Patent ID: 8369019

Claim:
A projection display comprising a waveguide element into which image bearing light can be injected to propagate along the waveguide element by total internal reflection, the waveguide element including: a first layer of material with a first predetermined refractive index and/or first predetermined thickness; a second layer of material with a second predetermined refractive index and/or second predetermined thickness, at least one of the second predetermined refractive index and the first predetermined thickness being different from the second predetermined refractive index and the second predetermined thickness, respectively; a grating element arranged on either the first or the second layer of material and arranged to provide beam splitting of image bearing light passing through the grating element and to direct image bearing light propagating along the waveguide element which impinges on the grating element such that the incidence angle of the directed light on the internal surfaces of the waveguide element is greater than the critical angle so that light is output from the waveguide element; the first and second layers of material are arranged to abut one another such that the grating element is arranged between the first and the second layers of material; and wherein the first predetermined refractive index and second predetermined refractive index and/or the first predetermined and second predetermined thickness are arranged to vary the spatial periodicity of image bearing light radiated from the waveguide element.