4 kW single-mode laser output assisted by a double-tapered double-clad fiber

In this study, we design and fabricate a novel type of active fiber——double-tapered double-clad fiber (DT-DCF). Based on this self-developed DT-DCF, we have constructed an all-fiberized fiber amplifier that is operating under a continuous-wave (CW) regime at 1080 nm wavelength. The maximum output power of the system reaches 4 kW, which, to the best of our knowledge, is the highest output power of tapered fiber-based laser systems. The amplifier exhibits near-single-mode beam quality (M2=1.33) at the highest output power with a slope efficiency of 83%. Our result successfully verifies the potential of power scalability of DT-DCF, and the performance of our system can be further enhanced by fiber design optimization.