Ultra-broadband gradient-pitch Bragg-Berry mirrors

TL;DR

This paper introduces ultra-broadband gradient-pitch Bragg-Berry mirrors using 3D varying chiral nematic liquid crystals, enabling wide spectral range optical vortex generation and broadening the spectral capabilities of geometric phase devices.

Contribution

It presents a novel design of gradient-pitch cholesteric liquid crystal slabs that significantly extend the spectral range of Bragg-Berry mirrors for optical applications.

Findings

Demonstrated ultra-broadband optical vortex generation in the visible spectrum.

Achieved polychromatic control of orbital angular momentum of light.

Validated the practical use of gradient-pitch cholesterics for broadband optical devices.

Abstract

The realization of geometric phase optical device operating over a broad spectral range is usually confronted with intrinsic limitations depending of the physical process at play. Here we propose to use chiral nematic liquid crystal slabs with helical ordering that varies in three dimensions. Namely, gradient-pitch cholesterics endowed with in-plane space-variant angular positioning of the supramolecular helix. By doing so, we show that the recently introduced Bragg-Berry mirrors [Opt. Lett. {\bf 41}, 3972-3975 (2016)] can be endowed with ultra-broadband spectral range. Experimental demonstration is made in the case of ultra-broadband optical vortex generation in the visible domain. These results offer practical solution to the polychromatic management of the orbital angular momentum of light combining the circular Bragg reflection of chiral media with the Berry phase.