Design and fabrication of 10×10 micro-spatial light modulator array for phase and amplitude modulation

Abstract

In this paper, a 10×10 micro-spatial light modulator (micro-SLM) array for phase and amplitude modulation of incident light is designed and fabricated using surface micromachining technology. Hidden spring structure is used in order to maximize the fill-factor and minimize diffraction effect. A designed micro-SLM is composed of a mirror plate, upper electrodes, five support posts, and bottom electrodes. The spring structures are composed of four double crab leg springs for phase modulation (piston mode operation) and two torsional springs for amplitude modulation (tilt mode operation). The micro-SLM is actuated by electrostatic force generated between upper electrode and bottom electrode. In case of phase modulation, the maximum deflection length of mirror plate is designed to be 4 μm and in case of amplitude modulation, micro-SLM is designed to be capable of tilting ±5.4° to reflect incident light. The designed micro-SLM array is successfully fabricated with surface micromachining technology using thick photoresist as a sacrificial layer and aluminum as a structural material. Mirror plate and spring structure are fabricated without initial bending problem. The resulting fill-factor is about 91.7%. Static and dynamic characteristics of the fabricated micro-SLM in the case of amplitude modulation are measured with optical measurement system. In the fields of adaptive optics and pattern recognition system, SLM is used to modulate the phase and amplitude of incident light in order to correct aberration in an optical system through active control of mirror array.