Tunable Raman soliton beyond 2 Micron

We report a compact and efficient Raman soliton laser system with continuous spectra tunability based on thulium doped fibers. It delivers sub-200 fs pulses with tunable range from 1.98 to 2.31 μm by varying the pump power. The longest wavelength is limited by the background loss of silica fiber. By optimizing the chirp value of the input signal, the high conversion efficiency of 76% to 97% over the whole tunable range can be achieved.