Gallium nitride laser diodes with integrated absorber: On the dynamics of self-pulsation

The dynamics of self-pulsation in monolithic multi segment GaN-based laser diodes (LDs) with integrated absorber, and operating at 410 nm is investigated. The bias-dependent modal absorption of the devices is determined by high resolution Hakki-Paoli gain spectroscopy. Using a streak camera detection system we measure the pulsation frequency, applying bias voltages up to -40 V to the absorber section of the multi segment LD. Under moderate reverse voltages, to approximately -15 V, the absorption features a quadratic dependence on the bias voltage with a clear minimum corresponding to the flat band conditions. In this regime we observe stabilized relaxation oscillations, with a pulse repetition rate which depends only on the current in the gain section, but not on the reverse bias in the absorber section. At higher reverse voltages a linear increase of the modal absorption is observed. There, the devices switch to the self-Q-switching regime which exhibits a linear decrease of the pulsation frequency with increasing reverse bias.