Superluminal k-gap solitons in nonlinear photonic time-crystals

TL;DR

This paper introduces superluminal solitons in nonlinear photonic time-crystals that propagate faster than light without violating causality, expanding understanding of wave dynamics in engineered optical media.

Contribution

It presents the first theoretical demonstration of superluminal k-gap solitons in nonlinear photonic time-crystals, highlighting their unique properties and causality-preserving superluminal propagation.

Findings

Superluminal solitons reside in the momentum gap of nonlinear photonic time-crystals.

These solitons are structured as plane-waves in space and self-reconstructing in time.

Superluminal propagation does not violate Einstein's causality.

Abstract

We propose superluminal solitons residing in the momentum gap (k-gap) of nonlinear photonic time-crystals. These gap solitons are structured as plane-waves in space while being periodically self-reconstructing wavepackets in time. The solitons emerge from modes with infinite group velocity causing superluminal evolution, which is opposite to the stationary nature of the analogous Bragg gap soliton residing at the edge of an energy gap (or a spatial gap) with zero group velocity. We explore the faster-than-light pulsed propagation of these k-gap solitons in view of Einstein's causality by introducing a truncated input seed as a precursor of signal velocity forerunner, and find that the superluminal propagation of k-gap solitons does not break causality.