Strongly coupled relative humidity sensor coated with graphene oxide/polyvinyl alcohol composite

A novel coupled fibre-optic humidity sensor based on a biconical fibre-optic graphene oxide/polyvinyl alcohol (GO/PVA) structure is reported for the first time. The sensor itself adopts a 1 × 2 coupler structure with a waist diameter of 24 μm. A GO/PVA composite film is coated in the strong coupling region to improve the sensitivity of the sensor. The thickness of the composite film is relatively uniform, with the thinnest point being only 1.41 μm. The sensor can realise linear sensing in a relative humidity (RH) range of 55%–75% RH, with a sensitivity as high as 0.003/% RH and a sensor linearity as high as 99.44%. Its dynamic response time and recovery time are 0.85 s and 1.69 s. In addition, the sensor has good stability, repeatability, reversibility, and low-temperature crosstalk. Based on these characteristics, it is foreseeable that the sensor will bring a great breakthrough in applications that require sensitive monitoring of humidity.