2014 Vol. 35, No. 3
Display Method:
2014, 35(3): 365-370.
Abstract:
Apparent magnitude represents the observed level of aster to human eyes. The calculation of the satellite apparent magnitude is useful for the design of the optical system to observe and track the satellite.Based on the principle of astronomy,dynamics of orbits, radiometry,photometry and computational mathematics, a physical mathematical model for computing satellite magnitude was built. Firstly, the amount of visible light energy reflected by orbit satellite was calculated. Secondly, the calculation method was given after deducing the association character of human eyes. Then a kind of brevity method to calculate the apparent magnitude for grey-reflection satellite was given. Finally, the calculated curve for apparent magnitude observed from subastral point was obtained. The result shows that the apparent magnitude observed from subastral point varies obviously with the change of the satellite position in orbit.The magnitude difference for one satellite under different subastral points is up to 5 magnitudes only within sunshine region.
Apparent magnitude represents the observed level of aster to human eyes. The calculation of the satellite apparent magnitude is useful for the design of the optical system to observe and track the satellite.Based on the principle of astronomy,dynamics of orbits, radiometry,photometry and computational mathematics, a physical mathematical model for computing satellite magnitude was built. Firstly, the amount of visible light energy reflected by orbit satellite was calculated. Secondly, the calculation method was given after deducing the association character of human eyes. Then a kind of brevity method to calculate the apparent magnitude for grey-reflection satellite was given. Finally, the calculated curve for apparent magnitude observed from subastral point was obtained. The result shows that the apparent magnitude observed from subastral point varies obviously with the change of the satellite position in orbit.The magnitude difference for one satellite under different subastral points is up to 5 magnitudes only within sunshine region.
2014, 35(3): 371-376.
Abstract:
In order to improve the environmental worthiness of the shipborne electro-optical system, we analyzed the effect and hazard of the ship environment on the electrooptical system, conducted the research of environmental worthiness design, and suggested reinforcing and protecting all equipments. From the aspects such as material selection, optical system design,structure design and three-proofing, we gave some methods and measures for ameliorating the properties of anticorrosion, resistant to temperature change,shock and vibration. Through the experimentation and application in these years，the results show that we improve the protection ability of the equipment by using the material of good corrosion resistance,optimizing structure,and taking threeproofing measures;we reduce the annexable temperature rise whose maximum is 8.1 ℃ in the sun and improve the work environment of the electro-optical sensors；we ensure the infrared imaging quality because the maximum dispersion root-mean-square(RMS) radius is less than the pitch of the detector in -40 ℃～+60 ℃ with the mechanical compensation method;we improve the radial rigidity more than 25.9% and realize the work stabilization of the system by installing the thrust bearing．
In order to improve the environmental worthiness of the shipborne electro-optical system, we analyzed the effect and hazard of the ship environment on the electrooptical system, conducted the research of environmental worthiness design, and suggested reinforcing and protecting all equipments. From the aspects such as material selection, optical system design,structure design and three-proofing, we gave some methods and measures for ameliorating the properties of anticorrosion, resistant to temperature change,shock and vibration. Through the experimentation and application in these years，the results show that we improve the protection ability of the equipment by using the material of good corrosion resistance,optimizing structure,and taking threeproofing measures;we reduce the annexable temperature rise whose maximum is 8.1 ℃ in the sun and improve the work environment of the electro-optical sensors；we ensure the infrared imaging quality because the maximum dispersion root-mean-square(RMS) radius is less than the pitch of the detector in -40 ℃～+60 ℃ with the mechanical compensation method;we improve the radial rigidity more than 25.9% and realize the work stabilization of the system by installing the thrust bearing．
2014, 35(3): 377-380.
Abstract:
In order to achieve the target of long-focal length miniaturized near-infrared (NIR) system ,the telephoto optical structure was adopted to compress the axial dimension, and the telephoto ratio reached 0.53.Furthermore,the stray light was eliminated by properly setting the stop, and by choosing appropriate mechanical and optical materials,the athermal design was realized.In working temperature（40 ℃～+65 ℃），the image surface drift is smaller than focal depth, the modulation transfer function(MTF) 0.7 at 20 lp/mm,the spot is 4.7 m which is smaller than CCD pixel of 6 m, and the optical axis stability is 0.04 mrad.The system can gain good imaging quality and optical axis stability in worsened environment without focusing.Test result shows both the detection and recognition distances meet the requirements.
In order to achieve the target of long-focal length miniaturized near-infrared (NIR) system ,the telephoto optical structure was adopted to compress the axial dimension, and the telephoto ratio reached 0.53.Furthermore,the stray light was eliminated by properly setting the stop, and by choosing appropriate mechanical and optical materials,the athermal design was realized.In working temperature（40 ℃～+65 ℃），the image surface drift is smaller than focal depth, the modulation transfer function(MTF) 0.7 at 20 lp/mm,the spot is 4.7 m which is smaller than CCD pixel of 6 m, and the optical axis stability is 0.04 mrad.The system can gain good imaging quality and optical axis stability in worsened environment without focusing.Test result shows both the detection and recognition distances meet the requirements.
2014, 35(3): 381-385.
Abstract:
In order to realize optical axis parallelism and stability adjustment for multiple field TV sight, an adjustment program combining the CCD target surface with the dual optical wedges was described, according to the structure of the opto-mechanical system. Through the design and establishment for the alignment device of which the mounting surface paralleled the optical axis, the uniform alignment benchmark was built with collimator auto-collimation method. Meanwhile, through the analysis of the principle of dual wedges, the adjustment program was optimized, the progress requirements of dual wedges pairing and coarse error control were added. The adjustment and test results show that the optical axis parallel accuracy is up to 0.1 mrad, and the optical axis stability accuracy is up to 0.05 mrad.
In order to realize optical axis parallelism and stability adjustment for multiple field TV sight, an adjustment program combining the CCD target surface with the dual optical wedges was described, according to the structure of the opto-mechanical system. Through the design and establishment for the alignment device of which the mounting surface paralleled the optical axis, the uniform alignment benchmark was built with collimator auto-collimation method. Meanwhile, through the analysis of the principle of dual wedges, the adjustment program was optimized, the progress requirements of dual wedges pairing and coarse error control were added. The adjustment and test results show that the optical axis parallel accuracy is up to 0.1 mrad, and the optical axis stability accuracy is up to 0.05 mrad.
2014, 35(3): 386-390.
Abstract:
Switch-zoom optical system is composed of the subsystem with wide field of view and the subsystem with narrow field of view. Due to the errors from many aspects such as the refractive index of optical material, the optical manufacturing and assembling, the actual image surfaces of both subsystem deviate from their ideal image surfaces, and the drifts are different, that is, the two subsystems are not confocal. To solve the problem, a variety of confocal design schemes, the selection principle and an optimal scheme which fixed long focus and adjusted short focus, adjusted the compensating set for a mid-wave infrared (MWIR) switch-zoom optical system were given.
