An optical waveguide comprises a core guiding layer; a cladding layer positioned adjacent to the core guiding layer; a reflective layer positioned adjacent to the cladding layer; and a grating for coupling light into the core guiding layer; wherein the cladding layer has a thickness such that a ray reflected from the reflective layer is phase matched to an incident ray at the grating. A method of coupling electromagnetic radiation into the optical waveguide is also described.