# Directional supercontinuum generation: the role of the soliton

## TL;DR

This study numerically investigates how solitons influence supercontinuum generation in silicon nitride waveguides with two zero-dispersion wavelengths, demonstrating directional spectral broadening controlled by dispersion regimes.

## Contribution

It introduces the concept of directional supercontinuum generation driven by soliton interactions in waveguides with engineered dispersion profiles.

## Key findings

- Spectral broadening occurs mainly towards the second normal-dispersion regime.
- Pumping in either normal-dispersion regime enables broadening towards the other.
- The approach is confirmed in silica microstructured fibers with two zero-dispersion wavelengths.

## Abstract

In this paper we numerically study supercontinuum generation by pumping a silicon nitride waveguide, with two zero-dispersion wavelengths, with femtosecond pulses. The waveguide dispersion is designed so that the pump pulse is in the normal-dispersion regime. We show that because of self-phase modulation, the initial pulse broadens into the anomalous-dispersion regime, which is sandwiched between the two normal-dispersion regimes, and here a soliton is formed. The interaction of the soliton and the broadened pulse in the normal-dispersion regime causes additional spectral broadening through formation of dispersive waves by non-degenerate four-wave mixing and cross-phase modulation. This broadening occurs mainly towards the second normal-dispersion regime. We show that pumping in either normal-dispersion regime allows broadening towards the other normal-dispersion regime. This ability to steer the continuum extension towards the direction of the other normal-dispersion regime beyond the sandwiched anomalous-dispersion regime underlies the directional supercontinuum notation. We numerically confirm the approach in a standard silica microstructured fiber geometry with two zero-dispersion wavelengths.