Journals > > Topics > COHERENCE OPTICS AND STATISTICAL OPTICS
COHERENCE OPTICS AND STATISTICAL OPTICS|12 Article(s)
Self-Healing Properties of Twisted Elliptical Gaussian Schell-Model Beams
Yinlong Guo, Xinyu Nie, Jinhong Li, Xianmei Qian, Wenyue Zhu, and Jing Wang
In this study, the analytical expression of field distribution of twisted elliptical Gaussian Schell-Model beams after they pass through a Gaussian absorption-type obstacle is derived based on the Collins formula, and a basic twisted-beam model is obtained that effectively enhances the beam's self-healing capability. The effects of the light source parameters on the beam's self-healing properties are analyzed. The laws of intensity, coherence, and orbital angular momentum flux density transmitted when partially blocked by obstacles and the intrinsic connection among the three quantities are revealed. The intrinsic self-healing properties of twisted beams are explained. It is shown that appropriately reducing the coherence length and twist factor can enhance the beam's self-healing capability while preserving the characteristics of the twisted beam. The findings can help optimize the overall performance of partially coherent light transmission in free space, thus enhancing potential applications in free space optical communication, LIDAR, remote sensing imaging, and other fields. In this study, the analytical expression of field distribution of twisted elliptical Gaussian Schell-Model beams after they pass through a Gaussian absorption-type obstacle is derived based on the Collins formula, and a basic twisted-beam model is obtained that effectively enhances the beam's self-healing capability. The effects of the light source parameters on the beam's self-healing properties are analyzed. The laws of intensity, coherence, and orbital angular momentum flux density transmitted when partially blocked by obstacles and the intrinsic connection among the three quantities are revealed. The intrinsic self-healing properties of twisted beams are explained. It is shown that appropriately reducing the coherence length and twist factor can enhance the beam's self-healing capability while preserving the characteristics of the twisted beam. The findings can help optimize the overall performance of partially coherent light transmission in free space, thus enhancing potential applications in free space optical communication, LIDAR, remote sensing imaging, and other fields.
Laser & Optoelectronics Progress
- Publication Date: Sep. 10, 2023
- Vol. 60, Issue 17, 1703001 (2023)
Quadrature Phase Shift Keying Coherent Receiving Technology Based on Field Programmable Gate Array
Baishuo Zhang, Yansong Song, Lei Xiao, and Dechun Zhao
Coherent laser communication has the advantages of high speed and long-distance transmission capabilities, both of which play an important role in inter-satellite communication. A coherent optical communication system makes full use of information on light intensity, phase, frequency, and polarization, which cannot only improve the efficiency of frequency band utilization, but also extend the relay distance across which optical communication is possible. As a type of multi band modulation, quadrature phase shift keying (QPSK) modulation and demodulation can greatly improve the utilization of spectrum resources. Aiming to resolve the problem of the response rate of QPSK modulation and demodulation in coherent optical laser communication, an improved Costas loop is proposed in this study. The results of the experiment verify the entire QPSK modulation and demodulation system and the performance feasibility of the improved Costas loop. Coherent laser communication has the advantages of high speed and long-distance transmission capabilities, both of which play an important role in inter-satellite communication. A coherent optical communication system makes full use of information on light intensity, phase, frequency, and polarization, which cannot only improve the efficiency of frequency band utilization, but also extend the relay distance across which optical communication is possible. As a type of multi band modulation, quadrature phase shift keying (QPSK) modulation and demodulation can greatly improve the utilization of spectrum resources. Aiming to resolve the problem of the response rate of QPSK modulation and demodulation in coherent optical laser communication, an improved Costas loop is proposed in this study. The results of the experiment verify the entire QPSK modulation and demodulation system and the performance feasibility of the improved Costas loop.
