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We have fabricated sub-millimeter-sized quad corner-cube retroreflectors (CCRs) for free-space optical communication. Each quad CCR structure comprises three mirrors micromachined from silicon-on-insulator wafers, and is designed to facilitate manual assembly with accurate angular alignment. Assembled CCRs exhibit mirror nonflatness less than 50 nm, mirror roughness less than 2 nm, and mirror misalignment less than 1 mrad, leading to near-ideal optical performance. The quad CCR incorporates a gap-closing actuator to deflect a base mirror common to the four CCRs, allowing their reflectivity to be modulated up to 7 kb/s by a drive voltage less than 5 V. We have demonstrated a 180-m free-space optical communication link using a CCR as a passive optical transmitter. Quad CCRs have been integrated into miniature, autonomous nodes that constitute a distributed wireless sensor network. We present an analysis of the signal-to-noise ratio of CCR-based links, considering the impact of CCR dimensions, ambient light noise, and other factors.
Zhou et al. (Sun,) studied this question.