Piezoelectrically operated MEMS corner cube retroreflector for optical communications

A bulk-micromachined corner cube retroreflector (CCR) was designed and fabricated for free-space optical communications with ultra-low voltage operation and negligible power consumption. The proposed CCR was comprised of a bulk-micromachined vertical mirror which has two mutually orthogonal reflective surfaces and a horizontal mirror with piezoelectric actuator. The fabricated vertical and horizontal mirrors have sizes of 300 m × 300 m and 150 m×150 m, respectively. The vertical mirror was fabricated using a double silicon-on-insulator wafer and the anisotropic wet etching of a (110) silicon wafer. The horizontal mirror was comprised of two supporting and one actuating lead zirconate titanate (PZT) cantilevers. The supporting cantilevers were utilized for the accurate angular alignment of the mirror by balancing and isolating the residual stresses occurring in the PZT cantilevers. The bottom-actuated mirror exhibited an angular displacement of 1.37° at an applied voltage of 5 V. The fabricated CCR exhibited a good angular misalignment of less than 0.35° and switching characteristics with an off-to-on-state transition of 163 s and on-to-off-state transition of 276 s at a rectangular input voltage and switching frequency of 10 V and 1 kHz, respectively. The fabricated CCR also exhibited a cutoff frequency of 2.5 kHz and could be digitally modulated up to about 5 kb s ¹.