Broadband, high-reflectivity, and low-stress optical thin film with a composite of metallic film and DBR for MEMS FSM

This paper introduces an optimized design for a broadband, high-reflectivity and low-stress optical thin film for MEMS Fast Steering Mirrors (FSMs) in satellite laser communication systems. The study addresses the challenge of heat dissipation in compact MEMS FSMs, particularly under high-power laser reflection, which can lead to significant thermal stress and potential device failure. Through computation and simulation, a composite film structure is proposed, integrating a metallic film with Distributed Bragg Reflectors (DBRs) to achieve over 99.9% reflectivity at 1550nm and 98.7% at 905nm, while minimizing thermal stress and strain. The design selects SiO2 and TiO2 as the materials for the DBRs, utilizes Al2O3 as the adhesion layer, and carefully calculates the thickness of each layer to optimize performance. Computation results demonstrate a substantial reduction in thermal strain compared to pure DBRs and composite films with different materials. The design also minimizes reflectivity’s angle dependence and effectively manages temperature increase, crucial for the reliability and performance of MEMS FSMs in space applications.