Circularly polarized topological edge states derived from optical Weyl points in semiconductor-based chiral woodpile photonic crystals

TL;DR

This study numerically demonstrates topological edge states with circular polarization in chiral woodpile photonic crystals derived from optical Weyl points, offering robust, confined waveguides for circularly polarized light in semiconductor structures.

Contribution

It reveals the existence of circularly polarized topological edge states in chiral photonic crystals with Weyl points, which can be fabricated in semiconductor materials for advanced photonic applications.

Findings

Topological edge states are confined below the light line at air interfaces.

Edge states exhibit a specific circular polarization depending on chirality.

Chiral photonic crystals can be fabricated in GaAs or Si for practical devices.

Abstract

The polarizations of topological edge modes in the vicinity of optical Weyl points were numerically studied in chiral photonic crystals. We investigated two kinds of rotationally stacked woodpile structures in which planar rod arrays were vertically stacked one-by-one with an in-plane rotation angle of 60 or 45 degrees. Both structures showed pairs of optical Weyl points having topological numbers of opposite signs for photonic bands in low orders. Topological edge states derived from the Weyl points appeared below the light line, and were strongly confined at the air interfaces in a length shorter than the wavelength. Their polarizations in a direction perpendicular to the propagation direction were found to be one particular circular polarization that depended on the handedness of the structural chirality. Since these chiral photonic crystals can be fabricated using semiconductor materials such as GaAs or Si, the obtained robust planar waveguides for circularly polarized light at the interface between air and the semiconductor structure can be useful not only in photonics but also in spintronics or quantum information technology through spin-photon interfaces.