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Coherence and statistical optics|9 Article(s)
Initial Displacement Estimation Method for Speckle Image Based on Marker Matching
Zhang Hongying, and Yu Zhijing
For digital speckle correlation methods, the reliable initial displacement estimation is particularly important to achieve sub-pixel accuracy. Utilizing marker matching technology, a new initial value estimation method is proposed. This method sticks circular markers with high reflection coefficient on the speckles. In order to eliminate the effects of speckles on extracting points, an improved scale invariant feature transform algorithm detecting extreme points within significant edge region is presented, so the redundant feature points are greatly reduced in this way. At last, the homography transformation is executed to complete full field deformation, and the initial value of each pixel in the region of interest is estimated rapidly. Experiments are performed through making speckle plate and the results show that the initial values obtained by the proposed method can reach a fast convergence within 3-4 iterations and consequently get accurate and reliable measurement results. For digital speckle correlation methods, the reliable initial displacement estimation is particularly important to achieve sub-pixel accuracy. Utilizing marker matching technology, a new initial value estimation method is proposed. This method sticks circular markers with high reflection coefficient on the speckles. In order to eliminate the effects of speckles on extracting points, an improved scale invariant feature transform algorithm detecting extreme points within significant edge region is presented, so the redundant feature points are greatly reduced in this way. At last, the homography transformation is executed to complete full field deformation, and the initial value of each pixel in the region of interest is estimated rapidly. Experiments are performed through making speckle plate and the results show that the initial values obtained by the proposed method can reach a fast convergence within 3-4 iterations and consequently get accurate and reliable measurement results.
Acta Optica Sinica
- Publication Date: Jan. 01, 2017
- Vol. 37, Issue 3, 303001 (2017)
Ghost Imaging Based on Sparse Array Pseudothermal Light System
Chen Mingliang, Li Enrong, Wang Hui, Shen Xia, Gong Wenlin, and Han Shensheng
Great breakthroughs have been made in research of ghost imaging in recent years. The application value of ghost imaging is increasingly obvious. The precondition of ghost imaging is that its light source should be random fluctuating thermal light. Presently, pseudothermal light is usually generated by passing a laser beam through a revolving ground glass. In view of the limitations of such a method, this paper proposes to generate pseudothermal light via sparse array independent source combining system, and discusses the differences between two algorithms, i.e., linear correlation algorithm and sparsity constraint nonlinear algorithm, in ghost imaging. Great breakthroughs have been made in research of ghost imaging in recent years. The application value of ghost imaging is increasingly obvious. The precondition of ghost imaging is that its light source should be random fluctuating thermal light. Presently, pseudothermal light is usually generated by passing a laser beam through a revolving ground glass. In view of the limitations of such a method, this paper proposes to generate pseudothermal light via sparse array independent source combining system, and discusses the differences between two algorithms, i.e., linear correlation algorithm and sparsity constraint nonlinear algorithm, in ghost imaging.
Acta Optica Sinica
- Publication Date: Jan. 01, 2012
- Vol. 32, Issue 5, 503001 (2012)
Characteristics Analysis of the Photons Arrival Time Interval of Laser Beat Signal
Liu Lisheng, Zhang Heyong, Zhao Shuai, and Guo Jin
In order to get the frequency of periodic laser beat signal, the probability density function (PDF) of time interval between two successive photoelectrons is derived theoretically. The difference of the shape in the PDF curve between the beat signal and stable light signal is obvious, and the beat frequency can be derived from the difference. An experiment system is designed in which a multi-pixel photon counter (MPPC) is used to record the photoelectrons time of the beat signal with beat frequency of 6, 8, 10 MHz and 12 MHz to give a potent verification to the theory. The experimental result is even much better in the condition that the photons count rate is 1/5 of the beat frequency, and an estimation of the mixing efficiency can be obtain using the statistics method which is 0.65 in our experiment. In the limitation of the dark count noise of the MPPC, the minimum beat frequency of periodic signal is 0.2333 MHz detected using this method. In order to get the frequency of periodic laser beat signal, the probability density function (PDF) of time interval between two successive photoelectrons is derived theoretically. The difference of the shape in the PDF curve between the beat signal and stable light signal is obvious, and the beat frequency can be derived from the difference. An experiment system is designed in which a multi-pixel photon counter (MPPC) is used to record the photoelectrons time of the beat signal with beat frequency of 6, 8, 10 MHz and 12 MHz to give a potent verification to the theory. The experimental result is even much better in the condition that the photons count rate is 1/5 of the beat frequency, and an estimation of the mixing efficiency can be obtain using the statistics method which is 0.65 in our experiment. In the limitation of the dark count noise of the MPPC, the minimum beat frequency of periodic signal is 0.2333 MHz detected using this method.
