Synthesis and Integration of Functional Nanomaterials on Optical Fiber Platforms for Points and Distributed Sensing for Energy Applications

As relatively clean and abundant energy sources, large-scale utilization of natural gas and hydrogen gas fuel for automobile and electricity productions have been considered by many countries as key energy strategies to reduce greenhouse emission and to improve air quality. Methane, the major constituent of natural gas, is an extremely potent greenhouse gas, while hydrogen is highly flammable. The extraction, production, storage, transportation, and combustion of both gas fuels requires extensive deployment of low-cost sensors with sufficient sensitivity to monitor emissions of these gas species throughout energy infrastructure. Fiber optical sensors, compared with conventional electrical sensors, has been considered effective sensing tools for energy applications due to their resilience to harsh environment, inert for reactive/flammable gases, and immune to electromagnetic fields. A unique trait for fiber optics sensors is their capability to perform distributed measurements along the entire length of optical fibers across great distance using a single fiber. However, optical fiber based on silica materials are insensitive to changes of ambient gas compositions. This dissertation describes research efforts to synthesize novel functional nanomaterials including rare-earth doped metal oxide nanocomposite, metal organic frameworks doped polymer, nanoscale metal alloy that is sensitive to hydrogen and methane gas from the room temperature to 750 ℃. These functional nanomaterials were integrated with various optical fiber sensors platforms including both telecom fibers and D-shaped micro-structured fibers. Nanostructure-textured optical fiber was utilized to increase the surface-to-volume ratio of the metal alloy sensory film while dimension and density of the nanostructure was specifically chosen to limit the light scattering. Through on-fiber transaction mechanism such as evanescent interaction and gas-absorption induced on-fiber strain, Rayleigh-based distributed fiber sensors based on optical frequency domain reflectometry and intrinsic Fabry–Perot interferometer were used to measure fuel gas concentration from 0.25% to 40% from room temperature to 750 oC with excellent repeatability. Research works documented in this dissertation shows that highly controllable VLSI microfabrication schemes and novel functional nanomaterials can be used to enhance functionality of optical fibers to produce high performance fiber optical chemical sensors for both distributed and point measurements for both fossil energy and renewable energy applications