2007 Vol. 28, No. 2
Display Method:
2007, 28(2): 121-124.
Abstract:
The properties of the semiconductor glass microchannel plates (MCPs) are described and compared with traditional glass MCPs. The preparation technique is presented in detail. Moreover, the approach for developing microchannel plates made of semiconductor glass is investigated. The semiconductor glass microchannel plates, whose aperture is 20μm and the external diameter is 12mm, were fabricated. The gain, scintillation noise and imaging properties of MCP samples were tested with UV optoelectronic system. The experimental results show that the semiconductor microchannel plates can be fabricated with semiconductor glass materials.
The properties of the semiconductor glass microchannel plates (MCPs) are described and compared with traditional glass MCPs. The preparation technique is presented in detail. Moreover, the approach for developing microchannel plates made of semiconductor glass is investigated. The semiconductor glass microchannel plates, whose aperture is 20μm and the external diameter is 12mm, were fabricated. The gain, scintillation noise and imaging properties of MCP samples were tested with UV optoelectronic system. The experimental results show that the semiconductor microchannel plates can be fabricated with semiconductor glass materials.
2007, 28(2): 125-128.
Abstract:
The low-light-level (LLL) weapon sight measurement under different environment conditions are always interested by military equipment manufacturers. Due to the impact of shock, vibration, shooting, high temperature or low temperature environment as well as other environmental factors, the mechanics, optics and electric performance of the LLL sights will be changed, and the LLL sights can′t function properly. A test and measurement device was designed to test weapon LLL sights operating in different test conditions. The working principle of the detection system established with CCD is given, and the detailed imaging process of the system is analyzed. Based on the calculation of the focal length for the collimator and CCD zoom lens as well as the practical application, the system is deigned with measurment accuracy better than 0.05 mil and the measuring range greater than 40 mil.
The low-light-level (LLL) weapon sight measurement under different environment conditions are always interested by military equipment manufacturers. Due to the impact of shock, vibration, shooting, high temperature or low temperature environment as well as other environmental factors, the mechanics, optics and electric performance of the LLL sights will be changed, and the LLL sights can′t function properly. A test and measurement device was designed to test weapon LLL sights operating in different test conditions. The working principle of the detection system established with CCD is given, and the detailed imaging process of the system is analyzed. Based on the calculation of the focal length for the collimator and CCD zoom lens as well as the practical application, the system is deigned with measurment accuracy better than 0.05 mil and the measuring range greater than 40 mil.
2007, 28(2): 129-132.
Abstract:
The quality of Al2O3 film evaporated on the input side of micro-channel plate is analyzed with electron microscope and mass spectrometer, and the influence of the film on the device performance is investigated to solve the problem of lifetime of 3rd generation low-light-level (LLL) tube. The effect of Al2O3 film on the imaging quality of 3rd generation LLL imaging devices is discussed. The research result shows that Al2O3 film affects the imaging quality of the LLL tube seriously, makes images dim and reduces the noise-to-signal ratio though it can effectively prevent the ion feedback. Another effective measure for solving the problem of device lifetime essentially is proposed, in which the vacuum isolation is implemented between photoelectric cathode and display screen to avoid the bombardment of ion feedback to the photoelectric cathode.
The quality of Al2O3 film evaporated on the input side of micro-channel plate is analyzed with electron microscope and mass spectrometer, and the influence of the film on the device performance is investigated to solve the problem of lifetime of 3rd generation low-light-level (LLL) tube. The effect of Al2O3 film on the imaging quality of 3rd generation LLL imaging devices is discussed. The research result shows that Al2O3 film affects the imaging quality of the LLL tube seriously, makes images dim and reduces the noise-to-signal ratio though it can effectively prevent the ion feedback. Another effective measure for solving the problem of device lifetime essentially is proposed, in which the vacuum isolation is implemented between photoelectric cathode and display screen to avoid the bombardment of ion feedback to the photoelectric cathode.
2007, 28(2): 133-137.
Abstract:
In order to meet the real-time processing requirement for the infrared sequential image processing and some algorithms such as image denoising, non-uniformity correction, image adaptive dissection, image measurement and mathematic model resolving in a specific infrared imaging position system, an effective scheme for transferring and exchanging infrared image data by DSP DMA is proposed. The application of DMA operation in the high-speed infrared real-time image processing system is introduced through a digital image processing system composed of AD21D62 and EP1C6. The experiment results show that the scheme can free DSP from the transmission of mass data, the customized image processing algorithm can effectively improve the real-time performance of digital image processing system and overcome the bottleneck problem existing in the system.