Laser & Optoelectronics Progress
- Publication Date: Jan. 10, 2023
- Vol. 60, Issue 1, 0103001 (2023)
Parameter Analysis and Experimental Study of Influence on Laser Speckle Suppression in Laser Projection Imaging
Yan Huang
Laser speckles create a bottleneck that hinders the development of laser projection display technology. Based on the compound speckle contrast analysis method, the parameters affecting the composite speckle lining ratio in a laser projection system are analyzed. These parameters include the number N of independent speckle samples and the number M of scattered light wave coherent elements within a single imaging-lens resolution element on the projection screen. The occurrence of speckles in the laser projection system can be reduced by changing parameters N and M. These changes can be achieved by adjusting the numerical apertures of the projection-lens and imaging-lens, projection distance, and observation distance. In the simplified projection model, the effects of the random-diffuser spot area and projection-lens numerical aperture on the speckle contrast in laser projection imaging were experimentally analyzed. The results reveal that for a certain size of the projection lens, the contrast of the secondary speckle pattern on the scattering screen can be reduced by increasing the area of the diffuser spot. The occurrence of speckles increases when the numerical aperture is reduced, thereby posing a challenge for the miniaturization of the laser projection system. The findings of this work can provide guidance for the use of a rotating random diffuser in the design of speckle suppression systems for laser projection imaging. Laser speckles create a bottleneck that hinders the development of laser projection display technology. Based on the compound speckle contrast analysis method, the parameters affecting the composite speckle lining ratio in a laser projection system are analyzed. These parameters include the number N of independent speckle samples and the number M of scattered light wave coherent elements within a single imaging-lens resolution element on the projection screen. The occurrence of speckles in the laser projection system can be reduced by changing parameters N and M. These changes can be achieved by adjusting the numerical apertures of the projection-lens and imaging-lens, projection distance, and observation distance. In the simplified projection model, the effects of the random-diffuser spot area and projection-lens numerical aperture on the speckle contrast in laser projection imaging were experimentally analyzed. The results reveal that for a certain size of the projection lens, the contrast of the secondary speckle pattern on the scattering screen can be reduced by increasing the area of the diffuser spot. The occurrence of speckles increases when the numerical aperture is reduced, thereby posing a challenge for the miniaturization of the laser projection system. The findings of this work can provide guidance for the use of a rotating random diffuser in the design of speckle suppression systems for laser projection imaging.
Laser & Optoelectronics Progress
- Publication Date: Jul. 10, 2022
- Vol. 59, Issue 13, 1303001 (2022)
Radially Polarized Twisted Rectangular Multi-Gaussian Schell-Model Beam and Its Propagation Properties
Rui Zhang, Xinge Liu, and Huafeng Xu
In recent years, the partially coherent beam carrying the twisted phase has received extensive attention due to its unique properties. A new partially coherent vector beam endowed with a twisted phase and a special spatial correlation structure is introduced, which is radially polarized twisted rectangular multi-Gaussian Schell-model beam. The cross-spectral density matrix elements of such beam passing through the ABCD optical system were derived, and the evolution properties, such as the normalized intensity distribution, the spectral degree of coherence (SDOC), and the spectral degree of polarization (SDOP) were investigated in detail. Numerical results show that the intensity distribution of the radially polarized rectangular multi-Gauss Schell-model beam without the twist phase gradually evolves from the hollow ring profile in the source plane into the rectangular flat-top profile in the focal plane. In comparison, the twisted phase carried by the radially polarized twisted rectangular multi-Gaussian Schell-model beam will not only induce the rotation of the beam spot, but also cause a series of changes in the SDOC and SDOP of the beam during the propagation process. The research results provide some theoretical guidance for the control of new vector structured beams with twisted phases, and have potential applications in beam shaping, optical micro-manipulation, and free space optical communications. In recent years, the partially coherent beam carrying the twisted phase has received extensive attention due to its unique properties. A new partially coherent vector beam endowed with a twisted phase and a special spatial correlation structure is introduced, which is radially polarized twisted rectangular multi-Gaussian Schell-model beam. The cross-spectral density matrix elements of such beam passing through the ABCD optical system were derived, and the evolution properties, such as the normalized intensity distribution, the spectral degree of coherence (SDOC), and the spectral degree of polarization (SDOP) were investigated in detail. Numerical results show that the intensity distribution of the radially polarized rectangular multi-Gauss Schell-model beam without the twist phase gradually evolves from the hollow ring profile in the source plane into the rectangular flat-top profile in the focal plane. In comparison, the twisted phase carried by the radially polarized twisted rectangular multi-Gaussian Schell-model beam will not only induce the rotation of the beam spot, but also cause a series of changes in the SDOC and SDOP of the beam during the propagation process. The research results provide some theoretical guidance for the control of new vector structured beams with twisted phases, and have potential applications in beam shaping, optical micro-manipulation, and free space optical communications.
