自适应光学系统几种随机并行优化控制算法比较

直接对系统性能指标进行优化是自适应光学系统中一种重要的波前畸变校正方法,选择合适的随机并行优化控制算法是该技术成功实现的关键。以32单元变形镜为校正器,基于多种随机并行优化算法建立自适应光学系统仿真模型。从算法的收敛速度、校正效果、局部极值3个方面对遗传算法、单向扰动随机并行梯度下降、双向扰动随机并行梯度下降及模拟退火算法进行了比较。仿真结果表明,遗传算法收敛速度太慢,不适用于需要实时控制的自适应光学系统;双向扰动随机并行梯度下降算法收敛速度、校正效果要优于单向扰动随机并行梯度下降,且能够适应各种情况下的扰动电压;模拟退火几乎以概率1收敛到全局极值附近,且收敛速度是上述算法中最快的。     

自适应光学系统几种随机并行优化控制算法比较

 直接对系统性能指标进行优化是自适应光学系统中一种重要的波前畸变校正方法,选择合适的随机并行优化控制算法是该技术成功实现的关键。以32单元变形镜为校正器,基于多种随机并行优化算法建立自适应光学系统仿真模型。从算法的收敛速度、校正效果、局部极值3个方面对遗传算法、单向扰动随机并行梯度下降、双向扰动随机并行梯度下降及模拟退火算法进行了比较。仿真结果表明,遗传算法收敛速度太慢,不适用于需要实时控制的自适应光学系统;双向扰动随机并行梯度下降算法收敛速度、校正效果要优于单向扰动随机并行梯度下降,且能够适应各种情况下的扰动电压;模拟退火几乎以概率1收敛到全局极值附近,且收敛速度是上述算法中最快的。     

随机并行梯度下降光束净化实验研究

利用自适应光学技术进行光束净化是高能激光系统中一项重要的研究内容.为实现光束净化系统的小型化和低成本,基于系统性能评价函数无模型最优化的波前畸变校正方法是适合的技术方案.就随机并行梯度下降(SPGD)最优化算法在光束净化系统中的应用展开研究.针对高能激光束常见的像差分布进行了SPGD波前校正的数值模拟,在此基础上构建了37单元自适应光学光束净化实验平台,讨论了双边扰动梯度估计和迭代增益系数自适应变化对算法收敛特性的影响.数值模拟与实验结果验证了SPGD算法对不同程度波前畸变的校正能力,表明了SPGD光束净化方案的可行性.     

自适应光学系统随机并行梯度下降算法

随机并行梯度下降（SPGD）算法可以对系统性能指标直接优化来校正畸变波前。对基于SPGD算法的61单元自适应光学系统进行仿真模拟,分析了对不同初始静态畸变波前的校正能力,并比较了不同性能指标情况下的算法增益系数、扰动幅度值的选取及校正情况。仿真结果表明:算法收敛速度很大程度上依赖于增益系数和扰动幅度值,对畸变较大的波前,随机扰动幅度在0.50～0.85范围内,性能指标采用焦斑平均半径比采用斯特列尔比取得的校正效果好。     

自适应光学系统随机并行梯度下降算法

随机并行梯度下降(SPGD)算法可以对系统性能指标直接优化来校正畸变波前。对基于SPGD算法的61单元自适应光学系统进行仿真模拟,分析了对不同初始静态畸变波前的校正能力,并比较了不同性能指标情况下的算法增益系数、扰动幅度值的选取及校正情况。仿真结果表明:算法收敛速度很大程度上依赖于增益系数和扰动幅度值,对畸变较大的波前,随机扰动幅度在0.50~0.85范围内,性能指标采用焦斑平均半径比采用斯特列尔比取得的校正效果好。     

Hybrid approach used for extended image-based wavefront sensor-less adaptive optics

The stochastic parallel gradient descent(SPGD) algorithm is widely used in wavefront sensor-less adaptive optics(WSAO) systems. However, the convergence is relatively slow. Modal-based algorithms usually provide much faster convergence than SPGD; however, the limited actuator stroke of the deformable mirror(DM) often prohibits the sensing of higher-order modes or renders a closed-loop correction inapplicable. Based on a comparative analysis of SPGD and the DM-modal-based algorithm, a hybrid approach involving both algorithms is proposed for extended image-based WSAO, and is demonstrated in this experiment. The hybrid approach can achieve similar correction results to pure SPGD, but with a dramatically decreased iteration number.     

