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Coherence and statistical optics|7 Article(s)
Correspondence imaging based on correlation coefficients
Xuri Yao, Xuefeng Liu, Wenkai Yu, and Guangjie Zhai
In the context of correspondence ghost imaging, we utilize the correlation coefficients to separate the reference detector speckle patterns into positive and negative correlated parts. A positive image and a negative image of the object are obtained by averaging over corresponding speckle patterns. The visibility and contrast-to-noise ratio of the positive image are discussed, and it is found that the latter will reach a maximum by averaging over a little less than half of the total number of reference speckle patterns. In the context of correspondence ghost imaging, we utilize the correlation coefficients to separate the reference detector speckle patterns into positive and negative correlated parts. A positive image and a negative image of the object are obtained by averaging over corresponding speckle patterns. The visibility and contrast-to-noise ratio of the positive image are discussed, and it is found that the latter will reach a maximum by averaging over a little less than half of the total number of reference speckle patterns.
Chinese Optics Letters
- Publication Date: Dec. 30, 2014
- Vol. 13, Issue 1, 010301 (2015)
Speckle reduction of synthetic aperture imaging ladar based on wavelength characteristics
Qian Xu, Zhiwei Sun, Jianfeng Sun, Yu Zhou, Zhiyong Lu, Xiaoping Ma, and Liren Liu
We propose a speckle-reduction method based on wavelength characteristics of speckle effect in synthetic aperture imaging ladar (SAIL). The return signal, which is the back scattering field with speckle effect from the rough surface of target, can be integrated over N chirp periods and heterodyne detected with a local-oscillator signal. After performing image processing respectively, the final image can be regarded as the incoherent superposition of the N sub-images. Numerical simulations indicate the effectiveness of this method. Our research may facilitate practical applications of SAIL. We propose a speckle-reduction method based on wavelength characteristics of speckle effect in synthetic aperture imaging ladar (SAIL). The return signal, which is the back scattering field with speckle effect from the rough surface of target, can be integrated over N chirp periods and heterodyne detected with a local-oscillator signal. After performing image processing respectively, the final image can be regarded as the incoherent superposition of the N sub-images. Numerical simulations indicate the effectiveness of this method. Our research may facilitate practical applications of SAIL.
Chinese Optics Letters
- Publication Date: Jul. 18, 2014
- Vol. 12, Issue 8, 080301 (2014)
Speckle noise reduction in digital holography with spatial light modulator and nonlocal means algorithm
Junmin Leng, Xinzhu Sang, and Binbin Yan
An integrated method based on optical and digital image processing is presented to suppress speckle in digital holography. A spatial light modulator is adopted to introduce random phases to the illuminating beam. Multiple holograms are reconstructed and superimposed, and the intensity is averaged to smooth the noise. The adaptive algorithm based on the nonlocal means is designed to further suppress the speckle. The presented method is compared with other methods. The experimental results show that speckle reduction is improved, and the proposed method is effective and feasible. An integrated method based on optical and digital image processing is presented to suppress speckle in digital holography. A spatial light modulator is adopted to introduce random phases to the illuminating beam. Multiple holograms are reconstructed and superimposed, and the intensity is averaged to smooth the noise. The adaptive algorithm based on the nonlocal means is designed to further suppress the speckle. The presented method is compared with other methods. The experimental results show that speckle reduction is improved, and the proposed method is effective and feasible.
Chinese Optics Letters
- Publication Date: Apr. 04, 2014
- Vol. 12, Issue 4, 040301 (2014)
Laser coherence measurement based on optical pulses interference
Zhihao Wang, Zhengyong Li, Lanlan Liu, and Chongqing Wu
By using a feedback-stabilized fiber Mach-Zehnder interferometer (MZI) with a PZT-based phase shifter, a novel method for measurement of laser coherence length is demonstrated based on pulses interference. Experimental results show that the coherence length is closed to that measured by the commercial optical spectrometer, and the partial coherence phenomenon is observed. Our scheme can measure not only the high-coherence laser but also low-coherence pulses, which is widely used in coherent laser measurement and application. By using a feedback-stabilized fiber Mach-Zehnder interferometer (MZI) with a PZT-based phase shifter, a novel method for measurement of laser coherence length is demonstrated based on pulses interference. Experimental results show that the coherence length is closed to that measured by the commercial optical spectrometer, and the partial coherence phenomenon is observed. Our scheme can measure not only the high-coherence laser but also low-coherence pulses, which is widely used in coherent laser measurement and application.
