Resonant mode conversion in the waveguides with an unbroken and broken PT-symmetry

TL;DR

This paper investigates resonant mode conversion in PT-symmetric multimode waveguides, revealing how symmetry breaking affects resonance behavior and how mode coupling can stabilize power growth.

Contribution

It demonstrates that resonant mode conversion persists despite symmetry breaking and introduces a new understanding of mode stabilization in PT-symmetric waveguides.

Findings

Resonance width increases dramatically near symmetry-breaking point.

Resonant coupling can stabilize exponentially growing modes.

Mode conversion remains efficient even with complex refractive index modulation.

Abstract

We study resonant mode conversion in the PT-symmetric multimode waveguides, where symmetry breaking manifests itself in sequential destabilization (appearance of the complex eigenvalues) of the pairs of adjacent guided modes. We show that the efficient mode conversion is possible even in the presence of the resonant longitudinal modulation of the complex refractive index. The distinguishing feature of the resonant mode conversion in the PT-symmetric structure is a drastic growth of the width of the resonance curve when the gain/losses coefficient approaches a critical value, at which symmetry breaking occurs. We found that in the system with broken symmetry the resonant coupling between exponentially growing mode with stable higher-order one effectively stabilizes dynamically coupled pair of modes and remarkably diminishes the average rate of the total power growth.