基于嵌入式平台控制的变形镜面形展平研究

Research on deformable mirror flattening based on embedded platform

变形镜是自适应光学系统中最主要的波前矫正器,它可以通过高频地改变镜面的面形来实时补偿波前像差。由压电陶瓷驱动的变形镜在自由状态下并非理想的平坦表面。由这种初始面形误差所产生的光学畸变将严重削弱变形镜闭环控制的性能。在使用变形镜进行光学像差矫正之前,需要首先对变形镜进行镜面展平。拟设计一种基于嵌入式平台的变形镜控制系统来实现面形展平和镜面变形。嵌入式平台选用英伟达公司的Jetson Nano开发平台。面形展平的关键环节是需要精确地获得变形镜对每个促动器行程(电压)的光学响应(影响函数),进而计算出响应矩阵。我们设计了基于Arm多核处理器的多线程算法显著提高了响应矩阵的计算速率。受压电材料的迟滞效应影响,变形镜的展平过程需要进行迭代收敛。经过数次迭代后,变形镜的面形误差RMS值由初始时的0.92λ降低到0.03λ,变形镜获得了比较好的展平效果。该系统的设计不但有利于变形镜系统的商用化,且较大程度地提高了变形镜闭环控制的能力,消除了自适应光学系统中变形镜自身的初始像差。

Deformable mirror(DM) is the most important wavefront corrector in adaptive optics. It can compensate wavefront aberration by changing the reflective mirror’s surface frequently. However, the commercial piezoelectric deformable mirror can’t obtain an ideal flat surface under the initial voltage. The optical aberration caused by this initial distortion will seriously weaken the performance of closed-loop control of deformable mirror. Therefore, it is necessary to flatten the surface of deformable mirror before using it for optical aberration correction. In the paper, a deformable mirror control system based on embedded platform is designed to realize surface flattening and mirror deformation. The embedded platform is Jetson Nano development board of NVIDIA company. In order to properly control the optical figure of the deformable mirrorwe have to obtain an response matrix which is the response of optical surface to the DM actuator’s stroke. Here, the multithreading algorithm is used to improve the computing speed of the response matrix. Because of the hysteresis effect of compressed electrical materials, the flatteing of deformable mirror needs to be carried out iteratively. After several close-loop iterations, the surface error RMS of the deformable mirror is reduced from 0.92λ to 0.03λ, The deformable mirror has a good flattening effect. The system is not only conducive to the commercialization of the deformable mirror system, but also greatly improves the closed-loop control ability of the deformable mirror and eliminates the initial aberration of the deformable mirror itself in the adaptive optical system.