Light modulation in planar aligned short-pitch deformed-helix ferroelectric liquid crystals

TL;DR

This paper investigates light modulation in short-pitch deformed-helix ferroelectric liquid crystals through experiments and theory, revealing weak biaxial anisotropy and demonstrating minimal impact on axicon performance at 50 μm thickness.

Contribution

It provides a combined experimental and theoretical analysis of light modulation in short-pitch DHFLCs, including effective optical tensor modeling and application to spatial light modulation devices.

Findings

Optical anisotropy is weakly biaxial.

Theoretical model fits experimental data well.

Field-induced rotation effects are negligible at 50 μm thickness.

Abstract

We study both experimentally and theoretically modulation of light in a planar aligned deformed-helix ferroelectric liquid crystal (DHFLC) cell with subwavelength helix pitch, which is also known as a short-pitch DHFLC. In our experiments, azimuthal angle of the in-plane optical axis and electrically controlled parts of the principal in-plane refractive indices were measured as a function of voltage applied across the cell. Theoretical results giving the effective optical tensor of a short-pitch DHFLC expressed in terms of the smectic tilt angle and the refractive indices of FLC are used to fit the experimental data. Optical anisotropy of the FLC material is found to be weakly biaxial. For both the transmissive and reflective modes, the results of fitting are applied to model phase and amplitude modulation of light in the DHFLC cell. We demonstrate that, if the thickness of the DHFLC layer is about 50 $\mu$m, the detrimental effect of field-induced rotation of the in-plane optical axes on the characteristics of an axicon designed using the DHFLC spatial light modulator in the reflective mode is negligible.