Abstract: The laser device of the present invention comprises: a semiconductor substrate; a first cladding layer of semiconductor formed on the substrate; an active layer of semiconductor formed on the first cladding layer, thereby forming a junction plane between the active layer and the first cladding layer; a second cladding layer of semiconductor formed on the active layer and a cap layer of semiconductor formed on the second cladding layer; the active layer having a lattice constant parallel to the junction plane sufficiently larger than the lattice constant normal to the junction plane so as to increase the optical gain of the TM mode relative to the optical gain of the normally operating TE mode, such that at a first injection current level, the laser device operates in the TM mode and at a second injection current level, the laser device operates in the TE mode.

Abstract: An InGaAsP laser structure having a support structure which contains an equal number of buffer layers and substrate layers is provided. The buffer layers of the support structure drastically reduce the tensile stress in the active layer, thereby eliminating the occurrence of undesired TM emission during normal operation. The semiconductor laser device of the present invention comprises: a support structure having one or more substrate layers and one or more buffer layers, the support structure containing an equal number of substrate layers and buffer layers, the substrate layers consisting of InP, the buffer layers consisting of In.sub.1-x' Ga.sub.x' As.sub.y' P.sub.1-y' with x'.perspectiveto.0.47y' and 0<y'.ltoreq.1, one of the substrate layers providing the lower surface of said semiconductor laser device; a first cladding layer of InP formed on the exposed buffer layer of the support structure; an active layer formed on the first cladding layer, the active layer consisting of In.sub.1-x Ga.sub.x As.sub.