An optical waveguide including: an optical substrate arranged to transmit light under total internal reflection; a first diffractive grating region associated with the optical substrate and arranged to receive light and to diffract the received light along the optical waveguide; an intermediate diffraction grating associated with the optical waveguide and optically coupled to the optical substrate and to the first diffractive grating region, arranged to receive light diffracted from the first diffractive grating region and to expand the received light in a first dimension by diffraction; and a second diffractive grating region associated with the optical substrate and optically coupled to the intermediate diffraction grating, arranged to receive light expanded in the first dimension by the intermediate diffraction grating, to expand the received light in a second dimension orthogonal to the first dimension by diffraction and to output the light expanded in the first and second dimensions from the optical waveguide by diffraction, the optical waveguide being characterised in that the first diffractive grating region and the second diffractive grating region are diffractive regions formed on a first grating structure, the intermediate diffraction grating is formed on a second grating structure, separate to the first grating structure, and the first grating structure comprises a substantially non-diffractive grating region; wherein the substantially non-diffractive grating region comprises parts of the first grating structure having an optically transmissive coating applied thereto which substantially suppresses diffraction by the parts of the first grating structure coated thereby ;and the optically transmissive coating has a refractive index which substantially matches the refractive index of the material of the first grating structure. an optical substrate arranged to transmit light under total internal reflection; a first diffractive grating region associated with the optical substrate and arranged to receive light and to diffract the received light along the optical waveguide; an intermediate diffraction grating associated with the optical waveguide and optically coupled to the optical substrate and to the first diffractive grating region, arranged to receive light diffracted from the first diffractive grating region and to expand the received light in a first dimension by diffraction; and a second diffractive grating region associated with the optical substrate and optically coupled to the intermediate diffraction grating, arranged to receive light expanded in the first dimension by the intermediate diffraction grating, to expand the received light in a second dimension orthogonal to the first dimension by diffraction and to output the light expanded in the first and second dimensions from the optical waveguide by diffraction, the optical waveguide being characterised in that the first diffractive grating region and the second diffractive grating region are diffractive regions formed on a first grating structure, the intermediate diffraction grating is formed on a second grating structure, separate to the first grating structure, and the first grating structure comprises a substantially non-diffractive grating region; wherein the substantially non-diffractive grating region comprises parts of the first grating structure having an optically transmissive coating applied thereto which substantially suppresses diffraction by the parts of the first grating structure coated thereby ;and the optically transmissive coating has a refractive index which substantially matches the refractive index of the material of the first grating structure. <EOS>