Silicon Surface Micromachined Deformable Mirrorsfor Fast Light Valves

摘要

Moving mirror structures are electrostatically deflected to modulate an incident lightrnbeam into discrete binary elements, with switching speeds at 10 MHz and above. Thernmirror elements display a high reflectivity in the "on" state, making them useful forrnapplications where optical throughput is important. Zeroth-order contrast has beenrnobserved as high as 65:1. The mirror to mirror spacing can be as close as is allowed byrnlithographic methods; we demonstrate 1 micron spacing with 40 micron pixel size. Therndesign delivers extremely high speeds, due to the large restoring force of a tautrnmembrane-like structure.rnThe fabrication techniques allow high yield and ease of manufacture. A nine layer stackrnof thin films is deposited in sequence with no intervening processing steps, providing arnmirror surface with extremely low roughness. The selective nature of the subsequentrnetching processes then allow device fabrication using only three lithography steps.rnThe relatively simple design within a MEMS-specific fabrication facility also allows forrnmaterials control and choices not available within a CMOS fabrication facility. Materialsrnand process optimization were the dominant hurdles to overcome in the six yearrndevelopment cycle, but with control over these parameters and processes, highrnperformance is available from a very simple and robust process.rnApplications for this device are varied and still being explored. Early results in fieldrntrials after 5 years of bench testing are extremely encouraging. Any application whichrnrequires modulation of high energy lasers into discrete elements is a candidate for such arndevice.