Piezo-electrically Actuated Micro Corner Cube Retroreflector (CCR) for Free-space Optical Communication Applications

Abstract

In this paper, an extremely low voltage operated micro corner cube retroreflector (CCR) was fabricated for free-space optical communication applications by using bulk silicon micromachining technologies. The CCR was comprised of an orthogonal vertical mirror and a horizontal actuated mirror. For low voltage operation, the horizontal actuated mirror was designed with two PZT cantilever actuators, torsional bars, hinges, and a mirror plate with a size of <TEX>$400{\mu}m{\times}400{\mu}m$</TEX>. In particular, the torsional bars and hinges were carefully simulated and designed to secure the flatness of the mirror plate by using a finite element method (FEM) simulator. The measured tilting angle was approximately <TEX>$2^{\circ}$</TEX> at the applied voltage of 5 V. An orthogonal vertical mirror with an extremely smooth surface texture was fabricated using KOH wet etching and a double-SOI (silicon-on-insulator) wafer with a (110) silicon wafer. The fabricated orthogonal vertical mirror was comprised of four pairs of two mutually orthogonal flat mirrors with <TEX>$400{\mu}m4</TEX> (length) <TEX>$\times400{\mu}m$</TEX> (height) <TEX>$\times30{\mu}m$</TEX> (thickness). The cross angles and surface roughness of the orthogonal vertical mirror were orthogonal, almost <TEX>$90^{\circ}$</TEX> and 3.523 nm rms, respectively. The proposed CCR was completed by combining the orthogonal vertical and horizontal actuated mirrors. Data transmission and modulation at a frequency of 10 Hz was successfully demonstrated using the fabricated CCR at a distance of approximately 50 cm.