Prediction control method to improve the dynamic performance of a close-loop adaptive optics system

Abstract

The prediction control method can be used to reduce the dynamic performance of an adaptive optics system (AOS) correcting the wavefront distortion of atmosphere turbulence. Some researchers have proved this idea but usually in open-loop condition and based on the wavefront or sub-aperture gradients of wavefront sensors. It is difficult to predict wavefront distortion in close-loop. But nearly all AOS are running in close-loop in practice to reduce the nonlinear error of wavefront sensor and deformable mirror (DM). In this paper, two prediction methods were proposed to improve the dynamic performance of an AOS both in open-loop and in close-loop. In one method, the Recursive Least-Square (RLS) algorithm was used to calculate the prediction and control parameters of an AOS based on the voltages of DM with 61 actuators. In another method, the Lucas-Kanade optical flow method was used to estimate transverse wind speed and calculate the predicted voltages of DM with 127 actuators. Numerical simulations were carried out with dynamic atmosphere turbulence in different conditions. The residual wave-front error, the Strehl Ratio, and the power spectrum densities were calculated and compared between an AOS with and without the prediction method. The results show that the dynamic control performances of an AOS will be improved significantly by using prediction control methods.