Optical fiber gas sensors based on the interaction of evanescence waves with active layers detecting pure gases and liquid vapours

This manuscript explores the potential for detecting gases and liquid vapours using a microfiber coated with a graphene oxide layer as an active coating. The graphene oxide interacts with target agents, altering the boundary conditions for light propagating within the microfiber and its evanescent wave. The paper details methods for producing microfibers, activating the glass surface, applying selected coatings, and identifying specific gases or liquid vapours. Analyses are conducted over a broad wavelength range of 600–1800 nm in transmission light modes. Results are presented for selected gases, such as pure hydrogen, a propane-butane mixture, and liquid vapours, including ammonia water and trimethyl phosphate. Measurements employed a differential method, comparing detection results with a reference system without the target agent, enabling the detection of small concentrations. Observed measurement differences remained below 5% of the initial power. For all tested factors, an increased power was observed as a function of the microfiber's exposure duration to gas or liquid vapour.