (ANSYS), and a 3-D sample model was designed to provide the detection with preview of the previous experiment result. The temperature field profiles of the model surface are drawn at different times with the preprocessor and general postprocessor of the software, and then the defect types are confirmed according to the given temperature distribution diagrams. The curves of temperature variation of different defects are drawn based on the analysis of the simulated data. The defect types are determined according to the different slope of the curves. The simulation result indicates that the finite element analyze software can be used for nondestructive evaluation, the simulation result matches with the experiment one. The method can be extended to the detection and the quantitative identification for other kinds of defects under material surfaces.
Since the shape, size, material and defect of UUT in the infrared thermal wave nondestructive detection are different, three types of uniformity materials with different characteristics were selected by means of the finite element analyze software (ANSYS), and a 3-D sample model was designed to provide the detection with preview of the previous experiment result. The temperature field profiles of the model surface are drawn at different times with the preprocessor and general postprocessor of the software, and then the defect types are confirmed according to the given temperature distribution diagrams. The curves of temperature variation of different defects are drawn based on the analysis of the simulated data. The defect types are determined according to the different slope of the curves. The simulation result indicates that the finite element analyze software can be used for nondestructive evaluation, the simulation result matches with the experiment one. The method can be extended to the detection and the quantitative identification for other kinds of defects under material surfaces.
2007, 28(5): 564-568.
Abstract:
Miniature spectrometers based on linear charge couple devices (CCD) find wide applications in field detection because of their compact size and high-speed measurement. Photometric performances such as photometric reproducibility and photometric accuracy are most important specifications for a spectrometer. A self-developed miniature grating spectrometer was introduced, which incorporated the Czerny-Turner optical system and a lineaer CCD detector. The photometric performance of the prototype was tested in experiments according to the relevant standards in UV/Vis/NIR spectrophotometer. The results show that the photometric reproducibility of the spectrometer is better than ±0.04Abs, and the photometric accuracy is ±0.04Abs (0～1Abs). Moreover, the influence of stray light, photometric noise and baseline flatness of the spectrometer on photometric accuracy were analyzed with experiment results and theoretical calculation. Finally, the solutions to improve the photometric performance were discussed based on the characteristics of the miniature spectrometer.
Miniature spectrometers based on linear charge couple devices (CCD) find wide applications in field detection because of their compact size and high-speed measurement. Photometric performances such as photometric reproducibility and photometric accuracy are most important specifications for a spectrometer. A self-developed miniature grating spectrometer was introduced, which incorporated the Czerny-Turner optical system and a lineaer CCD detector. The photometric performance of the prototype was tested in experiments according to the relevant standards in UV/Vis/NIR spectrophotometer. The results show that the photometric reproducibility of the spectrometer is better than ±0.04Abs, and the photometric accuracy is ±0.04Abs (0～1Abs). Moreover, the influence of stray light, photometric noise and baseline flatness of the spectrometer on photometric accuracy were analyzed with experiment results and theoretical calculation. Finally, the solutions to improve the photometric performance were discussed based on the characteristics of the miniature spectrometer.
2007, 28(5): 569-572.
Abstract:
Based on the features and specifications of the visible optics for a detection system, the selection of optical layouts, the parameter calculation of initial layout and the method of aberration balance for a long focal length, largeaperture optical zoom system are introduced. The optical system design incorporated with mechanical compensation is presented. The image quality test, scene imaging evaluation and environment test for the optical system were carried out. The test result shows that the optical system designed with this method meets the system requirement.
Based on the features and specifications of the visible optics for a detection system, the selection of optical layouts, the parameter calculation of initial layout and the method of aberration balance for a long focal length, largeaperture optical zoom system are introduced. The optical system design incorporated with mechanical compensation is presented. The image quality test, scene imaging evaluation and environment test for the optical system were carried out. The test result shows that the optical system designed with this method meets the system requirement.
2007, 28(5): 573-577.
Abstract:
The design of a low-cost and middle accuracy panoramic sight is introduced. It features with one mechanical gyroscope for both stabilization and inertial navigation. The key technology of this method is to quickly converge the sensitive axes of the mechanical gyroscope to the intersection line of the meridional plane and the horizontal plane based on the principle of gyroscope compass, to isolate payload from platform disturbance with the gyroscope and two degrees of freedom gimbals, to obtain the attitude angle of the platform by electro-optical sensor on the gimbals, and to make the sight slaved to the sensitive axes of the gyroscope to realize the indirect stabilization. During the calculation, the moving command for the sight was input in the form of slave correction. The projection of platform disturbance along the stabilized coordinates was acquired by resolving the attitude matrix. The navigation function can be realized by combining the information of the platform attitude and an odometer.
