Lightweight, optically flat micromirrors for fast beam steering

We have demonstrated flat, lightweight micromirrors with high resonant frequencies for fast beam steering. The low mass of these tensile-optical-surface (TOS) micromirrors, which consist of tensile polysilicon membranes stretched across stiff, single-crystal silicon-rib structures, enables the mirrors to have both high resonant frequencies and large DC deflection angles. The TOS mirrors can scan at frequencies up to 65.2 kHz while limiting dynamic deformation to be less than ~70 nm, (approximately λ/10 at the measurement wavelength of 655 nm). Dynamic deformation as low as 20 nm has been shown on a lower-frequency design having a wider support rib. The effect of adding a 50 nm-thick layer of gold to improve reflectivity is negligible on the deformation of the micromirror