Analytical model of supercontinuum coherence degradation induced by pump intensity noise

Abstract

The coherence of supercontinuum (SC), which presents the pulse-to-pulse stability, is important for optical frequency combs because it determines the phase noise performance of the detected carrier-envelope offset frequency. However, researches on coherence degradation of an octave SC induced by the inherent intensity noise of pump pulses injected into highly-nonlinear photonic crystal fiber (HN-PCF) are incomplete. In this study, we propose a novel characterization method for SC coherence under pump intensity noise, which uses the coherence of soliton with the maximum red-shifted rate to represent the overall SC coherence. This method is verified by numerically solving the nonlinear Schrödinger equation. An analytical model which converts the soliton coherence into phase stability of the optical field is further present to prove the simulation results. Our investigations show that, when the pump pulse is injected into anomalous-dispersion region of the HN-PCF, for a fixed SC spectral range and root-mean-square relative intensity noise value of pump light, coherence degradation across an octave SC band is more intense with a decline of the injected pulse peak power, the adoption of HN-PCF with a smaller nonlinear parameter and when the pump wavelength lies further away from the zero dispersion point of HN-PCF. Moreover, it is found that, for a fixed pulse peak power and HN-PCF parameters, the impacts of injected pulse duration are negligible. Our research provides effective avenues to improve the octave SC coherence under pump intensity noise.