Concave silicon micromirrors for stable hemispherical optical microcavities

A detailed study of the fabrication of silicon concave micromirrors for hemispherical microcavities is presented that includes fabrication yield, surface quality, surface roughness, cavity depth, radius of curvature, and the aspect ratio between the cavity depth and radius of curvature. Most importantly, it is shown that much larger cavity depths are possible than previously reported while achieving desirable aspect ratios and nanometer-level roughness. This should result in greater frequency stability and improved insensitivity to fabrication variations for the mode coupling optics. Spectral results for an assembled hemispherical microcavity are presented, demonstrating that high finesse and quality factor are achieved with these micromirrors, F = 1524 and Q = 3.78 x 10⁵, respectively.