Optimum design of 1.55-microm double heterostructures and ridge-waveguide lasers

The dependence of threshold current density and lateral-index difference for transverse guiding in a 1.55-microm InGaAsP/InP ridge-waveguide laser on the number of cladding layers, their thicknesses, and their compositions is presented. It is found that two cladding layers of intermediate band-gap InGaAsP (lambda(g) = 1.2-1.3 microm) are desirable to reduce the threshold current density and to reduce its sensitivity to layer-thickness variations. The use of active- and cladding-layer thicknesses between 0.1 and 0.15 microm minimizes the threshold current density and its sensitivity to layer-thickness variations. This regime of layer thicknesses results in relatively strong lateral-index guiding (Deltan(eff) approximately 0.06) in the 1.55-microm ridge-waveguide laser structure.