Graphene oxide coated optical fiber Mach-Zehnder interferometers

Gao, Bowen (2023) Graphene oxide coated optical fiber Mach-Zehnder interferometers. Masters thesis, Memorial University of Newfoundland.

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Abstract

Optical fibers are extensively utilized in the telecommunication industry for their exceptional light-guiding capabilities. Furthermore, their remarkable attributes, including high flexibility, low loss, compact size, immunity to electromagnetic interference, and operation in harsh environments, have sparked extensive research into their applications across diverse sensor fields. The emergence of nanomaterials with unique physical and chemical properties offers many new applications. As one of the graphene derivatives with various oxygen-containing functional groups, graphene oxide (GO) based materials enable a wide range of sensing applications owing to their interaction with external water molecules and various organic solvents. This study investigates the spectral properties of two GO-coated symmetric fiber Mach-Zehnder interferometers (FMZIs), i.e., tapered and bulge-fused structures, under varying environmental conditions, in comparison with uncoated FMZIs. The light energy density distribution along those microstructures is simulated by COMSOL Multiphysics software. The study begins by examining the sensitivity of FMZIs to refractive index, temperature, and humidity by observing the shift of dip wavelength at different environmental conditions. Then, the interferometers are coated with GO using the in-situ layer self-assembly method, which are silanization-treated fibers to create a positively charged surface, enabling the attraction and accumulation of negatively charged materials. Next, coating effects on different fiber structures and sensitivities to environmental conditions are compared. Additionally, two different GO-based coatings (graphene oxide-sodium alginate composite, and graphene oxide-fullerenol nano- composite encapsulated by the hydrogel) are applied to the tapered structure to assess their effects on the optical properties of the sensor under different environmental conditions. Finally, the spectra of the tapered FMZIs with and without different coatings are measured at various curvatures. The sensitivity of the interferometer in curvature measurement is analyzed using the conformal mapping technique to explore the properties of the coatings under different curvatures. This study demonstrates the effectiveness and great potentials of the graphene oxide-based nanomaterials in fiber-optic sensing.

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