Patent ID: 7483604

Claim:
A virtual image display device, comprising an imager for providing an image light wave; and a diffractive grating element, responsive to said image light wave, for enlarging an exit pupil of said virtual image display device for displaying said image light wave as graphics, said diffractive grating element in turn comprising a waveguiding substrate and a diffractive grating element arranged on or embedded within said substrate and arranged to interact with said image light wave in order to couple energy from said image light wave into said substrate to form at least one diffracted image light wave propagating within said substrate in a direction of selected diffraction order, said grating element comprising at least two different grating regions having different diffractive properties and arranged on opposite sides with respect to a transition point, wherein diffractions generated by said at least two different grating regions are arranged to mutually compensate for an effect of a variation in input angle of said image light wave at a given point of the grating on a total diffraction efficiency of said at least one diffracted image light wave propagating within said substrate.