Switch-zoom optical system is composed of the subsystem with wide field of view and the subsystem with narrow field of view. Due to the errors from many aspects such as the refractive index of optical material, the optical manufacturing and assembling, the actual image surfaces of both subsystem deviate from their ideal image surfaces, and the drifts are different, that is, the two subsystems are not confocal. To solve the problem, a variety of confocal design schemes, the selection principle and an optimal scheme which fixed long focus and adjusted short focus, adjusted the compensating set for a mid-wave infrared (MWIR) switch-zoom optical system were given.
2014, 35(3): 391-394.
Abstract:
Based on the theory of coaxial three-mirror reflective optical system and by decentering the aperture stop and the field of view, a compact and multispectral off-axial three-mirror reflective optical system with 1 200 mm focal length was designed. Furthermore, the image quality was evaluated. The design results prove that the modulation transfer function(MTF) is above 0.5 at 80 lp/mm for 0.486 m ~0.656 m, above 0.35 at 17 lp/mm for 3 m ~5 m and the rootmean-square (RMS) radius is less than 2.096 m in full waveband. Moreover, three mirrors which use cone surfaces instead of high order aspherical surfaces are not decentered or tilted and only the aperture stop is decentered, so it is easy to fabricate and assemble.
Based on the theory of coaxial three-mirror reflective optical system and by decentering the aperture stop and the field of view, a compact and multispectral off-axial three-mirror reflective optical system with 1 200 mm focal length was designed. Furthermore, the image quality was evaluated. The design results prove that the modulation transfer function(MTF) is above 0.5 at 80 lp/mm for 0.486 m ~0.656 m, above 0.35 at 17 lp/mm for 3 m ~5 m and the rootmean-square (RMS) radius is less than 2.096 m in full waveband. Moreover, three mirrors which use cone surfaces instead of high order aspherical surfaces are not decentered or tilted and only the aperture stop is decentered, so it is easy to fabricate and assemble.
2014, 35(3): 395-399.
Abstract:
A compound parabolic collector light distribution system was established for light distribution of LED lamps in the classroom．First the characteristics of the LED light source were analyzed, as well as the necessity of the secondary light distribution for the LED light source. The 3D nonimaging optics compound parabolic collector (CPC) model was established. The relationship between its parameters and the maximum exit half angle m was calculated by the edge light principle and the restricting factors of m were given．Then the values of all parameters of CPC model were determined according to the reading lamp illumination uniformity requirements, the CPC model was built in the optical analysis software Tracepro.The LED light source was placed on the focal plane of CPC model and the LED classroom lighting illumination distribution based on CPC was simulated combining with classroom desktop and the lamp distance．Results showed that the light uniformity cound reach more than 0.7 and satisfy the building lighting design standard GB 50034-2004 for reading lighting requirements as m was greater than 30, the effective optical flux was more than 95%.
A compound parabolic collector light distribution system was established for light distribution of LED lamps in the classroom．First the characteristics of the LED light source were analyzed, as well as the necessity of the secondary light distribution for the LED light source. The 3D nonimaging optics compound parabolic collector (CPC) model was established. The relationship between its parameters and the maximum exit half angle m was calculated by the edge light principle and the restricting factors of m were given．Then the values of all parameters of CPC model were determined according to the reading lamp illumination uniformity requirements, the CPC model was built in the optical analysis software Tracepro.The LED light source was placed on the focal plane of CPC model and the LED classroom lighting illumination distribution based on CPC was simulated combining with classroom desktop and the lamp distance．Results showed that the light uniformity cound reach more than 0.7 and satisfy the building lighting design standard GB 50034-2004 for reading lighting requirements as m was greater than 30, the effective optical flux was more than 95%.
2014, 35(3): 400-403.
Abstract:
To meet the need of 4k short distance movie projection, a wide-angle projection lens was designed, which is suitable for projectors with threedigitalmicromirror-device (DMD) chips. The largest projection ratio could be 0.75∶1, the relative aperture is 1/2.2, the inverted telephoto ratio is 4.6∶1. At the Nyquist frequency of 66lp/mm, the resolution of center field is 0.42,and the resolution of marginal field is 0.25. The max lateral chromatic aberration is 3.7 m, which is less than 0.5 pixel, and the max distortion is 2.5%. The feature of inverted telephoto was deeply analyzed, and the methods for choosing structure, distributing focal power and calculating key parameters were provided in the paper, additional, the issues needing pay attention during aberration correction were contained. Finally, a wide-angle projection lens with high resolution which could meet all the indices was designed, besides that, the lens has the feature of easy structure, low cost and high quality.
To meet the need of 4k short distance movie projection, a wide-angle projection lens was designed, which is suitable for projectors with threedigitalmicromirror-device (DMD) chips. The largest projection ratio could be 0.75∶1, the relative aperture is 1/2.2, the inverted telephoto ratio is 4.6∶1. At the Nyquist frequency of 66lp/mm, the resolution of center field is 0.42,and the resolution of marginal field is 0.25. The max lateral chromatic aberration is 3.7 m, which is less than 0.5 pixel, and the max distortion is 2.5%. The feature of inverted telephoto was deeply analyzed, and the methods for choosing structure, distributing focal power and calculating key parameters were provided in the paper, additional, the issues needing pay attention during aberration correction were contained. Finally, a wide-angle projection lens with high resolution which could meet all the indices was designed, besides that, the lens has the feature of easy structure, low cost and high quality.
2014, 35(3): 404-408.
Abstract:
For the purpose of studying light attenuation principle of warship foam-water dual-purpose curtain, the visible light scattering model was established for calculating the optical scattering intensity distribution based on geometrical optics. Light intensity scattered by spherical foam/water drop restricted by scattering angle from 1 to 10, relative bubble radius r from 0 to 0.99 and liquid refractive index m2 within 1.20 to 1.50 was calculated using the computational model above. Results show that light is scattered strongly by the foam/water drop. The ratio of scattering intensity to incident intensity T increases by at most 2 orders of magnitude along with the increase of from 1to 10. T reduces up to 11.6% along with the increase of m2 from 1.30 to 1.40. T firstly declines and then increases to the extent of 0(minimum) and 80.8% (maximum) with the increase of r. The optimized bubble radius ro, corresponding to the lowest T value, enlarges from 0.1 to 0.4 with the increase of scattering angle and the decrease of liquid refractive index. The research can provide theoretical foundation for the development techniques of warship foam-water dual-purpose curtain.
