Orientational "Kerr effect" and phase modulation of light in deformed-helix ferroelectric liquid crystals with subwavelength pitch

TL;DR

This paper investigates the electro-optical behavior of deformed helix ferroelectric liquid crystals with subwavelength pitch, revealing an electric-field-induced Kerr effect and phase modulation capabilities through theoretical analysis and experiments.

Contribution

It introduces a theoretical model describing the quadratic nonlinear optical response of VADHFLCs and experimentally confirms the electric-field-induced biaxiality and phase modulation effects.

Findings

Biaxiality proportional to square of electric field at weak fields

Observation of 2π phase modulation without ellipticity change

Theoretical confirmation of quadratic nonlinear optical behavior

Abstract

We study both theoretically and experimentally the electro-optical properties of vertically aligned deformed helix ferroelectric liquid crystals (VADHFLC) with subwavelength pitch that are governed by the electrically induced optical biaxiality of the smectic helical structure. The key theoretical result is that the principal refractive indices of homogenized VADHFLC cells exhibit the quadratic nonlinearity and such behavior might be interpreted as the orientational "Kerr effect" caused by the electric-field-induced orientational distortions of the FLC helix. In our experiments, it has been observed that, for sufficiently weak electric fields, the magnitude of biaxiality is proportional to the square of electric field in good agreement with our theoretical results for the effective dielectric tensor of VADHFLCs. Under certain conditions, the 2$\pi$ phase modulation of light, which is caused by one of the induced refractive indices, is observed without changes in ellipticity of incident light.