Semiconductor lasers with a thin active layer (>0.1 microm for optical communications

Double heterostructure lasers with a thin active layer have been investigated. Device parameters have been optimized for using laser diodes as light sources in optical communication systems. Threshold current density takes a minimum value for an active layer thickness of around 800 A in the case of undoped active layers. Full width of beam divergence for active layer thicknesses smaller than 0.1 microm is smaller than 30 degrees , and the resultant coupling efficiency into an optical fiber of a numeric aperture as small as 0.05 is 50% on the average and is 80% at maximum in conjunction with a focusing lens. Other features of the thin active layer discussed are polarization and available output powers.