The design of a low-cost and middle accuracy panoramic sight is introduced. It features with one mechanical gyroscope for both stabilization and inertial navigation. The key technology of this method is to quickly converge the sensitive axes of the mechanical gyroscope to the intersection line of the meridional plane and the horizontal plane based on the principle of gyroscope compass, to isolate payload from platform disturbance with the gyroscope and two degrees of freedom gimbals, to obtain the attitude angle of the platform by electro-optical sensor on the gimbals, and to make the sight slaved to the sensitive axes of the gyroscope to realize the indirect stabilization. During the calculation, the moving command for the sight was input in the form of slave correction. The projection of platform disturbance along the stabilized coordinates was acquired by resolving the attitude matrix. The navigation function can be realized by combining the information of the platform attitude and an odometer.
2007, 28(5): 578-581.
Abstract:
Resolution and MTF are two important parameters for an image intensifier. Up to now, there is no unified understanding on the primary electronic energy distribution from generation Ⅲ image intensifier cathode, and no wellestablished theoretical model on resolution and MTF. A resolution calculation model under a specific condition was obtained by theoretical analyses and assumptions. The theoretical resolution value was obtained by substituting the measured parameters such as 1st proximity distance, 2nd proximity distance, photocathode voltage and phosphor screen voltage into the resolution calculation model. By comparing it with the measured value, it is found that the value of deviation between the calculated and the measured resolution values is less than 12.3%. The method and results are helpful for people engaged in the design of generation Ⅲ image intensifier.
Resolution and MTF are two important parameters for an image intensifier. Up to now, there is no unified understanding on the primary electronic energy distribution from generation Ⅲ image intensifier cathode, and no wellestablished theoretical model on resolution and MTF. A resolution calculation model under a specific condition was obtained by theoretical analyses and assumptions. The theoretical resolution value was obtained by substituting the measured parameters such as 1st proximity distance, 2nd proximity distance, photocathode voltage and phosphor screen voltage into the resolution calculation model. By comparing it with the measured value, it is found that the value of deviation between the calculated and the measured resolution values is less than 12.3%. The method and results are helpful for people engaged in the design of generation Ⅲ image intensifier.
2007, 28(5): 582-586.
Abstract:
In order to have great electron flux for scrubbing Φ30nm microchannel plate and complete the process in less time，the trace of electron was analyzed and the electron deflection was calculated, according to the operation principle of the axial electron gun and the theory of the function of electrostatic field on electron. Based on the calculation result, the structure of the new electron gun was designed and all the parameters of the electron gun were determined, the filament material was Φ0.05mm tungsten rhenium alloy（75%, 25%）, the filament was in “∨” type, the radius of the electron gun was Φ35mm and its height was 20mm, and the current density of electron emission reached 1.26×10-5A/cm2 while the maximum filament heating power was 12.6W. The gain of the four microchannel plates reached 500±50 after being scrubbed with the electron gun for four hours. The result indicates that the old electron gun RUSA can be replaced by the new one with better performance.
In order to have great electron flux for scrubbing Φ30nm microchannel plate and complete the process in less time，the trace of electron was analyzed and the electron deflection was calculated, according to the operation principle of the axial electron gun and the theory of the function of electrostatic field on electron. Based on the calculation result, the structure of the new electron gun was designed and all the parameters of the electron gun were determined, the filament material was Φ0.05mm tungsten rhenium alloy（75%, 25%）, the filament was in “∨” type, the radius of the electron gun was Φ35mm and its height was 20mm, and the current density of electron emission reached 1.26×10-5A/cm2 while the maximum filament heating power was 12.6W. The gain of the four microchannel plates reached 500±50 after being scrubbed with the electron gun for four hours. The result indicates that the old electron gun RUSA can be replaced by the new one with better performance.
2007, 28(5): 587-592.
Abstract:
The spectral responsivity of IRFPA imaging detector is a basic physical parameter for the space infrared remote sensing. In order to use this parameter to eliminate the influence of the non-uniformity on the product quality in the fabrication process, the spectral responsivity of detectors must be calibrated and the real value should be obtained before the systems are put into use. Because of the uncertainty of the calibration data-acquisition methods and the limitation of some calibration methods, the measured value is not accurate. Thus it is very important to select a proper method and to analyze its error. In this paper some methods for calibrating the spectral responsivity of IRFPA detectors were analyzed, and the limitations of the calibration methods available were investigated. The standard substitution method for the products was selected, and the possible errors were analyzed based on the obtained data. Some important issues in the calibration process of IRFPA products were summarized. An integration time adjustment method is put forward to overcome the big error caused by the low radiation rate of calibration blackbody in some wave bands.
