Contents
2008
Volume: 28 Issue 3
38 Article(s)
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Fiber Optics and Optical Communications
Propagation Characteristics Analyses of Step-Index Fibers with Gain or Loss Using Davidenko′s Method
Zhao Chujun, Zhou Ping, Zeng Xiahui, Tang Zhixiang, and Fan Dianyuan
Gain and loss characteristics play important roles for the fiber. Davidenko′s method is adopted to analyze characteristics of optical fibers with complex refractive index. The step-index fibers with complex refractive index in the core or cladding are discussed. Numerical results are in good agreement with those obtainGain and loss characteristics play important roles for the fiber. Davidenko′s method is adopted to analyze characteristics of optical fibers with complex refractive index. The step-index fibers with complex refractive index in the core or cladding are discussed. Numerical results are in good agreement with those obtained by exact analysis. For the fibers with complex refractive index in the core, the gain deviation of HE11 and LP01 modes is about 0.6%. For the fibers with complex refractive index in the cladding, the above deviation is about 2%. In practical work, to get more accurate results, full-vector complex characteristic equation must be considered, especially for fiber with cladding of gain or loss..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 28, Issue 3, 409 (2008)
Linearly Chirped Fiber Gratings Using Uniform Phase Mask
Li Bin, Liu Yan, Tan Zhongwei, Xu Ou, Lu Shaohua, and Jian Shuisheng
A novel linearly chirped fiber grating was analyzed and fabricated by using uniform phase mask instead of chirped mask. The chirp of the grating is realized by precisely setting the distance between the fiber and the phase mask at every point of the fiber. The spectral characteristic and delay characteristic of such a A novel linearly chirped fiber grating was analyzed and fabricated by using uniform phase mask instead of chirped mask. The chirp of the grating is realized by precisely setting the distance between the fiber and the phase mask at every point of the fiber. The spectral characteristic and delay characteristic of such a chirped fiber grating were analyzed. And the influence on the grating by refractive index modulation variation caused by the variation of distance between the fiber and phase mask was also analyzed. In experiments we derived linearly chirped fiber grating by putting the fiber on the curved face behind the uniform phase mask to get ultraviolet light exposure. The fabricated chirped fiber grating has -1102 ps/nm dispersion, and time delay ripple of 17 ps. Gratings with different chirp with one uniform phase mask conveniently by only changing the curve function of the fiber, can be fabricated..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 28, Issue 3, 414 (2008)
Mechamism of Radiation Effects on Fiber Optic Gyros
Liu Dewen, Xiao Wen, and Wei Bo
The polarization-maintaining fiber coil in a fiber optic gyro (FOG) is a sensitive element, its loss will increase when it works in radiation environment such as the spatial, and the performance of FOG also degracles. The spatial radiation enviroment is simulated with 60Co as the radiation source, and influences of spaThe polarization-maintaining fiber coil in a fiber optic gyro (FOG) is a sensitive element, its loss will increase when it works in radiation environment such as the spatial, and the performance of FOG also degracles. The spatial radiation enviroment is simulated with 60Co as the radiation source, and influences of spatial radiation on elements of fiber optic gyro especially the polarization-maintaining fiber, were researched based on lots of simulation experiments of spatial radiation. It is found the polarization-maintaining fiber suffers from the spatial radiation most seriously, and the radiation effect mechanism of polarization-maintaining fiber has been proposed. Furthermore, the radiation effect on fiber opti gyro owing to the increase of loss in polarization-maintaining fiber under radiation has been discussed, which provides theoretical foundation for radiation hardening design of fiber optic gyro..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 28, Issue 3, 419 (2008)
A Novel Multi-Rate All-Optical Packet Clock Recovery System of Return-to-Zero Code
Wang Wenrui, Yu Jinlong, Zhang Aixu, Han Bingchen, Hu Hao, Zhang Litai, and Yang Enze
We propose a novel, economical multi-rate all-optical packet clock extraction scheme of return-to-zero code, which comprises a Fabry-Pérot (F-P) filter, a semiconductor optical amplifier (SOA) and polarization dependent delay interferometers (PDIs). Fabry-Pérot (F-P) filter with low finesse and low free spectWe propose a novel, economical multi-rate all-optical packet clock extraction scheme of return-to-zero code, which comprises a Fabry-Pérot (F-P) filter, a semiconductor optical amplifier (SOA) and polarization dependent delay interferometers (PDIs). Fabry-Pérot (F-P) filter with low finesse and low free spectral range was used to directly extract the multi-rate packet clock from the packet data stream, which ensures that the clock establishes and vanishes quickly. Different PDIs, combined with F-P filter was used to form comb filters with different FSRs to extract mult-rate packet clock. The packet clock then goes into SOA to reduce the low-frequency amplitude noise and temporal fluctuation with the self-gain modulation effect of SOA. We demonstrate instantaneous 10 GHz, 20 GHz and 40 GHz packet clock extraction experimentally by switching different PDI and forming filters with different FSR. Multi-rate packet clock signals with high quality and low temporal fluctuation are obtained..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 28, Issue 3, 423 (2008)
Known-Plaintext Attack on Optical Cryptosystem Based on Projection-Onto-Constraint-Sets Algorithm and a 4f Correlator
Wei Hengzheng, and Peng Xiang
The security of the cryptosystem based on projection-onto-constraint-sets (POCS) and a 4f correlator is examined. A method of known-plaintext attack based on phase retrieval algorithm from two-intensity information is presented. In the field of information security the cryptosystem based on POCS and the 4f correlator iThe security of the cryptosystem based on projection-onto-constraint-sets (POCS) and a 4f correlator is examined. A method of known-plaintext attack based on phase retrieval algorithm from two-intensity information is presented. In the field of information security the cryptosystem based on POCS and the 4f correlator is a typical approach. But its decryption system can be equivalent to the standard 4f system and the encryption and decryption keys are identical. So this linearity characteristic opens avenues of attacks. With the known-plaintext attack method, an attacker is able to break down the cryptosystem by only a pair of input phase data and output intensity data..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 28, Issue 3, 429 (2008)