Acta Optica Sinica
- Publication Date: Jan. 01, 2012
- Vol. 32, Issue 4, 403001 (2012)
Coherence Properties of the Three-Dimensional Scattering Field Generated by an Anisotropic Quasi-Homogeneous Medium
Chen Jingjing, Xin Yu, Chen Yanru, Chen Feinan, and Wang Yongqing
Based on the scattering theory of electromagnetic wave, the electromagnetic scattering field generated by an anisotropic quasi-homogeneous medium is investigated. Then the analysis formulas for spectral density and spectral degree of coherence of the electromagnetic scattering field are derived. Simulation results show that when the scattering potential matrix of the anisotropic quasi-homogeneous medium is Gaussian-correlated, the normalized spectral density of the anisotropic medium is close to the average of the corresponding isotropic medium. But the weight of every component is not only different from each other but also changing as the scattering angle changes. The spectral degree of coherence of the anisotropic medium is greatly different from that of of its corresponding isotropic medium. The spectral degree of coherence of the anisotropic medium is oscillating as a function of the angle by three phases. And at some certain scattering angles, the spectral degree of coherence of the anisotropic medium is nearly the same as that of the corresponding isotropic medium. Based on the scattering theory of electromagnetic wave, the electromagnetic scattering field generated by an anisotropic quasi-homogeneous medium is investigated. Then the analysis formulas for spectral density and spectral degree of coherence of the electromagnetic scattering field are derived. Simulation results show that when the scattering potential matrix of the anisotropic quasi-homogeneous medium is Gaussian-correlated, the normalized spectral density of the anisotropic medium is close to the average of the corresponding isotropic medium. But the weight of every component is not only different from each other but also changing as the scattering angle changes. The spectral degree of coherence of the anisotropic medium is greatly different from that of of its corresponding isotropic medium. The spectral degree of coherence of the anisotropic medium is oscillating as a function of the angle by three phases. And at some certain scattering angles, the spectral degree of coherence of the anisotropic medium is nearly the same as that of the corresponding isotropic medium.
Acta Optica Sinica
- Publication Date: Jan. 01, 2011
- Vol. 31, Issue 12, 1203001 (2011)
Phase Stabilized Distribution of Millimeter Wave Local Oscillator Based on Michelson Interferometer
Man Xiaojing, Zhang Lumin, Dong Yi, He Hao, and Hu Weisheng
A system of phase stabilized distribution of millimeter wave local oscillator is proposed,which is based on the principle of Michelson interferometer.In the system,the signal phase drift during transition is modulated on the reflected optical signal,which is later coherent heterodyne with reference signal to control the fiber stretcher.Then system phase can be corrected and the phase of output millimeter wave can keep stable.Based on the theoretical model and experimental system,the relationship of phase drift of local oscillator,the length drift of optical fiber and coherent heterodyne output signal are measured.The experimental results agree with the theoretical model,which indicates that the proposed system is feasible. A system of phase stabilized distribution of millimeter wave local oscillator is proposed,which is based on the principle of Michelson interferometer.In the system,the signal phase drift during transition is modulated on the reflected optical signal,which is later coherent heterodyne with reference signal to control the fiber stretcher.Then system phase can be corrected and the phase of output millimeter wave can keep stable.Based on the theoretical model and experimental system,the relationship of phase drift of local oscillator,the length drift of optical fiber and coherent heterodyne output signal are measured.The experimental results agree with the theoretical model,which indicates that the proposed system is feasible.
