Breathers in PT-symmetric optical couplers

TL;DR

This paper demonstrates that PT-symmetric optical couplers can support stable, localized oscillatory structures called breathers, which oscillate between waveguides and coexist with solitons, with their dynamics described by coupled nonlinear Schrödinger equations.

Contribution

It introduces the existence and stability of breathers in PT-symmetric optical waveguides, modeled by coupled nonlinear Schrödinger equations, expanding understanding of nonlinear localized structures in such systems.

Findings

PT-breathers oscillate and balance gain and loss

Breathers coexist with solitons and are prevalent after collisions

Small-amplitude breathers are shown to be stable

Abstract

We show that the parity-time (PT) symmetric coupled optical waveguides with gain and loss support localised oscillatory structures similar to the breathers of the classical $\phi^4$ model. The power carried by the PT-breather oscillates periodically, switching back and forth between the waveguides, so that the gain and loss are compensated on the average. The breathers are found to coexist with solitons and be prevalent in the products of the soliton collisions. We demonstrate that the evolution of the small-amplitude breather's envelope is governed by a system of two coupled nonlinear Schr\"odinger equations, and employ this Hamiltonian system to show that the small-amplitude PT-breathers are stable.