Laser & Optoelectronics Progress
- Publication Date: Jun. 10, 2022
- Vol. 59, Issue 11, 1103001 (2022)
Space Separated Four-Light Coherent Moving Target Detection Using Polarization Spectroscopy Technology
Ren Jianying, Sun Huayan, Zhang Laixian, and Zhao Yanzhong
Aiming at the problem of limited speed measurement of moving targets in a large dynamic range， a four-light coherent mixing detection method is proposed. By extracting the Doppler frequency and the difference frequency between frequency shift and Doppler frequency， the speed measurement with a larger dynamic range can be achieved. In the process of four-optical coherent mixing detection， there are many output signals and the problem of difficult signal discrimination. In order to solve the above problems， a four-light coherent mixing detection structure with spatial polarization splitting structure is proposed and designed. Polarization splitting technology is used to achieve complete spatial separation of four output signals， avoiding mutual influence between signals and reducing the difficulty of signal processing. In theory， the structure is analyzed in principle， and the optical simulation software is used to simulate and analyze it to verify the feasibility of the theory and structure. At the same time， the direction of the target movement can be judged according to the output signals of different detectors. Aiming at the problem of limited speed measurement of moving targets in a large dynamic range， a four-light coherent mixing detection method is proposed. By extracting the Doppler frequency and the difference frequency between frequency shift and Doppler frequency， the speed measurement with a larger dynamic range can be achieved. In the process of four-optical coherent mixing detection， there are many output signals and the problem of difficult signal discrimination. In order to solve the above problems， a four-light coherent mixing detection structure with spatial polarization splitting structure is proposed and designed. Polarization splitting technology is used to achieve complete spatial separation of four output signals， avoiding mutual influence between signals and reducing the difficulty of signal processing. In theory， the structure is analyzed in principle， and the optical simulation software is used to simulate and analyze it to verify the feasibility of the theory and structure. At the same time， the direction of the target movement can be judged according to the output signals of different detectors.
Laser & Optoelectronics Progress
- Publication Date: Feb. 01, 2021
- Vol. 58, Issue 3, 3030011 (2021)
Optimized Oversampling and Readout Circuit Design for Quanta Image Sensor
Tong Zhao, Jing Gao, Jiangtao Xu, and Kaiming Nie
The data redundancy and dynamic range (DR) of quanta image sensor (QIS) are different under different oversampling bit-depth, and the requirements for readout circuit are also different. The reading noise introduced in the imaging process of QIS is studied, and the mathematical model of QIS imaging is optimized. Under the constraints of DR and offset tolerance, the optimal bit-depth of sub-pixel oversampling is obtained. The simulation results show that when the imaging bit-depth of the QIS is 12 bit and the equivalent full well capacity is 4095 electron, the optimal bit-depth of sub-pixel oversampling is 3. In order to ensure that the interval bit error rate is less than one thousandth, the readout circuit offset should be less than 0.22 electron. According to the sampling strategy, a flash low noise readout circuit based on multiplexing structure is designed. Compared with the traditional flash analog-to-digital converter (ADC), the number of ADC comparators is reduced by 4, and the power consumption is reduced by 17.5% when the sampling frequency is 10 MSa/s; when the sampling frequency is 1 MSa/s, the power consumption of ADC is 116 nW and the offset of ADC is 0.196 electron. The data redundancy and dynamic range (DR) of quanta image sensor (QIS) are different under different oversampling bit-depth, and the requirements for readout circuit are also different. The reading noise introduced in the imaging process of QIS is studied, and the mathematical model of QIS imaging is optimized. Under the constraints of DR and offset tolerance, the optimal bit-depth of sub-pixel oversampling is obtained. The simulation results show that when the imaging bit-depth of the QIS is 12 bit and the equivalent full well capacity is 4095 electron, the optimal bit-depth of sub-pixel oversampling is 3. In order to ensure that the interval bit error rate is less than one thousandth, the readout circuit offset should be less than 0.22 electron. According to the sampling strategy, a flash low noise readout circuit based on multiplexing structure is designed. Compared with the traditional flash analog-to-digital converter (ADC), the number of ADC comparators is reduced by 4, and the power consumption is reduced by 17.5% when the sampling frequency is 10 MSa/s; when the sampling frequency is 1 MSa/s, the power consumption of ADC is 116 nW and the offset of ADC is 0.196 electron.
