High Energy All-Fiber Tm-Doped Femtosecond Soliton Laser Mode-Locked by Nonlinear Polarization Rotation

A high-energy thulium-doped all-fiber soliton laser passively mode-locked by nonlinear polarization rotation (NPR) technology is presented, generating 350 fs pulses with spectral width of 11.5 nm at 1890 nm wavelength. Kelly sidebands of the soliton spectrum are well suppressed due to the NPR effect in the fiber laser. The average output power reaches 90 mW, corresponding to the pulse energy up to 7.8 nJ and the pulse peak power of 22.3 kW, leading to the higher order soliton generation. This has been testified by the relationship between the soliton period and the cavity length. Thus, the laser can deliver high-energy ultrashort soliton pulses while the pulse shape is close to one of the fundamental solitons. We believe that this represents one of the best observations of short pulse duration as well as high pulse power coexisting in Tm-doped soliton fiber lasers.