Multistate passively mode-locked thulium-doped fiber laser with nonlinear amplifying loop mirror

In this paper, a multistate passively mode-locked thulium-doped fiber laser with nonlinear amplifying loop mirror is reported. An ultra-high numerical aperture fiber is employed to compensate the cavity abnormal dispersion, and the net cavity dispersion value is fixed at -0.046 ps(2). By changing the pump power, three different mode-locked regions, namely Q-switched mode-locking operation, mode-locking operation, and dual-wavelength mode-locking operation, are observed sequentially. When the pump power is raised to the threshold of 1.60 W, the transition state of the Q-switched mode locking begins to be observed. When the pump power increases from 2.88 W to 8.75 W, stable single-wavelength mode-locking operation is obtained. And the center wavelength is 1988.73 nm corresponding to the 3 dB spectral bandwidth of 11.21 nm. As the pump power is raised beyond 8.75 W, dual-wavelength mode-locking operation is developed, where the dual wavelengths are 1969.70 nm and 1984.12 nm with the 3 dB spectral bandwidth of similar to 4.11 nm and similar to 6.14 nm, respectively. (C) 2018 Optical Society of America