Broadband field enhancement and giant nonlinear effects in terminated unidirectional plasmonic waveguides

TL;DR

This paper demonstrates that terminated unidirectional plasmonic waveguides can produce significant electric field enhancements, leading to greatly increased nonlinear effects like third-harmonic generation, without resonant conditions.

Contribution

It introduces a nonresonant, broadband field enhancement mechanism in unidirectional waveguides that boosts nonlinear interactions significantly.

Findings

Achieved large electric field hot-spots at waveguide terminations.

Demonstrated orders-of-magnitude increase in third-harmonic-generation efficiency.

Showed potential for enhanced wave-matter interactions in nonreciprocal structures.

Abstract

Unidirectional wave propagation in nonreciprocal structures enables exciting opportunities to control and enhance wave-matter interactions in extreme ways. Within this context, here we investigate the possibility of using terminated unidirectional plasmonic waveguides to enhance typically weak nonlinear effects by orders of magnitude. We theoretically demonstrate remarkable levels of electric field enhancement and confinement (field hot-spots) when the unidirectional waveguiding structure is terminated with a suitable boundary that fully stops the one-way mode. Such a large field enhancement, originating from a nonresonant effect, is fundamentally different from the narrow-band field concentration effects in resonant plasmonic structures. Instead, it is analogous to the broadband response of plasmonic tapers, but without the need for any adiabatic impedance matching. We show that this effect can indeed lead to a substantial boosting of nonlinear light-matter interactions, exemplified by an improvement of several orders of magnitude in the third-harmonic-generation efficiency, which is of large significance for several applications. More broadly, our findings show the potential of extreme nonreciprocal configurations for enhanced wave-matter interactions.