For the purpose of studying light attenuation principle of warship foam-water dual-purpose curtain, the visible light scattering model was established for calculating the optical scattering intensity distribution based on geometrical optics. Light intensity scattered by spherical foam/water drop restricted by scattering angle from 1 to 10, relative bubble radius r from 0 to 0.99 and liquid refractive index m2 within 1.20 to 1.50 was calculated using the computational model above. Results show that light is scattered strongly by the foam/water drop. The ratio of scattering intensity to incident intensity T increases by at most 2 orders of magnitude along with the increase of from 1to 10. T reduces up to 11.6% along with the increase of m2 from 1.30 to 1.40. T firstly declines and then increases to the extent of 0(minimum) and 80.8% (maximum) with the increase of r. The optimized bubble radius ro, corresponding to the lowest T value, enlarges from 0.1 to 0.4 with the increase of scattering angle and the decrease of liquid refractive index. The research can provide theoretical foundation for the development techniques of warship foam-water dual-purpose curtain.
2014, 35(3): 409-413.
Abstract:
Currently, most studies focus on the calculation model of the information content, rarely involve the quantitative relation between spatial resolution and information content. In order to quantitatively evaluate different spatial resolution remote sensing images, this paper was based on the theory of information and fuzzy mathematics and the information entropy was used as the criterion. Through calculating the information content of panchromatic and multispectral image at different levels, a mathematical simulation of the relationship between information content and spatial resolution was provided. The results show that, as the spatial resolution of the image reduces, the amount of information exponentially reduces. Doubling the spatial resolution, the image information content increases 3 to 5 times.
Currently, most studies focus on the calculation model of the information content, rarely involve the quantitative relation between spatial resolution and information content. In order to quantitatively evaluate different spatial resolution remote sensing images, this paper was based on the theory of information and fuzzy mathematics and the information entropy was used as the criterion. Through calculating the information content of panchromatic and multispectral image at different levels, a mathematical simulation of the relationship between information content and spatial resolution was provided. The results show that, as the spatial resolution of the image reduces, the amount of information exponentially reduces. Doubling the spatial resolution, the image information content increases 3 to 5 times.
2014, 35(3): 414-419.
Abstract:
In the realtime remote sensing of gas based on inteferogram imaging, fast inversion processing of original data is required.But the data acquired in this way is a large quantity,and the inverse algorithm is also complicated while using CPU for processing is time-consuming.A parallel inversion algorithm using compute unified device architecture (CUDA) was realized by analyzing the patten of data obtained by time-space mix-modulation long-wave infrared interference spectrometer. The results show that the parallel computing technique using CUDA can enhance the efficiency of spectrum inversion by 5 to 20 times,which provides foundations for further application like spectral recognition.
In the realtime remote sensing of gas based on inteferogram imaging, fast inversion processing of original data is required.But the data acquired in this way is a large quantity,and the inverse algorithm is also complicated while using CPU for processing is time-consuming.A parallel inversion algorithm using compute unified device architecture (CUDA) was realized by analyzing the patten of data obtained by time-space mix-modulation long-wave infrared interference spectrometer. The results show that the parallel computing technique using CUDA can enhance the efficiency of spectrum inversion by 5 to 20 times,which provides foundations for further application like spectral recognition.
2014, 35(3): 420-426.
Abstract:
In order to effectively improve the image encryption effect and security，according to the study on image encryption algorithm based on chaotic system and bit operations，a image encryption algorithm based on combined chaotic system and bit operations was proposed. Firstly, the original image was decomposed into bit-planes. Considering the massive contained information of the four high-planes of the image, scrambling transformation was conducted on the four high-planes, followed by scrambling transformation of combination with the four low high-planes. Then the encrypted image was obtained by conducting exclusive or(XOR) operation between binary matrix and the combination of scrambled bit-planes. The experimental result shows that compared with the pixel location permutation (PLP) algorithm and the enhanced two-dimensional circulation encryption algorithm(TDCEA), the modified algorithm achieves a better encryption and the key space is near to 2192. It has a better security and can be against the attack of salt-pepper noise and Gauss noise. It also can- recover the original picture.
In order to effectively improve the image encryption effect and security，according to the study on image encryption algorithm based on chaotic system and bit operations，a image encryption algorithm based on combined chaotic system and bit operations was proposed. Firstly, the original image was decomposed into bit-planes. Considering the massive contained information of the four high-planes of the image, scrambling transformation was conducted on the four high-planes, followed by scrambling transformation of combination with the four low high-planes. Then the encrypted image was obtained by conducting exclusive or(XOR) operation between binary matrix and the combination of scrambled bit-planes. The experimental result shows that compared with the pixel location permutation (PLP) algorithm and the enhanced two-dimensional circulation encryption algorithm(TDCEA), the modified algorithm achieves a better encryption and the key space is near to 2192. It has a better security and can be against the attack of salt-pepper noise and Gauss noise. It also can- recover the original picture.
2014, 35(3): 427-431.
Abstract:
Based on the solid immersion lenses (SILs), a new super-resolution system with nanometer scale was designed by using the SU-8 photoresist and a 4.87 m diameter spherical lens. The computation process of the magnification was introduced. The focal distance was simulated by softwares in addition. By changing the thickness of the SU-8 layer from 3.4 m to 0, the system-s magnification was changed from 1.6x to 2.6x. Experiment results show that the thickness of SU-8 photoresist influences the magnification directly,the stripe patterns of the blu-ray disc can be observed in ordinary optical microscopes by using the superresolution system.
Based on the solid immersion lenses (SILs), a new super-resolution system with nanometer scale was designed by using the SU-8 photoresist and a 4.87 m diameter spherical lens. The computation process of the magnification was introduced. The focal distance was simulated by softwares in addition. By changing the thickness of the SU-8 layer from 3.4 m to 0, the system-s magnification was changed from 1.6x to 2.6x. Experiment results show that the thickness of SU-8 photoresist influences the magnification directly,the stripe patterns of the blu-ray disc can be observed in ordinary optical microscopes by using the superresolution system.
2014, 35(3): 432-437.
Abstract:
In order to improve the efficiency of coupling Cassegrain telescope image disk into multimode fiber, we put forward a new method of putting an axicon duct close to the import of multimode fiber. By using total internal reflection several times in axicon duct, the rays could rip into multimode fiber. To determine the initial structural parameters of axicon duct, we analyzed the maximum coupling angle of image spot of Cassegrain at 0 field of view(FOV) by employing geometrical optical theory and numerical method. These parameters were used as the initial conditions of simulation in Zemax. After simulation optimization and tolerance analysis, the conclusions show that when the fabrication tolerance is controlled in 0.03mm, the coupling efficiency of image spot at full FOV is at least 4 times as the direct coupling.
In order to improve the efficiency of coupling Cassegrain telescope image disk into multimode fiber, we put forward a new method of putting an axicon duct close to the import of multimode fiber. By using total internal reflection several times in axicon duct, the rays could rip into multimode fiber. To determine the initial structural parameters of axicon duct, we analyzed the maximum coupling angle of image spot of Cassegrain at 0 field of view(FOV) by employing geometrical optical theory and numerical method. These parameters were used as the initial conditions of simulation in Zemax. After simulation optimization and tolerance analysis, the conclusions show that when the fabrication tolerance is controlled in 0.03mm, the coupling efficiency of image spot at full FOV is at least 4 times as the direct coupling.
