Guiding light via geometric phases

TL;DR

This paper introduces a novel light waveguiding method based on geometric Berry phases, utilizing polarization states in structured anisotropic media, demonstrated through theoretical analysis and experimental proof-of-concept.

Contribution

It presents a new waveguiding approach using geometric phases and polarization control, expanding the design space beyond scalar refractive index changes.

Findings

Theoretical analysis and numerical simulations confirm the feasibility.

Experimental demonstration validates the concept in a discrete element setup.

The method enables spin-orbit optical interactions in integrated photonics.

Abstract

Known methods for transverse confinement and guidance of light can be grouped into a few basic mechanisms, the most common being metallic reflection, total internal reflection and photonic-bandgap (or Bragg) reflection. All of them essentially rely on changes of the refractive index, that is on scalar properties of light. Recently, processes based on "geometric Berry phases", such as manipulation of polarization states or deflection of spinning-light rays, have attracted considerable interest in the contexts of singular optics and structured light. Here, we disclose a new approach to light waveguiding, using geometric Berry phases and exploiting polarization states and their handling. This can be realized in structured three-dimensional anisotropic media, in which the optic axis lies orthogonal to the propagation direction and is modulated along it and across the transverse plane, so that the refractive index remains constant but a phase distortion can be imposed on a beam. In addition to a complete theoretical analysis with numerical simulations, we present a proof-of-principle experimental demonstration of this effect in a discrete element implementation of a geometric phase waveguide. The mechanism we introduce shows that spin-orbit optical interactions can play an important role in integrated optics and paves the way to an entire new class of photonic systems that exploit the vectorial nature of light.