Transient Characteristic Testing of Fiber Optic Gyro Fiber Coil Based on Temperature ExcitationLi Maochun
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
A fiber optic gyro (FOG) uses Sagnac effect in fiber coil to detect rotation component about a sensing axis that is perpendicular to the plane of the fiber coil. The fiber coil is the key component of FOG, and its winding quality affects the integrated performance of FOG directly, so it is necessary to roundly test theA fiber optic gyro (FOG) uses Sagnac effect in fiber coil to detect rotation component about a sensing axis that is perpendicular to the plane of the fiber coil. The fiber coil is the key component of FOG, and its winding quality affects the integrated performance of FOG directly, so it is necessary to roundly test the fiber coil winding quality. In view of the limitation of present testing methods of FOG fiber coil, a transient characteristic testing method of FOG fiber coil based on temperature excitation was proposed, which could completely represent the winding quality of fiber coil. A computational three-dimensional fiber coil model was established. With finite element analysis technique, numerical simulations were carried out to quantitatively analyze the influence of fiber coil unsymmetry and sectional temperature excitation position accuracy on the transient response of fiber coil. At the meantime, the corresponding temperature excitation experiments were made. The experimental results are in good agreement with numerical simulation results. Finally, the transient characteristic testing method is identified feasible and acceptable by theory and experiment..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 28, Issue 3, 435 (2008)
Fourier Optics and Signal Processing
Suitability of Different Sampling Methods for Digital Simulations of the Optical Diffraction
Guo Chengshan, Li Chuantao, Hong Zhengping, and Liu Tingting
Sampling methods for digital simulations of the optical diffraction based on scalar diffraction theory and fast Fourier transform are analyzed. There exist three sampling methods according to the sampling objects: the transfer function sampling, the point-spread function sampling and the weighting function sampling. ThSampling methods for digital simulations of the optical diffraction based on scalar diffraction theory and fast Fourier transform are analyzed. There exist three sampling methods according to the sampling objects: the transfer function sampling, the point-spread function sampling and the weighting function sampling. Theoretical analysis reveals that these sampling methods hold true in different ranges of diffractive distances, which can be distinguished by a feature diffraction distance. Under definite sampling space and sampling number, the sampling methods hold true only when the diffraction distance is smaller than, larger than and equal to the feature distance, respectively. For demonstration of the correctness of the theoretical analysis, a digital simulation based on Matlab solfware and an experimental result are given and discussed. Finally, an adaptive sampling algorithm is proposed for reconstruction of a digital hologram, which could be suitable for any diffraction distances..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 28, Issue 3, 442 (2008)
Image Processing
An Image Fusion Algorithm Using Region Segmentation and Contourlet Transform
Ye Chuanqi, Miao Qiguang, and Wang Baoshu
An image fusion algorithm using region segmentation and contourlet transform is proposed. Firstly, region segmentation is done for source images, and ratio of region energy (RRE) and ratio of region sharpness (RRS) are presented to measure and extract region information. Then multiscale decomposition of the source imagAn image fusion algorithm using region segmentation and contourlet transform is proposed. Firstly, region segmentation is done for source images, and ratio of region energy (RRE) and ratio of region sharpness (RRS) are presented to measure and extract region information. Then multiscale decomposition of the source images is carried out with the nonsubsampled contourlet transform. The high-frequency coefficients are fused with larger absolute value operator, and the low-frequency coefficients are fused with the region-based fusion rules and operators proposed. Finally the fused coefficients are reconstructed to obtain the fusion image. The fusion experiment for infrared and visible images is taken, and comparison between pixel-based à trous wavelet transform and contourlet transform is given. The results show that the fused image obtained by the presented algorithm can not only hold spectrum information of the visible image, but also inherit object information of the infrared image. The entropy of the fused image is about 10% greater than that of pixel-based fusion methods, and the cross entropy of the fused image is only 1% of that of pixel-based fusion methods..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 28, Issue 3, 447 (2008)
A Robust Image Registration Algorithm Based on Feature Points Matching
Liu Guixi, Liu Dongmei, Liu Fengpeng, and Zhou Yaping
To extract exactly feature points and match reliably feature point pairs, a robust image registration method based on feature points matching is proposed. Firstly, corners are extracted with the improved Plessey operator which can improve the precision and speed of the feature points extraction, the initial feature poiTo extract exactly feature points and match reliably feature point pairs, a robust image registration method based on feature points matching is proposed. Firstly, corners are extracted with the improved Plessey operator which can improve the precision and speed of the feature points extraction, the initial feature point pairs are extracted with the methods of normalized cross correlation (NCC) and bidirectional greatest correlative coefficient (BGCC), and the false feature point pairs are rejected by the random sample consensus (RANSAC) algorithm. Finally, the correct matching feature point pairs are used to realize image registration. The experimental results indicate that this method can fast and accurately extract the corresponding feature points between two images and greatly reduce the probability of false feature points matching. Image registration can be carried out effectively even under varions of conditions of different light, bigger rotation, and repetitive texture..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 28, Issue 3, 454 (2008)
Novel denoising Method for Remote Sensing Image Based on Contourlet Transform
Zhang Jingjing, and Fang Yonghua
