2015 Vol. 36, No. 4

OE System and Engineering
FEM modal analysis and test validation for sight-stabilization turret structure
Song Dong-sheng, Yang Yuan-cheng, Gao Ya, Wang Jing, Bu Zhong-hong
2015, 36(4): 497-502. doi: 10.5768/JAO201536.0401001
The structure dynamic effect is a key factor to affect the stabilization accuracy. Currently, the most effective method to analyze the structure dynamics is to combine finite-element modal(FEM) analysis and experimental modal analysis. A two-axis and four-frame structure of a sight-stabilization system was taken as the research object of this paper. Firstly, the modal pre-analysis was completed using FEM. According to the vibration mode characteristics of simulation results, the modal for the out frames of two-axis and four-frame structure was tested. The natural frequencies, vibration modes and modal damp ratio were listed for the former 8-order modals. The mutual authentication between modal simulation and test shows that the accuracy level of the natural frequencies for two-axis and four-frame structure can be lower than 15% using FEM and the relevance of the vibration modes are good in the case of enough test point density.
Methods for testing disturbance isolation of EO system
Shou Shao-jun, Liu Jing-li, Guo Xin-sheng
2015, 36(4): 504-508. doi: 10.5768/JAO201536.0401002
According to the derived calculation formula of disturbance isolation of optoelectronic tracking device,two methods for testing disturbance isolation were given: simulation environment test scheme and platform test scheme. Through analyzing the experimental data of the two testing methods, the advantages,disadvantages and their applications were elaborated.It was pointed out that the bandwidth of speed loop was the key factor to influence the disturbance isolation ability of system under the double-loop control mode. Additional, the optimization solution for control mode of disturbance isolation was suggested to add.
Novel measurement method of azimuth for photoelectric equipment
Liang Qing-qian, Tao Yu, Zhou Li-hua, Liu Yu
2015, 36(4): 509-512. doi: 10.5768/JAO201536.0401003
Aiming at the photoelectric equipment working on the stationary base mast,a low cost measurement method of azimuth was presented. The azimuth variation of photoelectric equipment was computed by using two dip instruments to measure the angular velocity of the equipments pitch axis and roll axis and using one gyroscope to measure the angular velocity of the yaw axis. The real-time azimuth was computed when the beginning azimuth was gotten. The theory and system construction of the method were analyzed. The results of prototype test show that when using 0.01 dip instruments and 0.015/h gyro,the real-time azimuth precision is 0.09.
Dual-band common aperture optical system for infrared camera
Tang Tian-jin, Li Yan
2015, 36(4): 513-518. doi: 10.5768/JAO201536.0401004
Dual-band/dual-channel imaging system can effectively improve the detection and identification capability for infrared camera. A dual-band catadioptric optical system was designed, in which the mid-wave band and long-wave band could image at the same time. The Cassegrain optics system is shared by two channels, the dichroic lens and independent relay lens are adopted, and by combining with the secondary imaging technology, 100% cold stop efficiency could be realized. The focal length for two channels is 800mm and the wavelengths are 3.7 m~4.8 m and 7.7 m~10.3 m, respectively,the relative aperture is 1/2.3 for mid-wave band and 1/2.8 for long-wave band with the field of view of 1.2. The modulation transfer functions of each band at respective fields are all near the diffractive limit, which satisfies the needs of practical applications.
Reverse engineering application of 3D optical scanning technology
Zhang De-hai, Li Yan-qin, Xie Gui-zhong, Yang Yong, Wang Liang-wen
2015, 36(4): 519-525. doi: 10.5768/JAO201536.0401005
The 3D scanning measurement data have the problems including bigger density of the point clouds, much complicated operation and longer calculation period caused by inevitable noise points, flying spots, overlapping point clouds restricted by environment and other objective conditions, when the original point clouds are obtained. The 3D optical scanning technology in reverse engineering has the function for changing 3D solid information into digital signal that a computer can be directly handled, providing convenient and fast means of real digital model.Based on this, that main equipment, the commonly-used software, using method and solid modeling software related to 3D scanning technology were studied,as well as the basic theory and math model of 3D optical scanning technology. Scanning strategy was formulated combined with XJTUOM. Moreover,a certain type of belt wheel and shock absorber tray were taken as examples to prove the applicability of 3D scanning technology in reverse engineering practice. Results show that the scanning similarity accuracy is 98% close to original model.
