OPTIMAL CAVITY DESIGN FOR LOW-THRESHOLD CURRENT-DENSITY OPERATION OF DOUBLE-HETEROJUNCTION DIODE-LASERS

A simple and accurate closed-form expressed for the threshold-current density Jth in symmetric DH structures is presented. The novel expresion allows analytical solutions for do, the active-layer thickness corresponding to minimum threshold-current density. Optimization of the cavity thickness for minimum Jth 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 do should vary between 0.12 and 0.20 μm as the cavity parameters (length and facet reflectivity) change; and that minimum Jth values should be comparable to the Jth values for AlGaAs lasers with the same cavity parameters.