Chinese Optics Letters
- Publication Date: Sep. 23, 2012
- Vol. 10, Issue s2, S20301 (2012)
Speckle reduction in line scan laser display system by static diffuser with 2D binary code
Wenhong Gao, Shuyuan Ma, and Xuyuan Chen
A set of two-dimensional (2D) binary codes are created by the calculation of the speckle contrast in line scan laser display system. According to the 2D binary code, phase plates are fabricated by etched glass or photoresist with different thicknesses corresponding to the code. It is introduced on the intermediate image plane to reduce speckle in laser based line scan display system. The experimental results show that the phase plate with the 2D binary code of order 5 can successfully reduce speckle contrast to 17.5%. A set of two-dimensional (2D) binary codes are created by the calculation of the speckle contrast in line scan laser display system. According to the 2D binary code, phase plates are fabricated by etched glass or photoresist with different thicknesses corresponding to the code. It is introduced on the intermediate image plane to reduce speckle in laser based line scan display system. The experimental results show that the phase plate with the 2D binary code of order 5 can successfully reduce speckle contrast to 17.5%.
Chinese Optics Letters
- Publication Date: Jun. 20, 2012
- Vol. 10, Issue s1, S10301 (2012)
Transformation of general astigmatic Gaussian beams in a four-dimensional phase space
Baoxin Chen
A phase space model of two-dimensional (2D) Gaussian beam propagation is generalized for three-dimensional (3D) general astigmatic Gaussian beam passing through first-order optical system. The general astigmatic Gaussian beam is represented by a four-dimensional (4D) phase super-ellipsoid that defined by an associated 4*4 real matrix, then the transformation formula of the phase super-ellipsoid of the beam through first-order optical system is derived. In particular, in the phase space framework, the beam propagation factor M2 value is proved to be a ratio of phase area of real beam to ideal beam, and a novel approach for a qualitative examination of the properties of fractional Fourier transform (FRT) for the beam is also provided. A phase space model of two-dimensional (2D) Gaussian beam propagation is generalized for three-dimensional (3D) general astigmatic Gaussian beam passing through first-order optical system. The general astigmatic Gaussian beam is represented by a four-dimensional (4D) phase super-ellipsoid that defined by an associated 4*4 real matrix, then the transformation formula of the phase super-ellipsoid of the beam through first-order optical system is derived. In particular, in the phase space framework, the beam propagation factor M2 value is proved to be a ratio of phase area of real beam to ideal beam, and a novel approach for a qualitative examination of the properties of fractional Fourier transform (FRT) for the beam is also provided.
Chinese Optics Letters
- Publication Date: Jan. 01, 2006
- Vol. 4, Issue 5, 05255 (2006)
Invariance of spectrum and polarization of electromagnetic Gaussian Schell-model beams propagating in free space
Jixiong Pu
The propagation of polychromatic electromagnetic Gaussian Schell-model (EGSM) beams in free space is investigated. It is shown that the spectral degree of polarization, spectral degree of coherence, and normalized spectrum change generally on propagation. The conditions of keeping the spectral invariance and keeping polarization invariance for the polychromatic EGSM beams are derived respectively. The results indicate that the constraints on the parameters of EGSM source to keep polarization invariance on propagation are more rigorous than those to keep invariance of the normalized spectrum. The propagation of polychromatic electromagnetic Gaussian Schell-model (EGSM) beams in free space is investigated. It is shown that the spectral degree of polarization, spectral degree of coherence, and normalized spectrum change generally on propagation. The conditions of keeping the spectral invariance and keeping polarization invariance for the polychromatic EGSM beams are derived respectively. The results indicate that the constraints on the parameters of EGSM source to keep polarization invariance on propagation are more rigorous than those to keep invariance of the normalized spectrum.
Chinese Optics Letters
- Publication Date: Jan. 01, 2006
- Vol. 4, Issue 4, 04196 (2006)
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