Graphene oxide for improved sensitivity and response time of fibre-Bragg-grating-based humidity sensors

We report on the characterisation of relative humidity sensors based on fibre Bragg gratings coated with two hygroscopic materials: polyimide (PI) and graphene oxide (GO). In both cases, sensitivity and response time could be tuned by varying the coating thickness, but graphene oxide provided significantly higher sensitivity and a faster response time than polyimide: for PI-coated sensors, a 1 pm/% increase in sensitivity resulted in a 94 s increase in response time, whereas for GO-coated sensors, the same increase in sensitivity only cost an additional 1 s increase in response time. These results show that graphene oxide is a promising material for faster-responding humidity sensors that can maintain high sensitivity.