Research on optical alignment technology for Cassegrain system
Zhang Xiang-ming, Jiang Feng, Kong Long-yang, Li Yu-xi, Liu Yi-chen, Zhang Jin-liang, Zhao Hong-jun, Wang Zhi-chao, Zhong Li-ping
2015, 36(4): 526-530. doi: 10.5768/JAO201536.0401006
The centering alignment scheme for the aspherical primary mirror of Cassegrain system in the use of three-coordinate measuring machine was presented, which could achieve rapid centering and meet the accuracy requirement in the process of computer-aided alignment. In order to reduce the mirror deformation because of adhesive stress and thermal stress to a minimal range, the microstress adhesive manner was used to position the mirrors, especially for the primary mirror of 300mm aperture. The wavefront information of the Cassegrain system proposed in this paper was obtained with Zygo interferometer. With the primary aberration converted by the wavefront aberration measured above, the computer-aided alignment of the Cassegrain system could be completed according to the corresponding relationship between the misalignment and aberration of optical system. After alignment,the system root-mean-square(RMS) value reached 0.1,the solution was less than 1.The testing results show that the imaging quality of the system is close to the theoretical diffraction value,the centering alignment can achieve rapid centering and meet the accuracy requirement in the process of computeraided alignment.
Integral field spectroscopy imaging technology
Zhang Tian-yi, Ji Hang-xin, Hou Yong-hui, Hu Zhong-wen, Wang Lei
2015, 36(4): 531-536. doi: 10.5768/JAO201536.0401007
Based on the development trend of integral field technique locally and internationally, the experimental platform for an integrated field 3-D spectral technique was set up. The design and manufacture for the slicing mirror of integrated field unit(IFU)was carried out. A performance testing method and a calibration method were studied. An IFU which divided the telescopic field of view into 9 sub-fields was designed, A performance analysis was conducted by simulating the input end of the telescope. Furthermore,the 3-D spectral data was processed and calibrated.Results show that the stray light can be controlled well and the overall optical efficiency is better than 40%.
OE Information Acquisition and
Super-resolution video restoration system based on ZedBoard
Wang Yuan-yuan, Su Bing-hua, Qiu Wen-sheng
2015, 36(4): 537-542. doi: 10.5768/JAO201536.0402001
In order to realize real-time super-resolution restoration of video image, a super-resolution video restoration system based on the ZedBoard programmable system on a chip was designed. The system includes the USB camera video acquisition based on video for Linux 2 (V4L2), the super-resolution restoration algorithm based on wavelet transform, and the graphical user interface and video output based on Qt. The bilinearity, double cube and wavelet transform methods were used to restore Lena image, and the peak signal noise ratio (PSNR) values between the original image and the restored images respectively are 29.516, 29.843 and 31.368,respectively. The experiment results show that the wavelet transform method proposed is better than traditional interpolation methods, and the super-resolution video restoration system based on ZedBoard is effective.
Time-domain optical coherence tomography system based on stationary wavelet transform
Luo Man-ting, You Teng-fei, Zhang Qiu-kun, Zhong Jian-feng, Zhong Shun-cong
2015, 36(4): 543-549. doi: 10.5768/JAO201536.0402002
Based on the balanced detection and stationary wavelet transform (SWT) algorithm, a broadband low coherent white light source with center wavelength of 700 nm was employed to set up a time-domain optical coherence tomography (TDOCT) system in free space. The resolution of the developed OCT system was down to 0.93 m and it was applied to nondestructive evaluation of plastic sheets and transparent-tape multi-layered thin-film structures.The imaging enhancement methods in the process of OCT images were compared. To resolve the problem of unsatisfactory reconstruction results using current algorithms, the SWT decomposition algorithm was introduced to deal with the OCT images of the multi-layered structures. The experimental results show that this SWT-based method could extract more distinct interface interference signal from the SWT detail coefficients and therefore the interface imaging quality of multi-layered structures could be enhanced.
