Low-loss fiber-to-semiconductor waveguide coupling using integrated optical mode expanders

In this paper we report improved optical mode expanders resulting in coupling losses of below 1 dB and relaxed alignment tolerances of 2.5 /spl mu/m in the horizontal and vertical directions for 1 dB in addition measured with standard single mode fiber (SMF). In a first fabrication step the OEIC waveguide components are grown by low-pressure metal-organic vapor-phase epitaxy. An oxide mask is deposited and patterned with narrowing mask openings in the optical mode expanders.