Ferroelectric chiral nematic liquid crystals: New photonic materials with multiple bandgaps controllable by low electric fields

TL;DR

This study explores ferroelectric chiral nematic liquid crystals, revealing their ability to exhibit multiple tunable photonic bandgaps under low electric fields, with potential applications in nonlinear optics.

Contribution

It demonstrates that the NF* phase of ferroelectric nematic liquid crystals can be controlled to produce multiple, tunable photonic bandgaps using low electric fields, a novel property for photonic materials.

Findings

NF* phase exhibits multiple, tunable photonic bandgaps under low electric fields.

The pitch of NF* phase increases with electric field, unlike N* phase.

The study provides a dispersion relation analysis of optical eigenmodes in NF* phase.

Abstract

We have carried out a spectroscopic study on a prototype ferroelectric nematic material (RM7343) doped with a non-polar chiral compound. The mixture presents two chiral nematic phases, one conventional (N*) and the other polar (NF*), whose behaviours under electric fields E are totally different. On the one hand, the N* phase shows a single reflection band if E is not very high, while fields perpendicular to the helix of a few V/mm are already sufficient to produce multiple bands in the NF* phase. On the other hand, the pitch of the NF* phase grows notably on increasing fields, however remaining practically constant in the N* phase. Both effects have been explained in terms of the different type of interaction with E in each phase (ferroelectric in NF* and dielectric in N*). We argue that the NF* phase behaves as a photonic material with multiple gaps tunable by small fields, which presents important potentialities for applications. A study of the bandgaps has been carried out through the analysis of the dispersion relation of the optical eigenmodes in the NF* phase under field. Finally, an example of the potentialities of the NF* phase within the field of nonlinear optics is briefly presented.