Auto-focus windows selection algorithm for optical microscope
Peng Guo-jin, Yu Zhen-ming, Yu Jian-hai
2015, 36(4): 550-558. doi: 10.5768/JAO201536.0402003
Aiming at the problem that traditional auto-focus windows selection algorithms are susceptible to content distribution, impurities and noise, an auto-focus windows selection method depending on variation of content pixels is proposed. The method takes a weighted average of the amount of gray-leveldifference pixels and the amount of edge pixels as the number of content pixels, then measures image content of sub-block in blurred state and divides focusing windows by the variation of content pixels. In the meantime, the proposed method estimates content distribution information of original image using image content of each sub-block in downsampling image. Besides, the proposed method detects out-of-blurred areas using combined detection of local standard deviation and sharp edge pixels, and it effectively excludes the misjudgments of focal plane caused by the impurities on coverslips. Compared with the traditional auto-focus windows selection algorithms, the proposed method could obtain effective focusing windows for each microscopic sequence varying in richness and distribution of the image content, the corresponding mean gradient of pixels is higher, and the acquired focus measure curve has fewer local extreme values and sharp performance, therefore, the proposed method has more advantages in success ratio and robustness.
Optical Metrology and Measurement
Technique of mirror spectrum reflectivity measurement in situ under simulated space environment
Yang Lin-hua, Xu Jie, Jiang Shan-ping
2015, 36(4): 559-565. doi: 10.5768/JAO201536.0403001
In order to study the technique for spectrum reflectivity measurement of calibrated optic system in vacuum and low-temperature environment, a small test system which was applied to measure the spectrum reflectivity of the off-axis parabolic mirror in situ was built. The system consists of solar simulator, collimating lens, folding mirror, off-axis parabolic mirror, spectrometer and control system. The measurement was carried out in atmospheric environment and simulated space environment,respectively. The measured spectrum was from 350nm to 950nm. The average spectrum reflectivity of the mirror was 0.882 in atmospheric environment, it was 0.863 in simulated space environment. When the mirror went back in the atmospheric environment, the average spectrum reflectivity of the mirror was 0.883. In the test, the measurement repeatability was 1.1%, the uncertainty was less than 2.4%. The test results show that the spectrum reflectivity of the off-axis parabolic mirror decreases in simulated space environment, and increases when the environment is back to the atmospheric environment.
Wavefront fitting with interpolation to detect optical surface deviation
Guo Qiao-shuang, Wang Min, Liao Xiao-dong
2015, 36(4): 566-571. doi: 10.5768/JAO201536.0403002
In order to realize on-line automatic detection of surface form deviation of spherical optical elements based on the existing optical detection system, the steps of image processing of interferogram were introduced and the method of fitting the wavefront of interferograms was mainly studied.Firstly the introduction of interferogram pretreatment process was presented. According to the optical elements which were mostly circular, the boundary circle of interferogram was fitted by the least-square method, so as to determine the circle center and raduis accurately. Then the algorithm of wavefront fitting with multi-quadric(MQ) interpolating function was analyzed.After the wavefront of optical elements was reconstructed, the values of EPV and ERMS were calculated. Finally the comparative analysis of the processing results of national standard interferogram was presented.Experimental results indicate that the wavefront fitting accuracy can be improved through boundary processing,the wavefront can be reconstructed ideally by fitting with MQ interpolation method,moreover, the measurement error can be controlled in 0.2 range for national standard interferogram, and in 0.03 rang for Zygo interferometer result, which can satisfy the requirements of the optical element on-line measuring precision.
Calibrating method traced to cryogenic absolute radiometer for solar irradiance spectroradiometer
Zhang Yan-na, Zheng Xiao-bing, Li Xin, Wei Wei, Pang Wei-wei
2015, 36(4): 572-579. doi: 10.5768/JAO201536.0403003
To improve the observation precision of solar spectrum, a calibration method based on standard detector for a novel prism dispersion solar irradiance spectroradiometer was developed in the visible-near infrared bands. With the standard irradiance detector, and the uniform irradiance source acquired from the tunable laser-illuminated integrating sphere, the spectral irradiance responsibility of the spectroradiometer was traced to the cryogenic absolute radiometer in the 10 bands. The uncertainty of this method is better than 0.95%. The deviations with the standard lamp calibratin method traced to the blackbody are less than 4.67%, which validate the rationality of the radiometer standard transfer method for solar irradiance spectroradiometer.
