Thulium-doped all-fiber mode-locked laser based on NPR and 45°-tilted fiber grating

A nonlinear polarization rotation based all-fiber passively modelocked Tm3+-doped fiber laser is demonstrated by using a 45 degrees tilted fiber grating (TFG) as an in-line polarizer. The 45 degrees TFG centered at 2000 nm with polarization dependent loss (PDL) of > 12 dB at 1850 nm similar to 2150 nm range was UV inscribed for the first time in SM28 fiber using a 244 nm Ar+ continuous wave laser and a phase mask with 25 mm long uniform pitch and titled period pattern of 33.7 degrees with respect to the fiber axis. 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. As 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 degrees TFG, both stable soliton and noise-like mode-locking centered at similar to 1970 nm and similar to 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 mu m band. (C) 2014 Optical Society of America