Feedback-stabilized deformable membrane mirrors for focus control

摘要

This paper describes a method to extend the range of motionnof a deformable, continuous membrane mirror beyond the limit of open-nloop electrostatic instability through feedback control. The feedbacknscheme employs capacitive sensing directly at the mirror actuation elec-ntrodes and is based on frequency modulation of a coupled ring oscillatornusing a differential measurement technique. Analysis of the systemnshows that the range of stable deflection depends on the relative dynam-nics of the device and the feedback control circuitry. Experimental resultsndemonstrate stable closed-loop deflection of our silicon nitride mem-nbrane test device to 69% of the air gap and confirm the dependence ofnthe maximum stable displacement on overall loop dynamics