An optical device, includes a light-transmitting substrate (20) having an input aperture and first and second major surfaces (26, 32) parallel to each other and edges, one partially reflecting surface located in the substrate which is non-parallel to the major surfaces of the substrate and an external optical arrangement having an output aperture for coupling light into the substrate by total internal reflection. The optical arrangement for coupling light having an output aperture optically attached to the input aperture of the substrate with the part of the substrate located next to the substrate input aperture, being substantially transparent.