Sensing Characteristics of Side-Polished Fiber Based on the Alterations in Helical Structure of Thermo-Sensitive Cholesteric Liquid Crystals

Yuqi Han,Yan Jiang,Wei Guo

doi:10.3390/cryst9090465

Yuqi Han, Yan Jiang + Show 1 more

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https://doi.org/10.3390/cryst9090465

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Abstract

Cholesteric liquid crystals (CLCs) are sensitive to environmental temperature changes, and have been employed as a specific intermediary for biosensors. Considering the temperature-dependent structural changes of CLCs, this study aimed to determine the sensing properties of side-polished fibers (SPFs) after coating with CLCs. The experimental results demonstrated that, with regard to the transmitted spectrum, the loss peak of CLC-coated SPFs exhibited a positive linear relationship with temperature changes over a range of 20 to 50 °C. The linear correlation coefficient achieved 97.8% when the temperature increased by 10 °C, and the loss peak drifted by 12.72 nm. The reflectance spectrum of CLCs coated on the polished surface were obtained using optical fiber sensors. The feasibility of measuring the helical structure of CLCs was further verified using SPF transmission spectroscopy. The findings indicated that the transmitted spectrum of SPFs could be adopted to characterize the helical structure of CLCs, which lays a solid foundation for further study on SPF-based biosensors.

Highlights

Cholesteric liquid crystals (CLCs) with orientational order are capable of undergoing liquid to solid phase transition
The findings provide the feasibility of measuring the helical structure changes of CLCs by side-polished fibers (SPFs) via transmission spectroscopy, as well as laying a foundation for future research on CLC-coated SPF biosensor
The sensing properties of CLC-coated SPFs in response to the ambient temperature-modulated structural change of CLCs were assessed in the present study

Summary

Introduction

Cholesteric liquid crystals (CLCs) with orientational order are capable of undergoing liquid to solid phase transition. They exhibit both liquid fluidity and crystal anisotropy, which lie primarily in optical anisotropy, such as birefringence. In addition to optical anisotropy, CLCs display a selective reflection of light due to their periodic helical structure. The selective reflection properties of CLCs have been shown to be associated with their helical pattern. CLC selected in this study was the same as the wavelength of visible light. When the spiral axis of CLC is perpendicular to the substrate surface, the Bragg reflection of visible light can appear

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