MOEMS for adaptive optics

This paper presents an overview of research and development programs at AFRL/VS in micro-opto-electro-mechanical systems (MOEMS) for adaptive optics. Adaptive optic systems typically consist of a wavefront phase sensor, focusing optics, a spatial light modulator (SLM) for correcting phase errors, imaging sensors, and the control and processing electronics. These systems have a simple purpose: they improve image quality by reducing the phase aberrations introduced when the wavefront travels through turbulent atmosphere or aberrations introduced by the optical system itself. As will be shown, aberration correction and controllable focus can also enable new system functions. Adaptive optic systems are becoming practical for space, missile, and man-portable applications. Comparisons are made between current macro-optical aberration correction systems and the micromirror based systems currently under development. These comparisons show how micromirrors are the crucial enabling technology for compacting these systems down to a size where their use in space can be contemplated. As an example of a space application, a proposed star tracker system is used as an example of a complete micro-optical system that employs not only a micromirror based SLM, but also a novel wavefront sensor, analog processing electronics, and new sensor electronics. Research on surface-micromachined polycrystalline silicon micromirrors will be reported, including work on several fabrication technologies for piston micromirrors and also for highly advanced micromirrors with tilting as well as piston motion. Design techniques for both individual micromirrors and arrays of micromirrors will be detailed for both the most advanced of these processes, the Sandia Ultra-planar Multi-level MEMS Technology (SUMMiT) process, and for the most widely available process, the Multi-User MEMS Process (MUMPS). Results of characterization testing and device modeling will be presented to show the advantages of each of- the various design approaches.