Design Fabrication And Characterization Of High Stroke High Aspect Ratio Micro Electro Mechanical Systems Deformable Mirrors For Adaptive Optics

Microelectromechanical Systems (MEMS) is a rapidly emerging field of research in which batch fabrication processes are used to construct miniature devices. MEMS devices are particularly well suited to optical applications. Foundry microfabrication offers a substantial cost advantage for prototype system development. In this research, foundry MEMS processes are used to fabricate low-cost deformable mirror systems (MEM-DMs) for adaptive optics. The challenges and design trades associated with fabrication of continuous and segmented deformable mirrors in foundry processes are examined in detail. Micromirror surface figure is shown to be critically important. Beam steering and optical aberration correction experiments conclusively demonstrate the potential of low-cost MEM-DMs. The prototype MEM-DM systems are approximately 1/ 500th the cost of conventionally manufactured deformable mirrors. An innovative direct digital control scheme further reduces adaptive optic system cost by eliminating the digital to analog converter typically required for each controlled element. In addition to the MEM-DMs, other MEMS devices are shown. The thermally actuated piston micromirrors offer greater deflections for operation at longer optical wavelengths. Other MEMS devices examined include a series of tilting mirrors, pressure gauges, test structures, electrostatic scratch drive actuated rotors, and a new type of electrostatic cantilever motor with lateral motion output.

Micromachined Mirrors provides an overview of the performance enhancements that will be realized by miniaturizing scanning mirrors like those used for laser printers and barcode scanners, and the newly enabled applications, including raster-scanning projection video displays and compact, high-speed fiber-optic components. There are a wide variety of methods used to fabricate micromachined mirrors - each with its advantages and disadvantages. There are, however, performance criteria common to mirrors made from any of these fabrication processes. For example, optical resolution is related to the mirror aperture, the mirror flatness, and the scan angle. Micromachined Mirrors provides a framework for the design of micromirrors, and derives equations showing the fundamental limits for micromirror performance. These limits provide the micromirror designer tools with which to determine the acceptable mirror geometries, and to quickly and easily determine the range of possible mirror optical resolution and scan speed.

This research conducted the first demonstrated use of a micro- electro-mechanical structure (MEMS) mirror array to correct a static optical aberration. A well developed technique in adaptive optics imaging systems uses a deformable mirror to reflect the incident wave front to the imaging stage of the system. By matching the surface of the deformable mirror to the shape of the wave front phase distortion, the reflected wave front will be less aberrated before it is imaged. Typical adaptive optics systems use piezo-electric actuated deformable mirrors. This research used an electrostatically actuated, segmented mirror array, constructed by standard MEMS fabrication techniques, to investigate its performance as a deformable mirror. The relatively cheap cost of MEMS fabrication promises new adaptive optics applications if a suitable design can be found. In the demonstration, the point spread function (PSF) of the corrected and uncorrected aberrated image were compared. A 43 percent improvement in the peak intensity of the PSF was noted in the corrected image.

Adaptive optics is set to revolutionise the future of astronomy; this is the first book on the subject and is set to become the standard reference.