Integrated mirror in a semiconductor waveguide device

An integrated circuit optical backplane die and associated semiconductor fabrication process are described for forming optical backplane mirror structures for perpendicularly deflecting optical signals out of the plane of the optical backplane die by selectively etching an optical waveguide semiconductor layer (103) on an optical backplane die wafer using an orientation-dependent anisotropic wet etch process to form a first recess opening (107) with angled semiconductor sidewall surfaces (106) on the optical waveguide semiconductor layer, where the angled semiconductor sidewall surfaces (106) are processed to form an optical backplane mirror (116) for perpendicularly deflecting optical signals to and from a lateral plane of the optical waveguide semiconductor layer.