We propose a new and efficient denoising method for remote sensing image based on the contourlet transform. Firstly, we introduce a geometrical prior model, and estimate the Bayesian framework by combining the noise with the useful signal. Then, we compute each coefficient as the probability of evailable signal, modifyWe propose a new and efficient denoising method for remote sensing image based on the contourlet transform. Firstly, we introduce a geometrical prior model, and estimate the Bayesian framework by combining the noise with the useful signal. Then, we compute each coefficient as the probability of evailable signal, modifying the wavelet shrinkage factor. Finally, we reconstruct multi-resolution wavelet coefficient and process it using recursive cycle spinning. The experimental results show that the denoised image eliminates pseudo-Gibbs phenomena, the peak signal-to-noise ratio increases 1～2 dB..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 28, Issue 3, 462 (2008)
Imaging Systems
Orientation of Mouse Using Digital Speckle Correlation Method
Yan Haitao, and Wang Ming
Based on the working principle of laser mouse, the digital speckle correlation method is used to realize orientation of laser mouse. The orientation principle is investigated. The experiment is designed to obtain the speckle pattern by a digital camera. The CCD is used to scan the moving spackle picture through the imaBased on the working principle of laser mouse, the digital speckle correlation method is used to realize orientation of laser mouse. The orientation principle is investigated. The experiment is designed to obtain the speckle pattern by a digital camera. The CCD is used to scan the moving spackle picture through the image acquisition board. Two parameters of optimum sampling, pixel and image displacement, are obtained by data analysis. The speckle picture is moved by a definite trace and shot by a digital camera, and the experiment is simulated by solfware Matlab. The displacement of speckle picture is processed by digital speckle correlation method. The simulated results are compared with the experimental results. The results prove the digital speckle correlation method can confirm allocation, and the obtained resolution is 1 μm, which is higher than the resolution 30 μm of the laser mouse in market..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 28, Issue 3, 467 (2008)
Optimization of Double Bottom Antireflective Coating for Hyper Numerical Aperture Lithography
Zhou Yuan, and Li Yanqiu
In hyper numerical aperture lithography, the incident angle of imaging rays varies in a wide range. Conventional single bottom antireflective coatings (BARC) cannot control reflectivity (substrate reflectivity) at the resist-substrate interface. A novel dual BARC optimization method is developed by taking into account In hyper numerical aperture lithography, the incident angle of imaging rays varies in a wide range. Conventional single bottom antireflective coatings (BARC) cannot control reflectivity (substrate reflectivity) at the resist-substrate interface. A novel dual BARC optimization method is developed by taking into account light source shape and mask diffraction for specific applications. A weighted average of the substrate reflectivity for the 0st order as well as a higher order is used when optimizing the dual BARC. BARC structures are optimized with the new method in the cases of binary mask, attenuated phase-shift mask and altering phase-shift mask. The results show that, the higher diffraction orders are captured by the objective lens (or larger the intensity of high orders is), more noteworthy the influence of mask is for BARC optimization. In some cases, such as imaging with altering phase-shift mask, it is indispensable to take the mask into account in BARC optimization..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 28, Issue 3, 472 (2008)
Instrumentation, Measurement and Metrology
Non-Destructive Measurement of Soluble Solid Content in Gannan Navel Oranges by Visible/Near-Infrared Spectroscopy
Liu Yande, Chen Xingmiao, and Ouyang Aiguo
Non-destructive measurement of soluble solid content in Gannan navel oranges was carried out by visible/near-infrared spectroscopy detection method. Effective information of spectra was obtained by principal component analysis, and was used as the input variables of artificial neural network for building the nonlinear Non-destructive measurement of soluble solid content in Gannan navel oranges was carried out by visible/near-infrared spectroscopy detection method. Effective information of spectra was obtained by principal component analysis, and was used as the input variables of artificial neural network for building the nonlinear model. The results, based on calibration for 90 samples, are 0.9147 and 0.5203 for calibration correlation coefficient and root mean square error of calibration. The results, based on prediction for 38 unknown samples, are 0.9033, 0.6964 and 4.5709% for prediction correlation coefficient, root mean square error of prediction, and relative standard deviation (RSD), respectively. Experimental results show that visible/near-infrared spectroscopy detection method, based on artificial neural network, for non-destructive measurement of soluble solid content in Gannan navel oranges is feasible..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 28, Issue 3, 478 (2008)
A Structured Light Thre-Dimensional Measurement Method Based on Unconstrained System Configuration
Wu Di, Lü Naiguang, and Ouyang Jing
In the most conventional structured light system, the camera must be perpendicular to the reference plane, and the connecting line between the exit pupil of the projecting system and the entrance pupil of the camera must be parallel to reference plane. Aiming at this problem, an unconstrained system configuration is buIn the most conventional structured light system, the camera must be perpendicular to the reference plane, and the connecting line between the exit pupil of the projecting system and the entrance pupil of the camera must be parallel to reference plane. Aiming at this problem, an unconstrained system configuration is built up, and the parallel and perpendicular constrained conditions are removed. A camera and a fringe projector consisting of the system can be posed freely depending on the objects and the purpose. Based on aforementioned unconstrained system, a new calibration method is presented. In the method, the spatial relationship of “projector-camera-reference plane” can be calibrated and reconstructed accurately, and therefore the important parameters—distance of two pupils and distance from camera to reference plane in the conventional structured light system can be obtained easily. Meanwhile, the new phase-height mapping relationship and height calculating formulas corresponding to the unconstrained system are derived. The experimental results prove that this method can obtain a range data in the accuracy of error about 0.1 mm..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 28, Issue 3, 482 (2008)
A New Method to Measure the Optical-Axis Azimuth of Quarter-Wave Plate in Light Path Accurately
[in Chinese], and [in Chinese]
