All fiber monolithic highly multimode 4.03 kW fiber laser

We are reporting a monolithic all-fiber highly multimode laser reaching up to 4.03 kW stable output power. The phosphosilicate glass matrix used as a gain medium is highly multimode optical fiber. This allows to enhance dramatically the Stimulated Raman Scattering rejection without observation of a Transverse Mode Instability neither a photodarkening phenomenon. The achievement of a high reflectivity fiber Bragg grating written on highly multimode passive fiber made the multimode laser cavity feasible.