Enlarged-taper tailored Fiber Bragg grating with polyvinyl alcohol coating for humidity sensing

Yanhong Liang; Guofeng Yan; Sailing He

doi:10.1117/12.2193414

10 August 2015 Enlarged-taper tailored Fiber Bragg grating with polyvinyl alcohol coating for humidity sensing

Yanhong Liang, Guofeng Yan, Sailing He

Proceedings Volume 9620, 2015 International Conference on Optical Instruments and Technology: Optical Sensors and Applications; 962007 (2015) https://doi.org/10.1117/12.2193414
Event: International Conference on Optical Instruments and Technology 2015, 2015, Beijing, China

Abstract

In this paper, a novel optical fiber sensor based on an enlarged-taper tailored fiber Bragg grating (FBG) is proposed and experimentally demonstrated for the measurement of relative humidity. The enlarged-taper works as a multifunctional joint that not only excites cladding modes but also recouples the cladding modes reflected by the FBG back into the leading single mode fiber. Due to the fact that cladding modes have a strong evanescent field penetrating into the ambient medium, the intensity of the reflected cladding modes is greatly influenced by the refractive index (RI) of the ambient medium. Polyvinyl alcohol (PVA) film is plated on the fiber surface by dip-coating technique, as a humidity-to-refractive index transducer, whose RI variance from 1.49 to 1.34 when the ambient humidity increases from 20%RH to 95%RH. The relative humidity response of the sensing structure is investigated in our home-made humidity chamber with a commercial hygrometer. By monitoring the intensity of the reflected cladding modes, the RH variance can be demodulated. Experimental results show that RH sensitivity depends on the RH value, and a sensitivity up to 1.2 dB/%RH can be achieved within the RH range of 30-90%. A fast and reversible time response has also been investigated. Such a probe-type and reusable fiber-optic RH sensor is a very promising technology for biochemical sensing applications, e.g., breath analysis, chemical reaction monitoring.

Citation Download Citation

Yanhong Liang, Guofeng Yan, and Sailing He "Enlarged-taper tailored Fiber Bragg grating with polyvinyl alcohol coating for humidity sensing", Proc. SPIE 9620, 2015 International Conference on Optical Instruments and Technology: Optical Sensors and Applications, 962007 (10 August 2015); https://doi.org/10.1117/12.2193414

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