Phase transition in multimode nonlinear parity-time-symmetric waveguide couplers

TL;DR

This paper investigates nonlinear effects in multimode $ ext{PT}$-symmetric waveguide couplers, revealing a nonlinearity-induced phase transition and diverse intensity patterns, with implications for integrated optical signal processing.

Contribution

It introduces the study of nonlinear properties in finite-size multimode $ ext{PT}$-symmetric couplers and predicts a nonlinearity-triggered phase transition that depends on the number of dimers.

Findings

Nonlinear dispersion relations in multimode $ ext{PT}$ couplers.

Prediction of a $ ext{PT}$ transition triggered by nonlinearity.

Transition threshold decreases with increasing number of dimers.

Abstract

Parity-time-symmetric ($\mathcal{PT}$-symmetric) optical waveguide couplers have become a key component for integrated optics. They offer new possibilities for fast, ultracompact, configurable, all-optical signal processing. Here, we study nonlinear properties of finite-size multimode $\mathcal{PT}$-symmetric couplers and report a peculiar type of dispersion relation in couplers made of more than one dimer. Moreover, we predict a $\mathcal{PT}$ transition triggered by nonlinearity in these structures, and we demonstrate that with the increase of the number of dimers in the system, the transition threshold decreases and converges to the value corresponding to an infinite array. Finally, we present a variety of periodic intensity patterns that can be formed in these couplers depending on the initial excitation.