In order to meet the real-time processing requirement for the infrared sequential image processing and some algorithms such as image denoising, non-uniformity correction, image adaptive dissection, image measurement and mathematic model resolving in a specific infrared imaging position system, an effective scheme for transferring and exchanging infrared image data by DSP DMA is proposed. The application of DMA operation in the high-speed infrared real-time image processing system is introduced through a digital image processing system composed of AD21D62 and EP1C6. The experiment results show that the scheme can free DSP from the transmission of mass data, the customized image processing algorithm can effectively improve the real-time performance of digital image processing system and overcome the bottleneck problem existing in the system.
2007, 28(2): 138-141.
Abstract:
Based on the principle analysis of thermal IR image reconstruction, thermal image negative of corresponding transmission was made according to gray distribution characters of the required reproduction thermal image，and a new method to generate thermal IR image by coating different transmission films is put forward, for investigating the effect of the description accuracy of the object and background thermal radiation characteristics on the target acquisition, recognition and tracking by IR target seeker. It is verified that this method could reproduce the properties and details of both targets and backgrounds by the thermal IR reproduction experiment and the algorithm of image correlation coefficient. The new method can not only be used in testing and assessing the properties of thermal IR target seekers and highprecision guided weapons, but also can be taken as a new camouflage technique for military targets.
Based on the principle analysis of thermal IR image reconstruction, thermal image negative of corresponding transmission was made according to gray distribution characters of the required reproduction thermal image，and a new method to generate thermal IR image by coating different transmission films is put forward, for investigating the effect of the description accuracy of the object and background thermal radiation characteristics on the target acquisition, recognition and tracking by IR target seeker. It is verified that this method could reproduce the properties and details of both targets and backgrounds by the thermal IR reproduction experiment and the algorithm of image correlation coefficient. The new method can not only be used in testing and assessing the properties of thermal IR target seekers and highprecision guided weapons, but also can be taken as a new camouflage technique for military targets.
2007, 28(2): 142-145.
Abstract:
A new algorithm method of image enhancement based on K-means clustering is presented, according to the characteristics of infrared gray-image. In this method, firstly, the value of K is determined with the specific image, then the statistic analysis is carried out for the radiation temperature data of the infrared image to sort the data in ascending order, finally, the data of an arithmetical progression are selected as initial clustering centers and the temperature data are clustered by K-means algorithm with the generated clustering centers. At last, the self-adaptive enhancement is completed for the image with the clustering result. The satisfactory result is achieved in the experiment with gray infrared images. Compared with the histogram equalization method, the simulation result indicates that this method could further improve the visual effect, and provide detailed information and better gradation.
A new algorithm method of image enhancement based on K-means clustering is presented, according to the characteristics of infrared gray-image. In this method, firstly, the value of K is determined with the specific image, then the statistic analysis is carried out for the radiation temperature data of the infrared image to sort the data in ascending order, finally, the data of an arithmetical progression are selected as initial clustering centers and the temperature data are clustered by K-means algorithm with the generated clustering centers. At last, the self-adaptive enhancement is completed for the image with the clustering result. The satisfactory result is achieved in the experiment with gray infrared images. Compared with the histogram equalization method, the simulation result indicates that this method could further improve the visual effect, and provide detailed information and better gradation.
2007, 28(2): 146-150.
Abstract:
In order to meet the requirement of DFRFT(discrete fractional Fourier transform) real-time computation on DSP(digital signal processor), several DFRFT computation methods are compared and the Ozaktas′s DFRFT fast algorithm is chosen to do the implementation processing based on DSP. On the basis of theoretical analysis for the fast algorithm, the computation procedure of fast algorithm is optimized, and the complete statistical result of the implementation is given. The amount of real number multiplication computation can be minimized by the proposed fast algorithm for the given accuracy. Engineering practice proves that this solution meets the accuracy requirement and real-time property of DSP computation.
In order to meet the requirement of DFRFT(discrete fractional Fourier transform) real-time computation on DSP(digital signal processor), several DFRFT computation methods are compared and the Ozaktas′s DFRFT fast algorithm is chosen to do the implementation processing based on DSP. On the basis of theoretical analysis for the fast algorithm, the computation procedure of fast algorithm is optimized, and the complete statistical result of the implementation is given. The amount of real number multiplication computation can be minimized by the proposed fast algorithm for the given accuracy. Engineering practice proves that this solution meets the accuracy requirement and real-time property of DSP computation.
2007, 28(2): 151-155.
Abstract:
The medium infrared band is widely used as an observation channel in applications such as space flight, meteorology and remote sensing. High quality medium bandpass infrared filters are often adopted in optical systems to improve signal-to-noise ratio. Relative bandwidth is a key specification for the medium bandpass infrared filter, which depends on the film structure and its design. Several film structures such as double cut-off structure, F-P structure, multi-half-wave structure are given, and their bandwidth estimation formulas are concluded. The relative bandwidths of the multi-half-wave structures were estimated and analyzed. The results indicate that half-wave structure is the most feasible solution. Relative bandwidth adjustment methods are put forward, such as using interval layer material, selecting optical thickness, using equivalent film, adjusting film refractive index. A medium infrared filter is designed with the suggested relative bandwidth adjustment method. The coating result shows that the relative bandwidth specification of the film meets the design requirement.
