Niobium-gallate fiber optics for high-power 1–5  µm supercontinuum generation [Invited]

Over the past decades, fiber-based supercontinuum (SC) sources spanning 1–5 µm have been extensively investigated for a wide range of applications. To meet the growing demand for higher output power and stability, the development of glass fibers combining excellent thermomechanical properties with high nonlinearity is essential. In this work, we report the fabrication of robust niobium-containing gallate glasses. Incorporating niobium oxide up to 20 mol.% significantly improves thermomechanical performance, with a 20% hardness increase and a two-order-of-magnitude improvement in water corrosion resistance over niobium-free glass. Simultaneously, the nonlinear refractive index more than doubles, exceeding that of silica by over an order of magnitude. Importantly, the thermal dilatometric properties remain largely unaffected, enabling the fabrication of niobium-rich gallate step-index multimode fibers. These fibers were successfully employed to generate a supercontinuum spanning from 600 nm to 4.5 µm. Numerical simulations further optimized the step-index design under realistic pumping conditions near 2 µm, consistent with mature thulium-doped fiber lasers. Owing to their unique balance of thermomechanical robustness and high nonlinearity, niobium gallate fibers emerge as strong candidates for power-scalable, reliable all-fiber SC sources, with the potential to deliver high average powers across the 0.5–4.5 µm range.