2.7 kW co-pumped fiber amplifier based on constant-cladding tapered-core fiber

• Fabricate an Yb-doped constant-cladding tapered-core (CCTC) fiber. • Investigate the laser properties of CCTC fiber under different bending schemes. • The output power of CCTC fiber is up to 2.7 kW with a slope efficiency of 82.1%. A constant-cladding tapered-core (CCTC) fiber with the core size varying monotonously along the length was fabricated. The core/cladding diameters of narrow end and wide end are 24/400 μm and 31/400 μm, respectively. A forward-pumping master oscillator power amplifier (MOPA) was constructed to investigate the laser performance of this fiber under two bending schemes (8–14 cm and 12–16 cm). The maximum output power is scaled up to 2704 W with a slope efficiency of 82.1% in the case of bending diameter ranges from 12 cm to 16 cm, the M 2 factor at 2548 W output power is 2.16, and no signs of transverse modal instability (TMI) and stimulated Raman scattering (SRS) were observed in whole experiment. The above result verifies the potential of power scalability of CCTC fiber, and the laser performance can be further enhanced by fiber design optimization and other TMI suppression methods.