2 µm mode-locked thulium doped fiber laser using tilted fiber grating

A nonlinear polarization rotation based all-fiber passively mode-locked Tm³⁺-doped fiber laser is demonstrated by using a 45° tilted fiber grating (TFG) as an in-line polarizer. Stable soliton pulses centered at 1992.7 nm with 2.02 nm FWHM bandwidth were produced at a repetition rate of 1.902 MHz with pulse duration of 2.2 ps and pulse energy of 74.6 pJ. With the increased pump power, the laser also can operate at noise-like regime with 18.1 nm FWHM bandwidth and pulse energy of up to 250.1 nJ. Using the same 45° TFG, both stable soliton and noise-like mode-locking centered at ~1970 nm and ~2050 nm, were also achieved by shortening and extending the length of Tm³⁺-doped fiber, respectively, exhibiting advantages of broadband and low insertion loss at 2 μm band.