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

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.