There is provided an optical device, including an input aperture, an output aperture, at least first and second light-transmitting substrates each having two major surfaces and edges, an input surface for coupling light waves into the substrate for effecting total internal reflection inside the substrate, and an output surface for coupling light waves out of the substrate, a major surface of the first substrate is attached to a major surface of the second substrate and the input surface of the first substrate is a partially reflecting surface, such that part of the light waves passing through the input aperture is partially reflected by the partially reflecting input surface and coupled into the first substrate and another part passes through the partially reflecting input surface and is coupled by the input surface of the second substrate into the second substrate.
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