Fiber Humidity Sensor Based on a Graphene-Coated Core-Offset Mach–Zehnder Interferometer

A novel humidity sensor based on a core-offset fiber Mach-Zehnder interferometer (MZI) coated with graphene oxide has been presented. The MZI consists of three single-mode fibers, which are spliced by the core-offset. The sensing head is a core-offset fiber with a length of 35 mm and a 5 μm core-offset, which is coated with the graphene oxide. The intensity and wavelength of the resonant dip of the MZI will vary when the ambient humidity changes. The experimental results show that the sensitivity of 0.104 dB/%RH and 0.0272 nm/%RH with a linear correlation coefficient of 99.61% and 99.21% in the relative humidity from 30% to 60% could be obtained. Its low manufacturing cost and high stability will be their absolute advantages of future applications in agricultural production, storage, and other fields.