A 5 kW Nearly-Single-Mode Monolithic Fiber Laser Emitting at ~1050 nm Employing Asymmetric Bi-Tapered Ytterbium-Doped Fiber

Abstract

Limited by stimulated Raman scattering (SRS), amplified spontaneous emission (ASE) and transverse mode instability (TMI), it is challenging to achieve high-power laser output in ytterbium-doped fiber (YDF) lasers with operating wavelengths less than 1060 nm. In high-power fiber lasers, bi-tapered YDF can provide a balance between the suppression of SRS and TMI. In this work, we designed and fabricated a new double-cladding asymmetric bi-tapered YDF to suppress ASE and SRS in the 1050 nm monolithic fiber laser. The asymmetric bi-tapered YDF has an input end with a core/cladding diameter of ~20/400 μm, a middle section with a core/cladding diameter of ~30/600 μm and an output end with a core/cladding diameter of ~25/500 μm. The working temperature of the non-wavelength-stabilized 976 nm laser diodes was optimized to improve the TMI threshold. An output power of over 5 kW with an efficiency of 83.1% and a beam quality factor M2 of about 1.47 were achieved. To the best of our knowledge, this represents the highest power nearly-single mode in 1050 nm fiber lasers. This work demonstrates the potential of asymmetric bi-tapered YDF for achieving a high-power laser with high beam quality in 1050 nm fiber lasers.