2014, 35(3): 438-440.
Abstract:
High energy laser (HEL) meter by means of calorimetric method is used to measure continuous wave (CW) laser with energy more than 50 kJ. The photoelectricity calibration is usually made by CW laser illumination with known power for more than 20 minutes, and because of the heat loss, the uncertainty is up to 12%. The influence of heat radiation and heat convection on energy measurements of CW high energy laser was analyzed theoretically based on the model of calorimetric plane absorbing HEL energy meter. The cooling down model for laser energy meter with plane absorbing chamber was deduced accurately which made it possible to compensate for heat loss of energy meter. The experiments apparatus was established to verify the correctness of the model. With this model, the measurement uncertainty of photoelectricity calibration decreases to 1% above.
High energy laser (HEL) meter by means of calorimetric method is used to measure continuous wave (CW) laser with energy more than 50 kJ. The photoelectricity calibration is usually made by CW laser illumination with known power for more than 20 minutes, and because of the heat loss, the uncertainty is up to 12%. The influence of heat radiation and heat convection on energy measurements of CW high energy laser was analyzed theoretically based on the model of calorimetric plane absorbing HEL energy meter. The cooling down model for laser energy meter with plane absorbing chamber was deduced accurately which made it possible to compensate for heat loss of energy meter. The experiments apparatus was established to verify the correctness of the model. With this model, the measurement uncertainty of photoelectricity calibration decreases to 1% above.
2014, 35(3): 441-445.
Abstract:
Pipe inner surface defects detection is very important to ensure transmission safety and avoid leaking and explosion accidents. Based on the analysis of the geometry characteristic of the 3D points distribution, for the pipe inner side 3D data which are obtained based on circle structured light machine vision technology, a defect detection method about pipe inner side is proposed by comparing the normal vector angle between adjacent points which are on the same circumference. The point normal vector is calculated by the weighted average of adjacent triangles normal vectors. As the 3D points distribute circumferentially, the adjacent points are adopted to do fast triangulation. By using above method, we conducted defects detection and 3D reconstruction of measured and simulated 3D points inside the pipe, respectively. Results show that the method can detect and identify pipe defects of less than 0.1 mm racial variation with 0.081 mm accuracy.
Pipe inner surface defects detection is very important to ensure transmission safety and avoid leaking and explosion accidents. Based on the analysis of the geometry characteristic of the 3D points distribution, for the pipe inner side 3D data which are obtained based on circle structured light machine vision technology, a defect detection method about pipe inner side is proposed by comparing the normal vector angle between adjacent points which are on the same circumference. The point normal vector is calculated by the weighted average of adjacent triangles normal vectors. As the 3D points distribute circumferentially, the adjacent points are adopted to do fast triangulation. By using above method, we conducted defects detection and 3D reconstruction of measured and simulated 3D points inside the pipe, respectively. Results show that the method can detect and identify pipe defects of less than 0.1 mm racial variation with 0.081 mm accuracy.
2014, 35(3): 446-451.
Abstract:
A novel method to measure duty cycles of rectangular gratings and evaluate the spatial uniformity of duty cycles was presented on the basis of top-down scanning electron microscope(SEM) images. This method first conducts image grayscale profile preprocessing on target images, then performs border detection based on dynamic programming and least-squares spline approximation, and finally computes the mean and standard deviations of duty cycles in the target area in light of the provided evaluation standards. Using this method, we can not only quickly and accurately measure grating duty cycles and perform quantitative analysis on the spatial uniformity of duty cycles, but also avoid damaging sample preparation process, which greatly make up the deficiency of traditional method. A top-down SEM image processing software, GradUI, for detecting duty cycles of rectangular gratings was developed. The top-down SEM images of several 1 200 lines/mm self-made gratings were processed with the software, and the root-mean-square deviation of the average duty cycle and the estimated value was 0.017 3. The results show that the approach to calculate duty cycles based on top-down SEM images is feasible and of high efficiency, and the software is robust.
A novel method to measure duty cycles of rectangular gratings and evaluate the spatial uniformity of duty cycles was presented on the basis of top-down scanning electron microscope(SEM) images. This method first conducts image grayscale profile preprocessing on target images, then performs border detection based on dynamic programming and least-squares spline approximation, and finally computes the mean and standard deviations of duty cycles in the target area in light of the provided evaluation standards. Using this method, we can not only quickly and accurately measure grating duty cycles and perform quantitative analysis on the spatial uniformity of duty cycles, but also avoid damaging sample preparation process, which greatly make up the deficiency of traditional method. A top-down SEM image processing software, GradUI, for detecting duty cycles of rectangular gratings was developed. The top-down SEM images of several 1 200 lines/mm self-made gratings were processed with the software, and the root-mean-square deviation of the average duty cycle and the estimated value was 0.017 3. The results show that the approach to calculate duty cycles based on top-down SEM images is feasible and of high efficiency, and the software is robust.
2014, 35(3): 452-458.
Abstract:
Deflection in each optical path of binocular microscope system and unparallelism between them can increase the off-axis aberration, reduce the imaging quality, cause the nonidentity of binocular vision and lead to discomfort when used. A set of new method using laser is introduced to detect light path deflection and unparallelism. First of all, the system under test is divided into components and detected in each element, and then the parts are put together. A light path deflection distance more over than 0.5mm was detected in the experiment and a angle of about 0.8 was formed between the two outgoing beams after parallel light passing through the system. It is concluded that this method can be applied to industrial production and detection of microscope.
Deflection in each optical path of binocular microscope system and unparallelism between them can increase the off-axis aberration, reduce the imaging quality, cause the nonidentity of binocular vision and lead to discomfort when used. A set of new method using laser is introduced to detect light path deflection and unparallelism. First of all, the system under test is divided into components and detected in each element, and then the parts are put together. A light path deflection distance more over than 0.5mm was detected in the experiment and a angle of about 0.8 was formed between the two outgoing beams after parallel light passing through the system. It is concluded that this method can be applied to industrial production and detection of microscope.
2014, 35(3): 459-465.
Abstract:
This paper focuses on radiometric calibration of triple-band optical imaging system which includes near ultraviolet (300 nm~380 nm), visible (380 nm~760 nm) and near infrared (760 nm~1 100 nm) ranges. The radiometric calibration system was set up, the mathematical model was established and the radiometric calibration experiment was conducted. As the optical system operated at three wavebands, technique of sub-band radiometric calibration was adopted. The calibration data were fitted by linear least squares and then the algorithm was modified. At last the calibration data were processed. Experimental results verify the calibration accuracy of two methods. The calibration curve obtained by the modified algorithm is with higher accuracy. The relative error of measurements can be less than 5%, which meets the needs of actual projects.