Acta Optica Sinica
- Publication Date: Jun. 18, 2020
- Vol. 30, Issue 8, 2185 (2010)
A Partial-Coherence Model Describingthe Far-Field Distribution of Laser Diode
Liang Yiping, He Huawei, Xiong Lingling, Dai Teli, and Zhao Dongsheng
Based on the fact that the light from laser diode is partially coherent,a novel theoretical model is proposed using partially coherent light theory.This model can describe the close relation between the parameters of diode laser and its far-field.The different experimental far-field distribution patterns of laser diodes also can be well described by this model.This work provides a theoretical basis for the studying the laser diode output beam characteristics and its beam shaping technology. Based on the fact that the light from laser diode is partially coherent,a novel theoretical model is proposed using partially coherent light theory.This model can describe the close relation between the parameters of diode laser and its far-field.The different experimental far-field distribution patterns of laser diodes also can be well described by this model.This work provides a theoretical basis for the studying the laser diode output beam characteristics and its beam shaping technology.
Acta Optica Sinica
- Publication Date: Jun. 18, 2020
- Vol. 30, Issue 8, 2180 (2010)
Spectrum Properties of Partially Coherent Beams in Turbulent Atmosphere
[in Chinese], and [in Chinese]
The spectrum properties of partially coherent beams propagating in turbulent atmosphere are studied. Basing on the extended Huygens-Fresnel principle, an analytical propagation formula for the cross-spectral density of partially coherent beams in turbulent atmosphere is derived. The degree of spatial coherence and spectral shift of partially coherent beams through turbulent atmosphere are analyzed by using the derived formula. The results show that the spectrum of the partially coherent beam on axis in turbulent atmosphere is blueshifted in the beginning, the mount of the shift firstly increases, afterwards decreases, and finally a red shift appears with the increase of propagation distance. The lower the beam coherence is, the farther propagation distance is needed when red shift appears. At first the degree of spatial coherence increases, then decreases and approaches to zero finally. Comparing with the propagation of the partially coherent beam in free space, the atmospheric turbulence has small influence on the spectrum properties of the partially coherent beam in a short distance propagation, while has a strong influence on it in a sufficient long distance propagation. The spectrum properties of partially coherent beams propagating in turbulent atmosphere are studied. Basing on the extended Huygens-Fresnel principle, an analytical propagation formula for the cross-spectral density of partially coherent beams in turbulent atmosphere is derived. The degree of spatial coherence and spectral shift of partially coherent beams through turbulent atmosphere are analyzed by using the derived formula. The results show that the spectrum of the partially coherent beam on axis in turbulent atmosphere is blueshifted in the beginning, the mount of the shift firstly increases, afterwards decreases, and finally a red shift appears with the increase of propagation distance. The lower the beam coherence is, the farther propagation distance is needed when red shift appears. At first the degree of spatial coherence increases, then decreases and approaches to zero finally. Comparing with the propagation of the partially coherent beam in free space, the atmospheric turbulence has small influence on the spectrum properties of the partially coherent beam in a short distance propagation, while has a strong influence on it in a sufficient long distance propagation.
Acta Optica Sinica
- Publication Date: Jan. 01, 2005
- Vol. 25, Issue 3, 293 (2005)
Orthogonal coherent phase detection of phase modulated gratings
[in Chinese], and [in Chinese]
A new method for phase detection of the phase modulated grating is proposed.. Phase distribution of the grating can be acquired quickly and sensitively by taking a phase modulated grating image into computer and processing it by using orthogonal coherent phase detection algorithm. The principle of the technique is introduced in detail and the experimental results are shown. Finally, the technique is compared: with other similar techniques. A new method for phase detection of the phase modulated grating is proposed.. Phase distribution of the grating can be acquired quickly and sensitively by taking a phase modulated grating image into computer and processing it by using orthogonal coherent phase detection algorithm. The principle of the technique is introduced in detail and the experimental results are shown. Finally, the technique is compared: with other similar techniques.
Acta Optica Sinica
- Publication Date: Jan. 01, 1990
- Vol. 10, Issue 12, 1102 (1990)
Study of coherent CW-CO2laser imaging
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
A coherent CW-CO2 laser imaging system is described, experimental results of one and two point targets are reported and some factors affecting the image quality discussed. With some improvments, the system can be used in velocity and 3-D range imaging. A coherent CW-CO2 laser imaging system is described, experimental results of one and two point targets are reported and some factors affecting the image quality discussed. With some improvments, the system can be used in velocity and 3-D range imaging.
Acta Optica Sinica
- Publication Date: Jan. 01, 1990
- Vol. 10, Issue 12, 1097 (1990)
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