Pure Passive Fiber Enabled Highly Efficient Raman Fiber Amplifier With Record Kilowatt Power

Kilowatt-level high-efficiency all-fiberized Raman fiber amplifier based on pure passive fiber is proposed for the first time in this paper. The laser system is established on master oscillator power amplification configuration, while a piece of graded-index passive fiber is utilized as Stokes shifting as well as gain medium, which is entirely irrelevant to the rare-earth-doped gain mechanism. When the pump power is 1368.8 W, we obtained 1002.3-W continuous-wave laser power at 1060 nm with the corresponding optical-to-optical efficiency of 84%. The beam parameter M-2 improves from 9.17 of the pump laser to 5.06 of the signal laser through the amplification process, and the brightness enhancement is about 2.57 at maximum output power as a consequence of the beam clean-up process in the graded-index fiber. To the best of our knowledge, we have demonstrated the first kilowatt-level high-efficiency Raman fiber amplifier based on pure passive fiber with brightness enhancement.