This paper focuses on radiometric calibration of triple-band optical imaging system which includes near ultraviolet (300 nm~380 nm), visible (380 nm~760 nm) and near infrared (760 nm~1 100 nm) ranges. The radiometric calibration system was set up, the mathematical model was established and the radiometric calibration experiment was conducted. As the optical system operated at three wavebands, technique of sub-band radiometric calibration was adopted. The calibration data were fitted by linear least squares and then the algorithm was modified. At last the calibration data were processed. Experimental results verify the calibration accuracy of two methods. The calibration curve obtained by the modified algorithm is with higher accuracy. The relative error of measurements can be less than 5%, which meets the needs of actual projects.
2014, 35(3): 466-471.
Abstract:
In order to realize the real-time detection of pattern fabric defects in the process of weaving, a machine vision-based rapid real-time detection method using area subtraction and automatic segmentation was proposed.This method first calculates the minimums of the horizonal and vertical superposition distance matching functions (DFMs) and analyzes the weight of every minimum, obtains the element period of pattern fabric accurately; then it determines the size of the area to be subtracted, calculates the gradient of the subtracted image, segments the gradient image with a marker-based watershed algorithm, it can fastly and accurately segment out the flaws area. Experiments shows that, the method can accurately test the flaws area, and has a high instantaneity that an average time of detection is about 200 ms and a low fallout ratio that the accuracy rate is above 98%, which fully meet the requirements of the industrial field.
In order to realize the real-time detection of pattern fabric defects in the process of weaving, a machine vision-based rapid real-time detection method using area subtraction and automatic segmentation was proposed.This method first calculates the minimums of the horizonal and vertical superposition distance matching functions (DFMs) and analyzes the weight of every minimum, obtains the element period of pattern fabric accurately; then it determines the size of the area to be subtracted, calculates the gradient of the subtracted image, segments the gradient image with a marker-based watershed algorithm, it can fastly and accurately segment out the flaws area. Experiments shows that, the method can accurately test the flaws area, and has a high instantaneity that an average time of detection is about 200 ms and a low fallout ratio that the accuracy rate is above 98%, which fully meet the requirements of the industrial field.
2014, 35(3): 472-477.
Abstract:
Spectrum-tunable light source is an integrating sphere source illuminated by a large number of LEDs with different spectral peaks and distributions. The spectral matching algorithm is an essential approach to produce varieties of spectra. Levenberg-Marquardt algorithm was proposed and a series of simulations using Gaussian curves with an equal interval were conducted. The results of simulations show that Levenberg-Marquardt algorithm can make spectrum-tunable source produce solar, dessert,ocean and vegetation spectrum, respectively, the relative spectrum differences are 2.17% , 1.76% , 2.03% and 1.7%,respectively. The validating experiment for a number of target distributions was performed, and the relative spectral differences are all no more than 5%. The experiment verifies that it is feasible to produce different spectral distributions by using Levenberg-Marquardt algorithm for spectrum-tunable integrating sphere light source.
Spectrum-tunable light source is an integrating sphere source illuminated by a large number of LEDs with different spectral peaks and distributions. The spectral matching algorithm is an essential approach to produce varieties of spectra. Levenberg-Marquardt algorithm was proposed and a series of simulations using Gaussian curves with an equal interval were conducted. The results of simulations show that Levenberg-Marquardt algorithm can make spectrum-tunable source produce solar, dessert,ocean and vegetation spectrum, respectively, the relative spectrum differences are 2.17% , 1.76% , 2.03% and 1.7%,respectively. The validating experiment for a number of target distributions was performed, and the relative spectral differences are all no more than 5%. The experiment verifies that it is feasible to produce different spectral distributions by using Levenberg-Marquardt algorithm for spectrum-tunable integrating sphere light source.
2014, 35(3): 478-483.
Abstract:
Traditional low-light-level(LLL) image intensifier and the image intensifier with InGaAs photocathode extending to shortwave infrared(SWIR) band were compared and analyzed,and the materiel characteristic of InGaAs was analyzed of which the response band could cover the main band of the night sky radiation through adjusting the component of InGaAs. It is revealed that the image intensifier with InGaAs photocathode has higher quantum efficiency and responsivity. The researching status home and abroad was presented. The response of InGaAs photocathode image intensifier is 100~1 000 times larger than the traditional image intensifier at shortwave infrared hand and the InGaAs detector can work between 0.4 m~1.7 m, the quantum efficiency is more than 80% between 0.9 m~1.7 m. It is indicated that this kind of image intensifier can be applied in laser detection, orientation at far distance, intelligence reconnaissance and assistant driving at night.
Traditional low-light-level(LLL) image intensifier and the image intensifier with InGaAs photocathode extending to shortwave infrared(SWIR) band were compared and analyzed,and the materiel characteristic of InGaAs was analyzed of which the response band could cover the main band of the night sky radiation through adjusting the component of InGaAs. It is revealed that the image intensifier with InGaAs photocathode has higher quantum efficiency and responsivity. The researching status home and abroad was presented. The response of InGaAs photocathode image intensifier is 100~1 000 times larger than the traditional image intensifier at shortwave infrared hand and the InGaAs detector can work between 0.4 m~1.7 m, the quantum efficiency is more than 80% between 0.9 m~1.7 m. It is indicated that this kind of image intensifier can be applied in laser detection, orientation at far distance, intelligence reconnaissance and assistant driving at night.
2014, 35(3): 484-488.
Abstract:
Microchannel plate as an electron multiplier plays an important role in the two-dimension position sensitive anode of the photon counting imaging detector. Its gain as one of the important parameters has effect on imaging performance. Hence the microchannel plate-s gain changing with volt was measured with a systematic testing platform, and the pulse height distribution of the photon counting detector was also obtained. According to the test results and the relationship between the pulse height distribution curve and energy resolution, the appropriate gain and volt were selected to optimize the performance of the detector. The resolution of detector increased from 3.56 lp/mm to 4.49 lp/mm and a clear image was got, providing technical support for the development of the detector.
Microchannel plate as an electron multiplier plays an important role in the two-dimension position sensitive anode of the photon counting imaging detector. Its gain as one of the important parameters has effect on imaging performance. Hence the microchannel plate-s gain changing with volt was measured with a systematic testing platform, and the pulse height distribution of the photon counting detector was also obtained. According to the test results and the relationship between the pulse height distribution curve and energy resolution, the appropriate gain and volt were selected to optimize the performance of the detector. The resolution of detector increased from 3.56 lp/mm to 4.49 lp/mm and a clear image was got, providing technical support for the development of the detector.
2014, 35(3): 489-493.
