An optical system, comprising: a display light source; a light-transmitting substrate having at least two major surfaces (26, 27) parallel to each other and edges, wherein the light waves emerging from said display source are p-polarized or s-polarized and enter said light-transmitting substrate through one of said major surfaces (26, 27), and an optical device for coupling light waves from the display light source into said substrate by total internal reflection, wherein said substrate has at least one partially reflecting surface located in the substrate which is non-parallel to the major surfaces (26, 27) for coupling the light waves out of the substrate, wherein said optical device for coupling light into said substrate is a polarizing beam splitter disposed non-parallel to the major surfaces (26, 27) of the substrate, the optical system being characterised in that said polarizing beam splitter is embedded inside said light-transmitting substrate, and in that a quarter-wavelength retardation plate is located next to one of said major surfaces (26, 27) and a converging lens is located next to said quarter-wavelength retardation plate, the light waves emerging from said display light source are divergent and are transmitted through the beam splitter, impinge on the quarter-wavelength retardation plate which converts the incoming light waves into circular polarized light, wherein the transmitted light waves are then reflected back through the quarter-wavelength retardation plate by a reflecting surface of the converging lens, wherein the light waves are collimated by the converging lens by the reflection back of the reflecting surface of the converging lens, wherein the light waves are now s-polarized or p-polarized, respectively, and are reflected by the beam splitter and trapped in the substrate by total internal reflection. a display light source; a light-transmitting substrate having at least two major surfaces (26, 27) parallel to each other and edges, wherein the light waves emerging from said display source are p-polarized or s-polarized and enter said light-transmitting substrate through one of said major surfaces (26, 27), and an optical device for coupling light waves from the display light source into said substrate by total internal reflection, wherein said substrate has at least one partially reflecting surface located in the substrate which is non-parallel to the major surfaces (26, 27) for coupling the light waves out of the substrate, wherein said optical device for coupling light into said substrate is a polarizing beam splitter disposed non-parallel to the major surfaces (26, 27) of the substrate, the optical system being characterised in that said polarizing beam splitter is embedded inside said light-transmitting substrate, and in that a quarter-wavelength retardation plate is located next to one of said major surfaces (26, 27) and a converging lens is located next to said quarter-wavelength retardation plate, the light waves emerging from said display light source are divergent and are transmitted through the beam splitter, impinge on the quarter-wavelength retardation plate which converts the incoming light waves into circular polarized light, wherein the transmitted light waves are then reflected back through the quarter-wavelength retardation plate by a reflecting surface of the converging lens, wherein the light waves are collimated by the converging lens by the reflection back of the reflecting surface of the converging lens, wherein the light waves are now s-polarized or p-polarized, respectively, and are reflected by the beam splitter and trapped in the substrate by total internal reflection.