Transverse mode instability considering bend loss and heat load

Previously, we developed a highly efficient transverse mode instability model by integrating stimulated thermal Rayleigh scattering and quasi-3D fiber amplifier models, enabling the consideration of the 3D gain saturation effect, with its accuracy verified by reasonable fit to experimental data. Bend loss was however ignored. Higher-order-mode bend loss can be very high especially for fibers with core diameters below 25µm and is sensitive to the local heat load. By using a FEM mode solver to account for bend loss and local heat-load-induced bend loss reduction, the transverse mode instability threshold is studied in detail, resulting in some interesting new insights.