Abstract:
In order to get low scattering and polarization-independent holographic polymer dispersed liquid crystal（HPDLC)grating, low functionality acrylate monomers were adopted and the fabricating temperature was increased gradually. First, two kinds of acrylate monomers were selected, one was pentafunctional dipentaerythritol hydroxyl pentaacrylate (DPHPA) , the other was difunctional phthalic diglycol diacrylate (PDDA). Besides N-vinylpyrrolidone (NVP) which served as solvent and chain extender was adopted. Then, the effects of fabricating temperature on the HPDLC grating was investigated, and it is found that the highly anisotropic grating fabricated at room temperature becomes polarization-independent by its clearing point（62 ℃）. Also a more complete phase separation of liquid crystal from polymer is demonstrated. Besides, optical measurement carried at the Bragg angle shows a 66.7% scattering loss decrease, this result is further conformed by scanning electron microscopy (SEM) analyses. And also this hightemperature fabricated grating shows a polarization independent behavior.
In order to get low scattering and polarization-independent holographic polymer dispersed liquid crystal（HPDLC)grating, low functionality acrylate monomers were adopted and the fabricating temperature was increased gradually. First, two kinds of acrylate monomers were selected, one was pentafunctional dipentaerythritol hydroxyl pentaacrylate (DPHPA) , the other was difunctional phthalic diglycol diacrylate (PDDA). Besides N-vinylpyrrolidone (NVP) which served as solvent and chain extender was adopted. Then, the effects of fabricating temperature on the HPDLC grating was investigated, and it is found that the highly anisotropic grating fabricated at room temperature becomes polarization-independent by its clearing point（62 ℃）. Also a more complete phase separation of liquid crystal from polymer is demonstrated. Besides, optical measurement carried at the Bragg angle shows a 66.7% scattering loss decrease, this result is further conformed by scanning electron microscopy (SEM) analyses. And also this hightemperature fabricated grating shows a polarization independent behavior.
2014, 35(3): 494-499.
Abstract:
Aiming at some deficiencies of traditional one-polishing-head magnetorheological finishing (MRF) technique, a new two-polishing-head MRF method was studied and a two-polishing-head computer controlled MRF machine with 8 axes was developed . The machine has the ability to produce large aperture flat, asphere and continuous phase plate with high figure accuracy and high material removal rate . Material removal characteristic and figure correction ability for each of large and small polishing heads were studied. Each of two heads individually acquired stable and valid polishing removal function and ultraprecision flat sample . After a single polishing iteration using small polishing head , the figure error peak value(PV) in 45 mm diameter of a 50 mm diameter small plano optics significantly improved from 0.21 to 0.08 (0.053 to 0.015 root-mean-square). After three polishing iterations using large polishing head,the figure error in 410 mm410 mm of a 430 mm430 mm large plano optics significantly improved from 0.40 to 0.10 PV (0.068 to 0.013 RMS). These results show that the two-polishing-head MRF machine has good material removal stability and excellent figure correction capability.
Aiming at some deficiencies of traditional one-polishing-head magnetorheological finishing (MRF) technique, a new two-polishing-head MRF method was studied and a two-polishing-head computer controlled MRF machine with 8 axes was developed . The machine has the ability to produce large aperture flat, asphere and continuous phase plate with high figure accuracy and high material removal rate . Material removal characteristic and figure correction ability for each of large and small polishing heads were studied. Each of two heads individually acquired stable and valid polishing removal function and ultraprecision flat sample . After a single polishing iteration using small polishing head , the figure error peak value(PV) in 45 mm diameter of a 50 mm diameter small plano optics significantly improved from 0.21 to 0.08 (0.053 to 0.015 root-mean-square). After three polishing iterations using large polishing head,the figure error in 410 mm410 mm of a 430 mm430 mm large plano optics significantly improved from 0.40 to 0.10 PV (0.068 to 0.013 RMS). These results show that the two-polishing-head MRF machine has good material removal stability and excellent figure correction capability.
2014, 35(3): 500-504.
Abstract:
The features of glass-ceramic processing in the Li2O-Al2O3-SiO2 system were introduced. The nano-scratch experiment on glass-ceramic in the Li2O-Al2O3-SiO2 system was performed based on nano-scratch technique,and the mean tested values of brittleness-ductility transition critical-depth-of-cut and critical load of glass-ceramic were 125.6 nm and 29.78 mN, respectively. The tested value of critical-depth-of-cut was compared with the calculated value according to the critical condition of brittleness-ductility transition based on indentation fracture mechanics. It was showed that the difference between the calculated value of critical-depth-of-cut given by T. G. Bifano based on micro-indentation and the experimental value was remarkable, thus, the model was corrected in accordance with experimental value; There was no obvious difference between the value of critical-depth-of-cut obtained from experiments and the calculation value of ductile-regime grinding critical condition based on indentation fracture mechanics. In addition, reasons for the difference were also discussed in this paper.
The features of glass-ceramic processing in the Li2O-Al2O3-SiO2 system were introduced. The nano-scratch experiment on glass-ceramic in the Li2O-Al2O3-SiO2 system was performed based on nano-scratch technique,and the mean tested values of brittleness-ductility transition critical-depth-of-cut and critical load of glass-ceramic were 125.6 nm and 29.78 mN, respectively. The tested value of critical-depth-of-cut was compared with the calculated value according to the critical condition of brittleness-ductility transition based on indentation fracture mechanics. It was showed that the difference between the calculated value of critical-depth-of-cut given by T. G. Bifano based on micro-indentation and the experimental value was remarkable, thus, the model was corrected in accordance with experimental value; There was no obvious difference between the value of critical-depth-of-cut obtained from experiments and the calculation value of ductile-regime grinding critical condition based on indentation fracture mechanics. In addition, reasons for the difference were also discussed in this paper.
2014, 35(3): 505-509.
Abstract:
Enhancing optical absorption is an important way to improve the photoelectric conversion efficiency of solar cells. A new metal grating-based solar cell structure was designed. The absorption spectrum and enhancement factor were calculated by rigorous coupled wave analysis (RCWA) method. The influences on optical absorption induced by the grating width, the angle and polarized states of the incident light were discussed. The results show that the optical absorption factor in the designed structure can be greatly enhanced up to 40% when the incident wave is transverse magnetic (TM) polarized, and nearly 16% under other incident waves condictions. These indicates that the new solar cell structure can significantly improve the overall optical absorption compared to bare a-Si thin film solar cells.
Enhancing optical absorption is an important way to improve the photoelectric conversion efficiency of solar cells. A new metal grating-based solar cell structure was designed. The absorption spectrum and enhancement factor were calculated by rigorous coupled wave analysis (RCWA) method. The influences on optical absorption induced by the grating width, the angle and polarized states of the incident light were discussed. The results show that the optical absorption factor in the designed structure can be greatly enhanced up to 40% when the incident wave is transverse magnetic (TM) polarized, and nearly 16% under other incident waves condictions. These indicates that the new solar cell structure can significantly improve the overall optical absorption compared to bare a-Si thin film solar cells.
2014, 35(3): 510-514.