The spectral responsivity of IRFPA imaging detector is a basic physical parameter for the space infrared remote sensing. In order to use this parameter to eliminate the influence of the non-uniformity on the product quality in the fabrication process, the spectral responsivity of detectors must be calibrated and the real value should be obtained before the systems are put into use. Because of the uncertainty of the calibration data-acquisition methods and the limitation of some calibration methods, the measured value is not accurate. Thus it is very important to select a proper method and to analyze its error. In this paper some methods for calibrating the spectral responsivity of IRFPA detectors were analyzed, and the limitations of the calibration methods available were investigated. The standard substitution method for the products was selected, and the possible errors were analyzed based on the obtained data. Some important issues in the calibration process of IRFPA products were summarized. An integration time adjustment method is put forward to overcome the big error caused by the low radiation rate of calibration blackbody in some wave bands.
2007, 28(5): 593-597.
Abstract:
The end and side composite pumping is an effective way to raise the Q-switching peak power and to compress the pulse width of the Q-switched pulse in a DPL. The influence of the space distribution of the composite pumping light on the characteristics of the Q-switching pulse was analyzed in theory by a set of acoustooptic Q-switching experiment results in an end and side compositepumped DPL and the Q-switching velocity equations. The numerical calculation results are consistent with the experimental results. It is found from the results of experiment and numerical calculation that the pulse width of a composite-pumped DPL are obviously narrower than that of a side-pumped DPL, and the pulse peak power is remarkably higher than that of the side-pumped DPL. The experiment and analysis results show that the larger the occupancy of the end-pumping power is, the narrower the pulse width and the higher the pulse peak power will be, when the total pumping power and the pumping structure are fixed. Therefore, the characteristics of the Q-switching pulse can be controlled by changing the space distribution of the composite pumping light through adjusting the occupancy of the end-pumping power.
The end and side composite pumping is an effective way to raise the Q-switching peak power and to compress the pulse width of the Q-switched pulse in a DPL. The influence of the space distribution of the composite pumping light on the characteristics of the Q-switching pulse was analyzed in theory by a set of acoustooptic Q-switching experiment results in an end and side compositepumped DPL and the Q-switching velocity equations. The numerical calculation results are consistent with the experimental results. It is found from the results of experiment and numerical calculation that the pulse width of a composite-pumped DPL are obviously narrower than that of a side-pumped DPL, and the pulse peak power is remarkably higher than that of the side-pumped DPL. The experiment and analysis results show that the larger the occupancy of the end-pumping power is, the narrower the pulse width and the higher the pulse peak power will be, when the total pumping power and the pumping structure are fixed. Therefore, the characteristics of the Q-switching pulse can be controlled by changing the space distribution of the composite pumping light through adjusting the occupancy of the end-pumping power.
2007, 28(5): 598-602.
Abstract:
Solid immersion lens (SIL) was employed to increase the optical writing density. The position of foci and numerical aperture of the focusing system with SIL were simulated, and the threedimensional optical data storage was conducted. The simulation result shows that the depth actually focused into the media is increased and the effective numerical aperture is enlarged with the suitable off-focus distance between the foci of focusing objectives and the bottom plane of SIL. With this result, a SIL with n=1.55 was positioned under a 0.55 NA micro objective to focus a 150 fs Ti∶sapphire pulse laser at 800nm, and a 5-layer reading and writing of data were achieved with 2.5mm separation between two layers and 0.6 mm separation between two bits. Accordingly, the storage density of 1.1×1012 bit/cm3 was obtained in this way.
Solid immersion lens (SIL) was employed to increase the optical writing density. The position of foci and numerical aperture of the focusing system with SIL were simulated, and the threedimensional optical data storage was conducted. The simulation result shows that the depth actually focused into the media is increased and the effective numerical aperture is enlarged with the suitable off-focus distance between the foci of focusing objectives and the bottom plane of SIL. With this result, a SIL with n=1.55 was positioned under a 0.55 NA micro objective to focus a 150 fs Ti∶sapphire pulse laser at 800nm, and a 5-layer reading and writing of data were achieved with 2.5mm separation between two layers and 0.6 mm separation between two bits. Accordingly, the storage density of 1.1×1012 bit/cm3 was obtained in this way.
