Threshold current analysis of InGaAsP¿InP ridge-waveguide lasers

The marked depression of the refractive index by injected carriers in the InGaAsP-lnP material system essentially influences the performances of laterally inhomogeneously pumped laser diodes such as the usual ridge-waveguide structures. This is because, together with the built-in index guiding, an M-shaped waveguide is formed that may become leaky even for the fundamental waveguide mode. The characteristics of these waveguides are calculated and compared with previous results. Hence, the waveguide structure is studied for a wide range of device parameters showing that optical losses can be kept within acceptable limits by applying effective index steps in excess of 0.02. Furthermore, the mode gain is calculated for the corresponding carrier profiles and the threshold current is estimated. According to experiment, the results show that threshold currents around 20 mA can be achieved with appropriate waveguide structures at wavelengths of 1.3 ¿m and 1.55 ¿m