Twisted weakly coupled relative humidity sensor coated with a graphene oxide/polyvinyl alcohol composite

Abstract

A new coupled fiber optic humidity sensor based on a double-tapered fiber twisted weakly coupled structure coated with a graphene oxide/polyvinyl alcohol (GO/PVA) film has been reported for the first time, to the best of our knowledge. The sensor adopts a 2 × 2 coupler structure with a waist diameter of 20 µm. The GO/PVA composite film is coated in the weakly coupled area to increase the sensitivity of the sensor. The thickness of the coating layer is about 3 µm. The sensor can realize linear sensing in the relative humidity (RH) range of 45%–85%RH with a dynamic response time of 1.9 s and a recovery time of 5.7 s. The sensitivity of the sensor is up to 0.002/%RH, and the linearity of the sensor is as high as 98.65%. Moreover, the sensor has good stability, reversibility, and low-temperature crosstalk.

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“…However, these materials exhibit low-refractive-index changes after adsorbing water molecules and require thick films to achieve a sufficient optical signal response. Consequently, most of these sensors have response times longer than 10 s. Moreover, graphene oxide (GO), as a derivative of 2D material graphene, is drawing extensive research in high-performance fiber RH sensors owing to the small size effect, high surface-area-to-volume ratio, and abundant hydrophilic groups [20][21][22] . The best performances of a GO enabled fiber humidity sensor were 45 ms and 115 ms in response and recovery progress, respectively [11] .…”