2007, 28(5): 603-607.
Abstract:
In laser-cluster interaction experiment, the gas target is usually generated by stuffing gas into vacuum chamber in high flow velocity via supersonic gas jet under the condition of very high backing pressure. To acquire the density distribution characteristics of the gas target in different experimental conditions, the density distribution of the gas target was measured with M-Z interferometry, and the fringes were obtained at different backing pressures, temperatures and time lapses. The total spatial distribution of gas molecular density under different experimental conditions was obtained via the interferometer pattern measured by Fourier transformation based fringe processing. The experiment shows that M-Z interferometer can effectively measure the gas target density distribution produced by the supersonic gas jet. The fringe processing method based on Fourier transformation is accurate and has real-time feature. Therefore, it provides the possibility for the real-time measurement of gas target density during targeting practice.
In laser-cluster interaction experiment, the gas target is usually generated by stuffing gas into vacuum chamber in high flow velocity via supersonic gas jet under the condition of very high backing pressure. To acquire the density distribution characteristics of the gas target in different experimental conditions, the density distribution of the gas target was measured with M-Z interferometry, and the fringes were obtained at different backing pressures, temperatures and time lapses. The total spatial distribution of gas molecular density under different experimental conditions was obtained via the interferometer pattern measured by Fourier transformation based fringe processing. The experiment shows that M-Z interferometer can effectively measure the gas target density distribution produced by the supersonic gas jet. The fringe processing method based on Fourier transformation is accurate and has real-time feature. Therefore, it provides the possibility for the real-time measurement of gas target density during targeting practice.
2007, 28(5): 608-613.
Abstract:
A new model that accounts for the effects of dispersion on stimulated Raman scattering crosstalk in wavelength division multiplexed systems with random initial binary data is proposed. The formula for calculating the middle distance step is given. According to the model, the output power from each communication channel, which passes through the wavelength division multiplexed fiber system that has dispersion “walk-off” under the random digital sequence modulation and the function of non-linear effects, was numerically calculated. The conclusion that fiber dispersion may reduce the output power fluctuation caused by SRS effect was obtained. The results show that the deviation of output power is significantly reduced in the presence of dispersion. The change of the standard deviation of system output power with the dispersion coefficient under the SRS effect is plotted. The mechanism causing the phenomenon was quantitatively analyzed. The model works with any fiber dispersion, input power and number of channels.
A new model that accounts for the effects of dispersion on stimulated Raman scattering crosstalk in wavelength division multiplexed systems with random initial binary data is proposed. The formula for calculating the middle distance step is given. According to the model, the output power from each communication channel, which passes through the wavelength division multiplexed fiber system that has dispersion “walk-off” under the random digital sequence modulation and the function of non-linear effects, was numerically calculated. The conclusion that fiber dispersion may reduce the output power fluctuation caused by SRS effect was obtained. The results show that the deviation of output power is significantly reduced in the presence of dispersion. The change of the standard deviation of system output power with the dispersion coefficient under the SRS effect is plotted. The mechanism causing the phenomenon was quantitatively analyzed. The model works with any fiber dispersion, input power and number of channels.
2007, 28(5): 614-618.
Abstract:
The cross-sensitivity is a key problem in the application of fiber grating sensors. Based on the sensing theory of fiber Bragg gratings (FBG), the physical mechanism of the cross sensitivity in simultaneous strain and temperature measurement with fiber grating is analyzed. The FBG reflected wavelength equation with the temperature-strain cross-sensitivity coefficient is established. The error analysis of the equation was made with the dual-wavelength matrix algorithm and the relative error curves of temperature and strain were obtained in the case of cross-sensitivity. The effects of the cross-sensitivity on the measurement were discussed and analyzed according to the expressions and curve diagram of the relative error. The result shows that the relative errors of temperature or strain grow significantly with the increase of temperature or strain variance during the measurement of temperature and stress, and the crosssensitivity is not negligible when the relative errors are great enough.
The cross-sensitivity is a key problem in the application of fiber grating sensors. Based on the sensing theory of fiber Bragg gratings (FBG), the physical mechanism of the cross sensitivity in simultaneous strain and temperature measurement with fiber grating is analyzed. The FBG reflected wavelength equation with the temperature-strain cross-sensitivity coefficient is established. The error analysis of the equation was made with the dual-wavelength matrix algorithm and the relative error curves of temperature and strain were obtained in the case of cross-sensitivity. The effects of the cross-sensitivity on the measurement were discussed and analyzed according to the expressions and curve diagram of the relative error. The result shows that the relative errors of temperature or strain grow significantly with the increase of temperature or strain variance during the measurement of temperature and stress, and the crosssensitivity is not negligible when the relative errors are great enough.
