Ultrashort pulse train generation through induced modulational polarization instability in a birefringent Kerr-like medium

Abstract

The nonlinear evolution of the polarization in a birefringent nonlinear dispersive medium is subject to two competing instabilities: degenerate steady-state polarization instability and nondegenerate three-wave mixing parametric instability. We predict that, by inducing modulational polarization instabilities, one may generate a train of ultrashort pulses from continuous-wave (cw) radiation propagating in a birefringent optical fiber, even in the normal dispersion regime. The input signal and the generated train of pulses are polarized along a principal axis of the fiber that is perpendicular to the pump polarization. Varying the choice of the fiber axis for the pump polarization and the sign of dispersion leads to substantially different shapes and bandwidths of the modulational instability gain curves. In turn, this may greatly affect the temporal characteristics of the generated pulses. The pulse width (on a picosecond or subpicosecond time scale), the repetition rate (up to a few terahertz), and the compression factor of the train can be adjusted by varying the initial sideband detuning or by tuning the fiber birefringence.