Micromirror Arrays as Optical Phase Modulators for Free-Space Beam Steering

Abstract

Abstract Generally, a group of sub-micron or nanometer sized optical phase shifters or modulators are used in an optical phased array (OPA) based scanner so as to selectively perturb wavefronts of outgoing laser beams. Similar to the concept of light propagation through a prism, an array of phase shifters is responsible for linearly delaying or advancing the propagating light waves. Optical phased array (OPA) systems have become an emerging technology for many applications due to the compact designs that eliminate the need for robust physical moving parts, leading to their fast response, high reliability, and low power requirements. Micromirror based OPA systems are fundamentally different than the conventional micromirror arrays that were being developed for numerous applications such as spectroscopy, digital light processing projectors, laser communication, and confocal microscopy. Those micromirror arrays provide significantly different motion types, actuation strokes, and operating speeds, due to the distinct task requirements by their target applications. Most of the previously designed conventional micromirror arrays are not suitable for high-speed laser beam steering at wide field of view due to either the large mirror sizes or the large array pitch sizes. MEMS based OPA systems generally demand narrow and tightly spaced suspended microstructures with high-aspect-ratio in lateral dimensions, rendering some significant challenges in the system design, fabrication, and integration. In addition, the scanners are required to generate hundreds to thousands of scan points along a far-field scan line which results in a large number of phase shifters in the arrays and high complexity in control.