A robust salinity sensor based on encapsulated long-period grating in microfiber
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Vol.16 No.6, 1 November 2020
A robust salinity sensor based on encapsulated longperiod grating in microfiber* WU Shu-hui (␁ភ)1, JIN Wa (䠁ဳ)1**, BI Wei-hong (∅ছ㓒)1, LI Xia (ᵾ䵎)1, ZHANG Lin-ke (ᕐ᷇)ݻ1, and JIN Yun (䶣Ӂ)2 1. Key Laboratory for Special Fiber and Fiber Sensor of Hebei Province, School of Information Science and Engineering, Yanshan University, Qinhuangdao 066004, China 2. Department of Mechanical and Electrical Engineering, Hebei Construction Material Vocational and Technical College, Qinhuangdao 066004, China (Received 30 December 2019; Revised 8 March 2020) ©Tianjin University of Technology and Springer-Verlag GmbH Germany, part of Springer Nature 2020 A robust fiber sensor for salinity measurement based on encapsulated long-period grating in microfiber is proposed. The long-period grating is fabricated in microfiber by inducing periodical deformation with CO2 laser, which is then encapsulated in a holey capillary tube. The encapsulation tube is designed to effectively protect the microfiber from external interference, but does not change the optical properties of the fiber and the response speed of the sensor, which makes the sensor more robust for real applications. Experimental results show that the sensor can achieve a sensitivity of 2.16 nm/% with a good linearity for concentration from 0% to 20%. It is theoretically proved that the sensitivity can be further improved by optimizing the diameter parameters. Such structure may be used as low loss evanescent-wave-coupled optical absorption, fluorescent and gain cells, photoacoustic cells, and etc. Document code: A Article ID: 1673-1905(2020)06-0418-5 DOIhttps://doi.org/10.1007/s11801-020-9224-9
Salinity is one of the significant parameters in oceanography, which affects many important processes in seawater. Therefore, the precise measurement of salinity in seawater is of great social and economic benefits for monitoring marine environment, predicting marine climate, research of oceanography, oil development in coastal, and marine fishery[1]. Optical fiber sensor has demonstrated strong potential in sensing area on account of the advantages of electromagnetic immunity, compact size, high sensitivity and low cost[2-4]. Techniques based on fiber grating[5]ˈ microstructure fiber[6], optical fiber interferometers[7], photonic crystal fiber[8] and microfiber (MF) knot resonators[9] have been proposed to develop salinity sensors. However, normal fiber grating sensors always have low sensitivity, microstructure fiber sensors are costly and always require complicated fabrication process, and the structures of interference sensors are generally very complex. MF is an ideal element for constructing optical sensing system due to its low loss[10] and large evanescent field[11] which enhances the interaction of light with the surrounding medium, provides high sensitivity, and is widely used in the fields of refractive index (RI)[12], salinity[13], humidity[14] and temperature measurement[15]. Some sensors utilize the change in light intensity transmission f
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