2007, 28(5): 619-622.
Abstract:
The strain sensor with an embedded fiber Bragg grating has a great potential as an intelligent element for monitoring large construction work. The sensing mechanism of the strain sensor with an embedded fiber Bragg grating was discussed. A strain measurement system with embedded fiber Bragg grating was designed. The structure of the grating sensing probe and its fabrication were elaborated. The cross sensitivity between strain and temperature was overcome by using the tunable F-P filter to demodulate the grating signals. The strain measurement ranging from 0 to 1500με was realized. The feasibility of the system was verified by the theoretical analysis.
The strain sensor with an embedded fiber Bragg grating has a great potential as an intelligent element for monitoring large construction work. The sensing mechanism of the strain sensor with an embedded fiber Bragg grating was discussed. A strain measurement system with embedded fiber Bragg grating was designed. The structure of the grating sensing probe and its fabrication were elaborated. The cross sensitivity between strain and temperature was overcome by using the tunable F-P filter to demodulate the grating signals. The strain measurement ranging from 0 to 1500με was realized. The feasibility of the system was verified by the theoretical analysis.
2007, 28(5): 623-626.
Abstract:
The coating techniques for preparing 0.4μm～1.1μm wide spectral AR film made up of TiO2, SiO2 and MgF2 are discussed. Some factors such as the spectral transmittance range, refractive index, vaporous mode, mechanical properties, chemical stability and anti radiation were considered in the selection of filmmaterials. TiO2, SiO2 and MgF2 film-materials were adopted for the preparation of AR film operating at wide spectrum of 0.4μm～1.1μm according to the experience of multilayer design, the understanding of film-material performance and the performance of the domestic equipments. The film structure is GHMHMHMHLA. This technique is convenient and robust. The film has good spectral and mechanical performance, and it meets the operational requirement of electro-optical system.
The coating techniques for preparing 0.4μm～1.1μm wide spectral AR film made up of TiO2, SiO2 and MgF2 are discussed. Some factors such as the spectral transmittance range, refractive index, vaporous mode, mechanical properties, chemical stability and anti radiation were considered in the selection of filmmaterials. TiO2, SiO2 and MgF2 film-materials were adopted for the preparation of AR film operating at wide spectrum of 0.4μm～1.1μm according to the experience of multilayer design, the understanding of film-material performance and the performance of the domestic equipments. The film structure is GHMHMHMHLA. This technique is convenient and robust. The film has good spectral and mechanical performance, and it meets the operational requirement of electro-optical system.
2007, 28(5): 627-631.
Abstract:
Since the central spot diameter of exit beam generated by the spherical wave beam passing through a conical lens is small and the focal depth of the exit beam is long, it is suitable for long distance measurement and alignment in laser communication. The diffraction mode of the conical lens for the spherical wave beam with eccentricity was emphatically investigated to reduce the effects of the off-axis phenomenon on measurement, and to prevent the center-line deviation or tilt of the spherical wave beam. Based on the diffraction theory and stationary phase method, the diffraction mode of the conical lens for the spherical wave beam with eccentricity was derived, and the characteristic of its radial energy distribution was analyzed. The experiments and simulations are performed by using a conical lens whose radius is 15 mm and basic angle is 1°. The experimental results are compared with the theoretical analysis and computer simulation results. The comparison indicates that the influence of eccentricity on the diffraction mode decreases as the radius of curvature of incidental spherical wave and the propagation distance decrease. Therefore, the spherical wave with small radius of curvature instead of plane wave can extend the focal depth and reduce the influence of eccentricity on the measurement.
Since the central spot diameter of exit beam generated by the spherical wave beam passing through a conical lens is small and the focal depth of the exit beam is long, it is suitable for long distance measurement and alignment in laser communication. The diffraction mode of the conical lens for the spherical wave beam with eccentricity was emphatically investigated to reduce the effects of the off-axis phenomenon on measurement, and to prevent the center-line deviation or tilt of the spherical wave beam. Based on the diffraction theory and stationary phase method, the diffraction mode of the conical lens for the spherical wave beam with eccentricity was derived, and the characteristic of its radial energy distribution was analyzed. The experiments and simulations are performed by using a conical lens whose radius is 15 mm and basic angle is 1°. The experimental results are compared with the theoretical analysis and computer simulation results. The comparison indicates that the influence of eccentricity on the diffraction mode decreases as the radius of curvature of incidental spherical wave and the propagation distance decrease. Therefore, the spherical wave with small radius of curvature instead of plane wave can extend the focal depth and reduce the influence of eccentricity on the measurement.