Abstract:
The infrared multi-band optical system can track the band information stretching from mid-wave infrared to long-wave infrared ,which can greatly improve the information acquisition capability. A infrared multi-band optical system composed of 4 spherical lenses was designed based on the compact principle. It could image clearly at 4.4 m~8.8 m continuously , the F# was 2.68 which strictly matched with the cold light bar so that the cold light bar effect reached 100% . The system used the passive athermalization method to get rid of temperature compensation problem and finally realized athermalization for continuous bands through selection of lens materials and formula derivation. The tube was made of titanium alloy,the lens was made of ZnSe,Germanium and ZnS materials.The modulation transfer funtion(MTF) at 40 ℃ to 60 ℃ was given, as well as the distortion over every wavebands.The result shows that the design of the system structure is relatively simple, which satisfies the requirements of a standard infrared thermal imager.
The infrared multi-band optical system can track the band information stretching from mid-wave infrared to long-wave infrared ,which can greatly improve the information acquisition capability. A infrared multi-band optical system composed of 4 spherical lenses was designed based on the compact principle. It could image clearly at 4.4 m~8.8 m continuously , the F# was 2.68 which strictly matched with the cold light bar so that the cold light bar effect reached 100% . The system used the passive athermalization method to get rid of temperature compensation problem and finally realized athermalization for continuous bands through selection of lens materials and formula derivation. The tube was made of titanium alloy,the lens was made of ZnSe,Germanium and ZnS materials.The modulation transfer funtion(MTF) at 40 ℃ to 60 ℃ was given, as well as the distortion over every wavebands.The result shows that the design of the system structure is relatively simple, which satisfies the requirements of a standard infrared thermal imager.
2014, 35(3): 515-519.
Abstract:
It is hard to calculate the operating distance of infrared system accurately in real time in the complex atmospheric conditions, so we proposed to build a realtime calculating system. MODTRAN software was combined with the operating distance model based on spectral bisection method of infrared imaging system. This system realized automatically written configurations for MODRTRAN software to simplify the configuration method of atmospheric model. Configuration file generated from MODTRAN was automatically read.The infrared system operating range of a target was calculated at different altitudes (1 km~6 km) and with different rainfall intensity (0 mm/h~4 mm/h) .The results show that the variation of the measuring height has obvious influence on the infrared system operating distance, and the influence is great at 1 km~3 km; the rainfall has huge impact on the infrared system operating distance, the operating distance attenuates to half of that with no rainfall when the rainfall intensity is 1mm/h, and the operating distance tends to stable when the rainfall intensity is more than 3mm/h.
It is hard to calculate the operating distance of infrared system accurately in real time in the complex atmospheric conditions, so we proposed to build a realtime calculating system. MODTRAN software was combined with the operating distance model based on spectral bisection method of infrared imaging system. This system realized automatically written configurations for MODRTRAN software to simplify the configuration method of atmospheric model. Configuration file generated from MODTRAN was automatically read.The infrared system operating range of a target was calculated at different altitudes (1 km~6 km) and with different rainfall intensity (0 mm/h~4 mm/h) .The results show that the variation of the measuring height has obvious influence on the infrared system operating distance, and the influence is great at 1 km~3 km; the rainfall has huge impact on the infrared system operating distance, the operating distance attenuates to half of that with no rainfall when the rainfall intensity is 1mm/h, and the operating distance tends to stable when the rainfall intensity is more than 3mm/h.
2014, 35(3): 520-524.
Abstract:
The laser pulse transmitted from satellite laser altimeter system would be refracted by atmosphere and the range error in the system was about a few meters. In this paper the atmospheric refraction delay based on refraction models and mapping function was calculated, and the method of air pressure correction were discussed. Combined with the elevation data of geoscience laser altimeter system (GLAS) and meteorological parameters of national center for environment prediction (NCEP), the atmospheric delay was calculated and compared to the GLAS results. The comparison shows the deviation of hydrostatic and wet atmospheric delay are less than 2 cm and 1 mm respectively.
The laser pulse transmitted from satellite laser altimeter system would be refracted by atmosphere and the range error in the system was about a few meters. In this paper the atmospheric refraction delay based on refraction models and mapping function was calculated, and the method of air pressure correction were discussed. Combined with the elevation data of geoscience laser altimeter system (GLAS) and meteorological parameters of national center for environment prediction (NCEP), the atmospheric delay was calculated and compared to the GLAS results. The comparison shows the deviation of hydrostatic and wet atmospheric delay are less than 2 cm and 1 mm respectively.
2014, 35(3): 525-530.
Abstract:
To solve the problem of 1 fJ~1 pJ laser energy measurement, a femto-Joule level pulse laser energy measurement method based on integration of the time domain waveform was proposed, which used a photomultiplier tube (PMT) to get the response signal of femto-Joule level pulse laser. It realized femtoJoule level pulse laser energy measurement finally after amplifying, calibrating this weak response signal and the laser pulse time domain waveform integration. According to this method, a femto-Joule level pulse laser energy measurement device was designed and the measurement uncertainty of the device was analyzed. Experiments show that the device implements the energy measurement of pulsed laser source with 1 064 nm wavelength, 5 ns~1 s pulse width and 1 fJ~1 pJ energy range, the measurement uncertainty is 15.8%.
To solve the problem of 1 fJ~1 pJ laser energy measurement, a femto-Joule level pulse laser energy measurement method based on integration of the time domain waveform was proposed, which used a photomultiplier tube (PMT) to get the response signal of femto-Joule level pulse laser. It realized femtoJoule level pulse laser energy measurement finally after amplifying, calibrating this weak response signal and the laser pulse time domain waveform integration. According to this method, a femto-Joule level pulse laser energy measurement device was designed and the measurement uncertainty of the device was analyzed. Experiments show that the device implements the energy measurement of pulsed laser source with 1 064 nm wavelength, 5 ns~1 s pulse width and 1 fJ~1 pJ energy range, the measurement uncertainty is 15.8%.
2014, 35(3): 531-536.
Abstract:
The defects of Fresnel lens was discussed and the design principle of parabolic ring array for solar-pumped laser was presented. A two-stage solar concentrator with parabolic ring array, Fresnel lens and compound parabolic concentrator(CPC) was designed . Ray-tracing simulations reveal that compared with the traditional Fresnel lens and CPC two-stage solar concentrator, the new concentrator can improve the optical efficiency by 18.5% and is more suitable for large aperture and high concentration ratio converging applications.
The defects of Fresnel lens was discussed and the design principle of parabolic ring array for solar-pumped laser was presented. A two-stage solar concentrator with parabolic ring array, Fresnel lens and compound parabolic concentrator(CPC) was designed . Ray-tracing simulations reveal that compared with the traditional Fresnel lens and CPC two-stage solar concentrator, the new concentrator can improve the optical efficiency by 18.5% and is more suitable for large aperture and high concentration ratio converging applications.
2014, 35(3): 537-540.
