Injection lasers with quantum size effect transparent waveguiding

In an injection laser comprising a plurality of contiguous semiconductor layers deposited on a substrate, one of said layers being an active layer and having a lower bandgap and higher index of refraction relative to at least cladding layers immediately adjacent to said active layer, said active layer having an active region to permit radiative recombination and support radiation propagating under lasing conditions in a cavity established between transverse end facets of the laser, means incorporated into said laser to confine current to said active region, the extremities of said active region falling short of said end facets so that the regions of said active layer between said active region and said end facets function as a passive waveguide for the propagating radiation, said passive waveguide regions of said active layer being sufficiently thin in layer thickness to form a transparent waveguide having a quantum well effect so that radiative recombination will not occur in these regions.