In order to fix quarter-wave plate accurately, a new method is presented to measure the optical-axis azimuth of quarter-wave plate. The errors influencing test results are analyzed by Müller matrix theory. The main theories were used including Müeller matrix theory, Fourier analysis and least squares method, In order to fix quarter-wave plate accurately, a new method is presented to measure the optical-axis azimuth of quarter-wave plate. The errors influencing test results are analyzed by Müller matrix theory. The main theories were used including Müeller matrix theory, Fourier analysis and least squares method, and the optimized Fourier coefficients of the signal are obtained by the least squares method. By the principle of extinction-ratio measuring system, the analyzing prism is fixed accurately. A high-accuracy step motor is used to control the rotation angle by the feedback loop system. The theoretical analysis of error proves that measurement error is related to the azimuth angle itself, and the experimental results have proved that the normal uncertainty in the measurement was 0.03..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 28, Issue 3, 487 (2008)
Lasers and Laser Optics
Orientation Effect on Phase Retardation of Rhomb-Type Achromatic Retarder
[in Chinese], and [in Chinese]
Rhomb-type retarder is a high-precision achromatic λ/4 phase retarder. Because of material dispersion of the refractive index, there is still 2° deviation of the delay in the visible range. In order to meet the demand of precise measurement and applications, the principle of phase retardation with oblique incidentRhomb-type retarder is a high-precision achromatic λ/4 phase retarder. Because of material dispersion of the refractive index, there is still 2° deviation of the delay in the visible range. In order to meet the demand of precise measurement and applications, the principle of phase retardation with oblique incident angle is expounded, based on the total-reflection phase transformation theory of the phase retardation. By means of Fresnel rhomb, the variation law of the phase retardation for rhomb-type retarder with the incident angle is analyzed. The result indicates that incident angle has obvious influence over the phase retardation.The phase retardation is sensitive to the incident angle, and also has close correlation to incident position of the incident ray, which is asymmetrical to the incident position of the incident ray. So when the wavelength of the incident light changes, only the position of rhomb-type retarder need to be changed to allow the light to represent oblique incidence in the front of rhomb, and then selecting suitable incident angle can compensate the dispersion phase deviation, and make the same rhomb possess standard λ/4 phase retarder under all different wavelengths. Deviation of the delay is less than ±0.009° when the precision of angle adjustment is ±0.01°. The precision cannot be obtained for quartz wave plate or mica wave plate..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 28, Issue 3, 492 (2008)
LD-End-Pumped Nd:YVO4 Slab Laser and Its Thermal Effects
Shao Jie, Li Xiaoli, Feng Yutong, and Lu Yutian
The use of slab geometric structure in laser can greatly reduce thermal effects of laser medium, but further analysis of its impact is necessary for optimizing the efficiency of lasers. We analyzed the thermal effects in the partially end-pumped slab laser with a hybrid resonator, using finite element analysis (FEA) meThe use of slab geometric structure in laser can greatly reduce thermal effects of laser medium, but further analysis of its impact is necessary for optimizing the efficiency of lasers. We analyzed the thermal effects in the partially end-pumped slab laser with a hybrid resonator, using finite element analysis (FEA) method. The calculated results of the thermal focal length match with the measured results. The thermal effect on mode-match was analyzed. The results are helpful for the optimization of laser efficiency and resonant cavity design. In the experiment, an output laser of 41.5 W power is obtained with the input power of 110 W. Optical-optical conversion efficiency is about 38%, and the slope efficiency is 58.8%, with M2x＝1.59 and M2y＝1.55..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 28, Issue 3, 497 (2008)
Acousto-Optically Q-Switched 1342 nm Laser with Nd:YVO4 Crystals
Gong Mali, and Lu Chengqiang
A high-power high-repetition-rate acousto-optically Q-switched 1342 nm laser with double Nd:YVO4 crystals pumped by fiber-coupled laser diodes and simulated results based on Q-switched rate equations considering gain distribution on spectrum are presented. With total 40 W pump power incidence, the highest pulse repetitA high-power high-repetition-rate acousto-optically Q-switched 1342 nm laser with double Nd:YVO4 crystals pumped by fiber-coupled laser diodes and simulated results based on Q-switched rate equations considering gain distribution on spectrum are presented. With total 40 W pump power incidence, the highest pulse repetition rate of 100 kHz was obtained. At 50 kHz repetition rate, average output power higher than 11 W and rather stable pulses were achieved. With the Q-switched rate equations considering gain distribution on spectrum, not only the pulse width, peak power and build-up time can be calculated, but the output distribution on the spectrum and its width can also be given. The experimental results are compared with the simulated ones. The model can be applied to analyze and design the spectrum of the laser output, and more exact results can be obtained because the practical gain distribution on the spectrum was taken into consideration..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 28, Issue 3, 502 (2008)
Stable, Tunable Single-Longitudinal-Mode Erbium-Doped Fiber Laser with Multiple Ring Cavities
Zhang Yan, Chen Wei, Ren Min, Ju Yu, Han Wei, Zhang Banghong, Zhang Yali, Xie Liang, and Zhu Ninghua
A stable, tunable single-longitudinal-mode erbium-doped fiber laser (EDFL) with multiple ring cavities (MRC) has been proposed. The MRC consists of two active ring-cavities and two passive subring cavities. The fiber Fabry-Pérot tunable filter and optical grating filter are combined with MRC for mode selection. ThA stable, tunable single-longitudinal-mode erbium-doped fiber laser (EDFL) with multiple ring cavities (MRC) has been proposed. The MRC consists of two active ring-cavities and two passive subring cavities. The fiber Fabry-Pérot tunable filter and optical grating filter are combined with MRC for mode selection. The output wavelength is tunable from 1528 to 1565 nm over the wide tuning range, the side-mode suppression ration (SMSR) is beyond 44.53 dB ,the maximum SMSR value is up to 51.18 dB around 1554 nm, and the output power is -8.84 dBm in the operating range. With the MRC configuration, the ring laser output is stable, the central wavelength variation is bellow 0.02 nm and the output power fluctuation is less than 0.04 dBm in 18 min, a wavelength-tunable EDFL with stabilized single-longitudinal mode is achieved..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 28, Issue 3, 507 (2008)
