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

: Weig, T.; Höck, H.; Holc, Katarzyna; Köhler, Klaus; Wagner, Joachim; Schwarz, U.T.


Physica status solidi. A 212 (2015), No.5, pp.986-991
ISSN: 0031-8965
ISSN: 1862-6300
ISSN: 1521-396X
ISSN: 1862-6319
Journal Article
Fraunhofer IAF ()
external cavities; GaN; laser diodes; mode locking; superluminescent diodes

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.