The medium infrared band is widely used as an observation channel in applications such as space flight, meteorology and remote sensing. High quality medium bandpass infrared filters are often adopted in optical systems to improve signal-to-noise ratio. Relative bandwidth is a key specification for the medium bandpass infrared filter, which depends on the film structure and its design. Several film structures such as double cut-off structure, F-P structure, multi-half-wave structure are given, and their bandwidth estimation formulas are concluded. The relative bandwidths of the multi-half-wave structures were estimated and analyzed. The results indicate that half-wave structure is the most feasible solution. Relative bandwidth adjustment methods are put forward, such as using interval layer material, selecting optical thickness, using equivalent film, adjusting film refractive index. A medium infrared filter is designed with the suggested relative bandwidth adjustment method. The coating result shows that the relative bandwidth specification of the film meets the design requirement.
2007, 28(2): 156-158.
Abstract:
The spectral difference between the sensors, complexity of optical bench mechanics, as well as alignment between the optical axes and revolving axes in stabilized electro-optical sight system make the system integration accuracy hard to achieve. The fine tuning for the optical axes boresight was achieved by setting a spatial transfer reference with several sets of autocollimators and adopting a large-aperture optical axis adjustment device. Based on the synchronous accuracy requirement of optical axes and mechanical revolving axes, the scheme to assemble various parts and the impact of the assembly errors on system accuracy were determined. With an azimuth/elevation zenith instrument designed for this work, the orthogonality accuracy of revolving axes was satisfactorily obtained. The design specification and accuracy achieved with this technology cannot be met by traditional technique or ordinary adjustment devices.
The spectral difference between the sensors, complexity of optical bench mechanics, as well as alignment between the optical axes and revolving axes in stabilized electro-optical sight system make the system integration accuracy hard to achieve. The fine tuning for the optical axes boresight was achieved by setting a spatial transfer reference with several sets of autocollimators and adopting a large-aperture optical axis adjustment device. Based on the synchronous accuracy requirement of optical axes and mechanical revolving axes, the scheme to assemble various parts and the impact of the assembly errors on system accuracy were determined. With an azimuth/elevation zenith instrument designed for this work, the orthogonality accuracy of revolving axes was satisfactorily obtained. The design specification and accuracy achieved with this technology cannot be met by traditional technique or ordinary adjustment devices.
2007, 28(2): 159-164.
Abstract:
The development of ultraviolet warning and its key device is introduced, including the characteristics and development of ultraviolet warning, ultraviolet radiation transmittance and the development of ultraviolet detector. A new vacuum ultraviolet detector is described, its photocathode is a solar-blind, a proximity focus tube with less dispersion and image distortion is adopted, its read-out system has light-coupling and electricity-coupling, the light-coupling read-out system is simpler and responds in real time, the electricity-coupling read-out has high sensitivity and resolution as well as long detection distance. Auto gating BSP power supply is adopted to extend dynamic range, protect photocathode and microchannel plate.
The development of ultraviolet warning and its key device is introduced, including the characteristics and development of ultraviolet warning, ultraviolet radiation transmittance and the development of ultraviolet detector. A new vacuum ultraviolet detector is described, its photocathode is a solar-blind, a proximity focus tube with less dispersion and image distortion is adopted, its read-out system has light-coupling and electricity-coupling, the light-coupling read-out system is simpler and responds in real time, the electricity-coupling read-out has high sensitivity and resolution as well as long detection distance. Auto gating BSP power supply is adopted to extend dynamic range, protect photocathode and microchannel plate.
2007, 28(2): 165-168.
Abstract:
A method to enhance the local regions in remote sensing images is proposed to meet the case that the information cannot be aquired due to the clouds and their shadows in the regions. The method of Huygens secondary wave is applied to extract the regions with clouds and their shadows in the remote sensing images. The wide ambiguity borders can be got when the convolution is made up of the extracted regions and bigsize smoothing convolution core whose size is 19×19 and each element is 1/381. The brightness is compensated in the regions with clouds and their shadows in original remote sensing image. The information of the regions covered by clouds and their shadows is obtained. The semi-automatic method plays an important role in the information extraction from the remote sensing images with clouds and their shadows.
