Coherent and incoherent rogue waves in seeded supercontinuum generation

Abstract

Summary form only given. The shot-to-shot stability of a supercontiuum (SC) can be controlled both in terms of coherence and intensity stability by modulating the input pulse with a weak seed [1-3]. In the long-pulse regime, the SC generation is initiated by noise-seeded modulation instability (MI), which breaks the pump into solitons and dispersive waves. To control the spectral evolution and reduce the noise, it has been proposed to provide a seed, i.e. a weak pulse with a frequency offset relative to the pump, within the MI gain spectrum in order to ensure a deterministic rather than noise-seeded pulse break-up [1, 2]. Seeding the pulse break-up has likewise been used to control the generation of otherwise statistically rare large-amplitude rogue solitons [2-4]. In this work, we numerically investigate the influence of the MI gain spectrum on the pulse break-up and rogue wave generation. We find that the results can be clearly divided into a number of distinct dynamical regimes depending on the initial four-wave mixing process and demonstrate that seeding can be used to generate coherent and incoherent rogue waves.Figure 1 shows simulation results of seeded SC generation in a fiber with a zero-dispersion wavelength (ZDW) at 1054 nm for pump wavelengths of 1055 and 1075 nm, respectively. The MI gain spectrum depends strongly on the pump wavelength and the MI gain bandwidth decreases when the pump is moved away from the ZDW, as seen in the insets in Fig. 1. The seed causes a beating of the temporal profile, which, if chosen correctly, leads to a deterministic pulse break-up. When the pump is close to the ZDW [Fig. 1(a)], the MI gain is relatively small at the seed wavelength (1070.1 nm) and slowly increasing with wavelength. The temporal profile is therefore only slowly broken up into solitons. This means that the solitons are mainly generated from the pulse center where the peak power is highest. The solitons have time to redshift before the cascade is amplified and the dynamics are relatively turbulent. In contrast to this, pumping further from the ZDW [Fig. 1(b)] gives a much larger gain at the seed wavelength (1090.6 nm) that increases more rapidly with wavelength. This causes a fast breakup of the temporal pulse, where the individual temporal fringes generate fundamental solitons in a controlled fashion that almost resembles soliton fission. The most powerful solitons are still generated near the center of the pulse where the power is highest. These powerful rogue solitons only collide with the smaller solitons generated from the trailing edge of the pulse. Interestingly, a closer inspection reveals that the rogue soliton is generated incoherently when pumping close to the ZDW, but coherently when the pump is shifted away from the ZDW.At the conference we will discuss the influence of the MI gain spectrum in more detail and demonstrate that the coherent pulse break-up afforded by seeding is washed out by turbulent solitonic dynamics when the pump peak power is increased to the kW level.