There is provided an optical device, including a light-transmitting substrate having a refractive index, at least two major surfaces and edges, an optical element for coupling light waves into the substrate for effecting total internal reflection, at least one element carried by the first substrate for coupling light waves out of the substrate, and a first transparent plate, having at least two major surfaces, one of the major surfaces of the first transparent plate being optically cemented, with a first optical adhesive having a refractive index, to one of the major surfaces of the light-transmitting substrate, defining a first interface surface, light waves coupled inside the substrate are partially reflected from the interface plane and partially pass through it, wherein the refractive index of the optical adhesive is different than the refractive index of the light transmitting substrate.