Method and system for beam expansion in a display device

A method of improving color uniformity in an optical device (10), the optical device comprising:

• a substantially planar light-guiding member (60) having a first surface (32) and an opposing second surface (52), and
• a light coupling structure (H1) positioned relative to the light-guiding member for coupling light waves (70) into the light-guiding member, the light-guiding member guiding the light waves (72, 74) within the light-guiding member based substantially on successive internal reflections as the light waves travel between the first and second surfaces, the light waves comprising at least first light waves of a first color (λ1) and second light waves of a second different color (λ2), wherein the first light waves are internally reflected at a first reflection angle (θm1) and the second light waves are internally reflected at a second reflection angle (θm2) greater than the first reflection angle in reference to a surface normal (N) of the second surface, said method characterized by
• providing at least one substantially planar interface (40) between the first surface and the second surface substantially parallel to the first surface to reflect the second light waves toward the second surface as the second light waves travel from the second surface toward the first surface, while allowing the first light waves to be transmitted through the planar interface.