Analysis of Radial Temperature Field for a Metal-Vapor Laser Tube with an Axial Temperature Controller
Mao Bangning, Wang Limin, Chen Li, Yao Zhixin, and Pan Bailiang
A concise mathematical model was established to describe the radial temperature distribution of a metal-vapor laser tube with an axial temperature controller. The analytical solution of the radial temperature caused by thermal radiation and thermal conduction was obtained. The influences of the axial temperature controA concise mathematical model was established to describe the radial temperature distribution of a metal-vapor laser tube with an axial temperature controller. The analytical solution of the radial temperature caused by thermal radiation and thermal conduction was obtained. The influences of the axial temperature controller on the discharge tube wall temperature and its radial temperature distribution were further calculated and analyzed. It is shown that the axial temperature controller can independently adjust the laser tube wall temperature, reduce the radial temperature gradient in some degree, and therefore improve the laser efficiency and stability..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 28, Issue 3, 512 (2008)
Numerical Simulation for Computer-Aided Precise Alignment of Unstable Resonator
Zhang Wenjing, Liu Wenguang, and Liu Zejin
The automatic alignment of resonator is one of the critical techniques in high-power laser technology. The method of computer-aided alignment of unstable resonator is presented and its numerical simulation results are given. The relation between mirror misalignments and its phase aberration coefficients is regarded as The automatic alignment of resonator is one of the critical techniques in high-power laser technology. The method of computer-aided alignment of unstable resonator is presented and its numerical simulation results are given. The relation between mirror misalignments and its phase aberration coefficients is regarded as linear to some extent, especially under the condition of small misalignments. After getting a series of aberrations representing a misaligned system, we get the data of each misalignment by solving linear equations. Then the misaligned resonator is modified according to these results. The whole process is simulated numerically. Presently, multi-misalignments including both tilt and decentration can be calculated in this way. The numerical analysis shows that it is easy to figure out a single misalignment. Complex misaligned condition needs iteration. Tilt misalignments that can be figured out is 10～104 μrad and the decentration range is 10-2～1 mm. This method can be used to guide resonator′s alignment effectively and provide another way for laser resonator’s automatic alignment in practical use..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 28, Issue 3, 516 (2008)
Influence of Gas Flow under Workpiece in CO2 Laser Cutting Silicon Steel
Hong Lei, Mi Chenglong, and Li Lijun
Compared with the traditional blanking technology such as punching and linear cutting, the laser cutting technology has many advantages. For example, it has large freedom and high working efficiency. It will not cause such problems that will affect the quality of iron core as injuries of insulation, extrusion of edge, Compared with the traditional blanking technology such as punching and linear cutting, the laser cutting technology has many advantages. For example, it has large freedom and high working efficiency. It will not cause such problems that will affect the quality of iron core as injuries of insulation, extrusion of edge, and so on. But during the laser cutting process, the generation of dross and the rough cutting edge limit its application. A new laser cutting technology is proposed which uses an additional nozzle under the workpiece to form lateral gas flow and control the flowing direction of the slag gas. The experiments prove that glossy and dross-free kerfs are obtained by controlling the technical parameters reasonably. The gas flow under the workpiece is simulated by finite element method (FEM). The variety of pneumatic fields when the additional nozzle is in different angle and flow velocity is analyzed, and the nozzle angle of 20° is preferred, which provide experimental and academic basis for controlling the flowing direction of the slag gas and achieving glossy kerfs..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 28, Issue 3, 522 (2008)
Materials
Dispersion Property in Highly Nonlinear Photonic Crystal Fiber
Wu Ming, Liu Hairong, and Huang Dexiu
The dispersion and nonlinear property of highly nonlinear photonic crystal fiber (HNLPCF) are simulated with the vectorial beam propagation method. The effective area of fundamental mode Aeff, nonlinear coefficient γ and dispersive coefficient D are evaluated. The relationship between Aeff, γ and D with the pitch Λ andThe dispersion and nonlinear property of highly nonlinear photonic crystal fiber (HNLPCF) are simulated with the vectorial beam propagation method. The effective area of fundamental mode Aeff, nonlinear coefficient γ and dispersive coefficient D are evaluated. The relationship between Aeff, γ and D with the pitch Λ and hole diameter d, is analyzed. The dispersion and nonlinear property of highly nonlinear photonic crystal fiber can be controlled by the structural parameters, Λ and d..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 28, Issue 3, 539 (2008)
Design of Core-Cladding Interface of Hollow-Core Photonic-Bandgap Fibers
Zhang Hu, Yang Bojun, and Wang Qiuguo
The photonic bandgap structure for a photonic crystal with rounded hexagons air hole arranged by triangular lattice was calculated by plane wave method (PWM), and based on the structure diagram, structure parameters of a seven-cell hollow-core photonic bandgap fiber (PBF) was designed to propagate a lightwave with λ=1.The photonic bandgap structure for a photonic crystal with rounded hexagons air hole arranged by triangular lattice was calculated by plane wave method (PWM), and based on the structure diagram, structure parameters of a seven-cell hollow-core photonic bandgap fiber (PBF) was designed to propagate a lightwave with λ=1.55 μm. And then numerical simulation for a hollow-core PBF with a silica ring introduced at the core-cladding interface was done with full-vectorial finite element method (FEM), and the intensity distribution, intensity contour distribution in z axis and a curve of leakage loss as a function of normalized core thickness were presented. The ranges of out core radius and the normalized thickness of a silica ring for the fiber free of surface modes and reducing loss are 1.55Λ～1.7Λ and 1.3～1.5 or 3.4～3.8 respectively. A silica ring can not only create surface modes but also remove surface modes, which depends on choices of the out core radius and a silica ring thickness..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 28, Issue 3, 543 (2008)
