Field-of-view shifted Shack-Hartmann wavefront sensor for daytime adaptive optics system

For the daytime adaptive optics system, a field-of-view shifted Shack-Hartmann wavefront sensor (FSWFS), which is used to measure the aberrant wavefront under daytime conditions, is proposed. Because the field angle of the object signal in adaptive optics systems is much less than that of the sky background, the effective object signal is separated from the strong sky background. Experimental results indicate that FSWFS with a single focal-plane array can precisely and stably measure the aberrant wavefront information with a strong sky background under daytime conditions.     

自参考干涉波前传感器中针孔直径对闭环自适应光学系统校正精度的影响

使用自参考干涉波前传感器(SRIWFS)进行波前的绝对测量时,为了获得近似平面波前的参考波,针孔直径应该不大于无畸变光学系统艾里斑直径(d_A)的一半,然而这必将导致光能利用率的严重下降.为了最大程度地提高光能利用率并改善干涉条纹的对比度,研究了SRIWFS应用于闭环校正中时所允许的最大针孔直径,这将在闭环开始阶段尤为重要.数值模拟和实验表明,直径不大于1.5d_A的针孔可以获得满意的校正结果,校正后远场斯特列尔比高于80％;同时光能 关键词： 自适应光学 自参考干涉波前传感器 针孔直径 闭环校正     

无调制两面锥波前传感器的衍射理论分析和数值仿真

两面锥波前传感器(two-sided pyramid wavefront Sensor,TSPWFS)是一种高空间采样率和高光能利用率的波前传感器.为了深入研究它的波前复原原理,采用波动光学理论详细推导了无调制TSPWFS的衍射理论,给出了无调制TSPWFS波前复原时线性重构矩阵的解析解,并且通过数值仿真确定出最佳的光瞳像中心间距,并对静态像差的波前复原及闭环校正进行数值仿真.分析结果表明,无调制TSPWFS具有波前复原时不需要现场测量响应矩阵,可以校正系统像差,闭环校正结果稳定等优点,可以在实际自适应光学系统中进行波前探测. 关键词： 自适应光学 两面锥波前传感器 波前复原     

Experimental validation of closed-loop adaptive optics based on a self-referencing interferometer wavefront sensor and a liquid-crystal spatial light modulator

A closed-loop adaptive optics system based on a self-referencing interferometer wavefront sensor (SRI WFS) using phase-shifting point-diffraction technique and an electrically addressed phase-only liquid-crystal spatial light modulator (LC SLM) is built and validated experimentally. The wavefront aberration of incoming beam is directly measured by analyzing four frames phase-shifted interferograms captured by a single CCD camera in two camera shots, and then by loading the conjugate function onto the SLM the wavefront aberration is corrected. The proposed scheme does not rely on any complicated control algorithm or wavefront-reconstruction algorithm and can achieve high-resolution and high-accuracy correction. Closed-loop correction results of single order Zernike aberrations and a Kolmogorov turbulence phase screen show that considerable improvements in the Strehl ratio (of greater than 0.94) is achieved.     

自适应光学波面传感器的研究

在讨论几种波面传感器的基础上,介绍了一种新型的自适应光学波面传感器。实验结果表明,软刀口型波面传感器具有良好的实际应用前景。给出了它的工作原理,并介绍了各种传感器的优点。     

Comparison of several stochastic parallel optimization algorithms for adaptive optics system without a wavefront sensor

Optimizing the system performance metric directly is an important method for correcting wavefront aberrations in an adaptive optics (AO) system where wavefront sensing methods are unavailable or ineffective. An appropriate “Deformable Mirror” control algorithm is the key to successful wavefront correction. Based on several stochastic parallel optimization control algorithms, an adaptive optics system with a 61-element Deformable Mirror (DM) is simulated. Genetic Algorithm (GA), Stochastic Parallel Gradient Descent (SPGD), Simulated Annealing (SA) and Algorithm Of Pattern Extraction (Alopex) are compared in convergence speed and correction capability. The results show that all these algorithms have the ability to correct for atmospheric turbulence. Compared with least squares fitting, they almost obtain the best correction achievable for the 61-element DM. SA is the fastest and GA is the slowest in these algorithms. The number of perturbation by GA is almost 20 times larger than that of SA, 15 times larger than SPGD and 9 times larger than Alopex.     