基于Zernike模式的自适应光学系统随机并行梯度下降算法

 控制算法的收敛速度一定程度上限制了无波前探测自适应光学技术在实时波前畸变校正中的应用。从理论分析角度提出将模式法和区域法结合起来以提高算法收敛速度,并以61单元变形镜为校正器,建立基于随机并行梯度下降算法自适应光学系统仿真模型。结果表明：达到同样的校正效果时,采用组合优化的算法收敛速度要明显优于基于区域法的收敛速度,从而验证了理论分析的合理性。     

基于Zernike模式的自适应光学系统随机并行梯度下降算法

控制算法的收敛速度一定程度上限制了无波前探测自适应光学技术在实时波前畸变校正中的应用。从理论分析角度提出将模式法和区域法结合起来以提高算法收敛速度,并以61单元变形镜为校正器,建立基于随机并行梯度下降算法自适应光学系统仿真模型。结果表明：达到同样的校正效果时,采用组合优化的算法收敛速度要明显优于基于区域法的收敛速度,从而验证了理论分析的合理性。     

Adaptive optics correction based on stochastic parallel gradient descent technique under various atmospheric scintillation conditions: numerical simulation

An adaptive optics system utilizing a Shack–Hartmann wavefront sensor and a deformable mirror can successfully correct a distorted wavefront by the conjugation principle. However, if a wave propagates over such a path that scintillation is not negligible, the appearance of branch points makes least-squares reconstruction fail to estimate the wavefront effectively. An adaptive optics technique based on the stochastic parallel gradient descent (SPGD) control algorithm is an alternative approach which does not need wavefront information but optimizes the performance metric directly. Performance was evaluated by simulating a SPGD control system and conventional adaptive correction with least-squares reconstruction in the context of a laser beam projection system. We also examined the relative performance of coping with branch points by the SPGD technique through an example. All studies were carried out under the conditions of assuming the systems have noise-free measurements and infinite time control bandwidth. Results indicate that the SPGD adaptive system always performs better than the system based on the least-squares wavefront reconstruction technique in the presence of relatively serious intensity scintillations. The reason is that the SPGD adaptive system has the ability of compensating a discontinuous phase, although the phase is not detected and reconstructed.     

自适应光学系统随机并行梯度下降控制算法仿真与分析

随机并行梯度下降算法能不依赖波前传感器直接对系统性能进行优化。以32单元变形镜为校正器,采用随机并行梯度下降算法建立了自适应光学系统仿真模型。通过分析该系统对静态波前畸变的校正能力,验证了随机并行梯度下降算法的收敛性;讨论了算法增益系数、随机扰动幅度与收敛速度的关系,并指出通过算法增益系数的自适应调整可以改进算法的收敛速度。     

一种基于全息术的光学系统闭环像差补偿方法

提出了一种基于21单元变形镜与全息波前传感器的全息自适应光学系统, 并对其像差校正能力进行了分析. 首先描述了全息波前传感器基本原理, 并在薄全息图近似下给出基于快速傅里叶变换算法的全息波前传感器数值模型; 然后基于21单元变形镜的数值模型, 分析了该变形镜的波前校正能力; 在此基础上, 数值模拟并实验验证了全息自适应光学系统对静态像差的闭环校正能力.     

37单元双压电片变形镜板条激光光束净化

为了校正板条激光器输出光束波前像差,改善输出光束质量,提出了基于37单元双压电片变形镜的板条激光光束净化系统。采用柱面反射式单向扩束器使主振荡功率放大结构板条激光器输出光束尺寸与37单元双压电片变形镜有效口径相匹配,利用随机并行梯度下降算法控制双压电片变形镜面形,进行波前像差闭环校正,校正后光束远场归一化桶中功率提高到净化前的2~3倍。     

37单元双压电片变形镜板条激光光束净化

为了校正板条激光器输出光束波前像差,改善输出光束质量,提出了基于37单元双压电片变形镜的板条激光光束净化系统。采用柱面反射式单向扩束器使主振荡功率放大结构板条激光器输出光束尺寸与37单元双压电片变形镜有效口径相匹配,利用随机并行梯度下降算法控制双压电片变形镜面形,进行波前像差闭环校正,校正后光束远场归一化桶中功率提高到净化前的2~3倍。     