Influence of incident angle of pumped beam on parametric down conversion
Xia Mao-peng, Gao Dong-yang, Li Jian-jun, ' Hu You-bo, Zheng Xiao-bing
2015, 36(4): 580-583. doi: 10.5768/JAO201536.0403004
Calibration for the quantum efficiency of detectors is a new research subject. Spontaneous-parametric-down-conversion (SPDC) has the disadvantages of low conversion efficiency and signal noise ratio (SNR). In order to improve the power of correlation photon, a shortwave laser was used to pump the periodically poled lithium niobate (PPLN) crystal. The influence of incident angle on the conversion efficiency, spatial distribution, bandwidth and crystal poling period was analyzed based on numerical simulation. It is proved that the conversion efficiency is high, the bandwidth of correlation photon is narrow and the divergence angle is large for normal incident pumped beam. While the incident angle increases, the conversion efficiency becomes lower, the bandwidth and divergence angle are smaller and the position of central wavelength can shift. The result presented is a theoretical support for correlated photon detection and highly accurate calibration for quantum efficiency of detector.
3D shape measurement system based on fringe projection in 4-step phase shifting
Shang Zhong-yi, Li Wei-xian, Dong Ming-li, Duan Liang-jun
2015, 36(4): 584-589. doi: 10.5768/JAO201536.0403005
In order to achieve the measurement of objects with significant jumping surface profile,a three-dimensional shape measurement system based on fringe projection in four-step phase shifting was established and the adopted four-step phase-shift measurement algorithm was studied. After introducing the principle of four-step phase shifting, a measurement algorithm for the apparent jumping faces was established, by taking a triangular pyramid rubber with significant jump faces for example. Firstly, the average gray image was calculated through a sum of the four phase shifting images and divided by four. Secondly,the binaryzation of average gray image was processed to position the obvious jumping surface or shadows. Last but not least, the convolution of binary image with wrapped phase map was done and then the wrapped phase map was unwrapped to get the correct continuous phase and reconstruct the 3D shape of the object. Experiments were taken to calculate the volume of the triangular pyramid rubber by shape measurement with the proposed algorithm. Experimental results show that the mean precision of volume measurement is 0.47%, which proves the effectiveness of the proposed algorithm and its good precision.
Method for improving precision of interferometric phase-recognization
Yang Lian-gen, Liu Bing-kang, Wang Xuan-ze, Zhai Zhong-sheng
2015, 36(4): 590-595. doi: 10.5768/JAO201536.0403006
For monochromatic light interferometry under open-loop phase shifter, a high precision method for phase recognization was developed to satisfy four-step phase-shift algorithm. Firstly two pixels with suitable phase-difference were selected from the interference field, and the interference equations of the two pixels gray values were established in one phase-shifting cycle. Secondly, the interference equations parameters could be obtained by using ellipse fitting algorithm, and the point-to-point driven step length and sequence phases could be determined through back calculation of sequence phases. Then four interference gray scales meeting the four-step phase-shift algorithm were designed and calculated through Lagrange parabolic interpolation, which were used to calculate the initial phase of every pixel. Finally, the surface topography was calculated through multi-wavelength algorithm and the measurement errors were analyzed. Experimental results show that the Ra value of square wave specimen with multiple grooves is 0.4390m, and the measurement error is 0.23%. This method decreases the requirement for hardware and environment. It can meet the high precision demands of surface topography measurement.
