Curved Silicon Micromirror for Linear Displacement-to-Angle Conversion With Uniform Spot Size

This paper reports a novel class of deeply etched curved micromirrors enabling linear conversion between the reflection angle of incident light beam and displacement of the beam axis with respect to the curved mirror principal axis. Moreover, the mirror provides phase-transformation of the light beam independent of the inclination angle of the incident light on the mirror surface. The micromirrors are fabricated on SOI substrate by deep reactive ion etching technology. The profile of the curved surface is optimized and controlled precisely, thanks to the photolithographic process. High optical throughput micromirrors exhibiting submillimeter focal lengths are fabricated with 200-μm etching depth and with a sidewall angle deviation from perfect verticality, which is smaller than 0.1°. Optical measurements at wavelengths of 675 and 1550 nm show transformation of the optical beam with high optical spot size stability during a beam steering process with less than ±5% dependence on the inclination/reflection angle over a scanning angle range of 120°. The presented micromirror has applications in MEMS scanners, displacement/rotation sensing, and optical imaging.