An optical device, comprising: a light-transmitting substrate having an input aperture and at least first and second major surfaces (26, 32) parallel to each other and edges; a display source producing image light waves; at least one partially reflecting surface located in said substrate which is non-parallel to the major surfaces (26, 32) of said substrate; optical means having an output aperture for coupling the image light waves from the display source into said substrate, such that the image light waves from the display source (3 8) are trapped inside the substrate by total internal reflection, wherein said optical means for coupling light is located outside of said substrate, wherein the output aperture is optically attached to the input aperture of said substrate, and the part of the substrate which is located next to the substrate input aperture is substantially transparent, wherein the part of the substrate which is located next to the substrate input aperture does not contain any reflecting surface, characterized in that the input aperture of said substrate is located at one of its major surfaces (26, 32) and in that the image light waves are coupled by the partially reflecting surface out of said substrate, wherein said optical means comprises a coupling-in prism, a lower surface of said coupling-in prism being cemented to said light-transmitting substrate, wherein said image light waves from said display source pass through said light-transmitting substrate and said coupling-in prism and are then reflected from a coupling-in reflecting surface of said coupling-in prism and after again passing through said coupling-in prism are coupled into said light-transmitting substrate by total internal reflection, wherein an off-axis angle (α in) of said image light waves coupled inside said light-transmitting substrate is larger than an off-axis angle of said coupling-in reflecting surface as well as the off-axis angle (α sur) of said partially reflecting surface. a light-transmitting substrate having an input aperture and at least first and second major surfaces (26, 32) parallel to each other and edges; a display source producing image light waves; at least one partially reflecting surface located in said substrate which is non-parallel to the major surfaces (26, 32) of said substrate; optical means having an output aperture for coupling the image light waves from the display source into said substrate, such that the image light waves from the display source (3 8) are trapped inside the substrate by total internal reflection, wherein said optical means for coupling light is located outside of said substrate, wherein the output aperture is optically attached to the input aperture of said substrate, and the part of the substrate which is located next to the substrate input aperture is substantially transparent, wherein the part of the substrate which is located next to the substrate input aperture does not contain any reflecting surface, characterized in that the input aperture of said substrate is located at one of its major surfaces (26, 32) and in that the image light waves are coupled by the partially reflecting surface out of said substrate, wherein said optical means comprises a coupling-in prism, a lower surface of said coupling-in prism being cemented to said light-transmitting substrate, wherein said image light waves from said display source pass through said light-transmitting substrate and said coupling-in prism and are then reflected from a coupling-in reflecting surface of said coupling-in prism and after again passing through said coupling-in prism are coupled into said light-transmitting substrate by total internal reflection, wherein an off-axis angle (α in) of said image light waves coupled inside said light-transmitting substrate is larger than an off-axis angle of said coupling-in reflecting surface as well as the off-axis angle (α sur) of said partially reflecting surface.