Demonstration of a helix side-pumping coupler with ultra-high pump coupling efficiency

Abstract

The integrated and all-fiberized space division multiplexing fiber amplifier (SDMFA) with high spatial signal gain is urgently needed. Due to the lack of fiber-based multimode wavelength division multiplexing coupling device, the side-pumping coupler is essential to form an all-fiberized SDMFA. Here, a helix side-pumping coupler with ultra-high pump coupling efficiency is proposed by winding a tapered pump fiber to the target fiber. First, we establish the theoretical model of the side-pumping coupler and analyze the influence of the tapered pump fiber parameters on the pump coupling efficiency. Then the coupler is fabricated by arcuate tapering and heating. Finally, a multimode pump source and three signal modes (LP01, LP11a, LP11b) are experimentally applied to verify the pump coupling efficiency and signal transmission efficiencies. Results show that the experimental results are in good agreement with the simulation conclusions, and under the premise that all signal modes transmission efficiencies are more than 94%, the pump coupling efficiency is higher than 97% by introducing a piece of coreless fiber as bridge fiber. This helix side-pumping coupler has advantages of low signal loss, ultra-high pump coupling efficiency and higher-order modes transmittable capability.