Laser & Optoelectronics Progress
- Publication Date: Nov. 24, 2021
- Vol. 58, Issue 24, 2403001 (2021)
Propagation Characteristics of Radially Polarized Partially Coherent Twisted Beam in Anisotropic Atmospheric Turbulence
Ning Yang, Liang Zhao, Ying Xu, Shengkai Yang, and Yonggen Xu
This study derives the analytical expressions for the propagation factor and spatial expansion of radially polarized partially coherent twisted beams (RPPCTBs) in anisotropic atmospheric turbulence, with a focus on the effects of beam parameters, such as twisting factors and atmospheric turbulence parameters including anisotropic factors, on beam propagation characteristics. Using numerical simulation calculations, the effects of the initial coherence length, beam waist width, wavelength, twist factor, anisotropy factor, turbulence inner scale, turbulence outer scale, and generalized exponential parameters on the beam transmission quality are analyzed. Simulation results show that by decreasing the initial coherence length of the beam and increasing the beam waist width and wavelength, the transmission quality of the beam can be improved. Moreover, the twisting factor of the beam is increased and the beam shows a small transmission factor, demonstrating that the beam can be adjusted reasonably and the twisting phase can effectively improve the antiturbulence ability of the beam. This study derives the analytical expressions for the propagation factor and spatial expansion of radially polarized partially coherent twisted beams (RPPCTBs) in anisotropic atmospheric turbulence, with a focus on the effects of beam parameters, such as twisting factors and atmospheric turbulence parameters including anisotropic factors, on beam propagation characteristics. Using numerical simulation calculations, the effects of the initial coherence length, beam waist width, wavelength, twist factor, anisotropy factor, turbulence inner scale, turbulence outer scale, and generalized exponential parameters on the beam transmission quality are analyzed. Simulation results show that by decreasing the initial coherence length of the beam and increasing the beam waist width and wavelength, the transmission quality of the beam can be improved. Moreover, the twisting factor of the beam is increased and the beam shows a small transmission factor, demonstrating that the beam can be adjusted reasonably and the twisting phase can effectively improve the antiturbulence ability of the beam.
Laser & Optoelectronics Progress
- Publication Date: Nov. 10, 2021
- Vol. 58, Issue 21, 2103001 (2021)
Minor Damage Location Method for Aircraft Skins Based on Marked Honeycomb Model
Zhijing Yu, Xin Li, Yanling Li, Zechuan Li, and Jingchang Zhuge
A location method for minor damages of aircraft skins based on a marked honeycomb model is proposed. A CCD camera is used to capture the damage location, and the image is processed at sub-pixel level to obtain its coordinates. According to the principles of harmonic conjugation and the invariance of cross-ratios, the actual position of the damage can be determined to achieve accurate positioning. Then, based on this, the base point is transmitted and the infinite and seamless extensibility of the honeycomb model are used to compare and match of main base points and other base points on the surface of the aircraft skin so as to achieve accurate detection of the aircraft skin damage. The comparative experimental results show that the proposed method has high accuracy and less time consuming, and can effectively realize damage detection and location for aircraft skins. A location method for minor damages of aircraft skins based on a marked honeycomb model is proposed. A CCD camera is used to capture the damage location, and the image is processed at sub-pixel level to obtain its coordinates. According to the principles of harmonic conjugation and the invariance of cross-ratios, the actual position of the damage can be determined to achieve accurate positioning. Then, based on this, the base point is transmitted and the infinite and seamless extensibility of the honeycomb model are used to compare and match of main base points and other base points on the surface of the aircraft skin so as to achieve accurate detection of the aircraft skin damage. The comparative experimental results show that the proposed method has high accuracy and less time consuming, and can effectively realize damage detection and location for aircraft skins.