A method to enhance the local regions in remote sensing images is proposed to meet the case that the information cannot be aquired due to the clouds and their shadows in the regions. The method of Huygens secondary wave is applied to extract the regions with clouds and their shadows in the remote sensing images. The wide ambiguity borders can be got when the convolution is made up of the extracted regions and bigsize smoothing convolution core whose size is 19×19 and each element is 1/381. The brightness is compensated in the regions with clouds and their shadows in original remote sensing image. The information of the regions covered by clouds and their shadows is obtained. The semi-automatic method plays an important role in the information extraction from the remote sensing images with clouds and their shadows.
2007, 28(2): 169-172.
Abstract:
Since the improvement of microcirculation image quality is the key for the application of such devices, a novel method and apparatus for the microcirculation detection is introduced. The experiments are done with orthogonal polarization spectral imaging apparatus based on this theory and some nail-fold microcirculation images with good contrast are obtained. When linear polarized light is focused on the tissue, the light reflected from the tissue surface remains original polarization state and is blocked by the orthogonal polarization analyzer placed before CCD. The light coming back from the inner of the tissue turns up the multi-scattering and is depolarized. The image is formed after it passes through the analyzer. If the wavelength is selected properly within the absorption spectrum of red cell, clear microcirculation images can be observed.
Since the improvement of microcirculation image quality is the key for the application of such devices, a novel method and apparatus for the microcirculation detection is introduced. The experiments are done with orthogonal polarization spectral imaging apparatus based on this theory and some nail-fold microcirculation images with good contrast are obtained. When linear polarized light is focused on the tissue, the light reflected from the tissue surface remains original polarization state and is blocked by the orthogonal polarization analyzer placed before CCD. The light coming back from the inner of the tissue turns up the multi-scattering and is depolarized. The image is formed after it passes through the analyzer. If the wavelength is selected properly within the absorption spectrum of red cell, clear microcirculation images can be observed.
2007, 28(2): 173-176.
Abstract:
An experiment platform for simulation of optic systems is introduced, based on the theory of the quaternion application in the calculation of light propagation. The visual simulation platform was established with the visual C++ and OpenGL based modeling and simulating method. This platform can be used for the auxiliary analysis of optic systems in vibration environment. The function and the overall structure of the simulation platform are introduced. The computational flow of light propagation and the key techniques of visualization are presented. An optical system was employed to verify the correctness and feasibility of quaternion method in the calculation of beam propagation, and the pincushion distortion caused by the optical system was successfully simulated.
An experiment platform for simulation of optic systems is introduced, based on the theory of the quaternion application in the calculation of light propagation. The visual simulation platform was established with the visual C++ and OpenGL based modeling and simulating method. This platform can be used for the auxiliary analysis of optic systems in vibration environment. The function and the overall structure of the simulation platform are introduced. The computational flow of light propagation and the key techniques of visualization are presented. An optical system was employed to verify the correctness and feasibility of quaternion method in the calculation of beam propagation, and the pincushion distortion caused by the optical system was successfully simulated.
2007, 28(2): 177-180.
Abstract:
The SG-Ⅲ 3ω laser auto-collimation system and its control algorithm are studied based on loop feedback control theory. The operation principle, control algorithm and software control flowchart of the system are analyzed. The mathematical model for the impact of motor-control on the control result during the collimation process was established to overcome the side effects on the collimating accuracy caused by the crosstalk of both azimuth and elevation motors. By adopting the auto-collimation scheme with two-dimensional mirror mount, the collimating error converges continuously in the given precision range. The results of the test on the spot show that this SG-Ⅲ auto-collimation system meets the design specification. The SG-Ⅲ 3ω laser auto-collimation system can fulfill the collimation of 8 beams in half an hour. The angle error of the system is less than 5% for pinhole diameter per space domain, and the translation error is less than 1.0% for the accuracy of the nearfield beam diameter.
The SG-Ⅲ 3ω laser auto-collimation system and its control algorithm are studied based on loop feedback control theory. The operation principle, control algorithm and software control flowchart of the system are analyzed. The mathematical model for the impact of motor-control on the control result during the collimation process was established to overcome the side effects on the collimating accuracy caused by the crosstalk of both azimuth and elevation motors. By adopting the auto-collimation scheme with two-dimensional mirror mount, the collimating error converges continuously in the given precision range. The results of the test on the spot show that this SG-Ⅲ auto-collimation system meets the design specification. The SG-Ⅲ 3ω laser auto-collimation system can fulfill the collimation of 8 beams in half an hour. The angle error of the system is less than 5% for pinhole diameter per space domain, and the translation error is less than 1.0% for the accuracy of the nearfield beam diameter.
2007, 28(2): 181-186.
