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

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.

Design and Applications of Liquid Crystal Biophotonic Sensors for Ion Detection

“…[ 86 ] In addition, the reorientation from anisotropy to isotropy driven by the phase transition of the LCs is also an alternative. [ 81,87 ] The LC reorientation can directly affect the optical signals of the sensors. Considering the close relationship between the LC reorientation and the LC alignment, it is of great significance to subtly design the LC alignment in the initial state and therefore obtain the expected optical signals.…”

Optical Response Associated with the Orientation and Structure of Liquid Crystals with Respect to Phosphatidylcholine Concentration

“…In a previous study [9], the feasibility of characterizing the changes in the helical structures of cholesteric liquid crystals via the transmittance spectrum of the side-polished optical fiber has been verified. Moreover, the hydrophobic groups in the phospholipid molecules at the interface between the liquid crystal and water phases undergo hydrophobic association with the nematic liquid crystal, thus leading to changes in the orientation of the liquid crystal molecules.…”

“…The nematic liquid crystal 5CB (4-cyano-4′-pentylbiphenyl) was first mixed with the as-prepared cholesteric liquid crystal (cholesteryl ester liquid crystals, CLC) [9] at a volume ratio of 15%:85% (v/v). The mixed cholesteric liquid crystals were subsequently prepared according to the following procedure:…”

“…In our previous study, it has been reported that the power of the light transmitted in the side-polished optical fiber can be used to characterize the changes in the orientation of the nematic liquid crystals [8]. Furthermore, it has also been proved that the changes in the helical structures of the cholesteric liquid crystals can be characterized by using the transmittance spectrum of the side-polished optical fiber [9]. However, the characterization of the orientation and structure of the liquid crystals with respect to the interaction between the biomolecules is still needed so as to construct optical fiber bio-sensors based on the liquid crystal media.…”

Fiber-Optic Temperature Sensor Using Cholesteric Liquid Crystals on the Optical Fiber Ferrules

“…Wang et al [ 9 ] reported a Mach–Zehnder interferometer-based temperature sensor with a sensitivity of ~8.962 nm/°C and a measurable temperature range of 33–43 °C. In 2019, Noor et al [ 10 ] reported that the sensitivity of a temperature sensor using multimode interference generated by a single mode-multimode-single mode fiber was approximately 21 pm/°C; Han et al [ 11 ] reported a CLC film, based on a side polished fiber environmental temperature sensor with a sensitivity of ~1.7 nm/°C and a measurable temperature range of 20–50 °C. In 2021, Liu et al [ 12 ] reported a temperature and pressure sensor based on FBG and fiber-tip bubble, with a sensitivity of 11.1 pm/°C and a measurable temperature range of 20–100 °C.…”