2007, 28(5): 632-635.
Abstract:
Phase diverse speckle (PDS) is a novel imaging technique, which can be used to overcome the image degradation caused by unknown phase aberrations, such as atmospheric turbulence. The phase distortion generated by the unknown turbulence was fitted with Zernike polynomials. The wave-front phase was derived from a pair of images. Based on the mechanism analysis of the PDS technology and taking the genetic algorithm as the iterative algorithm, the feasibility of this technology was verified by the simulation data, and some factors including the Zernike polynomials′ mode and turbulence which influences the qualification of this technology were analyzed during the simulation. The efforts provide a new way for the recovery of blurred images.
Phase diverse speckle (PDS) is a novel imaging technique, which can be used to overcome the image degradation caused by unknown phase aberrations, such as atmospheric turbulence. The phase distortion generated by the unknown turbulence was fitted with Zernike polynomials. The wave-front phase was derived from a pair of images. Based on the mechanism analysis of the PDS technology and taking the genetic algorithm as the iterative algorithm, the feasibility of this technology was verified by the simulation data, and some factors including the Zernike polynomials′ mode and turbulence which influences the qualification of this technology were analyzed during the simulation. The efforts provide a new way for the recovery of blurred images.
2007, 28(5): 636-640.
Abstract:
A new measurement method,carrier fringe method of Moiré interferometry，was studied. The strain was analyzed with the initial carrier fringes according to the change of the carrier fringes before and after deformation of an object. The experiment justified that the accuracy was controlled within the range of ±10με when the strain caused by the deformation of UUT was measured with the grating of 1200lp/mm combined with appropriate digital image processing method. The research indicates that the strain sensitivity is less than 1με. The average strain values of every row of U field and every column of V field are given by the method. This makes it possible to investigate the tiny strain and the tiny strain difference between the adjacent areas of a microfield. The technology can be used for further analysis of the correlative mechanics in MEMS.
A new measurement method,carrier fringe method of Moiré interferometry，was studied. The strain was analyzed with the initial carrier fringes according to the change of the carrier fringes before and after deformation of an object. The experiment justified that the accuracy was controlled within the range of ±10με when the strain caused by the deformation of UUT was measured with the grating of 1200lp/mm combined with appropriate digital image processing method. The research indicates that the strain sensitivity is less than 1με. The average strain values of every row of U field and every column of V field are given by the method. This makes it possible to investigate the tiny strain and the tiny strain difference between the adjacent areas of a microfield. The technology can be used for further analysis of the correlative mechanics in MEMS.
2007, 28(5): 641-644.
Abstract:
The hyperacuity eye model is critical for making human eyesight like an eagle. The anterior cornea surface is described by Zernike polynomials, and the refractive index profile of the crystalline lens is described by the graded refractive index. The hyperacuity eye model is established by the optical design software Zemax, with the influence of the angle between optical axis and visual axis of human eye on imaging taken into account. To apply the rise surface of Zernike fringe to anterior cornea of the human eye model may improve the imaging quality in the direction of the visual axis (5°visual field in Zemax model) and increase the value of point spread function (PSF). The aberration of human eye can be reduced by adopting the graded refractive index of the crystalline lens, which conforms with the anatomical structure of the human eye. By analyzing the resolution limits of the human eye and the wave aberration of the eye model, it is pointed out that the modulability of the human eye model for sensing the object′s highfrequency details can reach 0.55 when the spatial frequency is 60 period/ degree.
The hyperacuity eye model is critical for making human eyesight like an eagle. The anterior cornea surface is described by Zernike polynomials, and the refractive index profile of the crystalline lens is described by the graded refractive index. The hyperacuity eye model is established by the optical design software Zemax, with the influence of the angle between optical axis and visual axis of human eye on imaging taken into account. To apply the rise surface of Zernike fringe to anterior cornea of the human eye model may improve the imaging quality in the direction of the visual axis (5°visual field in Zemax model) and increase the value of point spread function (PSF). The aberration of human eye can be reduced by adopting the graded refractive index of the crystalline lens, which conforms with the anatomical structure of the human eye. By analyzing the resolution limits of the human eye and the wave aberration of the eye model, it is pointed out that the modulability of the human eye model for sensing the object′s highfrequency details can reach 0.55 when the spatial frequency is 60 period/ degree.
