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Proceedings Paper

High-contrast grating MEMS optical phase-shifters for two-dimensional free-space beam steering
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Paper Abstract

We report an optical phased array (OPA) for two-dimensional free-space beam steering. The array is composed of tunable MEMS all-pass filters (APFs) based on polysilicon high contrast grating (HCG) mirrors. The cavity length of each APF is voltage controlled via an electrostatically-actuated HCG top mirror and a fixed DBR bottom mirror. The HCG mirrors are composed of only a single layer of polysilicon, achieving >99% reflectivity through the use of a subwavelength grating patterned into the polysilicon surface. Conventional metal-coated MEMS mirrors must be thick (1-50 μm) to prevent warpage arising from thermal and residual stress. The single material construction used here results in a high degree of flatness even in a thin 350 nm HCG mirror. Relative to beamsteering systems based on a single rotating MEMS mirror, which are typically limited to bandwidths below 50 kHz, the MEMS OPA described here has the advantage of greatly reduced mass and therefore achieves a bandwidth over 500 kHz. The APF structure affords large (~2π) phase shift at a small displacement (< 50 nm), an order-of-magnitude smaller than the displacement required in a single-mirror phase-shifter design. Precise control of each all-pass-filter is achieved through an interferometric phase measurement system, and beam steering is demonstrated using binary phase patterns.

Paper Details

Date Published: 19 February 2014
PDF: 8 pages
Proc. SPIE 8995, High Contrast Metastructures III, 89950Q (19 February 2014); doi: 10.1117/12.2045341
Show Author Affiliations
Mischa Megens, Univ. of California, Davis (United States)
Byung-Wook Yoo, Univ. of California, Berkeley (United States)
Trevor Chan, Univ. of California, Davis (United States)
Weijian Yang, Univ. of California, Berkeley (United States)
Tianbo Sun, Univ. of California, Berkeley (United States)
Connie J. Chang-Hasnain, Univ. of California, Berkeley (United States)
Ming C. Wu, Univ. of California, Berkeley (United States)
David A. Horsley, Univ. of California, Davis (United States)

Published in SPIE Proceedings Vol. 8995:
High Contrast Metastructures III
Connie J. Chang-Hasnain; David Fattal; Fumio Koyama; Weimin Zhou, Editor(s)

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