Highly efficient compact head-mounted display system having small input aperture

An optical device includes a light-transmitting substrate, input and output apertures, eye-motion box, intermediate element outside of the substrate for coupling light waves into the substrate through the input aperture, a first reflecting surface between two major surfaces of the light-transmitting substrate for reflecting the coupled-in light waves to effect total internal reflection from the major surfaces of the substrate, a second flat reflecting surface parallel to the first reflecting surface located between the major surfaces of the light-transmitting substrate, for coupling light waves out of the substrate, and an optical element for redirecting light waves coupled-out from the substrate through the output aperture, into the eye-motion-box. The input aperture is substantially smaller than the output aperture, active areas of the first and second reflecting surfaces are similar, and each of the coupled light waves covers the entire aperture of the eye-motion-box.