(6+1)x1 taper-fused side pump and signal combiner for kW-class fiber laser applications

With the rapid advancement of kW-class fiber laser sources in recent years, taper-fused side pump and signal combiners have been confirmed as the essential tool for further power scaling these laser sources. The taper-fused side-pump coupler involves direct fusion splices between several tapered multi-mode pump fibers and a double-clad signal fiber. In this research, we present the design and fabrication of a (6+1) x1 taper-fused side pump and signal combiner specifically tailored for high-power fiber laser application. Notably, this combiner has six pump arms, surpassing previous research in this area. For numerical simulations, a commercial beam propagation method software, Rsoft BeamPROP, is utilized for the 3D simulations of laser propagation and higher-order modal characteristics in optical waveguides. We have successfully optimized the device design to achieve high coupling efficiency, minimal signal loss, and exceptional high backward pump isolation. By avoiding the need for bridging fibers, the tapered side-coupler eliminates fusion-splice points, thus enabling low signal insertion loss and maintaining excellent spatial beam quality. The combiner experimentally demonstrates an impressive total pump efficiency of 97.98% while carrying a pump power of 2230 W. Furthermore, the measured signal insertion loss is approximately -0.11dB. The numerical and experimental results agree with each other and successfully confirm the outstanding performance of the combiners and validate their suitability for kW-class fiber laser applications. Moving forward, we anticipate that the integration of these side-pumping combiners into kW-class fiber lasers will further unlock the advantages of side-pumping technology and facilitate advancements in high-power laser applications.