Theory of Raman multipeak states in solid-core photonic crystal fibers

TL;DR

This paper provides a theoretical framework for understanding multipeak soliton states in highly nonlinear photonic crystal fibers, explaining recent experimental observations of metastable two-peak states and predicting new exotic multipeak configurations.

Contribution

It introduces a gravity-like potential model to analytically describe 'magic' peak power ratios and temporal separations, and predicts the existence and stability of exotic multipeak states.

Findings

Derived simple equations for 'magic' peak power ratio and pulse separation.

Predicted the existence of exotic multipeak states that violate standard pulse splitting laws.

Developed a model to calculate the 'magic' input power for observing these states.

Abstract

Pulse splitting is a crucial and common process in nonlinear fiber optics. When an intense laser pulse is launched into a highly nonlinear fiber, a stream of fundamental solitons is generated, their temporal separations increasing during propagation. This is due to the onset of a variety of perturbations, including higher-order dispersion and the Raman effect. Recently, it has been experimentally observed that the well-known law determining the amplitudes and the temporal widths of each soliton, however, breaks down due to the unexpected formation of metastable 2-peak localised states with constant temporal separation between the two maxima. In the vicinity of certain 'magic' input powers the formation of 2-peak states is quite common in many types of highly nonlinear photonic crystal fibers. In this study, we provide a full theoretical understanding of the above recent observations. Based on a 'gravity-like' potential approach we derive simple equations for the 'magic' peak power ratio and the temporal separation between pulses forming these 2-peak states. We develop a model to calculate the magic input power of the input pulse around which the phenomenon can be observed. We also predict the existence of exotic multipeak states that strongly violate the perturbative pulse splitting law, and we study their stability and excitation conditions.