Fabrication and performance study of high coupling efficiency side-pump coupler based on fluorotellurite glass fiber

We demonstrate the fabrication of side-pump coupler with high coupling efficiency using low-loss, homemade fluorotellurite glass fiber for the first time. Benefiting from the optimization of pump fiber waist diameter and winding turns, the coupler fabricated by the tapered winding method achieves a maximum coupling efficiency of 88.66%. To the best of our knowledge, this represents the highest reported coupling efficiency for a side-pump coupler based on homemade mid-infrared (MIR) soft glass fibers. Furthermore, the coupler's maximum handling power reaches 10 W at 976 nm, with an RMS stability of 0.4619%. Additionally, the experimental results reveal that the refractive index of the pump fiber closely matching that of the inner cladding of the signal fiber is significantly helpful in improving the coupling efficiency of the side-pump coupler. Fluorescence output of 2.7 µm was achieved by fabricating a side-pumped coupler on an Er-doped fluorotellurite fiber. This study provides an effective approach and reference for the fabrication of high coupling efficiency MIR side-pump couplers.