Hydrogel Coated Long Period Grating Sensor for High Relative Humidity Measurement

A novel relative humidity (RH) sensor, based on an in-line microfiber interferometer (MFI), is proposed and demonstrated in an experiment. The microfiber interferometer is fabricated by tapering multi-core fiber down to the micrometer scale in diameter, and the coupling occurs between the center core mode and the multiple side core modes. To enhance the sensing performance, the microfiber sensor is fixed as U-shaped. The variation of RH is monitored by observing the wavelength shift of the transmission spectrum. The experimental results show that the sensor has a good linear response to RH. A thinner MFI diameter of 8.52 µm can offer a better RH sensitivity of 59.8 pm/(%RH) in the range of 35–95% RH. When temperature changes from 35°C to 85°C, the temperature sensitivity of the sensor is 4.2 pm/°C, which demonstrates that the sensor is insensitive to temperature. The simultaneous measurement of temperature and RH can be realized by cascading with fiber Bragg grating. The microfiber sensor is easy to fabricate and does not have any functional coating, which makes it widely used in accurate RH measuring.

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Mach-Zehnder interferometer based on fiber taper and fiber core mismatch for humidity sensing

Jun-Ni¹

2018

Acta Phys. Sin.

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A simple and high sensitivity optical fiber relative humidity (RH) sensor based on Mach-Zehnder interferometer (MZI) is proposed and demonstrated in this paper. A single-mode fiber and a graded-index multimode fiber are connected by a fiber taper to form a section. Then an uncoated dispersion compensation fiber is sandwiched between two short sections of the graded-index multimode fiber.Therefore, a sensing structure is set up as a single-mode fiber-taper fiber-graded-index multimode fiber-dispersion compensation fiber-graded-index multimode fiber-taper laser-single-mode fiber. The taper fiber is used to augment the energy of the cladding mode. The two nodes of the graded-index multimode fiber can be looked as a mode coupler. Thus an MZI is constructed. Since the external RH change can make the transmission spectrum energy changed, we can obtain the RH by detecting the peak energy variation of the interference pattern induced by the evanescent-field interaction. The experimental results show that the peak energy changes linearly with surrounding relative humidity. Under the condition of 35%Rh-85%RH, the sensitivity of the sensor with a 20 mm dispersion compensation fiber is -0.0668 dB/%RH and the linearity is 0.995. Moreover, temperature response characteristics are investigated. Experimental results suggest that the transmission spectrum energy of the sensor is insensitive to temperature. With temperature increasing, the transmission spectrum presents obviously a red-shift, yet the peak energy of the monitoring point barely moves, which demonstrates its potential for measuring simultaneously RH and temperature. The proposed sensor has a small size and simple manufacturing process, which can make it widely used to measure RH.

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Hydrogel Coated Long Period Grating Sensor for High Relative Humidity Measurement

Cited by 3 publications

References 9 publications

Low Temperature Cross-Sensitivity Humidity Sensor Based on a U-Shaped Microfiber Interferometer

Low Temperature Cross-Sensitivity Humidity Sensor Based on a U-Shaped Microfiber Interferometer

In-fiber Mach–Zehnder interferometer based on multi-core microfiber for humidity and temperature sensing

Mach-Zehnder interferometer based on fiber taper and fiber core mismatch for humidity sensing

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