New testing method of aging LED lamp online
Wang Qiao-bin, Weng Ji-zhao, Li Mao-wen, Zhang Pei-qiang
2015, 36(4): 596-599. doi: 10.5768/JAO201536.0403007
In order to solve the problems of complex operation,low degree of automation,discontinuous monitoring for aging process and the difficult to precisely obtain the failure node and other issues, commonly in the aging test for LED lamp life, we proposed a new method of on-line automatic aging testing, and developed the automation on-line aging test system of LED lighting, the whole process was controlled by computer programming and out of manual operation.The system can monitor the indices such as luminous decay and electrical parameters continuously during the aging process of LED lamp realtimely, it can realize the automation of LED lighting lamp aging test.
Optical Element and Fabrication
Design of uniform LED light source
Xiao Shao-rong, Li Man
2015, 36(4): 600-605. doi: 10.5768/JAO201536.0405001
In order to meet the requirements of uniform lighting in visibility meter using the digital camera method and improve the uniformity of LED lighting, a design method based on digital image analysis technique was presented. Firstly,according to the measurement of the brightness distribution of a single LED in the module area, the distribution function was fitted. Then by using the principle of brightness superposition, the arrangement of the multi-LED module with the lowest inhomogeneity or the best size of a fixed uniform was calculated. Furthermore,the simulated data and the measured data were comparative analyzed. Experimental results show that the uniformity is improved significantly in the arrangement of multi-LED module proposed in this paper, compared with in unilateral arrangement. The highest uniformity is above 95%.
Optimized double-sided hemispherical pattern design on patterned sapphire substrate for flip-chip GaN-based LED
Che Zhen, Zhang Jun, Yu Xin-yu, Chen Zhe
2015, 36(4): 606-611. doi: 10.5768/JAO201536.0405002
In order to improve the light extraction efficiency of GaN-based light-emitting diodes(LEDs), a model was built to optimize the double-sided hemispherical patterned sapphire substrate(PSS) for highly efficient flip-chip GaN-based light LEDs,and an optical simulation was conducted to study how light extraction efficiency changed with the change in the parameters of the unit hemisphere for flip-chip LEDs fabricated on hemispherical PSS. Results show that the light extraction efficiency of flip-chip LEDs can be enhanced by the optimized hemispherical PSS by over 50.8% and is approximately 115.3% higher than that of flip-chip LEDs with non-PSS when the radius is 3m and the distance is 7m. This results confirm the high efficiency and excellent capability of the optimized hemispherical PSS pattern to improve LED efficacy.
Design of fuzzy controller for high-powerLED cooling system
Wang Li, Liu Yong-cheng, Wang Zhi-bin
2015, 36(4): 612-617. doi: 10.5768/JAO201536.0405003
Based on the chip-on-board(COB) packaging LED chip, the thermal resistance model of LED was analyzed,and the substrates temperature when the junction was working at the ideal temperature was deduced. For the heat dissipation problem existing in the high-power LED, a fuzzy controller based on the double-in and double-out water jet cooling system developed by the research group was designed. The temperature change and temperature change rate were chosen as the inputs of the controller,and their ranges were described. According to the designed controller, programs were written and downloaded to the control chip. Through experiment under the environment temperature being 20℃, the LEDs substrate temperature is between 35.5℃ and 36.5℃, which ensures the light working stable. It provides a controller design for high-power LED heat dissipation system and has some practical significance.
Phase shifter based on bacteriorhodopsin film and its application
Yang Chen-xiao, Han Jun-he, Yao Bao-li, Li Ruo-ping, Huang Ming-ju
2015, 36(4): 618-623. doi: 10.5768/JAO201536.0405004
A phase shifter based on photoinduced anisotropy of bacteriorhodopsin film was designed and applied in phase-shifting interferometry. Photoinduced anisotropy in bacteriorhodopsin film is based on photoanisotropic selective bleaching of bacteriorhodopsin molecules under polarized excitation light. It is modulated by the polarization orientation of the linearly polarized excitation light. While it passes through the anisotropic bacteriorhodopsin film, a circularly polarized light is converted into an elliptical polarized light. The polarization properties of the elliptical polarized light are dependent on the polarization orientation of the linearly polarized excitation light. A phase shifter based on the photoinduced anisotropy of bacteriorhodopsin film was presented theoretically by Jones matrix and experimentally. Phase shift is controlled by the polarization orientation of the external excitation light, thus, it can be controlled without moving parts inside the Mach-Zender interferometer, which contributes to the mechanical stability of the system. Least square method, which bases on four-step phase-shifting interferometry, was applied to the reconstruction of the profile of phase object. The experiments were conducted to verify the feasibility of this phase shifter on the phase-shifting interferometry.
