The Nonreciprocal Mie-surfaces

TL;DR

This paper introduces 'Nonreciprocal Mie-surfaces' made of hemispherical silicon nanoparticles that exhibit asymmetric optical scattering and nonreciprocal reflection and transmission due to interference effects related to anapole modes.

Contribution

It demonstrates a novel nonreciprocal surface based on Mie scattering and interference, independent of periodicity and material reciprocity, with potential applications in passive photonic devices.

Findings

Hemispherical silicon nanoparticles show asymmetric scattering for different illumination directions.

The structured surface exhibits nonreciprocal reflection and transmission dependent on hemisphere diameter.

Nonreciprocity is due to interference related to anapole modes, not material nonreciprocity.

Abstract

Hemispherical amorphous silicon nanoparticles exhibit asymmetric optical scattering for forward illumination (base-to-apex) and backward illumination (apex-to-base). There exists an anapole mode only for backward propagation, not for forward. Due to the anapole, light is allowed to scatter maximally along the forward direction, and not in the backward direction. A structured surface obtained by repeating hemispheres in a square grid in air exhibits nonreciprocal reflection and transmission for light propagating through it. This nonreciprocity only depends on the diameter of the hemisphere, not on the periodicity. The same surface on a glass substrate causes a minor spectral redshift in the nonreciprocity. Here, the individual materials are Lorentz reciprocal, but the current nonreciprocity is due to interference. The current nonreciprocity is purely based on anapole of Mie scattering; therefore, the surface is termed as ``Nonreciprocal Mie-surface''. Such surfaces could be used for the applications of passive linear nonreciprocal photonic devices.