Abstract:
Optical engine is one of the key components to affect the qualities of the chroma and luminosity in LCD projectors. Based on the structure characteristics of the optical engine and the principle of chromatometry, the chroma and luminosity simulation analysis software for optical engine design is developed by tracing the light beam. The software can be used to analyze and count the chroma and luminosity qualities of the optical engine. It also can be used to optimize the structure of the optical engine based on the chroma and luminosity index. Some experiments were carried out to compare the simulative engines and actual optical engines, and results were provided. An optical engine was optimized with the software, and the optimal data for the engine structure were acquired. The experiment result shows that the software can improve the design efficiency of optical engines.
Optical engine is one of the key components to affect the qualities of the chroma and luminosity in LCD projectors. Based on the structure characteristics of the optical engine and the principle of chromatometry, the chroma and luminosity simulation analysis software for optical engine design is developed by tracing the light beam. The software can be used to analyze and count the chroma and luminosity qualities of the optical engine. It also can be used to optimize the structure of the optical engine based on the chroma and luminosity index. Some experiments were carried out to compare the simulative engines and actual optical engines, and results were provided. An optical engine was optimized with the software, and the optimal data for the engine structure were acquired. The experiment result shows that the software can improve the design efficiency of optical engines.
2007, 28(2): 187-190.
Abstract:
The research status of InP nanocrystallite in the world is described in this paper. The InP nanocrystallite was prepared by reflowing and annealing of organic solvent. The 55nm average diameter of InP nanocrystallits was obtained by calculating X-ray diffraction spectrum. The Raman spectrum indicates that the two scattering peaks of Raman spectrum move towards low energy because of quantum size effect of nano particles. The obvious blue shift of the sample optical absorption edge relative to the bulk InP (970nm) was observed via UV-VIS absorption spectrum and it indicates that gap becomes wider and the effect of quantum size becomes obvious. The obvious blue shift of fluorescence spectrum luminescent peak relative to the bulk InP infrared region was observed with PLE spectrum at 380nm and PL spectrum at 573nm. It shows that the InP nanocrystallite will have a great potential in the field of photoelectronic devices and nonlinear optics.
The research status of InP nanocrystallite in the world is described in this paper. The InP nanocrystallite was prepared by reflowing and annealing of organic solvent. The 55nm average diameter of InP nanocrystallits was obtained by calculating X-ray diffraction spectrum. The Raman spectrum indicates that the two scattering peaks of Raman spectrum move towards low energy because of quantum size effect of nano particles. The obvious blue shift of the sample optical absorption edge relative to the bulk InP (970nm) was observed via UV-VIS absorption spectrum and it indicates that gap becomes wider and the effect of quantum size becomes obvious. The obvious blue shift of fluorescence spectrum luminescent peak relative to the bulk InP infrared region was observed with PLE spectrum at 380nm and PL spectrum at 573nm. It shows that the InP nanocrystallite will have a great potential in the field of photoelectronic devices and nonlinear optics.
2007, 28(2): 191-194.
Abstract:
Femtosecond laser pulses have the characteristics of ultra-short duration and ultra-high power. A series of nonlinear processes such as double photons effect, collision ionization and avalanche breakthrough will be induced, microexplosions will happen and micro-cavities will be formed at the focus in transparent materials when femtosecond laser is tightly focused into transparent materials. The micro-cavity structure induced by 25fs laser pulse in the interior of transparent materials is proposed. The energy threshold of the micro-cavity is analyzed. Three-dimensional micro-cavity dot-matrix was prepared with a three dimensional precision displacement instrument. The experiments indicate that the energy threshold for generating micro-cavity can be decreased by use of femtosecond pulse with shorter pulse width, the penetration depth of the micro-cavity can be improved by adjusting the power of femtosecond laser, the number of pulses and the beam focus, but the microcavity can not be formed if numerical aperture is too small because the tight focus can not be achieved.
Femtosecond laser pulses have the characteristics of ultra-short duration and ultra-high power. A series of nonlinear processes such as double photons effect, collision ionization and avalanche breakthrough will be induced, microexplosions will happen and micro-cavities will be formed at the focus in transparent materials when femtosecond laser is tightly focused into transparent materials. The micro-cavity structure induced by 25fs laser pulse in the interior of transparent materials is proposed. The energy threshold of the micro-cavity is analyzed. Three-dimensional micro-cavity dot-matrix was prepared with a three dimensional precision displacement instrument. The experiments indicate that the energy threshold for generating micro-cavity can be decreased by use of femtosecond pulse with shorter pulse width, the penetration depth of the micro-cavity can be improved by adjusting the power of femtosecond laser, the number of pulses and the beam focus, but the microcavity can not be formed if numerical aperture is too small because the tight focus can not be achieved.
2007, 28(2): 195-200.
