All-Fiber Mid-Infrared Seeded-Amplifier Enabled by an All-Fluoride Pump-Signal Combiner

We report, to the best of our knowledge, the first (2+1)×1 all-fluoride pump-signal combiner enabling a fully fiberized mid-infrared seeded-amplifier operating in the wavelength band around 2700 nm. The device, fabricated via a heat-and-pull technique using indium fluoride fibers and capillary, addresses the lack of integrated pump-signal combining technologies in the mid-infrared spectral region. The combiner is employed to couple two identical multimode pump inputs at λ = 976 nm and a single-mode signal into an erbium-doped ZBLAN active fiber, in a single-end-pumped forward configuration. A seed laser at λ = 2713 nm is amplified, achieving a maximum gain G = 22 dB, in good agreement with numerical modeling based on electromagnetic modal analysis and rate equations. This proof-of-concept demonstrates the feasibility of an all-fluoride pump-signal combining architecture, while further optimization of the fabrication process and thermal management is required to enable high-power operation.