High Speed Focus Control Capability of Electrostatic-Pneumatic MEMS Deformable Mirrors

MEMS deformable mirrors are versatile elements for optical focus control. Electrostatic-pneumatic actuation of the mirrors offers relatively large membrane stroke to increase focus range. Moreover, this novel actuation method provides high speed focus control with either positive or negative focus. The speed of focusing is dependent on membrane tension, membrane size, air channel configuration, and the size of the backchamber. A 3 mm diameter mirror with 5 mm diameter actuator membrane achieves 30 kHz bandwidth with electrostatic actuation and 8 kHz bandwidth with pneumatic actuation. The settling time of the step response for both electrostatic and pneumatic actuation is approximately 100 mu s.