自适应光学波前校正器

报告了自适应光学波前校正器——多元分立式压电变形反射镜和两维高速压电倾斜镜的研究工作。讨论了这两类波前校正器的主要性能及其检测方法等，并给出了若干典型的检测结果。研制的１９单元度形镜已成功用于ＩＣＦ驱动器的波前校正，而２１单元变形镜已成功用于天文观测星体成像校正     

Modal prediction for closed-loop adaptive optics

The correction efficiency of adaptive optics is limited mainly by measurement noise and time delay. To overcome this problem, we describe a new modal linear predictive controller whose parameters are optimized by means of a recursive least-squares algorithm to minimize the residual optical phase variance. The method copes with the recursivity of the closed-loop operation. We demonstrate that the optimal rejection transfer function for adaptive optics is proportional to the frequency signal-to-noise ratio. Finally, we present what we believe to be the first experimental results obtained with a predictor used to control the tip-tilt mirror of an adaptive-optics system.     

Wavefront sensorless adaptive optics for large aberrations

In some adaptive optics systems the aberration is determined not by using a wavefront sensor but by sequential optimization of the adaptive correction element. Efficient schemes for the control of such systems are essential if they are to be effective. A scheme is introduced that permits the efficient measurement of large amplitude wavefront aberrations that are represented by an appropriate series of modes. This scheme uses an optimization metric based on the root-mean-square spot radius (or focal spot second moment) and an aberration expansion using polynomials suited to the representation of lateral aberrations. Experimental correction of N aberration modes is demonstrated with a minimum of N+1 photodetector measurements. The geometrical optics basis means that the scheme can be extended to arbitrarily large aberrations.     

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.     

Optimization of the transmitted wavefront for the infrared adaptive optics system

The adaptive optics system for the second-generation Very Large Telescope-interferometer(VLTI)instrument GRAVITY consists of a novel cryogenic near-infrared wavefront sensor to be installed at each of the four unit telescopes of the Very Large Telescope(VLT).Feeding the GRAVITY wavefront sensor with light in the 1.4–2.4μm band,while suppressing laser light originating from the GRAVITY metrology system requires custom-built optical componets.In this paper,we present the development of a quantitative near-infraredpoint diffraction interferometric characterization technique,which allows measuring the transmitted wavefront error of the silicon entrance windows of the wavefront sensor cryostat.The technique can be readily applied to quantitative phase measurements in the near-infrared regime.Moreover,by employing a slightly off-axis optical setup,the proposed method can optimize the required spatial resolution and enable real time measurement capabilities.The feasibility of the proposed setup is demonstrated,followed by a theoretical analysis and experimental results.Our experimental results show that the phase error repeatability in the nanometer regime can be achieved.     

一种适于自适应光学的旋转软刀口波面传感器的研究

利用傅里叶光学理论,证明了一种新型波面传感器——旋转软刀口波面传感器的概念.在经典刀口法的刀口区,以渐变透过率代替突变透过率函数,在光瞳象面上可获得反映光瞳面位置待测波面位相梯度及位相梯度方向的调制信号.文中给出了实验结果和讨论.     

Comparison between iterative wavefront control algorithm and direct gradient wavefront control algorithm for adaptive optics system

Among all kinds of wavefront control algorithms in adaptive optics systems, the direct gradient wavefront control algorithm is the most widespread and common method. This control algorithm obtains the actuator voltages directly from wavefront slopes through pre-measuring the relational matrix between deformable mirror actuators and Hartmann wavefront sensor with perfect real-time characteristic and stability. However, with increasing the number of sub-apertures in wavefront sensor and deformable mirror actuators of adaptive optics systems, the matrix operation in direct gradient algorithm takes too much time, which becomes a major factor influencing control effect of adaptive optics systems. In this paper we apply an iterative wavefront control algorithm to high-resolution adaptive optics systems, in which the voltages of each actuator are obtained through iteration arithmetic, which gains great advantage in calculation and storage. For AO system with thousands of actuators, the computational complexity estimate is about O(n2) ～ O(n3) in direct gradient wavefront control algorithm, while the computational complexity estimate in iterative wavefront control algorithm is about O(n) ～(O(n)3/2), in which n is the number of actuators of AO system. And the more the numbers of sub-apertures and deformable mirror actuators, the more significant advantage the iterative wavefront control algorithm exhibits.     

