Self-pulsing dynamics of a dual-wavelength Tm3+:ZBLAN upconversion fiber laser emitting around 800 nm

We report on a self-pulsing Tm3+:ZBLAN upconversion fiber laser in the region of 800 nm. Lasing operation at one or two wavelengths corresponding to two different transitions is investigated. A new self-pulsing dynamics when lasing at two wavelengths is reported for the first time to our knowledge. We could reproduce numerically what we observed experimentally with a simple model based on the rate equations. This dynamical regime could be explained by the strong absorption of the ground state at the lasing wavelengths and the gain competition between the two transitions.