Magnetic spin-orbit interaction directs Bloch surface waves

TL;DR

This paper demonstrates that the magnetic field of light can control the directionality of Bloch surface waves via magnetic spin-orbit interaction, enabling new optical manipulation techniques.

Contribution

It introduces the concept of magnetic spin-orbit interaction controlling surface wave excitation, with experimental validation using a photonic crystal structure.

Findings

Magnetic helicity controls power distribution of surface waves.

Magnetic spin-orbit interaction is comparable to electric effects.

Magnetic field can direct surface wave excitation without electric dipoles.

Abstract

We study the directional excitation of optical surface waves controlled by the magnetic field of light. We theoretically predict that a spinning magnetic dipole develops a tunable unidirectional coupling of light to TE-polarized Bloch surface waves (BSWs). Experimentally, we show that the helicity of light projected onto a subwavelength groove milled in the top layer of a 1D photonic crystal (PC) controls the power distribution between two TE-polarized BSWs excited on both sides of the groove. Such a phenomenon is shown to be mediated solely by the helicity of the magnetic field of light, thus revealing a magnetic spin-orbit interaction. Remarkably, this magnetic optical effect is clearly observed with a near-field coupler governed by an electric dipole moment: it is of the same order of magnitude as the electric optical effects involved in the coupling. The magnetic spin-orbit interaction opens new degrees of freedom in the manipulation of light and offers appealing novel opportunities in the development of integrated optical functionalities.