Efficient single-mode operation in a 10 dB/m absorption very-large-mode-area ytterbium-doped optical fiber via curvature-induced mode filtering

In this paper we report our findings on the design, manufacturing and testing of low numerical aperture active step-index optical fibers with very large mode area, operating in a truly single-mode regime. Our approach to efficiently filter higher-order modes in the core relies on applying curvature in a specific direction at a given diameter on a specially designed fiber containing boron-doped silica rods on both sides of the core. The fabricated ytterbium-doped fibers exhibit a mode field diameter of 32μm, a cladding pump absorption of 10 dB/m and were designed for use in a compact monolithic configuration due to its all-solid nature and its 14 cm targeted bend diameter.