Design and fabrication of fiber optic sensors and systems for aerospace applications

The rapid evolution of fiber optic technology has revolutionized the field of communication and sensing, enabling unprecedented levels of accuracy, miniaturization, and scalability. This thesis describes the results obtained during my Ph.D. activity and concerning the development of fiber optic sensors, optical fiber components, and light sources tailored to advance the field of aerospace structure monitoring. The work has required the exploration of the research forefront in this field. The first part of the thesis focuses on the design, fabrication, and characterization of non-conventional fiber optic sensors. These sensors leverage Bragg gratings to detect several physical parameters, including temperature, strain, and bending, matching the stringent requirement of structural health monitoring of Carbon Fiber Reinforced Polymers (CFRP). The findings have been obtained in collaboration with the University of Southampton (Optoelectronic Research Centre - ORC, UK) trying to give a contribution to the ongoing evolution of aerospace sensor technologies. Bragg gratings are wavelength-selective structures also employed for multiplexing optical signals or for the construction of laser cavities. By considering these aspects and the growing interest in Medium-Infrared (Mid-IR) spectral range, the second part of the thesis delves into the design, fabrication, and characterization of Mid-IR optical fiber components, based on soft glasses, operating between 0.5 𝜇𝑚 and 12 𝜇𝑚. Optical fiber combiners/couplers are essential elements in communication and sensing systems that enable the splitting (or combining) of optical signals into (from) a single optical fiber preserving beam quality. The development of a custom manufacturing procedure for fluoride and chalcogenide glasses, in collaboration with the company Le Verre Fluoré (Bruz, France) made it possible, for the first time, to address the results described in the doctoral thesis. Moreover, Bragg gratings in combination with these optical fiber components allow the development of all-in-fiber Mid-IR amplifiers, lasers, and wavelength division multiplexing (WDM) systems. In particular, optical fiber lasers, operating in the Mid-IR spectral range, can be employed for material inspection purposes to assess the integrity and quality of composite materials via Non-Destructive Testing (NDT) techniques. Therefore, the design and optimization of Mid-IR continuous wave (CW) lasers, are reported in the last part of the Ph.D. research work. Part of the obtained results have been published in International Journals and in the Proceedings of National and International Conferences, as listed at the end of the thesis.