Experimental Validation of type II Tip—Tilt Control in a Woofer-Tweeter Adaptive Optics System

摘要

Woofer-Tweeter Adaptive Optics (AO) systems use two Deformable Mirrors (DM) with a single wavefront sensor (WFS) to correct for optical aberrations. The splitting of the DM commands derived from the WFS measurements must accommodate both the spatial and temporal bandwidth of the DMs. This paper reports on a woofer-tweeter experiment developed at the AO laboratory of the University of Victoria. This experiment uses a tip-tilt mirror as a woofer and a 9 x 9 CILAS PZT DM as a tweeter. The response of the woofer is slowed down in order to reproduce the behavior of the tip-tilt platform supporting the DM of the TMT/ NFIRAOS system. For this experiment, only the tip-tilt mode is considered, especially the off-loading of the low temporal frequencies of the tip-tilt mode from the DM to the slow tip-tilt mount is investigated. The closed-loop controller is a type II controller with a cascade of two integrators and a lead filter. The performance of this Woofer-Tweeter scheme as measured in the experiment is presented, and compared with the performance predicted by a hybrid Simulink model. The increased rejection achieved by the type II controller compared to a classical controller is quantified, as well as the increase in the associated noise propagation.