Monolithically integrated low-loss three-dimensional spot-size converter and silicon photonic waveguides constructed by nanotuned Bosch process and oxidation

Abstract

This paper presents a three-dimensional (3D) tapered spot-size converter connecting to silicon wire waveguide and silicon rib waveguide. The silicon 3D structure was essentially formed by a single-step deep anisotropic dry etching of arrayed submicron-scale line patterns with different pitches, resulting in a tailored depth profile which is controlled by the line pattern through loading effect. Subsequent thermal oxidation and removal of the oxidized portion with wet etching led to a bare 3D silicon structure with smooth surface. The optical mode from a 4.6 μm × 3.1 μm silicon rib waveguide was successfully coupled to a 280 nm × 500 nm nanowire waveguide by a silicon 3D tapered spot-size converter, with average coupling loss of 1.52 dB.