Highly Sensitive Twist Sensor Based on Partially Silver Coated Hollow Core Fiber Structure

• Published in: Journal of lightwave technology Vol. 36; no. 17; pp. 3672 - 3677
• Main Authors: Dejun Liu, Kumar, Rahul, Fangfang Wei, Wei Han, Mallik, Arun Kumar, Jinhui Yuan, Chongxiu Yu, Zhe Kang, Feng Li, Zhengyong Liu, Hwa-Yaw Tam, Farrell, Gerald, Semenova, Yuliya, Qiang Wu
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.09.2018; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Coating; Coatings; Optical fiber applications; Optical fiber communication; Optical fiber polarization; Optical fiber sensors; optical interferometry; optical polarization; Optical waveguides; Q factors; Sensitivity; Sensors; Silver; Spectral sensitivity; Splicing; Twisting
• ISSN: 0733-8724; 1558-2213
• DOI: 10.1109/JLT.2018.2842111

Interferometer based on multiple beam interferences inside a hollow core fiber (HCF) structure (also known as an antiresonant reflecting optical waveguide) has been attracting interest of many researchers due to its periodic transmission spectrum containing high quality factor spectral dips. Functionalized HCF structures have been demonstrated for a wide range of applications in humidity, magnetic field, and biosensing. Here, we report a new application of the HCF-based structure with a partial silver coating layer for sensing of twist. It is configured by a fusion splicing a section of 4.5-mm long HCF between two standard single mode fibers (SMFs), followed by a sputter-coating of a very thin layer of silver on one side of the HCF surface. It is found that the spectral response of the partially silver coated HCF structure is very sensitive to the changes of input light polarization. An increase in sensitivity of the fiber structure to twist after deposition of the silver coating when the twist is applied to both the SMF and HCF sections is demonstrated by comparison with an uncoated HCF fiber structure. Experimental results show that twisting of the HCF section results in much greater changes in a selected dip's strength compared to that in the case of twisting the SMF section of the structure. The proposed HCF fiber sensors with 4.5-nm and 6.7 nm-thick silver layers show the highest sensitivities of 0.647 dB/°and 0.717 dB/° in the twist angles range of up to 10°. To the best of our knowledge, this is the highest twist sensitivity reported for intensity modulation-based fiber sensors. Moreover, the proposed sensor offers excellent measurement repeatability.