Abstract: A group III-V compound semiconductor laser of a 1 .mu.m band having an excellent conversion efficiency and a high characteristic temperature. The semiconductor laser can emit light in a 1.3 .mu.m band or a 1.55 .mu.m, and has a laser structure including an active layer For emitting light, guide layers sandwiching the active layer and having a band gap larger than the active layer, and clad layers embracing the guide layers and having a band gap larger than the guide layers. The lattice constants of the guide layers and clad layers are larger than a1 by 0.5% or more and smaller than a2 by 0.5% or more, where a1 represents the lattice constant of GaAs and a2 is the lattice constant of InP.

Abstract: A laser amplifier comprises an active layer having a uniform width and a thickness and causing a stimulated emission of photons upon passage of an incident optical beam from an input end to an output end, an optical wave guide layer extending from the input end to the output end for guiding an optical beam therethrough, a first clad layer provided below the waveguide layer, a second clad layer provided above the active layer, a first electrode provided on the second clad layer, a second electrode provided on the first clad layer, a first anti-reflection coating provided on the input end, and a second anti-reflection coating provided on the output end.