D3. Optical coupling of cylindrical micromirrors in micro-optical benches

Free-space optical coupling is a critical performance feature in micro-optical benches, where coupling elements are designed to mitigate optical beam divergence phenomena associated with Gaussian beam propagation and to achieve phase/mode matching. In this paper, the free-space coupling of Gaussian beams using cylindrical micromirrors is analyzed. The treatment accounts for the non-idealities including limited mirror aperture and radius of curvature, surface roughness and misalignment between the mirror axis and the optical beam axis. The coupling efficiency is calculated based on the overlap integral and the ABCD transfer matrix. The analysis can treat astigmatic as well as simple stigmatic Gaussian beams. Throughout the whole of our analysis, parameter normalization is used such that our findings are independent of the specific values of the operating wavelength and the Gaussian beam parameters. The analysis is verified with optical measurements on micromachined cylindrical mirrors with radii of curvature of 50 µm and 300 µm.