Abstract
A simple and accurate closed‐form expressed for the threshold‐current density J th in symmetric DH structures is presented. The novel expresion allows analytical solutions for d o , the active‐layer thickness corresponding to minimum threshold‐current density. Optimization of the cavity thickness for minimum J th is presented for wide variations in cavity length (100–500 μm) and facet reflectivity values. The analytical formulas are applied to the AlGaAs/GaAs system and extended to the InGaAsP/InP system. By using previously published experimental results, a linear gain‐current relationship is estimated for InGaAsP (λ=1.2–1.3 μm), and thus it is found that d o should vary between 0.12 and 0.20 μm as the cavity parameters (length and facet reflectivity) change; and that minimum J th values should be comparable to the J th values for AlGaAs lasers with the same cavity parameters.