Abstract:
The effect of the vertical extinction characteristics of aerosol, cirrus and dust on laser pulse maximal threshold energy of the airborne lidar for eye safety is analyzed quantitatively according to U.S.A. ANSI standard. Airplane minimum altitude for eye safety was calculated and analyzed quantitatively according to the dust detected by the ground-based lidar in Hefei. The variation rule of laser pulse eye safety coefficient with altitudes was simulated and calculated with the characteristics of all kinds of atmospheric compositions detected by airborne lidars. The calculation result indicates that the influence amplitude of the dust on laser pulse maximum threshold energy for eye safety reaches tens of millijoules. The conclusion forms a baseline for the maximal energy setting of 532nm 1064nm laser pulse for the airborne lidar design for eye safety.
The effect of the vertical extinction characteristics of aerosol, cirrus and dust on laser pulse maximal threshold energy of the airborne lidar for eye safety is analyzed quantitatively according to U.S.A. ANSI standard. Airplane minimum altitude for eye safety was calculated and analyzed quantitatively according to the dust detected by the ground-based lidar in Hefei. The variation rule of laser pulse eye safety coefficient with altitudes was simulated and calculated with the characteristics of all kinds of atmospheric compositions detected by airborne lidars. The calculation result indicates that the influence amplitude of the dust on laser pulse maximum threshold energy for eye safety reaches tens of millijoules. The conclusion forms a baseline for the maximal energy setting of 532nm 1064nm laser pulse for the airborne lidar design for eye safety.
2007, 28(2): 201-204.
Abstract:
In order to improve the coding efficiency and the availability of frequency band in ultraviolet laser communication system, a technique is put forward, which integrates PPM（pulse position modulation）and Turbo code. This technique can improve the availability of frequency band, anti-jamming capability between codes, error correction and error bit rate. The coding formula of Turbo code is derived in PPM mode. The technique was simulated with Matlab software. The simulation result shows that this solution can reduce the bit error rate and improve the efficiency of the whole communication system.
In order to improve the coding efficiency and the availability of frequency band in ultraviolet laser communication system, a technique is put forward, which integrates PPM（pulse position modulation）and Turbo code. This technique can improve the availability of frequency band, anti-jamming capability between codes, error correction and error bit rate. The coding formula of Turbo code is derived in PPM mode. The technique was simulated with Matlab software. The simulation result shows that this solution can reduce the bit error rate and improve the efficiency of the whole communication system.
2007, 28(2): 205-208.
Abstract:
A system for measuring the drift of laser spot is designed and the drift of a He-Ne laser beam is measured. With a CCD camera and a frame grabber to capture the laser spot, the digital image is transferred to special software for further processing, the amount of the laser spot drift can be achieved. The amount of the drift in X direction, Y direction and in spatial angle can be obtained through geometrical optics. The reason that causes the beam drift is analyzed. The result shows that the direction of the emergent beam from He-Ne laser is influenced mainly by temperature, vibration, air disturbance and laser structure. The system can accurately measure the laser beam drift and the control of the beam drift is implemented.
A system for measuring the drift of laser spot is designed and the drift of a He-Ne laser beam is measured. With a CCD camera and a frame grabber to capture the laser spot, the digital image is transferred to special software for further processing, the amount of the laser spot drift can be achieved. The amount of the drift in X direction, Y direction and in spatial angle can be obtained through geometrical optics. The reason that causes the beam drift is analyzed. The result shows that the direction of the emergent beam from He-Ne laser is influenced mainly by temperature, vibration, air disturbance and laser structure. The system can accurately measure the laser beam drift and the control of the beam drift is implemented.
2007, 28(2): 209-211.
Abstract:
The temperature characteristics of high temperature resistant FBG and the ordinary FBG were experimentally investigated. The ordinary FBG becomes black and brittle, and can not be used in practice even though it still has sensing feature, when temperature reaches more than 300℃. The experiment with the high temperature FBG indicates that the high temperature resistant FBG has good linearity from 20℃ to 350℃, and it is not carbonized, the sensitivity is 0.01nm/MPa, but the linearity is deteriorated with the further increase of temperature. The result shows that the high temperature resistant FBG can be used for the high temperature oil downhole measurement.
The temperature characteristics of high temperature resistant FBG and the ordinary FBG were experimentally investigated. The ordinary FBG becomes black and brittle, and can not be used in practice even though it still has sensing feature, when temperature reaches more than 300℃. The experiment with the high temperature FBG indicates that the high temperature resistant FBG has good linearity from 20℃ to 350℃, and it is not carbonized, the sensitivity is 0.01nm/MPa, but the linearity is deteriorated with the further increase of temperature. The result shows that the high temperature resistant FBG can be used for the high temperature oil downhole measurement.
2007, 28(2): 212-215.
