Polarization noise places severe constraints on coherence of all-normal dispersion femtosecond supercontinuum generation

Supercontinuum (SC) generated with all-normal dispersion (ANDi) fbers has been of special interest in recent years due to its potentially superior coherence properties when compared to anomalous dispersion-pumped SC. However, care must be taken in the design of such sources since too long pump pulses and fber length has been demonstrated to degrade the coherence.

To assess the noise performance of ANDi fber SC generation numerically, a scalar single-polarization model has so far been used, thereby excluding important sources of noise, such as polarization modulational instability (PMI). In this work we numerically study the infuence of pump power, pulse length and fber length on coherence and relative intensity noise (RIN), taking into account both polarization components in a standard ANDi fber for SC generation pumped at 1064 nm.

We demonstrate that the PMI introduces a power dependence not found in a scalar model, which means that even with short ~120 fs pump pulses the coherence of ANDi SC can be degraded at reasonable power levels above ~40 kW. We further demonstrate how the PMI signifcantly decreases the pump pulse length and fber length at which the coherence of the ANDi SC is degraded.

The numerical predictions are confrmed by RIN measurements of fs-pumped ANDi fber SC.