自适应光学中扩展信标波前探测的研究与实验

讨论了一种基于Hartmann Shack (H S)传感器的扩展信标相关波前探测方法。通过在传统H S探测光路的物平面上加入视场光阑消除了子孔径像斑的重叠问题 ,并利用一种快速相关算法计算各像斑的相对位移 ,进而得到各子孔径波前的相对斜率。光学实验研究证实了该相关波前探测方法能够较精确地测算出波前像差 ,从而使目前使用最多的H S传感器具有扩展信标波前探测能力     

基于深度学习的自适应光学波前传感技术研究综述

波前传感是自适应光学系统的重要组成部分,在地基大口径望远镜、激光大气传输、无线光通信、激光驱动核聚变等领域发挥了关键作用,同时也常应用于自由曲面的光学测量中。与此同时,深度学习作为一种较为通用的前沿技术,成功在计算机视觉、自然语言处理等众多领域取得了革命性进展。使用深度学习的方法改进自适应光学系统中的波前传感器,以期实现更精准的波前探测,以及适应更复杂的应用场景是自适应光学的发展趋势,也是深度学习应用领域的一个新课题。介绍了深度学习在自适应光学波前传感中的应用现状,主要分析了在相位反演波前传感器和哈特曼波前传感器中的研究特点,并在最后进行了总结和展望。

     

用于白天自适应光学的波前探测方法分析

提出了两种视场偏移哈特曼波前传感器，用于探测白天条件下强背景中目标信号的波前信息.给出了哈特曼波前传感器子孔径中焦面上天光背景非均匀性分布特征的实验结果，详细分析了基于分光棱镜的双焦面视场偏移哈特曼波前传感器的探测误差，并通过基于倾斜镜的单焦面视场偏移哈特曼波前传感器实验给出了波前测量的结果，证明视场偏移哈特曼波前传感器能够精确、稳定的测量白天条件下目标信号的畸变波前信息，同时给出了其在白天条件下探测能力的估算结果及其受限因素，估算结果表明云南天文台的自适应光学系统在10 W/m²·sr天光背景条件下应用视场偏移哈特曼波前传感器能对5等星(可视星等值)目标进行准确的波前探测. 关键词： 自适应光学 波前传感器 白天工作 误差分析     

基于成像自适应光学的水下成像系统研究

水中湍流是影响水下光学系统性能的重要的潜在因素。用波前检测的方法对水中湍流对激光束传输的影响进行实验研究,测量了实验条件下水中湍流产生的波前畸变的大小,对波前畸变进行了Zernike分析,还对波前补偿自适应系统在水下成像的应用进行了探索。结果表明:水中湍流引起的激光束波前的起伏降低了图像的分辨率,自适应光学系统在其校正范围内能有效地校正畸变,提高图像质量。     

自适应光学系统倾斜校正回路的最优闭环带宽

基于实际自适应光学系统倾斜校正回路最常使用的比例积分控制器,分析了最优闭环带宽与大气湍流、测量噪声之间的关系.利用满足Kolmogorov湍流整体倾斜功率谱密度的时间序列进行了相关的数值仿真.结果表明,根据不同湍流强度及测量噪声选择合适的闭环带宽,可以充分发挥自适应光学系统倾斜校正回路的闭环校正能力,减小闭环残差.     

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.     

Hartmann－Shack波前传感器的Fourier光学分析

Ｈａｒｔｍａｎｎ－Ｓｈａｃｋ波前传感器是自适应光学中几种重要的波前传感器之一。本文利用Ｆｏｕｒｉｅｒ光学方法分析研究了Ｈａｒｔｍａｎｎ－Ｓｈａｃｋ波前传感器的原理，导出了辐照度分布质心与子孔径波前倾斜的解析表达式，说明了辐照度分布质心及其算法的物理意义，总结了该传感器的若干重要特点。