An optical element includes a substrate having a passive waveguide and a laser waveguide disposed therein. The laser waveguide is in direct contact with the passive waveguide over a surface of contact so as to provide a butt coupling between the passive waveguide and the laser waveguide. A step extends between an upper edge of the passive waveguide and an upper edge of the laser waveguide. A covering is disposed on the passive waveguide so that the covering and the substrate together provide a cladding of lower refractive index around the passive waveguide and so that a hollow space is disposed between a lower edge of the covering and the upper edge of the laser waveguide.