Monolithic integration of elliptic-symmetry diffractive optical element on silicon-based 45° micro-reflector

A monolithically integrated micro-optical element consisting of a diffractive optical element (DOE) and a silicon-based 45° micro-reflector is experimentally demonstrated to facilitate the optical alignment of noncoplanar fiber-to-fiber coupling. The slanted 45° reflector with a depth of 216 m is fabricated on a (100) silicon wafer by anisotropic wet etching. The DOE with a diameter of 174.2 m and a focal length of 150 m is formed by means of dry etching. Such a compact device is suitable for the optical micro-system to deflect the incident light by 90° and to focus it on the image plane simultaneously. The measured light pattern with a spot size of 15 m has a good agreement with the simulated result of the ellipticsymmetry DOE with an off-axis design for eliminating the strongly astigmatic aberration. The coupling efficiency is enhanced over 10-folds of the case without a DOE on the 45° micro-reflector. This device would facilitate the optical alignment of non-coplanar light coupling and further miniaturize the volume of microsystem.