Abstract:
In order to study the typical character of receiving light intensity signal in ground-to-satellite/satellite-to-ground short-infrared and medium-infrared laser propagation, based on atmospheric turbulence theory and phase screen method, the scintillation of power ratio in the receiving aperture was calculated under the condition of specific atmospheric coherent length. According to the statistical results, the difference of uplink and downlink atmospheric channel was discussed. The results show that the receiving signal intensity of downlink channel is one order of magnitude greater than that of uplink channel and the signal scintillation level of downlink channel is lower than that of uplink channel. Under the condition of moderate atmospheric turbulence, the receiving light intensity probability distribution function of downlink channel is logarithmic normal distribution, and the maximum probability point is corresponding to that under no turbulence condition, the maximum probability receiving light intensity of short-infrared and medium-infrared laser are 0.42%(1.315 m) and 0.26%(3.8 m),respectively.
In order to study the typical character of receiving light intensity signal in ground-to-satellite/satellite-to-ground short-infrared and medium-infrared laser propagation, based on atmospheric turbulence theory and phase screen method, the scintillation of power ratio in the receiving aperture was calculated under the condition of specific atmospheric coherent length. According to the statistical results, the difference of uplink and downlink atmospheric channel was discussed. The results show that the receiving signal intensity of downlink channel is one order of magnitude greater than that of uplink channel and the signal scintillation level of downlink channel is lower than that of uplink channel. Under the condition of moderate atmospheric turbulence, the receiving light intensity probability distribution function of downlink channel is logarithmic normal distribution, and the maximum probability point is corresponding to that under no turbulence condition, the maximum probability receiving light intensity of short-infrared and medium-infrared laser are 0.42%(1.315 m) and 0.26%(3.8 m),respectively.
2014, 35(3): 542-546.
Abstract:
The characteristics of Fabry-Perot(F-P) etalon can be easily affected by temperature, the transmission peaks of F-P etalon drift with the fluctuation of temperature, and when F-P etalon is applied in the fiber Bragg grating(FBG) wavelength demodulation, the fluctuation of temperature may cause wavelength demodulation error. The impact of F-P etalon temperature characteristics on the FBG wavelength demodulation accuracy was analyzed, and the stability experiment and repeatability experiment were carried out using F-P etalons with thermal stabilities of 1.5 GHz and 3 GHz respectively. The analysis and experimental results show that the standard deviation of the demodulation error which is generated by the temperature characteristics of the F-P etalon is different if the center wavelength of the FBG sensor is different; the maximum stability errors obtained by two F-P etalons are 0.528 pm and 0.676 pm, and the maximum repeatability errors are 1.77 pm and 2.01 pm respectively.
The characteristics of Fabry-Perot(F-P) etalon can be easily affected by temperature, the transmission peaks of F-P etalon drift with the fluctuation of temperature, and when F-P etalon is applied in the fiber Bragg grating(FBG) wavelength demodulation, the fluctuation of temperature may cause wavelength demodulation error. The impact of F-P etalon temperature characteristics on the FBG wavelength demodulation accuracy was analyzed, and the stability experiment and repeatability experiment were carried out using F-P etalons with thermal stabilities of 1.5 GHz and 3 GHz respectively. The analysis and experimental results show that the standard deviation of the demodulation error which is generated by the temperature characteristics of the F-P etalon is different if the center wavelength of the FBG sensor is different; the maximum stability errors obtained by two F-P etalons are 0.528 pm and 0.676 pm, and the maximum repeatability errors are 1.77 pm and 2.01 pm respectively.
2014, 35(3): 547-550.
Abstract:
Random drift is one of the main errors in fiber optical gyroscope (FOG). Modeling and revising random drift is an efficient method to improve system accuracy in filtering. Based on Allan variance, the differential equation model(DEM) of random drift is required to solve the shortages of traditional models which are time-consuming and over sensitive. In this paper, the power spectrum density (PSD) function was exploited to figure out the stochastic differential equation (SDE) of every noise. By using Allan variance to calculate the parameter of every noise and substituting the parameter in SDE which was driven by white noise, the random drift model was established. Experiment result illustrates that, the fitting error of random drift is no more than 8.6%，far lower than the traditional one of 58.3％. It is an effective method to build error model of random drift for FOG.
Random drift is one of the main errors in fiber optical gyroscope (FOG). Modeling and revising random drift is an efficient method to improve system accuracy in filtering. Based on Allan variance, the differential equation model(DEM) of random drift is required to solve the shortages of traditional models which are time-consuming and over sensitive. In this paper, the power spectrum density (PSD) function was exploited to figure out the stochastic differential equation (SDE) of every noise. By using Allan variance to calculate the parameter of every noise and substituting the parameter in SDE which was driven by white noise, the random drift model was established. Experiment result illustrates that, the fitting error of random drift is no more than 8.6%，far lower than the traditional one of 58.3％. It is an effective method to build error model of random drift for FOG.
2014, 35(3): 552-556.
Abstract:
To demonstrate high-power, broad-bandwidth and spectrum-flattened L-band erbium-doped fiber superfluorescent source (SFS), four different corepumped dual-stage double-pass configurations were proposed based on polarization multiplexing technique, offering Walt-level pump power. The impact of the pumping ratio and fiber length arrangement on the spectrum characteristics including flatness, bandwidth, center wavelength and total output power were numerically investigated with the same total length and total pump power. It shows that four structures can basically work at L band（1 565 nm~1 610 nm） and the bandwidth is less sensitive to structure change. Only the backward-pumped dual-stage double-pass configuration can simultaneously provide high flatness and high output power. A SFS with 314 mW output power, 32.41 nm bandwidth, 1 584.84 nm center wavelength and 2.23 dB flatness can be demonstrated while the total pump power and the pump powers of the first and second stages are 750 mW,300 mW and 450 mW，respectively, and the total fiber length, the fiber lengths of the first and second stages are 21 m,18 m and 3 m，respectively.
To demonstrate high-power, broad-bandwidth and spectrum-flattened L-band erbium-doped fiber superfluorescent source (SFS), four different corepumped dual-stage double-pass configurations were proposed based on polarization multiplexing technique, offering Walt-level pump power. The impact of the pumping ratio and fiber length arrangement on the spectrum characteristics including flatness, bandwidth, center wavelength and total output power were numerically investigated with the same total length and total pump power. It shows that four structures can basically work at L band（1 565 nm~1 610 nm） and the bandwidth is less sensitive to structure change. Only the backward-pumped dual-stage double-pass configuration can simultaneously provide high flatness and high output power. A SFS with 314 mW output power, 32.41 nm bandwidth, 1 584.84 nm center wavelength and 2.23 dB flatness can be demonstrated while the total pump power and the pump powers of the first and second stages are 750 mW,300 mW and 450 mW，respectively, and the total fiber length, the fiber lengths of the first and second stages are 21 m,18 m and 3 m，respectively.
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