Nonlinear optical properties of a channel waveguide produced with crosslinkable ferroelectric liquid crystals

TL;DR

This paper reports on a ferroelectric liquid crystal-based channel waveguide with high nonlinear optical properties, achieved through photopolymerization, offering promising applications in nonlinear optical devices.

Contribution

It introduces a novel waveguide fabrication method using ferroelectric liquid crystals with high nonlinear susceptibility and stability, without additional processing steps.

Findings

High off-resonant nonlinear coefficients comparable to inorganic materials

Waveguide exhibits low scattering and losses below 2 dB/cm

Stable, photopolymerized structure suitable for nonlinear optical devices

Abstract

A binary mixture of ferroelectric liquid crystals (FLCs) was used for the design of a channel waveguide. The FLCs possess two important functionalities: a chromophore with a high hyperpolarizability $\beta$ and photoreactive groups. The smectic liquid crystal is aligned in layers parallel to the glass plates in a sandwich geometry. This alignment offers several advantages, such as that moderate electric fields are sufficient to achieve a high degree of polar order. The arrangement was then permanently fixed by photopolymerization which yielded a polar network possessing a high thermal and mechanical stability which did not show any sign of degradation within the monitored period of several months. The linear and nonlinear optical properties have been measured and all four independent components of the nonlinear susceptibility tensor $\bar d$ have been determined. The off-resonant $d$-coefficients are remarkably high and comparable to those of the best known inorganic materials. The alignment led to an inherent channel waveguide for p-polarized light without additional preparation steps. The photopolymerization did not induce scattering sites in the waveguide and the normalized losses were less than 2 dB/cm. The material offers a great potential for the design of nonlinear optical devices such as frequency doublers of low power laser diodes.