Monolithic highly multi-mode XLMA-fiber resonator for high power operation.

Highly multi-mode fiber resonators can be an excellent solution to achieve high output power with homogeneous beam profiles, while nonlinear effects are suppressed due to the high number of modes and high mode-field areas. While highly reflective fiber-Bragg-gratings (HR-FBGs) are a well-developed technology in single-mode fibers, in multi-mode fibers HR-FBGs are under investigation to enable monolithic resonators. Here, we present a monolithic multi-mode fiber resonator in a > 50 µm core diameter XLMA-fiber. We achieve a slope efficiency of up to 50%, stable wavelength operation at 1074 nm and homogeneous beam profiles using an HR-FBG with app. 70% reflectivity.