A single-film fiber optical sensor for simultaneous measurement of carbon dioxide and relative humidity

Liu, Liang Liang; Morgan, Stephen P.; Correia, Ricardo; Korposh, Serhiy

Abstract

Colorimetric measurement is a versatile, low-cost method for bio-/chemical sensing and that has importance in biomedical applications. General carbon dioxide (CO2) sensors based on colorimetric change of a pH indicator report only one parameter at a time and are cross-sensitive to relative humidity (RH). This work describes a novel optical fiber sensor with a thin film on the distal end of the fiber, combining colorimetric measurement and a white light Fabry–Pérot interferometer (FPI) for the simultaneous measurement of CO2 and RH. The CO2 sensitive dye ion-pair: thymol blue and tetramethylammonium hydroxide are encapsulated inside organically modified silica forming an extrinsic FPI cavity (refractive index of 1.501 ± 0.02 and thickness of 5.83 ± 0.09 μm). The sensor reversibly responds to 0–6% CO2 and 0–90% RH with negligible cross-sensitivity and allows measurement of both parameters simultaneously. A sensitivity of ∼0.19 nm/%RH is obtained for RH measurement based on the wavelength shift of the FPI and there is a polynomial correlation between the average intensity of selected wavelengths and the concentration of CO2. The applicability of the sensor is demonstrated by measuring the CO2 and RH exhaled from human breath with a percent error of 3.1% and 2.2% respectively compared to a commercial datalogger. A simulation model is provided for the dye-encapsulated FPI sensor allowing simulation of spectra of sensors with different film thicknesses.

Citation

Liu, L. L., Morgan, S. P., Correia, R., & Korposh, S. (2022). A single-film fiber optical sensor for simultaneous measurement of carbon dioxide and relative humidity. Optics and Laser Technology, 147, Article 107696. https://doi.org/10.1016/j.optlastec.2021.107696

• Journal Article Type: Article
• Acceptance Date: Nov 15, 2021
• Online Publication Date: Nov 19, 2021
• Publication Date: Mar 1, 2022
• Deposit Date: Nov 23, 2021
• Publicly Available Date: Nov 23, 2021
• Journal: Optics and Laser Technology
• Print ISSN: 0030-3992
• Publisher: Elsevier BV
• Peer Reviewed: Peer Reviewed
• Volume: 147
• Article Number: 107696
• DOI: https://doi.org/10.1016/j.optlastec.2021.107696
• Keywords: Electrical and Electronic Engineering; Atomic and Molecular Physics, and Optics; Electronic, Optical and Magnetic Materials
• Public URL: https://nottingham-repository.worktribe.com/output/6784370
• Publisher URL: https://www.sciencedirect.com/science/article/pii/S0030399221007842