Abstract
We report how the complex intra-pulse polarization dynamics of coherent optical wavebreaking and incoherent Raman amplification processes in all-normal dispersion (ANDi) fibers vary for femto and picosecond pump pulses. Using high temporal resolution vector supercontinuum simulations, we identify deterministic polarization dynamics caused by wavebreaking and self-phase modulation for femtosecond pulses and quasi-chaotic polarization evolution driven by Raman amplification of quantum noise for picosecond pulses. In contrast to cross-phase modulation instability, the Raman-based polarization noise has no power threshold and is reduced by aligning the higher energy polarization component with the lower index axis of the fiber. The degree of polarization stability is quantified using new time domain parameters that build on the spectrally averaged degree of coherence used in supercontinuum research to quantify the output spectral stability. We show that the spectral coherence is intrinsically linked to polarization noise, and that the noise will occur in both polarization maintaining (PM) and non-PM fibers, spanning a broad range of pulse energies, durations, and fiber birefringence values. This analysis provides an in-depth understanding of the nonlinear polarization dynamics associated with coherent and incoherent propagation in ANDi fibers.
Highlights
Supercontinuum generation in all-normal dispersion (ANDi) photonic crystal fiber (PCF) offers an energy-scalable route to developing high brightness, single cycle sources with octave-spanning bandwidths [1,2,3,4]
We show that polarization noise occurs in both polarization maintaining (PM) and non-PM fibers, and is reduced when the group velocity mismatch (GVM) asymmetry of the XPM-assisted Raman amplification is exploited by aligning the highest energy polarization component to the low index fiber axis
ANDi supercontinuum generation is generally driven by optical wavebreaking when pumped using femtosecond pulses [6] so, we investigate the polarization dynamics of femtosecond pulses propagating through 1 m of PCF with a small orientation and zero birefringence to isolate nonlinear polarization effects from linear effects
Summary
Supercontinuum generation in all-normal dispersion (ANDi) photonic crystal fiber (PCF) offers an energy-scalable route to developing high brightness, single cycle sources with octave-spanning bandwidths [1,2,3,4]. Our observed polarization dynamics may occur in much shorter lengths of normal dispersion liquid core fiber than ANDi silica PCF [47,48] because of the larger nonlinear index of many liquids in comparison with silica [49], and because many gas and liquid core fibers permit strong polarization mode coupling Both deterministic and noise-dominated polarization dynamics are expected to occur in ANDi supercontinuum generation pumped by different pulsed sources, such as lasers used to seed chalcogenide or fluoride fiber for mid-infrared generation [15,50,51,52].
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