A photonic integration platform

A SOI device may include a waveguide adapter that couples light between an external light source -e.g., a fiber optic cable or laser -and a silicon waveguide on the silicon surface layer of the SOI device. In one embodiment, the waveguide adapter is embedded into the insulator layer. Doing so may enable the waveguide adapter to be formed before the surface layer components are added onto the SOI device. Accordingly, fabrication techniques that use high-temperatures may be used without harming other components in the SOI device -e.g., the waveguide adapter is formed before heat-sensitive components are added to the silicon surface layer. In general, a method is disclosed of forming a first waveguide in an insulation layer and a second waveguide in a crystalline semiconductor layer disposed on the first waveguide, wherein the second waveguide at least partially overlaps the first waveguide. An optical waveguide adapter is disclosed, wherein the adapter comprises a first prong and a plurality of second prongs, whereby a dimensions of the second prongs reduces as the second prongs extend in a direction away from a coupling surface of the waveguide adapter, and a dimension of the first prong increases as the first prong extends away from the coupling surface, and a length of the first prong in the direction extending away from the coupling surface is greater than each of the respective lengths of the second prongs.