2007, 28(5): 645-648.
Abstract:
The measurement of linear expansion coefficient of silicon was performed in high temperature with the high accuracy laser interferometric dilatometer developed by China National Institute of Metrology. The single frequency laser interferometer and symmetrical beam path are adopted in the dilatometer. The resolution of the interferometer is within 1nm. In order to make the measurement in the temperature of over 800 K, the furnace of this system was redesigned and the experiment method was modified. With the renovated system, the linear expansion coefficients of silicon were measured by stepwise heating in the temperature range of 800K～1200K. The changing process of specimens and the results of the measurement were analyzed. The linear expansion coefficient of silicon as a function of temperature was obtained. The measurement in nanometer level for the linear expansion coefficients of material was realized by laser interferometric method in 1200K.
The measurement of linear expansion coefficient of silicon was performed in high temperature with the high accuracy laser interferometric dilatometer developed by China National Institute of Metrology. The single frequency laser interferometer and symmetrical beam path are adopted in the dilatometer. The resolution of the interferometer is within 1nm. In order to make the measurement in the temperature of over 800 K, the furnace of this system was redesigned and the experiment method was modified. With the renovated system, the linear expansion coefficients of silicon were measured by stepwise heating in the temperature range of 800K～1200K. The changing process of specimens and the results of the measurement were analyzed. The linear expansion coefficient of silicon as a function of temperature was obtained. The measurement in nanometer level for the linear expansion coefficients of material was realized by laser interferometric method in 1200K.
2007, 28(5): 649-653.
Abstract:
The detection concept for large diameter beam parallelism with penta prism is introduced. The effect of penta prism angle and surface profile errors on parallelism detection was analyzed. It is concluded that the angle error has no impact on the detection results and the profile errors of the two refraction surfaces have little effect, but the profile errors of the two reflection surfaces have great influence on the detection. The methods for selecting penta prism and reducing the effect of surface profile error on detection are introduced. At the end, an example is given to illustrate the detection of the parallelism error of a single star simulator with penta prism.
The detection concept for large diameter beam parallelism with penta prism is introduced. The effect of penta prism angle and surface profile errors on parallelism detection was analyzed. It is concluded that the angle error has no impact on the detection results and the profile errors of the two refraction surfaces have little effect, but the profile errors of the two reflection surfaces have great influence on the detection. The methods for selecting penta prism and reducing the effect of surface profile error on detection are introduced. At the end, an example is given to illustrate the detection of the parallelism error of a single star simulator with penta prism.
New method for displacement measurement in nanometer level using speckle interference and gray level
2007, 28(5): 654-658.
Abstract:
The phase shifting method is widely used to eliminate the difficulty of the subwavelength displacement measurement in the speckle interference metrology, but it is very inconvenient to use. In this paper, the microdisplacement measurement method using the hybrid of gray-level and speckle interference is proposed, which is different from the previous phase shifting method. This method overcomes the difficulty of finding a complete fringe pattern when the deformation or displacement is less than half of a wavelength. The measurement principle of the method was described, and the experiment was carried out. The feasibility of this method was verified. Therefore, an easier method is given for speckle interference metrology.
The phase shifting method is widely used to eliminate the difficulty of the subwavelength displacement measurement in the speckle interference metrology, but it is very inconvenient to use. In this paper, the microdisplacement measurement method using the hybrid of gray-level and speckle interference is proposed, which is different from the previous phase shifting method. This method overcomes the difficulty of finding a complete fringe pattern when the deformation or displacement is less than half of a wavelength. The measurement principle of the method was described, and the experiment was carried out. The feasibility of this method was verified. Therefore, an easier method is given for speckle interference metrology.
2007, 28(5): 659-662.
Abstract:
The thermal energy loss of the bulk absorption laser energy meter caused by the thermal radiation, heat convection and conduction was analyzed based on the basic heat-transfer theory. The mathematical model of thermal loss for the energy meter is established according to the analytical result. The curves of the measured data were fitted with the math model and least square method. The fitted curve is quite similar to the actual curve of the temperature drop. The measurement repeatability of the energy meter is improved greatly after the measured data is compensated and corrected by the fitted curve. The work is useful for the development of bulk absorption laser energy meters.