Luminescence property of nano-flower-like CuCl2 film based on AAO template
Ren Jun-ying, Wang Kai-ge, Wei Hong-duo, Wu Jian-guo, Wu Qing-qing, Ba Han-qing, Bai Jin-tao
2015, 36(4): 624-629. doi: 10.5768/JAO201536.0405005
One novel kind of nano-flower-like film was firstly fabricated with the direct deposition method, that was, the CuCl22H2O aqueous solution was deposited on the top surface of porous anodic aluminum oxide(AAO) film. The morphology of this nano-flower-like membrane was investigated by the field emission scanning electron microscopy, and the constituent parts were analyzed with the X-ray photoelectron spectroscopy, all the results demonstrated that nanoflower-like film was CuCl2. Then, the characteristic photo luminescence spectra of the AAO film coated with nano-flower-like CuCl2 membrane were measured at room temperature. Results show that the position center of excitation is 290 nm and the emission center is 415 nm, these data are the same as the values of AAO film; however, it is excited that the intensity of luminescence increased significantly,from 127 cd to 183 cd.Furthermore, comparing with the excitation and emission spectra of CuCl2 powder and AAO film, the reason that improving the luminous intensity of the AAO film coated nanoflowerlike membrane is the morphology of CuCl2 nano-structures.
Infrared Technology
Detection of small, low contrast targets based on adaptive frequency filter
Zhang Hua-liang, Xie Yong-jie, Zhang Song, Zhao Yan, Jiao Jiao
2015, 36(4): 630-634. doi: 10.5768/JAO201536.0406001
Detection of small, low contrast infrared targets in complex backgrounds requires a significant improvement in the detective ability of photoelectric theodolites. An adaptive Gaussian high-pass filter was proposed based on a description of the dagree of infrared background complexity. The noise of images was reduced by updating a medial filter, and the degree of background complexity was quantitatively described by variance-weighted information entropy. The cutoff frequency of the filter was automatically adjusted according to the degree of background complexity.This technique resulted in the automatic detection of small, low contrast targets in different infrared backgrounds. The new method was verified by experiment and the result shows the new method can effectively detect small, low contrast targets in different infrared backgrounds.
Spectral characteristics of MWIR band-pass filters at cryogenic temperature
Chen Feng-jin, Ma Sheng-xi, Su Xian-jun, Jing Ling
2015, 36(4): 644-647. doi: 10.5768/JAO201536.0406002
In order to research the reliability of filters at cryogenic temperature, Ge-based and sapphire-based mid-wave infrared (MWIR) band-pass filters were coated, and the experiments at cryogenic temperature for 5 min,15 min,25 min,35 min and even more than 300 min were done,respectively, the transmittance curves were showed. Furthermore, the impact of cryogenic temperature on the spectral characteristics and fastness after were studied.The transmittance of passband zone reduces with the time increasing at cryogenic temperature, and there is a small shift of 13nm for center wavelength, resulted from the relative variation of the high and low refractivities of deposited coatings which can induce the ratio between center and cut-off wavelengths to change. Compared to the sapphire substrate,Ge substrate is more sensitive to temperature,so the fall range of transmittance shows obvious(about more than 10%)when the bandpass filters transit from room temperature to cryogenic temperature. The fastness of both the Ge-based and sapphire-based MWIR band-pass filters have never been damaged at cryogenic temperature for no more than 300min.
