Reorientational solitons in nematic liquid crystals with modulated alignment

TL;DR

This paper investigates the behavior of reorientational solitons in nematic liquid crystals with linearly varying alignment, comparing two theoretical approaches to predict their curved trajectories and power requirements.

Contribution

It introduces and compares adiabatic and elastic theory models for soliton propagation in modulated nematic liquid crystals, revealing consistent predictions of curved paths and power thresholds.

Findings

Models predict curved soliton trajectories with various curvatures.

Minimal power for soliton formation remains unchanged with alignment modulation.

Both approaches yield comparable results in non-homogeneous media.

Abstract

In uniaxial soft matter with a reorientational nonlinearity, such as nematic liquid crystals, a light beam in the extraordinary polarization walks off its wavevector due to birefringence, while it undergoes self-focusing via an increase in refractive index and eventually forms a spatial soliton. Hereby the trajectory evolution of solitons in nematic liquid crystals- nematicons- in the presence of a linearly varying transverse orientation of the optic axis is analysed. In this study we use and compare two approaches: i) a slowly varying (adiabatic) approximation based on momentum conservation of the soliton in a Hamiltonian sense; ii) the Frank-Oseen elastic theory coupled with a fully vectorial and nonlinear beam propagation method. The models provide comparable results in such a non-homogeneously oriented uniaxial medium and predict curved soliton paths with either monotonic or non-monotonic curvatures. The minimal power needed to excite a solitary wave via reorientation remains essentially the same in both uniform and modulated cases.