Implementation and investigation of mode locking in GaN-based laser diodes in external cavity configuration

Investigation of spectro-temporal characteristics of short-pulse generation from a violet-blue AlGaInN multi-section laser diode implemented in an external cavity is demonstrated. The front facet is coated with a single layer of anti-reflection coating, resulting in superluminescent diodes with a broad spectrum. The coated diode is placed in an external cavity in Littrow configuration for wavelength-tuning, and in Littman-Metcalf configuration for ultrashort pulse generation. We report on fundamental, harmonic, as well as hybrid mode locking. Compensating for the group velocity dispersion, we compress the pulse duration down to 2 ps, which is at the resolution limit of the streak camera. Mode locking and sub-ps pulse generation are hindered by the photon density-induced gain saturation, manifested as mode competition and mode clustering superimposed with mode locking. We show, that hybrid mode locking can suppress the mode competition successfully.