Fiber Optic Sensors Based on Specialty Optical Fibers

Fiber optic sensors have been one of the fastest developing research areas in optics during the past four decades. Due to their advantages of light weight, small size, immunity to electromagnetic interference, and multiplexing capability, fiber optic sensors are increasingly being used in various environments, particularly those that are challenging for traditional sensors. The fiber Fabry-Pérot interferometer (FFPI) and fiber Bragg grating (FBG) are two of the most developed fiber optic sensors. They have drawn much attention from both academia and industry over the past 40 years for sensing a variety of physical parameters, such as pressure, temperature, and acoustics. In this dissertation, we firstly discussed both the FFPI and FBG fiber optic sensors. Their numerical models were developed based on coupled mode theory. Simulations were run based on the variation in sensor characteristics, provided the numerical analysis and model simulation to improve the sensor design and optimize the sensor structure. Then, we discussed our fabricated FFPI sensors of using a single mode fiber and a microstructure fiber, such as a fiber tube and side-hole fiber. The sandwich structure was formed by a fiber splicer with the center microstructure fiber playing the role of the Fabry-Pérot (FP) cavity. Obtained the refractive index change inside the cavity by monitoring the reflection spectrum from an interrogator, and calculated the desired parameters, such as solution concentration, temperature, and air pressure, from the refractive index. The dissertation also proposed an FBG fabrication system that uses the 800 nm femtosecond laser. Regular FBG fabrication was accomplished with good grating performance and repeatability. The work described in this dissertation focused on the FBG fabrication through the polymer coating. It is anticipated that the FBG fabrication will be much more widely used in harsh environments due to its much better mechanical strength and sensing wavelength range. Results of the first fabrication attempt are presented, where the mechanical strength reached 73% of a pristine silica fiber.