Silicon photonic device, optical polarisation beam coupler and optical waveguide coupler

Abstract

A silicon photonic device () comprising: a silicon core () having a core refractive index; and a structure formed in the silicon core, comprising: a first refractive index variation pattern () across the core in a first direction (x) and having a first modulation depth (H); and a second refractive index variation pattern () across the core in a second, orthogonal, direction (y) and having a second modulation depth (H), less than the first modulation depth. The first refractive index variation pattern overlays the second refractive index variation pattern, forming a three-dimensional structure. The first refractive index variation pattern only supports propagation of light having a TM mode between the first direction and a third direction (z) and the second refractive index variation pattern only supports propagation of light having a TE mode between the second direction and the third direction. An optical waveguide coupler is also disclosed. The optical waveguide coupler comprises a plurality of planar waveguides, each supporting propagation of one of a TE and a TM mode, and a plurality of silicon diffractive gratings each comprising a planar silicon core and a grating structure formed by a periodic refractive index variation extending across the core in a first direction and having a grating period and a modulation depth, these selected to cause the grating to support propagation of the light between the first direction and a third direction substantially orthogonal to the planar silicon core. Additionally the optical waveguide coupler comprises a plurality of tapered planar waveguides.