Abstract:
According to the ideal approximation of the coupled-mode theory, the Bragg equation and the peak reflectivity expression of the fiber Bragg grating are derived. The relationship between the grating spacing, the grating length, the max of refractive index micro-disturbance and the reflectivity is analyzed. The simulation result shows the least narrow bandwidth of Bragg grating under the defined parameters is 0.02nm when its reflectivity is 1, which is much narrower than the fiber Bragg grating used in typical distributed sensor system. It is proved that this fiber Bragg grating can be used as a fiber grating sensor for distributed demodulation system, which will improve the bandwidth availability of light source in the distributed sensing systems, increase the number of sensing Bragg gratings, eliminate the crosseffect between signals, and reduce the cost of the demodulation system.
According to the ideal approximation of the coupled-mode theory, the Bragg equation and the peak reflectivity expression of the fiber Bragg grating are derived. The relationship between the grating spacing, the grating length, the max of refractive index micro-disturbance and the reflectivity is analyzed. The simulation result shows the least narrow bandwidth of Bragg grating under the defined parameters is 0.02nm when its reflectivity is 1, which is much narrower than the fiber Bragg grating used in typical distributed sensor system. It is proved that this fiber Bragg grating can be used as a fiber grating sensor for distributed demodulation system, which will improve the bandwidth availability of light source in the distributed sensing systems, increase the number of sensing Bragg gratings, eliminate the crosseffect between signals, and reduce the cost of the demodulation system.
2007, 28(2): 216-220.
Abstract:
The calibration of radiometric sensors is critical to ensure the accuracy of the remote sensing data and their usability. The current methods of the radiometric calibration are based on the establishment of high precision primary standard and standard transfer chain, and the transfer chain is the main source of errors. The entangled photons-based theory creates a new technical way to realize the radiometric calibration of “standardless transfer”. The method of absolute calibration of photodetectors based on a nonclassical effect of the nonlinear optics in the photon-counting regime was discussed. The measurement was realized with the technique of entangled photons at 702nm generated by a parametric down conversion process in a nonlinear crystal of BBO. The photomultiplier quantum efficiency at the wavelength was measured during the experiment. It is estimated that the deviation is 0.1%. The technique is independent of any externally calibrated radiometric standards.
The calibration of radiometric sensors is critical to ensure the accuracy of the remote sensing data and their usability. The current methods of the radiometric calibration are based on the establishment of high precision primary standard and standard transfer chain, and the transfer chain is the main source of errors. The entangled photons-based theory creates a new technical way to realize the radiometric calibration of “standardless transfer”. The method of absolute calibration of photodetectors based on a nonclassical effect of the nonlinear optics in the photon-counting regime was discussed. The measurement was realized with the technique of entangled photons at 702nm generated by a parametric down conversion process in a nonlinear crystal of BBO. The photomultiplier quantum efficiency at the wavelength was measured during the experiment. It is estimated that the deviation is 0.1%. The technique is independent of any externally calibrated radiometric standards.
2007, 28(2): 221-225.
Abstract:
Based on the pretreatment for smooth denoising and contrast enhancement of the speckle fringe patterns, the central skeleton lines of the interference fringes were obtained with the method of edgeextracting, filling and thinning for the electronic speckle fringes. The deficiency in extraction for the skeleton lines of the interference fringes, which can not be overcome by some common algorithms such as binaryzation and thinning due to the strong-noise characteristic of the electronic speckle interference fringes, was overcome by this method. The result shows that the method can find the skeleton lines precisely and provide a new method for achieving the line of equal displacement in the plane displacement field.
Based on the pretreatment for smooth denoising and contrast enhancement of the speckle fringe patterns, the central skeleton lines of the interference fringes were obtained with the method of edgeextracting, filling and thinning for the electronic speckle fringes. The deficiency in extraction for the skeleton lines of the interference fringes, which can not be overcome by some common algorithms such as binaryzation and thinning due to the strong-noise characteristic of the electronic speckle interference fringes, was overcome by this method. The result shows that the method can find the skeleton lines precisely and provide a new method for achieving the line of equal displacement in the plane displacement field.
2007, 28(2): 226-230.
Abstract:
The measurement principle and standard set up for the photometric and colorimetric measurement of digital displays panel are presented. The display principles and characteristics of the major products such as CRT, LCD and PDP are introduced. The whole system was calibrated by standard lamp with the standard transferred from the national primary photometric and colorimetric standard. Incorporated with a new spectral detector and a data collection analysis software based on virtual interface technology, the system can measure the unit under test in real time. The uncertainty of the luminance and chromatic coordinates is better than 2% and 0.005 respectively. Major digital flat panel displays in the market are tested, and their parameters such as relative spectral response, luminance, luminance uniformity, contrast ratio, color gamut are calibrated. The test results and performance comparisons are given.
