An optical device having a substrate with a waveguide layer on a surface thereof and a grating in the waveguide. The grating has a period such as to deflect light passing along the waveguide out of the optical device. The angle at which the light is emitted from the waveguide can be varied by varying the index of refraction of the material of the waveguide under the grating. This can be achieved by applying a voltage across the waveguide.