High-performance humidity sensor based on a polyvinyl alcohol-coated photonic crystal cavity

Abstract

We demonstrate a high-performance relative humidity (RH) sensor by coating a photonic crystal (PC) cavity with polyvinyl alcohol (PVA). Because a PC cavity's evanescent field strongly interacts with the coated moisture-sensitive PVA film, the resonant wavelength is modified remarkably under varying RH levels ranging from 30% to 90%. In a PC cavity coated with a 720 nm thick PVA, the sensor exhibits a linear spectrum sensitivity exceeding 129 pm/%RH over 40-90%RH, and the power interrogation presents a high sensitivity as 0.77 dB/%RH. The resolvable humidity variation could be much less than 0.1%RH. Relying on the sub-micron thick PVA, the sensor promises a response time less than 300 ms and good repeatability. The dependence of the sensor performances on the PVA thickness is studied as well, indicating a tradeoff between the sensing dynamic range and the response time.

Mechanism and Characteristics of Humidity Sensing with Polyvinyl Alcohol-Coated Fiber Surface Plasmon Resonance Sensor

“…Preliminary simulation results show that a 10 nm increment of the film-thickness may result in a resonant wavelength shift toward longer wavelengths for ~15 nm for a 100-nm-thick PVA film. On the other hand, the RI reduction of the PVA film due to moisture absorption may lead to the shift of the resonance toward shorter wavelengths [ 19 ]. Specifically, with the film-thickness increasing, the total shift of the resonant wavelength caused by this effect becomes gradually larger, from the order of tens to hundreds of nanometers.…”

“…Compared to a traditional electric RH sensor, optical fiber-based sensors exhibit a great number of advantages, such as security to the human body, miniaturization for integration, and good resistance to electromagnetic interference. In recent years, a variety of fiber devices have been implemented in to the design of optical fiber RH sensors, configurations including interferometers [ 1 , 2 , 3 , 4 , 5 , 6 , 7 ], long period fiber gratings [ 8 , 9 ], tapered fibers [ 10 , 11 , 12 , 13 ], fiber Bragg gratings (FBGs) [ 14 , 15 , 16 , 17 , 18 ], mode couplers [ 19 , 20 ], ZnO nanostructures [ 21 , 22 ], evanescent wave absorption structures [ 23 , 24 ], and so on. Among these configurations, light intensity demodulation is often used since it is simple and cost effective.…”

Single-Mode Modified Tapered Fiber Structure Functionalized With GO-PVA Composite Layer for Relative Humidity Sensing

“…The RH sensing mechanism in the tapered optical fiber sensor application involves the humidity sensitive coatings (hydrophilic materials) coated on the tapered region to enhance the transmission signal through the improvements on evanescent waves [6]. Some of the materials are used in the coating include polyvinyl alcohol (PVA) [7,8], chitosan [9], metallic oxide film [10], and graphene oxide (GO) [11,12]. With 880 gas sensor papers recorded in September, 2018, GO represents an important potential material for discussing [13].…”

Graphene oxide-deposited tilted fiber grating for ultrafast humidity sensing and human breath monitoring

“…One of the paths was inserted into the pure water to generate the saturated humid gas. Then, the two paths were mixed with another Y-tube to the inlet of the chamber, thus the RH level inside could be controlled by individually adjustable flow rates [24,37].…”