Micromachined Photodiode Submount with Integrated Mirror for Efficient Out-of-Plane Coupling to Planar Polymeric Waveguide Circuits

We report on a hybrid coupling concept which allows high-density integration of top illuminated photodetector arrays with planar polymeric waveguide circuits by means of a micromachined submount with an integrated mirror. The etching of a complementary alignment structure in the polymeric layer stack allows passive assembly. The fabrication process of the submount structure is described, focusing on the optimization of the mirroring facet surface quality in order to reduce the effect of topographic scattering. A prototype 8-channel detector module integrated with a straight polymeric waveguide array exhibited an average coupling efficiency of -6.1 dB and a cross-talk value of -21.3 dB between adjacent channels at 1300 nm.