Nonlinear Optics
Dynamic Behaviour of Open-Circuit Photovoltaic Spatial Solitons
Shen Yan, Zhang Guoquan, Xu Jingjun, Zhang Yu, Sun Xiudong, Zhao Yequan, and Zhou Lingjun
The time-dependent formation of one-dimensional (1D) photovoltaic solitons under open-circuit conditions are researched theoretically. The differential equations of profile of bright and dark photovoltaic solitons are obtained by the numerical method. The effects of the background light on the photovoltaic solitons andThe time-dependent formation of one-dimensional (1D) photovoltaic solitons under open-circuit conditions are researched theoretically. The differential equations of profile of bright and dark photovoltaic solitons are obtained by the numerical method. The effects of the background light on the photovoltaic solitons and their width full-width at half maximum (FWHM) are studied. The results show that applying the background light results in shorting the formation time of photovoltaic solitons, and the ratio of formation time without the background light to that with the background light quals the ratio of the intensity of background light to that of dark irradiation. The higher the ratio of soliton peak intensity to the sum of background light and dark irradiation intensity, the shorter the time of the FWHM of photovoltaic soliton reacheing steady-state..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 28, Issue 3, 528 (2008)
Optical Devices
Thermodynamic Effect on Transmitted Intensity Perturbance of Glan-Thompson Prism
Jia Peng, Li Guohua, and Peng Handong
An analytical study on transmitted intensity perturbance of Glan-Thompson prism with varying rotation angle is given, when the linearly polarized light enters in the normal incidence. The perturbance strongly affects the quality of transmitted polarizing light. In order to reduce this bad effect and hold the quality ofAn analytical study on transmitted intensity perturbance of Glan-Thompson prism with varying rotation angle is given, when the linearly polarized light enters in the normal incidence. The perturbance strongly affects the quality of transmitted polarizing light. In order to reduce this bad effect and hold the quality of transmitted polarized light, we reaserched the perturbance factor. Study shows that the transmitted intensity sensitively relies on the incident angle. In the experiment,a minute random variation of the incident angle around the structure angle of Glan-Thompson prism is found, which gaves rise to the perturbance. Selecting the right angle could reduce the perturbance. For the same purpose,we should reduce the thickness of the glue in certain wavelength to the full and select the hump at the average temperature when the temperature varied..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 28, Issue 3, 534 (2008)
Quantum Optics
Wigner Functions and Tomogram Functions of Even and Odd Pair Coherent States
Meng Xiangguo, Wang Jisuo, and Liang Baolong
With the entangled state η〉 representation of the Wigner operator, Wigner functions for even and odd pair coherent states (EOPCs) are reconstructed. In terms of variations of Wigner functions with the parameters ρ and γ in the phase space, nonclassical properties and quantum interference effects of EOPCSs are discussedWith the entangled state η〉 representation of the Wigner operator, Wigner functions for even and odd pair coherent states (EOPCs) are reconstructed. In terms of variations of Wigner functions with the parameters ρ and γ in the phase space, nonclassical properties and quantum interference effects of EOPCSs are discussed. It is found that EOPCSs always exhibit nonclassical properties, especially when q is odd. Quantum interference effects of EOPCSs depend on the value of q, but for a fixed q quantum interference effects of the odd pair coherent state are more prominent. Based on the Radon transform between the entangled state η〉 representation and the project operator of the entangled state η,τ1,τ2〉, the quantum tomogram functions for the EOPCSs are obtained..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 28, Issue 3, 549 (2008)
Analysis on Unsecurity of Quantum Secret Sharing Based on Smolin Bound Entangled States
Yu Yafei, and Zhang Zhiming
We analyze the security of quantum secret sharing (QSS) with bound entangled Smolin states as the channel quantum state. An intercept-resend strategy of the inner legal communicators is proposed to attack the security without being detected by the checking procedure compared with the results of single-qubit measurementWe analyze the security of quantum secret sharing (QSS) with bound entangled Smolin states as the channel quantum state. An intercept-resend strategy of the inner legal communicators is proposed to attack the security without being detected by the checking procedure compared with the results of single-qubit measurement. It is concladed that QQS only with Smolin bound entangled states as the channel quantum state is not unconditionally secure..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 28, Issue 3, 556 (2008)
Remote Sensing and Sensors
Time-Division-Multiplexing Scheme of the Folded Sagnac Sensor Array with Active Phase Bias
Song Zhangqi, Yang Mingye, Zhang Xueliang, Wang Xin, and Hu Yongming
To avoid the overlapping of signal and noise pulses in the folded Sagnac fiber sensor array (FSSA), a time-division-multiplexing (TDM) scheme with active phase bias is proposed. Noise pulses and signal pulses are controlled to return alternately, just by adjusting the length of the bus fiber of traditional sensor arrayTo avoid the overlapping of signal and noise pulses in the folded Sagnac fiber sensor array (FSSA), a time-division-multiplexing (TDM) scheme with active phase bias is proposed. Noise pulses and signal pulses are controlled to return alternately, just by adjusting the length of the bus fiber of traditional sensor array with ladder structure and adding a section of delay fiber at one end of the Sagnac interferometer. Analysis shows the input pulse repetition rate can reach half of the standard TDM scheme when the length of the delay coil is appropriate. The phase bias of the sensor array is realized through an integrated optical chip (IOC) driven by a pulse signal synchronizing with the input optical pulse. A two-sensor-array with this structure is demonstrated experimentally, and the input optical pulse repetition is rate 754.727 kHz. The phase sensitivity is about 7.3 μrad/Hz at 5 kHz, and the crosstalk between two sensors is measured to be about -51.75 dB..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 28, Issue 3, 560 (2008)
Analysis and Measurement on Refractive Index Sensing of Few Mode Fiber Bragg Gratings
Xu Junjiao, Li Jie, Rong Huabei, Shi Zhidong, and Dong Xiaopeng
