Nonsymmetric evanescent coupling in photonics

TL;DR

This paper investigates the often-overlooked asymmetry in evanescent coupling within photonic systems, revealing its origins and experimentally validating the phenomenon through detuned directional couplers.

Contribution

It analytically demonstrates the source of nonsymmetrical evanescent coupling and experimentally confirms the asymmetry in a photonic platform.

Findings

Nonsymmetrical coupling arises from wave function tail behavior.

Experimental validation with femtosecond laser written couplers.

Numerical simulations support the analytical and experimental results.

Abstract

Asymmetrical interactions are ubiquitous in nature, and in physics their study becomes fundamental. Despite the prevalence of evanescent coupling in physics, little attention has been paid to wave function profiles, with symmetrical reciprocal interactions often assumed for practical reasons. This work challenges that assumption by analytically demonstrating the origin of nonsymmetrical coupling in a photonic platform, focusing on the behavior of evanescent tails from adjacent waveguides. We experimentally validate an asymmetrical dynamics by studying detuned photonic directional couplers, fabricated via femtosecond laser writing, and corroborate our findings through continuous numerical simulations.