一种结合图像复原技术的自适应光学系统控制方法

在天文高分辨成像领域,自适应光学校正和事后图像复原都必不可少,但传统的自适应光学系统控制方法以提升光学成像质量为目的,并未考虑图像复原环节,因此,研究一种结合两者以获得高质量复原图像为目标的控制方法具有重要意义.本文对传统自适应光学技术结合事后图像解卷积的方法进行了分析,阐述了其存在的缺陷.首次提出了将自适应光学技术和图像复原技术相结合进行系统分析的思想,并提出了变形镜校正度(变形镜控制电压相对于传统方法控制电压的缩放比例)的概念,通过改变校正度可实现变形镜校正残差和波前传感器探测误差的调整,同时证明了复原图像质量在校正度下降的方向存在一个最优值,用最优校正度来修正变形镜控制电压,就得到了一种新的控制方法.针对点源目标成像,仿真表明该方法相比于传统方法,能够得到质量更好的复原图像.     

Laser beam cleanup using improved model-based wavefront sensorless adaptive optics

An improved model-based wavefront sensorless adaptive optics algorithm is proposed for laser beam cleanup.Deformable mirror(DM) eigenmodes are used to replace traditional Lukosz modes in order to avoid DM fitting errors. The traditional method is based on a sophisticated calibration process and solving linear equations. In our method, coefficients of DM eigenmodes are estimated by adding bidirectional modal biases into the system and then solving parabolic equations. The calibration process is omitted in our method, which makes it more feasible.From simulation and experimental results, the corrective accuracy of the improved method is higher than the traditional one.     

37-element solar adaptive optics for 26-cm solar fine structure telescope at Yunnan Astronomical Observatory

A 37-element solar adaptive optics （AO） system was built and installed at the 26-cm solar fine structure telescope of Yunnan Astronomical Observatory. The AO system is composed of a fine tracking loop with a tip/tilt mirror and a correlation tracker, a high-order correction loop with a 37-element deformable mirror, a correlating Shack-Hartmann wavefront sensor based on the absolute difference algorithm, and a real time controller. The system was completed on Sep. 28, 2009 and was used to obtain AO-corrected high-resolution solar images. The contrast and resolution of the images are clearly improved after wavefront correction by AO. To the best of out knowledge, this system is the first solar AO system in China.     

A parallel system for adaptive optics based on parallel mutation PSO algorithm

Wavefront sensor-less adaptive optics technology has a much higher requirement for the processing speed than ever before. To improve the efficiency of particle swarm optimization (PSO), this paper proposes a novel parallel mutation particle swarm optimization (PMPSO) algorithm based on a master-slave model. The parallel system based on PMPSO algorithm is applied in a 61-element adaptive optics system to control the deformable mirror. The experimental results show that the parallel system based on PMPSO algorithm has a rapid convergence speed, which can effectively correct the wavefront aberration.     

Combinational-deformable-mirror adaptive optics system for compensation of high-order modes of wavefront

A new kind of adaptive optics (AO) system, in which several low spatial frequency deformable mirrors(DMs) with optical conjugation relationship are combined to correct high-order aberrations, is proposed.The phase compensation principle and the control method of the combinational AO system are introduced.The numerical simulations for the AO system with two 60-element DMs are presented. The results indicate that the combinational DM in the AO system can correct different aberrations effectively as one single DM with more actuators, and there is no change of control method. This technique can be applied to a large telescope AO system to improve the spatial compensation capability for wavefront by using current DM.     

哈特曼波前探测及波前校正的仿真与误差分析

报道了以３７单元自适应光学系统为原型的波前校正计算机仿真模型，讨论了系统波前哈特曼探测误差，拟合误差以及变形镜波前复原误差，提出了自适应光学系统在校正大气湍流引直怕波前位相畸变时存在最佳有效孔径的设想。     

Adaptive aberration correction based on ant colony algorithm for solid-state lasers: numerical simulations

We describe an adaptive aberration correction technique based on an ant colony algorithm for solid-state lasers and a general class of other adaptive optics systems. We show that it is possible to compensate phase aberrations without wavefront sensing in this approach, which iteratively adjusts the control voltages of a deformable mirror to maximize certain system performance metrics of the far-field intensity distribution of the laser beam. The effectiveness of this approach is analyzed numerically by use of a 37-element piezoelectric deformable mirror and a variation of the Strehl ratio as the metric. Results demonstrate that this approach can effectively compensate the phase distortions of laser beams and significantly improve beam quality. A comparison indicates that this approach is much faster than a genetic algorithm while achieving almost the same beam quality.