Polarization independent waveguide structure

Abstract

A homogeneous semiconductor waveguide structure having an undoped core layer and doped cladding layers on both sides of the core layer is proposed wherein the waveguide core is substantially thick providing polarization independence. Because of the cladding layers having low refractive index contrast with respect to the core and being on opposing sides resulting in a substantially symmetrical structure, the waveguide, can be made single-mode with low polarization sensitivity, thus improving characteristics for conducting light therein. Furthermore, the enlarged mode size increases coupling efficiency. Also, since the waveguide is grown from a single semiconductor composition lattice matched to the substrate, wafer uniformity and reproducibility are enhanced. The three layer structure reduces birefringence sufficiently that a yield enhancing etch stop layer can be added to the structure without substantially adverse effects.