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 10μm, A GO film with the maximum thickness of 4–5μm 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 0.349dB/%RH with a good stability at the RH range of 60–77% was obtained, which has a linear correlation coefficient of 98.9%.