Towards power improvement of all-fiber laser oscillators with 30 μm-core Yb-doped fibers by suppressing transverse mode instability

Abstract

In this work, the transverse mode instability (TMI) behaviors in high-power all-fiber laser oscillators based on the ytterbium (Yb)-doped fiber (YDF) with a core diameter of 30 μm have been experimentally investigated for the first time. We have constructed all-fiber laser oscillators with the YDF with core/inner-cladding diameter of 30/400 μm and 30/600 μm, and investigated the corresponding TMI thresholds respectively. Experimental results manifest that the YDF with the larger cladding diameter corresponds to a higher TMI threshold for the two types of YDF with 30 μm core diameter. Compared with the 30/400 μm fiber, the 30/600 μm fiber can improve the TMI threshold by 2.0 times in the co-pumping configuration. By adopting bidirectional pumping configuration in the 30/600 μm fiber oscillator, a maximum output power is scaled to ∼ 3.6 kW without any sign of TMI, and no Raman Stokes light is observed in the output spectra. To the best of our knowledge, this is the first experimental demonstration of high-power all-fiber laser oscillators based on commercial 30/600 μm YDF. The experimental results show an excellent feasibility of all-fiber laser oscillators with large core and cladding diameter fiber for high-power operation.