The coupling and propagation characteristics of fundamental modes and high-order modes in the few mode fiber Bragg grating was numerically analyzed and simulated. It is indicated that the shifts of the Bragg wavelength corresponding to the coupling between the fundamental mode and the backward high-order mode is obviouThe coupling and propagation characteristics of fundamental modes and high-order modes in the few mode fiber Bragg grating was numerically analyzed and simulated. It is indicated that the shifts of the Bragg wavelength corresponding to the coupling between the fundamental mode and the backward high-order mode is obviously larger than the shift of the Bragg wavelength corresponding to the coupling between the forward and backward fundamental modes. The few mode fiber Bragg grating was fabricated, and the variations of Bragg wavelengths corresponding to fundamental modes coupling and fundamental-high-order modes coupling with external refractive index and temperature were measured. The experimental results agree with the theoretical analysis. Therefore by the means of Bragg wavelength difference calculation, the temperature induced fluctuation is overcome, which presents a new ray to measure the external refractive index change of fiber Bragg gratings..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 28, Issue 3, 565 (2008)
Distributed Optical Fiber Sensing System Based of Rayleigh Scattering Light φ-OTDR Using Single-Mode Fiber Laser with High Power and Narrow Linewidth
Xie Kongli, Rao Yunjiang, and Ran Zengling
A phase-sensitive optical-time-domain-reflectometer (φ-OTDR) using a fiber laser with high power and narrow linewidth is described. The sensing element is a single-mode telecommunication fiber cable with a 3 mm diameter buried outdoors. The phase changes of Rayleigh scattering light resulting from the pressure (vibratiA phase-sensitive optical-time-domain-reflectometer (φ-OTDR) using a fiber laser with high power and narrow linewidth is described. The sensing element is a single-mode telecommunication fiber cable with a 3 mm diameter buried outdoors. The phase changes of Rayleigh scattering light resulting from the pressure (vibration) of the intruder on the ground immediately above or near the buried fiber. By subtracting a present φ-OTDR trace signal from an earlier one with a time difference of 0.1 s, the system can locate the intrusion point where the optical intensity will change for the reason of interference. By processing the returned signal properly, a distance range of 14 km can be reached, with the best spatial resolution of ～50 m reported to date, and a signal-to-noise ratio of ～12 dB, to the best of our knowledge. Such a distributed sensing system is anticipated to be used widely in safety monitoring of military bases, national boarders, nuclear facilities, electrical power generation stations, jails, et al...
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 28, Issue 3, 569 (2008)
Parameter Design of Space-Borne Laser Altimeter
Yang Fu, He Yan, and Chen Weibiao
In order to realize the high spatial and range resolution for a space-borne laser altimeter based on frequency-modulated fiber laser and heterodyne-range detection is proposed. The detailed principle of detection is presented. The relationship of range accuracy and signal-to-noise ratio with laser power, telescope diamIn order to realize the high spatial and range resolution for a space-borne laser altimeter based on frequency-modulated fiber laser and heterodyne-range detection is proposed. The detailed principle of detection is presented. The relationship of range accuracy and signal-to-noise ratio with laser power, telescope diameter, and pulse width are numerically simulated. The relationship and the optimized parameters are given after the analysis of system parameters. The results show that the space-borne laser altimeter based on coherent range detection can achieve a range accuracy of less than 15 cm with telescope aperture of 400 mm, chirp rate of 1 MHz/μs, pulse width ranges of 150～350 μs, and average laser power of about 10 W..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 28, Issue 3, 573 (2008)
Spectroscopy
Fluorescence Properties of Municipal Wastewater
Chen Maofu, Wu Jing, Lü Yanli, and Chen Qingjun
The traditional parameters of water quality, shuch as chemical oxygen demand (COD) and biological oxygen demand (BOD), only present total organic substance concentration and are void for displaying pollutant compositions. Fluorescence spectrum, a novel method for water quality, is unique for each wastewater sample likeThe traditional parameters of water quality, shuch as chemical oxygen demand (COD) and biological oxygen demand (BOD), only present total organic substance concentration and are void for displaying pollutant compositions. Fluorescence spectrum, a novel method for water quality, is unique for each wastewater sample like ‘fingerprint’. Excitation-emission matrix (EEM) technology is used to study fluorescence properties of municipal wastewater. The results show that there are four typical fluorescence zones in EEMs of municipal wastewater. Locations and intensities of fluorescence peaks of each zone and the ratio of intensities at λex=280 nm,λem=340 nm (fluorescence center of the 1st zone) and λex=225 nm,λem=340 nm (fluorescence center of the 2nd zone) could exhibit main fluorescence features. Fluorescence fingerprint contains a great deal of pollutant information. By comparing EEMs of typical pollutants, the main fluorescence substances of wastewater are approximately identified. Fluorescence fingerprint method can present organic substance as well as their content and is well complementary to COD and BOD..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 28, Issue 3, 578 (2008)
Effect of Oblique Attitude on Image Quality of Spatio-Temporally Modulated Imaging Fourier Transform Spectrometers
Zhao Huijie, and Jia Guorui
The spatio-temporally modulated imaging Fourier transform spectrometers obtain two-dimensional spatial images modulated by interference pattern, and are sensitive to the change of attitude. According to the imaging principle of these instruments, image motion between two interference images should be one column of pixeThe spatio-temporally modulated imaging Fourier transform spectrometers obtain two-dimensional spatial images modulated by interference pattern, and are sensitive to the change of attitude. According to the imaging principle of these instruments, image motion between two interference images should be one column of pixels when the instruments are in a vertical attitude, and abnormal image motion would arise because of geometric distortion and rotation of the interference images when an attitude incline exists. The expression of the abnormal image motion was deduced from the collinear equation. It was proved by numeric simulation that the abnormal image motion would accumulate in the interference image series and would make the objects′ interference pattern distorted. The interference images should be corrected to ensure the reality of the restored spectra in one of the following cases: vertical photography with platform of low pointing accuracy, oblique photography, low orientation accuracy of detector array, and aerial photography with a drift angle..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 28, Issue 3, 583 (2008)
