We build an experimental system of adaptive optical (AO) system in a laboratory environment. When the light signal is transmitted through the turbulence chamber, the wavefront distortion is generated under the influen...
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ISBN:
(纸本)9781728187556
We build an experimental system of adaptive optical (AO) system in a laboratory environment. When the light signal is transmitted through the turbulence chamber, the wavefront distortion is generated under the influence of atmospheric turbulence. We employ a deformable mirror (DM) to correct the wavefront distortion. The AO system adopts stochasticparallelgradientdescent (SPGD) algorithm. Experimental results show that AO system is able to well correct the wavefront distortion.
We present the laboratory experiments of phase locking of a 37-channel tiled fiber array using a stochasticparallelgradientdescent (SPGD) feedback controller. The experimental setup comprises a hexagonally close-pa...
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ISBN:
(数字)9781510627598
ISBN:
(纸本)9781510627598
We present the laboratory experiments of phase locking of a 37-channel tiled fiber array using a stochasticparallelgradientdescent (SPGD) feedback controller. The experimental setup comprises a hexagonally close-packed array of thirty-seven 23-mm-diameter fiber collimator sub-apertures. The fraction of the output laser power within a solid angle of 1.22./D was measured in open loop state and then in closed loop state. The results show that the power in the bucket was increased from 0.028 in open loop to 0.890 in closed loop. When the 37 beams were phase-locked, the residual phase error was lambda/23. The power ratio in the bucket (PIB) was 28% that improved 32 times than the open loop state.
Multimode fibers are gaining a resurgence of interest in both fundamental and applied research in recent years. Thanks to the ability to see the weights and relative phase of the multimode fiber modes, mode decomposit...
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Multimode fibers are gaining a resurgence of interest in both fundamental and applied research in recent years. Thanks to the ability to see the weights and relative phase of the multimode fiber modes, mode decomposition (MD) has shown tremendous potential in wide applications of mode properties evaluation, mode-related processes measurement and fiber laser beams characterization. Among various MD techniques, numerical methods stand out for their simplicity and low hardware requirements. In this paper, the new horizon opened by the recently developed new numerical MD schemes will be reviewed. First, the background and basic principles of MD will be introduced, and some typical numerical MD methods will be summarized. Second, the multi-variable optimization approaches, including the stochasticparallelgradientdescent (SPGD) scheme and genetic algorithm (GA) assisted GA-SPGD strategy, will be presented in details. Third, a novel numerical MD method based on deep learning technique will be discussed, which solves the initial values sensitivity and relatively long-time cost of multi-variable optimization approaches. Last, several novel applications will be given, indicating the versatile applicability of numerical MD.
In this paper, a system of containing dual deformable mirrors (DMs) is proposed to adaptively conversion of input beam with wave front distortion into near-diffraction-limited flattop beam based on the stochastic para...
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ISBN:
(纸本)9780819483737
In this paper, a system of containing dual deformable mirrors (DMs) is proposed to adaptively conversion of input beam with wave front distortion into near-diffraction-limited flattop beam based on the stochasticparallelgradientdescent (SPGD) algorithm. In the analysis, the wave front distortion of the input beam is chosen as the Zernike representation of Kolmogoroff spectrum of turbulence. The whole shaping system is controlled by the SPGD algorithm. One DM adaptively redistributes the intensity of the input beam and the other adaptively compensates the wave front of the output beam. The near-diffraction-limited flattop beams with different parameters are realized by this technique. The near-diffraction-limited square flattop beam retains an flattop intensity distribution without significant diffraction peaks for a working distance of more than 60cm in the near field.
Multi-wavelength and non-single-frequency seed lasers can be used to suppress stimulated Brillouin scattering and improve the ultimate output power of a fiber laser amplifier. Coherent combining of non-single-frequenc...
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Multi-wavelength and non-single-frequency seed lasers can be used to suppress stimulated Brillouin scattering and improve the ultimate output power of a fiber laser amplifier. Coherent combining of non-single-frequency and/or multi-wavelength lasers/amplifiers is a promising way to obtain much higher total output power than from coherent combining of single-frequency lasers/amplifiers. Using a stochastic parallel gradient descent algorithm, we demonstrate coherent combining of four-channel multi-wavelength lasers in a master oscillator power amplifier (MOPA) configuration. Four lasers with different wavelengths, namely two non-single-frequency and two single-frequency lasers, are used. The mean power of the main lobe in the closed-loop case is three times that for the open-loop case, approaching 75% of its ideal value. The coherent combining of multi-wavelength and non-single-frequency lasers in a MOPA configuration is validated, and a feasible approach for scaling to high power coherent combining is provided.
