Polarization- and wave-vector selective optical metasurface with near-field coupling

TL;DR

This paper demonstrates a metasurface that manipulates light polarization and wave-vector dependence through near-field coupling, enabling angle-tunable polarization filtering and light source applications.

Contribution

It introduces a novel metasurface design where near-field coupling induces negative coupling, creating unique polarization eigenstates along lines in momentum space.

Findings

Existence of polarization eigenstates along lines in k-space.

Ability to tune polarization-dependent reflection by incident angle.

Validation of near-field coupling effects in silicon waveguides.

Abstract

Metasurfaces are a powerful tool for manipulating light using small structures on the nanoscale. In most meta-surfaces, near-field couplings are treated as unfavorable perturbations. Here, we experimentally investigate a structure consisting of sinusoidally modulated silicon waveguides where near-field coupling of local resonances leads to negative coupling, i.e. a negative coupling constant. This gives rise to wave-vector dependent eigenstates of elliptical, linear and circular polarizations. In particular, fully circular polarization states are not only present at a single point in momentum-space (k-space), but along a line. This circular polarization line, as well as a linear polarization line, emanates from a polarization degeneracy at the Dirac point. We experimentally validate the existence of these eigenstates and demonstrate the energy-, polarization- and wave-vector-dependence of this metasurface. By tuning the incident k-vector, certain polarization-energy eigenstates are strongly reflected allowing for uses in angle-tunable polarization filters and light sources.