Nonreciprocal plasmonics enables giant enhancement of thin-film Faraday rotation

TLDR

Light propagation is reciprocal, but a static magnetic field in magneto‑optical materials breaks time‑reversal symmetry, producing the Faraday effect that rotates polarization and is exploited in bulky optical isolators. The study aims to develop thin‑film Faraday rotators with enhanced Faraday effect for integrated optics. The authors explain the enhancement as arising from the interaction between plasmons and photonic waveguide modes in the hybrid structure. Hybridizing plasmonics with magneto‑optics on thin films yields a ten‑fold increase in Faraday rotation while preserving high transparency.

Abstract

Light propagation is usually reciprocal. However, a static magnetic field along the propagation direction can break the time-reversal symmetry in the presence of magneto-optical materials. The Faraday effect in magneto-optical materials rotates the polarization plane of light, and when light travels backward the polarization is further rotated. This is applied in optical isolators, which are of crucial importance in optical systems. Faraday isolators are typically bulky due to the weak Faraday effect of available magneto-optical materials. The growing research endeavour in integrated optics demands thin-film Faraday rotators and enhancement of the Faraday effect. Here, we report significant enhancement of Faraday rotation by hybridizing plasmonics with magneto-optics. By fabricating plasmonic nanostructures on laser-deposited magneto-optical thin films, Faraday rotation is enhanced by one order of magnitude in our experiment, while high transparency is maintained. We elucidate the enhanced Faraday effect by the interplay between plasmons and different photonic waveguide modes in our system.