Universal fibre laser model used for the simulation of 2 µm Thulium fibre lasers

A universal simulation model for rare earth doped cw fibre lasers is presented. The model is based on generic rate and gain equations and therefore is very compact. It can be used for any fibre doped with one or several rare earth ions. The model allows for spectral simulations as well as radial discretization of the fibre. An algorithm was developed which optimizes the longitudinal fibre segmentation of the model. Spectroscopic parameters for Thulium doped fibre lasers are taken from the literature or derived from calculations. Calculated multiphonon up-conversion rates take the thermalisation of closely spaced states into account. The simulation is compared with measurement results of a coupled wavelength shift observed in a tunable fibre ring laser. The simulation allows to investigate possible explanations and it indicates that the phenomenon is a measurement artefact.