Retroreflecting optical modulator using an MEMS deformable micromirror array

A modulating corner-cube reflector with one microelectromechanical-system (MEMS) mirror that deforms from a flat into a hexagonal array of concave reflective microlenses to disperse the retroreflected wavefront is demonstrated. It is shown that such retromodulators can operate under a wide range of wavelength and angle illumination using Huygens-Fresnel propagation analysis, and this analysis is verified using devices fabricated by surface micromachining. A gold-coated silicon-nitride membrane suspended over 1-mm-diameter circular cavities had a resonant frequency of 160 kHz and 0.55-μm maximum deformation with 79 V applied. While this deflection was only 2/3 of the design value of 0.8 μm, we measured an up to 7:1 modulation contrast ratio from a prototype retromodulator, which achieved 100-kHz modulation over a 100-nm optical bandwidth, a 35° range of incident angles, and temperatures ranging from 20 to 100°C.