A Global Decoupling Control Algorithm for LC-DM Adaptive Optics System

Yukun Wang,Quanquan Mu,Dayu Li,Xingyun Zhang,Li Xuan

doi:10.1109/access.2021.3120991

Abstract

The liquid crystal (LC) and deformable mirror (DM) cascaded adaptive optics (AO) system can be used to effectively extend the imaging waveband of a large aperture telescope from the infrared to the visible waveband. However, to maintain the effectiveness and stability of the LC-DM AO system, the issues of synchronization and cross-coupling must be resolved. This study proposed a global decoupling control algorithm to simultaneously control the two correctors with high precision. The global decoupling control matrix has been constructed using an eigenmode orthogonal basis and a constraint matrix. The eigenmode orthogonal basis has been derived from the response matrix of the DM and is used for selectively distributing the large stroke low-order aberration to the DM and the remaining aberration to the LC. The constraint matrix has been derived from the projection of the LC response matrix onto the DM eigenmode orthogonal basis, which is used for restraining the LC generating the cross-coupling shape with the DM. The control vectors for both correctors have been calculated simultaneously using the global decoupling control matrix. Numerical simulation indicates that this algorithm exhibits good performance in correcting the different spatial frequency aberrations simultaneously and suppressing the cross-coupling between the dual correctors. Compared to the typical Zernike decomposition algorithm, this algorithm can make full use of the compensation ability of LC-DM. An experiment was conducted on the LC-DM AO system for a 2 m telescope. The experimental results demonstrate that this algorithm is practical for the LC-DM AO system. The cross-coupling between the dual correctors can be restrained well for static and dynamic aberrations simultaneously.

Highlights

Adaptive optics (AO) is an efficient technology used for compensating wavefront aberration and has been widely used on ground-based large aperture telescopes such as the Very Large Telescope (VLT), Gemini, Keck, Subaru, etc. [1]–[7]
This is a simple and practical algorithm that was developed for enabling the liquid crystal (LC)-deformable mirror (DM) to simultaneously correct different spatial frequency aberrations and achieve diffraction-limited correction performance
The eigenmode orthogonal basis from the DM response matrix was derived for the DM correction

Summary

INTRODUCTION

Adaptive optics (AO) is an efficient technology used for compensating wavefront aberration and has been widely used on ground-based large aperture telescopes such as the Very Large Telescope (VLT), Gemini, Keck, Subaru, etc. [1]–[7]. This algorithm is effective and computationally simple, with the slope signal measured by the WFS. We directly distribute the aberration based on the slope response matrix of the DM, which avoids the process of reconstruction, and makes full use of the correction ability of the DM To achieve this goal, the coupling matrix C (mDM × mDM ) between the actuators is calculated as: C(i, j) = C(j, i) = D−1 RDM(i)RDM(j)dxdy (2). With the constraint matrix and the eigenmode orthogonal basis, we can selectively distribute the large-amplitude low-order aberration to the DM and the remaining aberration to the LC. The global decoupling control matrix is constructed using Equations (16)–(18)

CORRECTION PERFORMANCE

CONCLUSION