Conventional surface micromachining process for the fabrication of a linear optical phased array based on piston micromirrors

Abstract

Micro electromechanical system (MEMS) based optical phased array (OPA) technology generally demands narrow and tightly spaced suspended microstructures with high-aspect-ratio in the lateral dimensions. This paper presents an one dimensional OPA system which is fabricated using the standard PolyMUMPs process, leading to a low-cost, simplified and commercially accessible surface micromachining technique for the OPA technology. The proposed OPA device utilizes an array of metal-coated silicon micromirrors with high-aspect-ratio structures which act as optical phase shifters. Each micromirror along the array is individually actuated by an electrostatic parallel plate micro-actuator made of a micro-cantilever beam positioned above a fixed electrode. The field of view obtained by the device is measured as 4.76° which is comparable to those by the previous MEMS based OPA devices fabricated using custom-run and complex surface micromachining processes. The OPA device has a response time of 6.5 µs and an out of plane actuation stroke of 0.16 µm at a bias voltage of 55 V. The magnitude of the out of plane displacement by the phase shifters is equal to one-quarter of the laser wavelength (650 nm) used which leads to the desired optical phase shift of radian.