Adaptive optic correction using microelectromechanical deformable mirrors

Abstract

A micromachined deformable mirror (μ-DM) for optical wavefront correction is described. Design and manufacturing approaches for μ-DMs are detailed. The μ-DM employs a flexible silicon membrane supported by mechanical attachments to an array of electrostatic parallel plate actuators. Devices are fabricated through surface micromachining using polycrystalline silicon thin films. μ-DM membranes measuring 2 mm×2 mm×2 μm, supported by 100 actuators are described. Figures of merit include stroke of 2 μm, resolution of 10 nm, and frequency bandwidth dc to 7 kHz in air. The devices are compact, inexpensive to fabricate, exhibit no hysteresis, and use only a small fraction of the power required for conventional DMs. Performance of an adaptive optics system using a μ-DM is characterized in a closed-loop control experiment. Significant reduction in quasistatic wavefront phase error is achieved. Advantages and limitations of μ-DMs are described in relation to conventional adaptive optics systems and to emerging applications of adaptive optics such as high-resolution correction, small-aperture systems, and optical communication.