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Sensors 2017, 17(10), 2353;

Relative Humidity Sensor Based on No-Core Fiber Coated by Agarose-Gel Film

1,2,3,†, 1,2,†, 1,2, 1,2, 3, 3 and 1,2,*
Institute of Laser and Optoelectronics, College of Precision Instrument and Optoelectronic Engineering, Tianjin University, Tianjin 300072, China
Key Laboratory of Optoelectronic Information Science and Technology (Ministry of Education), Tianjin University, Tianjin 300072, China
Tianjin Key Laboratory of Optoelectronic Detection Technology and Systems, Tianjin Polytechnic University, Tianjin 300387, China
Author to whom correspondence should be addressed.
These authors contributed equally to this work.
Received: 27 August 2017 / Revised: 7 October 2017 / Accepted: 12 October 2017 / Published: 16 October 2017
(This article belongs to the Section Physical Sensors)
PDF [1475 KB, uploaded 16 October 2017]


A relative humidity (RH) sensor based on single-mode–no-core–single-mode fiber (SNCS) structure is proposed and experimentally demonstrated. The agarose gel is coated on the no-core fiber (NCF) as the cladding, and multimode interference (MMI) occurs in the SNCS structure. The transmission spectrum of the sensor is modulated at different ambient relative humidities due to the tunable refractive index property of the agarose gel film. The relative humidity can be measured by the wavelength shift and intensity variation of the dip in the transmission spectra. The humidity response of the sensors, coated with different concentrations and coating numbers of the agarose solution, were experimentally investigated. The wavelength and intensity sensitivity is obtained as −149 pm/%RH and −0.075 dB/%RH in the range of 30% RH to 75% RH, respectively. The rise and fall time is tested to be 4.8 s and 7.1 s, respectively. The proposed sensor has a great potential in real-time RH monitoring. View Full-Text
Keywords: relative humidity measurement; agarose; no-core fiber; multimode interference relative humidity measurement; agarose; no-core fiber; multimode interference

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Xu, W.; Shi, J.; Yang, X.; Xu, D.; Rong, F.; Zhao, J.; Yao, J. Relative Humidity Sensor Based on No-Core Fiber Coated by Agarose-Gel Film. Sensors 2017, 17, 2353.

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