Design and Fabrication of a Continuous Membrane Deformable Mirror

摘要

Adaptive optics systems are used to maintain an optical system at its optimum performance through real time corrections of a wavefront. Deformable mirrors have traditionally been relatively large, expensive devices, suitable for systems such as large telescopes. The objective of the present work is to expand the range of systems that can employ adaptive optics by developing a small, low-cost MEMS deformable mirror. This deformable mirror uses a continuous membrane and has 61 actuators arranged in to approximate a circular pattern. Each actuator has an associated spring suspension, allowing it to push as well as pull on the membrane, producing locally convex or concave curvature. The folded springs are positioned so as to maximize the lateral stability. Maximum actuator displacement is six microns at less than 200 volts. The actuator resonant frequency, is greater than 10 kHz, allowing high-frequency updates of the mirror shape. To operate at high speed, the device must be sealed in a low-pressure environment. Each microactuator uses a vertical comb drive to achieve large travel at a reasonable voltage. The continuous membranes are made of silicon or silicon nitride. Both the actuator and membrane are fabricated with bulk micromachine process technologies. The design targets laser based communication specifications and medical imaging applications.