Abstract

High power fiber lasers can benefit from the tailored pump absorption along the active fiber. The higher pump absorption mitigates the nonlinear effects thanks to shorter laser resonators. On the other hand it is often beneficial to decrease the pump absorption near pump injection locations. Based on recently reported rigorous theoretical description of the mode mixing in double-clad fibers, promising concepts of new fiber geometries and layouts for tailoring the pump absorption have been outlined [1, 2]. The new concepts shall finally result in highly efficient lasers of a small footprint and reduced need for cooling that shall have a great potential for applications where low power consumption, tightly limited space and low weight are required. One of the concepts was based on twisted double-clad fiber. It was successfully demonstrated for Tm-doped double-clad fiber that was twisted after drawing [3]. In this work we report for the first time fabrication and absorption measurements of Tm-doped double-clad fiber that was spun during the drawing so that the twist remain frozen in the drawn fiber.

© 2019 IEEE