Analysis of Saturation Mechanisms of High-Power Pulsed Semiconductor Lasers Based on the InGaAsP/InP Heterostructure Emitting at a Wavelength of 1.55 μm

We examine the main mechanisms limiting the optical power of InGaAsP/InP semiconductor lasers operating at 1.55 μm at high pump currents. Analysis is performed using a numerical calculation of a two-dimensional laser diode model, taking into account transverse drift-diffusion transport and nonuniform distribution of charge carriers and photons along the cavity axis. The calculation results demonstrate the dominant influence of internal losses from scattering by free carriers in the waveguide layer on saturation of the output laser power. As the pump current increases, the primary saturation mechanism becomes leakage current, generated by electron transport into the p-emitter and reducing the internal quantum efficiency. Analysis also shows that the uneven distribution of photons and gain along the cavity axis contributes to the limitation of the output laser power; however, this effect does not significantly affect the primary mechanisms—leakage current and free-carrier losses.