Laser & Optoelectronics Progress
- Publication Date: Sep. 07, 2019
- Vol. 56, Issue 18, 180301 (2019)
Colored Adaptive Compressed Imaging Based on Extended Wavelet Trees
Le Luo, Qian Chen, Xingjiong Liu, Yiyun Yan, Guohua Gu, Weiji He, and Ya Wang
An adaptive compressed sampling approach for color images is proposed based on extended wavelet tree theory and multitask Bayesian model. Exploiting the relationship of parent-children coefficients and sibling coefficients in extended wavelet trees, the images in the red, green, blue channels of the color images are adaptively compressed. Exploiting the correlation of the three channels of color images and multitask Bayesian model, the sampled high frequency wavelet coefficients of three channels are dealt, respectively, and then the color images are reconstructed and fused. The research results show that when the sampling times are 600 and the sampling rate is 14.6%, the peak signal to noise ratio values of the colored reconstructed images obtained by proposed method are all above 27 dB, while the mean value of color difference is the least, the color difference values tend to be stable, and the color consistency and stability of the images can be kept well. An adaptive compressed sampling approach for color images is proposed based on extended wavelet tree theory and multitask Bayesian model. Exploiting the relationship of parent-children coefficients and sibling coefficients in extended wavelet trees, the images in the red, green, blue channels of the color images are adaptively compressed. Exploiting the correlation of the three channels of color images and multitask Bayesian model, the sampled high frequency wavelet coefficients of three channels are dealt, respectively, and then the color images are reconstructed and fused. The research results show that when the sampling times are 600 and the sampling rate is 14.6%, the peak signal to noise ratio values of the colored reconstructed images obtained by proposed method are all above 27 dB, while the mean value of color difference is the least, the color difference values tend to be stable, and the color consistency and stability of the images can be kept well.
Laser & Optoelectronics Progress
- Publication Date: Jan. 08, 2019
- Vol. 56, Issue 1, 010301 (2019)
Effects of Coherent and Incoherent Light Sources on Resolution of Bessel Beam Imaging System
He Yanlin, Chen Ziyan, and Wu Fengtie
The effects of the coherent and incoherent light sources on the resolution of imaging system are studied in the process of non-diffracting beam imaging. In the limited diffraction imaging system, the formula of point spread function (PSF) of the imaging system is derived by the diffraction integral theory and Fourier optical theory. By simulating and comparing the different PSFs, it is found that the PSF is more concentrated and the imaging quality is better under the condition of incoherent light sources. He-Ne laser coherent light with the wavelength of 632.8 nm and incoherent light of blue light LED with the center wavelength of 458.5 nm and full width at half-maximum of 24.5 nm are used for experiment as light source, and Zemax software is used to simulate. Comparing the experimental and the numerical simulation results, the thickness of the stripes image of incoherent source is more uniform, clearer and its resolution is higher. The experimental results are consistent with theoretical analysis and numerical simulation results. The effects of the coherent and incoherent light sources on the resolution of imaging system are studied in the process of non-diffracting beam imaging. In the limited diffraction imaging system, the formula of point spread function (PSF) of the imaging system is derived by the diffraction integral theory and Fourier optical theory. By simulating and comparing the different PSFs, it is found that the PSF is more concentrated and the imaging quality is better under the condition of incoherent light sources. He-Ne laser coherent light with the wavelength of 632.8 nm and incoherent light of blue light LED with the center wavelength of 458.5 nm and full width at half-maximum of 24.5 nm are used for experiment as light source, and Zemax software is used to simulate. Comparing the experimental and the numerical simulation results, the thickness of the stripes image of incoherent source is more uniform, clearer and its resolution is higher. The experimental results are consistent with theoretical analysis and numerical simulation results.
Laser & Optoelectronics Progress
- Publication Date: Aug. 30, 2016
- Vol. 53, Issue 9, 90301 (2016)
Topics
© Copyright 2018-2021 | Chinese Laser Press. All Rights Reserved 沪ICP备15018463号-20