Polarization instability of ultrashort pulses as a source of vectorial supercontinuum

Polarization instability of ultrashort light pulses, giving rise to vectorial supercontinuum generation, is demonstrated using a subwavelength-core, highly birefringent, normally dispersive optical fiber. The evolution of ultrasort pulses in the regime of polarization instability is shown to radically differ from polarization-instability dynamics of continuous-wave fields and longer laser pulses. As the peak power of the laser field decreases along the propagation path due to dispersion-induced pulse stretching, the Poincaré-sphere map of field dynamics is shown to evolve from the behavior typical of polarization instability in the highly nonlinear regime toward the beating dynamics of uncoupled polarization modes, characteristic of low field intensities and continuous-wave fields.