Vision, Color, and Visual Optics
Background Modeling and Moving-Objects Detection Based on Cauchy Distribution for Video Sequence
[in Chinese], and [in Chinese]
A novel illumination-invariant change detection method of shading model based on Cauchy distribution for visual surveillance systems is proposed. It is assumed that the observed temporal intensity variation of each pixel in background images is caused by white noise. After each image being normalized by an initialized A novel illumination-invariant change detection method of shading model based on Cauchy distribution for visual surveillance systems is proposed. It is assumed that the observed temporal intensity variation of each pixel in background images is caused by white noise. After each image being normalized by an initialized Gaussian background model, the distribution of the intensity ratios between corresponding pixels of two background images obeys a Cauchy distribution. The parameter estimation of the Cauchy distribution model is simplified. Based on the change detection, the intensity, hue, and saturation in the YCbCr color space are employed to recognize and eliminate shadows and reflections in video sequences. The experimental results demonstrate that the proposed method of background modeling can tolerate the whole or local sudden or slow changes in illumination, and noises caused by some small motions, shadows or reflections in a background scene..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 28, Issue 3, 587 (2008)
Visible Characteristics of Space Satellite Based on Nth Cosine Scattering Distribution
Wang Hongyuan, Zhang Wei, and Wang Zhile
Visible scattering characteristics of a space satellite are studied based on geometrical optics and radiation theory. The background radiation of the space satellite consists of direct solar radiation and scattered radiation of the earth and atmosphere. Geometrical and illumination models of the space satellite are estVisible scattering characteristics of a space satellite are studied based on geometrical optics and radiation theory. The background radiation of the space satellite consists of direct solar radiation and scattered radiation of the earth and atmosphere. Geometrical and illumination models of the space satellite are established according to target structure and background characteristics. Target surface appearance is analyzed and the ray incident to target surface follows a Nth cosine scattering distribution approximately. A mathematical model of target scattering characteristics is established in terms of energy conservation law and Nth cosine scattering distribution properties of surface material. The relative position of the sun, the earth and the observation satellite in target body coordinate system is determined by vector coordinate conversion. Energy distribution and magnitude characteristics on the entrance pupil of the detector are simulated by its given physical dimension and surface physical parameters. The maximum magnitude of irradiance from target body and solar sail on the entrance pupil of the detector is 10-12 W/m2. Simulation results indicate the solar sail cannot be neglected when the target characteristics are analyzed and it can provide reference data to visible detection of space targets..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 28, Issue 3, 593 (2008)
Cathode-Ray Tube Color Perceptible Color Difference Threshold Evaluation in Visual Color Matching
Huang Min, Liao Ningfang, Liu Haoxue, and Xu Yanfang
For the evaluation of cathode-ray tube (CRT)perceptible color difference threshold characteristics of the visual color matching, the experiment is carried out. By using the compiled color-matching program, the CRT generates color under gray background randomly. The matching color and the random color can achieve visualFor the evaluation of cathode-ray tube (CRT)perceptible color difference threshold characteristics of the visual color matching, the experiment is carried out. By using the compiled color-matching program, the CRT generates color under gray background randomly. The matching color and the random color can achieve visual color matching by adjusting the R, G and B channels in the program, then the values of L*, a* and b* of the matching color and the random color are measured respectively. Upon the data processing and analysis of the experimental results, in terms of lightness, chroma and hue,the color difference formula CIEDE2000 is superior to CMC (2:1) and CIE L*a*b* in different aspects. Then experimental color discrimination are plotted in a*b* diagram. Furthermore, different color difference formulae have different thresholds for evaluating CRT perceptible color difference threshold..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 28, Issue 3, 599 (2008)
X-Ray Optics
In-Line X-Ray Phase-Contrast Computerized Tomography
Jiang Shiping, Li Meifang, Chen Yang, and Chen Liang
To develop the in-line X-ray phase-contrast computerized tomography (CT) method based on synchrotron radiation in Beijing Synchrotron Radiation Facility (BSRF). The comparison studies of in-line phase-contrast imaging with absorption-contrast imaging as well as the technique of in-line phase-contrast computerized tomogTo develop the in-line X-ray phase-contrast computerized tomography (CT) method based on synchrotron radiation in Beijing Synchrotron Radiation Facility (BSRF). The comparison studies of in-line phase-contrast imaging with absorption-contrast imaging as well as the technique of in-line phase-contrast computerized tomography were carried out using the 14 keV monochromatic X-ray from BSRF as the light source and the X-ray film with high-resolution power as the detector. The algorithm proposed by Bronnikov was employed for the phase-contrast CT reconstruction. Compared with conventional absorbing-contrast images, phase-contrast images have better contrast and higher spatial resolution. Phase-contrast CT reconstruction images of the experimental samples were acquired and some feature details of the objects could be seen in the reconstruction images. The above experimental results indicate that phase-contrast X-ray imaging method is more applicable to the studies of the materials with weakly absorbing and small absorption difference, and it is feasible to carry out in-line X-ray phase-contrast CT using X-ray source of BSRF..
Acta Optica Sinica
- Publication Date: Jan. 01, 1900
- Vol. 28, Issue 3, 609 (2008)
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