The thermal energy loss of the bulk absorption laser energy meter caused by the thermal radiation, heat convection and conduction was analyzed based on the basic heat-transfer theory. The mathematical model of thermal loss for the energy meter is established according to the analytical result. The curves of the measured data were fitted with the math model and least square method. The fitted curve is quite similar to the actual curve of the temperature drop. The measurement repeatability of the energy meter is improved greatly after the measured data is compensated and corrected by the fitted curve. The work is useful for the development of bulk absorption laser energy meters.
2007, 28(5): 663-666.
Abstract:
An electro-optical equipment to detect the boresight of multi-channel optical axes in laboratory is introduced．A collimator is adopted to provide an infinite target for the test system. An off-axis parabolic total reflection optical system is used to satisfy the full-wavelength test without central obstruction. A ZnS multispectral beam-splitter is adopted to offer pointing reference for laser spot, and a Gauss ocular with temperature controlled cross hair is adopted to offer pointing reference for visible light and infrared wave band. In this way, the boresight test between optical axes for visible light, infrared and laser is realized．This test system is accurate and reliable. According to the preliminary estimate, the measured boresight accuracy between visible light and infrared reached 4.01″, visible light and laser reached 1.08″, infrared and laser reached 4.05″. This system can be used effectively in multi-channel opticalaxes boresight test.
An electro-optical equipment to detect the boresight of multi-channel optical axes in laboratory is introduced．A collimator is adopted to provide an infinite target for the test system. An off-axis parabolic total reflection optical system is used to satisfy the full-wavelength test without central obstruction. A ZnS multispectral beam-splitter is adopted to offer pointing reference for laser spot, and a Gauss ocular with temperature controlled cross hair is adopted to offer pointing reference for visible light and infrared wave band. In this way, the boresight test between optical axes for visible light, infrared and laser is realized．This test system is accurate and reliable. According to the preliminary estimate, the measured boresight accuracy between visible light and infrared reached 4.01″, visible light and laser reached 1.08″, infrared and laser reached 4.05″. This system can be used effectively in multi-channel opticalaxes boresight test.
2007, 28(5): 667-670.
Abstract:
A system that uses Moiré fringe to detect the beam wander caused by atmospheric turbulence is presented. This system features tiny length and angle detection. The tiny angle of the beam wander was detected by using the Moiré fringe and amplified in the mode of fringe. The widest fringe obtained in the atmospheric turbulence was analyzed, and the width of the fringe was compared with the resolution of sophisticated CCD. Moiré fringe subdividing technique was used when the resolution of the CCD was not sufficient. The optical signal of the fringe was converted to the electric signal by a proper circuit, and the phase variation was converted to the pulse-width variation. The high frequency pulse was inserted into the formed square wave and the highmultiplyingpower subdivision was attained by measuring the numbers of the pulse. The high resolution can be achieved by this method which can make detection precision of the system reach 0.025μrad.
A system that uses Moiré fringe to detect the beam wander caused by atmospheric turbulence is presented. This system features tiny length and angle detection. The tiny angle of the beam wander was detected by using the Moiré fringe and amplified in the mode of fringe. The widest fringe obtained in the atmospheric turbulence was analyzed, and the width of the fringe was compared with the resolution of sophisticated CCD. Moiré fringe subdividing technique was used when the resolution of the CCD was not sufficient. The optical signal of the fringe was converted to the electric signal by a proper circuit, and the phase variation was converted to the pulse-width variation. The high frequency pulse was inserted into the formed square wave and the highmultiplyingpower subdivision was attained by measuring the numbers of the pulse. The high resolution can be achieved by this method which can make detection precision of the system reach 0.025μrad.
2007, 28(5): 671-674.
Abstract:
Digital laser plane interferometer is used to measure the surface of optical components and the wavefront aberration of non-confocal optical system. In order to unify digital laser interferometer measurement values,and guarantee the accuracy and traceability of the measured results, the digital laser interferometer calibration standard was laid down. The constitution of the calibration specification for digital laser plane interferometer is introduced. The specifications for the instruments under test, the main calibration parameters and the calibration method are described.
Digital laser plane interferometer is used to measure the surface of optical components and the wavefront aberration of non-confocal optical system. In order to unify digital laser interferometer measurement values,and guarantee the accuracy and traceability of the measured results, the digital laser interferometer calibration standard was laid down. The constitution of the calibration specification for digital laser plane interferometer is introduced. The specifications for the instruments under test, the main calibration parameters and the calibration method are described.
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