Hysteresis in an erbium doped ZBLAN waveguide GHz mode-locked laser

We report the experimental observation and numerical analysis of a new type of hysteresis behaviour in a passively mode-locked erbium-doped ZBLAN chip waveguide laser. By tuning the spectral transmission window through translating a collimation lens, or changing the net intracavity dispersion, we observe bistable pulse characteristics and different abrupt spectral transitions depending on the translation direction of the collimation lens. A hysteresis behaviour is observed in pulse width and spectral bandwidth, which is persistent in the single-pulse operation regime and is strongly dependent on the sign and magnitude of the intracavity dispersion. A numerical model is developed to investigate this phenomenon, which successfully confirms the experimental hysteresis behaviour. Further analysis reveals that the phenomenon arises from the interplay between dispersion-induced chirp and delayed absorption recovery of the SESAM.