A MEMS SLM with an array of 64×64 pixels, each 120 μm ×120 μm in size, with 98% fill-factor, has been developed.
Each reflector in the array is capable of 5 μm of stroke, and ±4° tip and tilt. From a prototype array, 14 contiguous pixels
have been independently wired-out to off-chip drive electronics. These 14 pixels have been demonstrated to be effective in
an off-the-shelf AO system (with requisite modifications to suit the SLM). For a low-order static aberration, the measured
Strehl ratio has been improved from 0.069 to 0.861, a factor of 12 improvement.
Membrane deformable mirror devices consist of a single large membrane that is suspended above an array of actuating electrodes. A transparent electrode is incorporated into the membrane mirror device in the optical path in an effort to provide significantly greater control of the membrane, and hence improved performance in an adaptive optics system. The devices presented here were fabricated from 1 mm thickness SOI; devices were bonded to electrode arrays with 1024 electrodes, packaged in ceramic pin grid arrays and driven by off chip D/A electronics. The transparent electrodes consist of glass that is ITO coated for electrical conductivity and visible light transmission. An electrode is inserted into a recessed cavity of each membrane chip, and is positioned 70 mm above the membrane. With 2x2 binned electrodes, the device demonstrates 10 mm deflection toward the electrode array at 40 V. Large deflection at low voltage is obtained because of the low intrinsic stress of the silicon membrane. These data also demonstrate modest deflection toward the transparent electrode, which may be improved with better alignment of the transparent electrode with the underlying membrane and electrode array in future devices.
Low stress membrane mirrors will allow improved wave front correction in vision science and astronomical adaptive optics systems. We have fabricated low stress membrane mirrors from single crystal silicon, and flip chip bonded membranes to electrode arrays. These devices operate at lower voltage and have greater stroke than existing membrane mirror devices; they have 256 control electrodes, and are driven by off chip electronics. Devices have a single electrode plane and are pre-biased to allow full wave front correction. We have demonstrated these devices in an adaptive optics system consisting of a coherent source, and a Shack-Hartmann wave front sensor. We compare the experimental performance of the devices to computer simulations and theoretical calculations.
A large-scale, high speed, high resolution, phase-only microelectromechanical system (MEMS) spatial light modulator (SLM) has been fabricated. Using polysilicon thin film technology, the micro mirror array offers significant improvement in SLM speed in comparison to alternative modulator technologies. Pixel opto-electromechanical characterization has been quantified experimentally on large scale arrays of micro mirrors and results are reported.
The National Science Foundation Center for Adaptive Optics (CfAO) is coordinating a program for the development of spatial light modulators suitable for adaptive optics applications based on micro-optoelectromechanical systems (MOEMS) technology. This collaborative program is being conducted by researchers at several partner institutions including the Berkeley Sensor & Actuator Center, Boston Micromachines, Boston University, Lucent Technologies, the Jet Propulsion Laboratory, and Lawrence Livermore National Laboratory. The goal of this program is to produce MEMS spatial light modulators with several thousand actuators that can be used for high-resolution wavefront control applications that would benefit from low device cost, small system size, and low power requirements. The two primary applications targeted by the CfAO are astronomy and vision science. In this paper, we present an overview of the CfAO MEMS development plan along with details of the current program status.