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

Abstract

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 ps2. 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 1.60W, the transition state of the Q-switched mode locking begins to be observed. When the pump power increases from 2.88W to 8.75W, stable single-wavelength mode-locking operation is obtained. And the center wavelength is 1988.73nm corresponding to the 3dB spectral bandwidth of 11.21nm. As the pump power is raised beyond 8.75W, dual-wavelength mode-locking operation is developed, where the dual wavelengths are 1969.70nm and 1984.12nm with the 3dB spectral bandwidth of ∼4.11 nm and ∼6.14 nm, respectively.