The measurement principle and standard set up for the photometric and colorimetric measurement of digital displays panel are presented. The display principles and characteristics of the major products such as CRT, LCD and PDP are introduced. The whole system was calibrated by standard lamp with the standard transferred from the national primary photometric and colorimetric standard. Incorporated with a new spectral detector and a data collection analysis software based on virtual interface technology, the system can measure the unit under test in real time. The uncertainty of the luminance and chromatic coordinates is better than 2% and 0.005 respectively. Major digital flat panel displays in the market are tested, and their parameters such as relative spectral response, luminance, luminance uniformity, contrast ratio, color gamut are calibrated. The test results and performance comparisons are given.
2007, 28(2): 231-235.
Abstract:
The grating projection method is used for the three-dimension profilometry measurement. But disconnected phase can′t be unwrapped when shadows exist in the grating stripes due to the steps on the object. In order to resolve the problem, the object is put on a precise rotary platform to achieve the clear grating-modulated image of the object by taking two images and mosaicing them together. In the image mosaic, the conception of contrast among successive regions is introduced. Where the contrast of the successive regions is the greatest, the place is regarded as the boundary of the black and white. The place of the boundary of the middle block can be accurately located and the image is mosaiced. At last, Fourier transform profilometry based on dualfrequency grating is used to realize the three-dimensional profilometry reconstruction. The result indicates that the method is simple and accurate, and can successfully solve the problem of the threedimensional profilometry reconstruction of the object with steps.
The grating projection method is used for the three-dimension profilometry measurement. But disconnected phase can′t be unwrapped when shadows exist in the grating stripes due to the steps on the object. In order to resolve the problem, the object is put on a precise rotary platform to achieve the clear grating-modulated image of the object by taking two images and mosaicing them together. In the image mosaic, the conception of contrast among successive regions is introduced. Where the contrast of the successive regions is the greatest, the place is regarded as the boundary of the black and white. The place of the boundary of the middle block can be accurately located and the image is mosaiced. At last, Fourier transform profilometry based on dualfrequency grating is used to realize the three-dimensional profilometry reconstruction. The result indicates that the method is simple and accurate, and can successfully solve the problem of the threedimensional profilometry reconstruction of the object with steps.
2007, 28(2): 236-239.
Abstract:
A simple method of direct-writing polymer waveguides by micro-pen is reported. The fluorinated polyamide strip waveguide were fabricated successfully by this technology, and the relationship of the gas pressure and writing speed with the waveguide width were established. Experimental results show that the directwriting method can fabricate high quality waveguides. The waveguides have the merits of straight edge, smooth surface, no ventage and impurity. Keeping other parameters unchanged, the waveguide width increases with the increase of the gas pressure, but decreases with the increase of the direct-writing speed. The waveguides successfully achieve the function of guiding the light. The minimum propagation loss measured is 0.59dB/cm at 1550nm.
A simple method of direct-writing polymer waveguides by micro-pen is reported. The fluorinated polyamide strip waveguide were fabricated successfully by this technology, and the relationship of the gas pressure and writing speed with the waveguide width were established. Experimental results show that the directwriting method can fabricate high quality waveguides. The waveguides have the merits of straight edge, smooth surface, no ventage and impurity. Keeping other parameters unchanged, the waveguide width increases with the increase of the gas pressure, but decreases with the increase of the direct-writing speed. The waveguides successfully achieve the function of guiding the light. The minimum propagation loss measured is 0.59dB/cm at 1550nm.
2007, 28(2): 240-244.
Abstract:
The effects of temperature on the evolution and self-deflection of bright photovoltaic spatial solitons in photovoltaic photorefractive media are investigated with numerical method by taking account of diffusion effect. It is found that the bright solitary beam appears in stable state, large periodic compression and expansion state, or breakdown state when the crystal temperature changes. The results show that the bending distance of the bright solitary beam centre increases with temperature rise, then reaches its maximum value at a specific temperature, and after that, decreases as temperature continuously rises; it approaches zero at low and high temperature ranges. The maximum deflection value and its corresponding specific temperature increase as the intensity of incident solitary wave increases. The self-deflection process of the bright solitary beam is further studied with the perturbation technique, and the results indicate that the values agree with those obtained from the numerical method.
The effects of temperature on the evolution and self-deflection of bright photovoltaic spatial solitons in photovoltaic photorefractive media are investigated with numerical method by taking account of diffusion effect. It is found that the bright solitary beam appears in stable state, large periodic compression and expansion state, or breakdown state when the crystal temperature changes. The results show that the bending distance of the bright solitary beam centre increases with temperature rise, then reaches its maximum value at a specific temperature, and after that, decreases as temperature continuously rises; it approaches zero at low and high temperature ranges. The maximum deflection value and its corresponding specific temperature increase as the intensity of incident solitary wave increases. The self-deflection process of the bright solitary beam is further studied with the perturbation technique, and the results indicate that the values agree with those obtained from the numerical method.
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