Kerr nonlinearity and dispersion characterization of core-pumped thulium-doped fiber at 2  μm.

A nonlinear coefficient of 3.6-4.1  W-1  km-1 and group velocity dispersion of -20  ps2/km of a commercial core-pumped thulium-doped fiber have been evaluated using degenerate four-wave mixing at 2 μm. The anomalous dispersion behavior of the fiber has been confirmed by linear measurements with an all-fiber Mach-Zehnder interferometer (MZI). Additionally, no pump-induced dispersion changes due to excitation of Tm3+ cations have been detected. These characteristics make these fibers attractive for pulsed fiber laser applications. A nonlinear-polarization rotation mode-locked laser involving nonlinear polarization evolution directly in the doped fiber is demonstrated.