US Patent 9310566 Optical waveguides

An optical waveguide (2) arranged to transmit light under total internal reflection has a first diffractive grating region (8) arranged to receive light and diffract the received light along the optical waveguide (2), an intermediate diffraction grating (10) optically coupled to the first diffractive grating region (8) arranged to expand received light in a first dimension and a second diffractive grating region (9) optically coupled to the intermediate diffraction grating (10) arranged to expand light in a second dimension, orthogonal to the first dimension and to output the light expanded in the first and second dimensions from the optical waveguide (2) by diffraction. The first and second diffractive grating regions (8,9) are fabricated as a common grating whereas the second grating is fabricated above the common grating in an area where the common grating is erased by a coating.