Sensitivity-enhanced humidity sensor based on a surface core fiber decorated with graphene oxide

An all-optical fiber humidity sensor based on a Mach-Zehnder interferometer (MZI) covered with graphene oxide (GO) film is demonstrated. The MZI is formed by inserting a section of etched surface core fiber (SCF) between two standard single mode fibers (SMFs) with a lateral-offset. Such configuration of the interferometer allows a strong evanescent field between the water molecules and the GO layer and hence enhances the change in refractive index of GO nanostructures after water absorption, which significantly improves the humidity sensitivity. Experimental results showed that the fabricated sensor exhibited a super-high humidity sensitivity of 707.3 pm/%RH in the RH range of 40-80% and a rapid response/recovery time (4.8/8.4 s). The high-performance of the proposed all fiber humidity sensor is potentially promising for industrial production, medical diagnoses, environmental and health monitoring.