Design and fabrication of mid-infrared devices for IoT applications

The advancement of photonics has transformed the fields of communication and sensing, allowing for outstanding improvements in transmission speed, accuracy, miniaturization, and scalability. This Ph.D. thesis reports the design and fabrication of Mid-InfraRed (Mid-IR) devices tailored for Internet of Things (IoT) applications, focusing on the use of optical fibers based on soft glasses. The research encompasses various optical components, including Bragg gratings inscribed on flat fibers and planar substrates, and optical fiber devices based on stretching and heating fabrication technique such as combiners, couplers, photonic lanterns, long period gratings (LPGs), non-adiabatic tapers, and S-tapers. Additionally, the modelling and design of a Praseodymium-doped laser is explored to enhance Mid-IR light generation. The initial section of this thesis concentrates on the design, fabrication, and characterization of innovative Bragg gratings. These are wavelength-selective mirrors, essential for the construction of laser cavities. Moreover, they can be used as sensors exploiting the Bragg wavelength shift to measure various physical parameters, such as strain, curvature, and temperature. These results were achieved in collaboration with the University of Southampton (Optoelectronic Research Centre - ORC, UK) and the University of Bristol (School of Civil, Aerospace and Design Engineering, UK). Considering the increasing interest in the Mid-IR spectral range, the second part of the thesis investigates the design, fabrication, and characterization of Mid-IR optical fiber components based on soft glasses, mainly operating within the wavelength range from λ=0.5 μm to λ=5.5 μm. Optical fiber combiners and couplers are key building blocks in communication and sensing systems, serving for spectral splitting/combining and the increasing of optical power. Photonic lanterns offer an efficient interface between multi-mode and single-mode waveguides, proving beneficial in astrophotonics where “every photon counts”. LPGs and tapers enable sensing capabilities in the Mid-IR, spectral range that allows to identify the typical bonds of many molecules. In collaboration with Le Verre Fluoré (Bruz, France), the development of a specialized manufacturing process for soft glasses permitted the fabrication and characterization of these devices. Finally, Bragg gratings in combination with some of the developed building blocks allow the fabrication of all-in-fiber Mid-IR amplifiers, and lasers systems. In this context, optical fiber lasers, emitting in the Mid-IR wavelengths, can be employed for novel communication and sensing schemes. Therefore, the design and optimization of a Mid-IR continuous wave (CW) laser based on Praseodymium, is reported in the last part of the Ph.D. research work. Some of the findings from this research have been published in International Journals and presented at National and International Conferences, as detailed in the list at the end of the thesis.