Polarization-dependent humidity sensor based on an in-fiber Mach-Zehnder interferometer coated with graphene oxide

A polarization-dependent humidity sensor based on an in-fiber Mach-Zehnder interferometer (MZI) coated with graphene oxide (GO) film was proposed. The MZI was constructed by fusion splicing a ∼15-mm long polarization maintaining fiber (PMF) between a waist-enlarged taper and a core-offset. The cladding of the PMF was etched off 10 μm, A GO film with the maximum thickness of 4-5 μm was coated on the etched cladding by optically driven deposition. With the strong hydrophilic of the GO and the characteristics of the MZI, the maximum sensitivity of 0.349 dB/%RH with a good stability at the RH range of 60-77% was obtained, which has a linear correlation coefficient of 98.9%.