Efficient Resonant Pumping of a Thulium-Doped Fiber Oscillator in an All-Fiber Pedestal-Pumped Configuration

High-power thulium-doped fiber lasers have various promising applications. Resonant pumping by 1.9 μm laser is a hopeful method to power scale a 2 μm thulium-doped fiber laser (TDFL) to surpass kilowatt level due to low quantum defect and high optical efficiency. Because of the acrylate coating absorption of 1.9 μm light, resonant pumping is usually realized by all-fiber core pumped or free-space pedestal pumped configurations, which leads to other power constraint challenges. In this work, we ingeniously engineer what we believe to be a novel all-fiber resonant pumping configuration comprising a mode-field matched signal combiner, a piece of pedestal-matched transition passive germania-doped fiber (GDF), and a homemade high refractive fiber Bragg grating (FBG) on the core of TDF. This architecture confines pump light within the pedestal waveguide while maintaining signal laser propagation through the core, effectively resolving 1.9 μm cladding leakage-induced thermal effect. A streamlined validation experimental setup was developed to obtain up to 80.9% slope efficiency at 2.02 μm by directly injecting a 1.94 μm laser into the 30 μm pedestal of a 10/30/130 μm TDF. This all-fiber pedestal resonant pump structure can be utilized to further establish a high-power monolithic oscillator at 2 μm waveband for flexible applications.