Laser Technology
Single frequency laser multiple feedback effects based onray tracing method
Zeng Zhao-li, Du Shuang-ge, Zhang Xiao-jun, Liu Yuan-sheng, Shang Yong-bing, Li Wei-na, Zhang Min
2015, 36(4): 639-643. doi: 10.5768/JAO201536.0407001
A ray tracing model of multiple optical feedback with asymmetric plane-concave cavity was presented. With this model, the generation mechanism of highresolution fringes in single frequency laser multiple feedback was elaborated. Also, the affecting factors of fringe-shape were analyzed, including tilted angle, curvature, reflectivity of feedback mirror and length of external cavity. In addition, the effective feedback order and coupling efficiency of feedback beams with different tilted angles were obtained. Theory analysis and experimental results show that the high-resolution feedback fringes without envelopment can be obtained when the tilted angle is 1.7. In particular, the resolution of feedback fringes can be /50, which is very important to explore high-precision displacement measurement system.
Analysis and calculation of influence of atmospheric turbulence onlaser irradiation accuracy
Lu Hong-qiang, Zheng Zhen-shan, Zhang Jing-yue, Zhou Lei
2015, 36(4): 644-647. doi: 10.5768/JAO201536.0407002
In order to investigate the effects of atmospheric turbulence on the designation accuracy of the laser designator, the designation accuracy was deduced and evaluated, which was changed with designation range, atmospheric turbulence and beam radius. The results show that the designation error would be increased significantly as designation range and atmospheric turbulence increase, as well as the receiver aperture decreases. The designation error induced by atmospheric turbulence is about 10 rad~30 rad.
Design and application of 500 nm bandwidth chirped mirror pair
Wang Jia-jie, Yang Gang, Liu Wen-jun, Li Jian
2015, 36(4): 648-651. doi: 10.5768/JAO201536.0407003
A chirped dielectric multilayer mirror pair with controlled dispersion in the wavelength range 600 nm~1100 nm with 825 nm centre wavelength was designed and fabricated. The group delay dispersion of the mirror pair is about -100 fs2. The reflectivity of the mirror is 99% and the theoretical group delay dispersion ripple is less than 50 fs2 in the working spectral range. The mirror pair was used to compensate the 10.3 fs ultra-short pulse passed through 0.5 mm lithium triborate (LBO) crystal and the frequency-resolved optical gating technique was used to measure pulse,then the 10.3 fs pulse was broadened to 39.6 fs due to the dispersion of LBO crystal.Experimental results show that the full width at half summit is 11.6fs after one bounce dispersion compensation of the chirped mirror pair;and the broaden pulse is compressed to 10.7 fs by using two bounces dispersion compensation.
Fiber Sensing and Optical Communication
Measurement of cladding thickness of side-polished fiber based on digital holography
Wang Feng, Ma Jie, Chen Zhe, Zhong Jin-gang, Yu Jian-hui, Zhong Yong-chun
2015, 36(4): 652-659. doi: 10.5768/JAO201536.0408001
A novel method to measure the cladding thickness of side-polished fiber (SPF) was demonstrated by using the digital holographic imaging technology. Using angular spectrum method and accurate least-squares phase unwrapping method,SPFs distribution of phase was reconstructed. Based on the reconstructed distribution of phase, the cladding thickness of SPF could be directly measured. Compared to the results measured by scanning electron microscope (SEM), the relative error is less than 0.5%. This is a non-destructive, real-time and direct measurement, it can reduce the errors due to fibers asymmetries and edge diffraction. This method could also be used to measure other special optical fibers such as photonic crystal fiber and nano-fiber.
Mixed interferometric distributed fiber optic sensor PGC demodulation module design and experimental data analysis
Zhu Jun, Wang Qiang, Gu Xiao-hong, Yang Qi-hua
2015, 36(4): 660-665. doi: 10.5768/JAO201536.0408002
The demodulation technology based on the Mach-Zehnder and Sagna mixed interferometer distributed optical fiber leak detection system was studied.The theory of phase generated carrier (PGC) demodulation technology was researched and analyzed. According to the characteristics of the selected leak distributed optical fiber sensor, we designed and tested the hardware circuit of PGC demodulation. The experiment signals to be measured are 0~50 kHz, the carrier frequency is 300 kHz and the cut-off frequency is 50 kHz. After phase shifting the correlation coefficient of signals to be measured is 0.95 and the harmonic distortion is less than 3%, the absolute positioning error of demodulation positioning system at the leak location of 7.865km is 235m, the relative positioning error is 2.35%.This demodulation positioning system has stability and anti-interference performance.