Investigation of mid-infrared parabolic pulse evolution in a mode-locked Er-doped fiber laser based on the nonlinear polarization rotation technique

Abstract

The parabolic pulse evolution in a mode-locked Er-doped fiber laser operating at 2.8 μm has been numerically investigated by utilizing the nonlinear polarization rotation technique. In this work, the parabolic pulse evolution has been investigated by utilizing a segment of chalcogenide dispersion-decreasing bandgap fiber and a piece of Er-doped ZBLAN around 2.8 μm, whose total dispersion is in normal dispersion regime. Stable parabolic pulses can be obtained in the soft-glass fiber resonator when the polarizing angles changes from 0.356 to 0.4 π and the net group velocity dispersion from 0.006 to 0.03 ps2, respectively. Through optimizing the dispersion (i.e. net dispersion is 0.014 ps2), the pulse with 7.35 ps duration and 1.7 nJ pulse energy fits quite well with the parabolic profile. The ratio of maximum to minimum pulse width in the cavity is about 10. The pulse energy and K parameter increase with the increase of the net dispersion. As the net dispersion increases to 0.03 ps2, the pulse energy can reach up to 2.5 nJ. These results can be regarded as guidance when designing a wave-breaking-free fiber laser in the mid-infrared region.