In this paper, the physical properties of multimode beam are analysed by using the theory of partially coherent light. Based on the spatial coherence measurement results of a multimode fiber laser, we provide a theore...
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ISBN:
(数字)9781510611160
ISBN:
(纸本)9781510611160;9781510611153
In this paper, the physical properties of multimode beam are analysed by using the theory of partially coherent light. Based on the spatial coherence measurement results of a multimode fiber laser, we provide a theoretical basis for aberration correction for multimode beams. To improve the beam quality of multimode lasers, phase correction of multimode laser based on a dual-phase-only liquid-crystal spatial light modulator is presented which is used as aberration correction device. The phase distribution was optimized by the stochastic parallel gradient descent algorithm. In this paper the power in the bucket of the far field was used as the evaluation function and the multimode beam included multiple higher order Laguerre-Gaussian beam modes. The real-time aberration correction of Multimode beam by stochastic parallel gradient descent algorithm is simulated studied and experimental analysed respectively. According to the results the parameters of stochastic parallel gradient descent algorithm can be adjusted and the efficiency and practicability of the algorithm are determined.
Active polarization control of a high power fiber amplifier has been demonstrated. The master oscillator power amplifier system consisted of a narrow linewidth laser seed and a three-stage Yb-fiber amplifier. The narr...
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Active polarization control of a high power fiber amplifier has been demonstrated. The master oscillator power amplifier system consisted of a narrow linewidth laser seed and a three-stage Yb-fiber amplifier. The narrow linewidth laser seed was generated by phase modulating a single frequency fiber laser using a white noise source. Maximum power of 1437W was obtained from the main amplifier, which was limited by the available pump power. When the polarization state of the narrow linewidth (similar to 0.17 nm) laser was actively controlled by using a polarization controller based on stochastic parallel gradient descent algorithm, the polarization extinction ratio of the laser beam was more than 11.1 dB at the maximum output power.
Adaptive optics correcting technique based on stochasticparallelgradientdescent (SPGD) control algorithm is an alternative approach which is independent of wavefront sensor and optimizes the performance metric dire...
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ISBN:
(纸本)9780819483799
Adaptive optics correcting technique based on stochasticparallelgradientdescent (SPGD) control algorithm is an alternative approach which is independent of wavefront sensor and optimizes the performance metric directly. In this paper we establish a simulation model of tip-tilt adaptive optics system, where SPGD optimization algorithm is used to correct the tip-tilt aberration induced by dynamic turbulence. The distance between the measured centroid of a blurring image and the demarcated centroid of the ideal image is considered as the system performance metric, and signals applied to compensation of the drifting atmosphere are generated for tip-tilt mirror. The sensitivity of the performance metrics is investigated, and the convergence rate and the stability are analyzed. By means of this optimization algorithm, the centroid of the image is modified in real time, which results in the improvement of the long exposure image.
Coherent summation of fibre laser beams, which can be scaled to a relatively large number of elements, is simulated by using the stochasticparallelgradientdescent (SPGD) algorithm. The applicability of this algorit...
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Coherent summation of fibre laser beams, which can be scaled to a relatively large number of elements, is simulated by using the stochasticparallelgradientdescent (SPGD) algorithm. The applicability of this algorithm for coherent summation is analysed and its optimisaton parameters and bandwidth limitations are studied.
We propose and demonstrate an coherent imaging technique by using defocus grating. For the imaging system, the defocus grating combined with lens with short focal length is used to realize multiplane imaging on the le...
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ISBN:
(数字)9781510603899
ISBN:
(纸本)9781510603882;9781510603899
We propose and demonstrate an coherent imaging technique by using defocus grating. For the imaging system, the defocus grating combined with lens with short focal length is used to realize multiplane imaging on the lens' focal plane, simultaneously. Based on these multiplane images, Gerchberg-Saxton (GS) algorithm is used to reconstruct the complex amplitude distribution of the input imaging beam. By using computational imaging and digital wavefront distortion correction with stochasticparallelgradientdescent (SPGD) algorithm, this technology can be used for joint estimation of both pupil aberrations and an high resolution image of the object, successfully.
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