In this work, a novel mid-infrared continuous wave laser, based on a fluoroindate fiber co-doped with holmium and neodymium, is designed to emit at ${{\bm{\lambda }}}_{\bm{s}} = {\bm{\ }}3.92{\bm{\ \mu m}}$ , when pumped at ${{\bm{\lambda }}}_{\bm{p}} = {\bm{\ }}808{\bm{\ nm}}$ . The laser is modeled considering a nine-level system, by taking into account experimental spectroscopical parameters. Since the energy transfer coefficients are unknown, they have been evaluated starting from the measured emission spectra of the bulk glass, reported in literature, and comparing their ratio with respect to the ratio between the simulated signal gain coefficients. The designed laser promises higher slope efficiency and power threshold lower than those obtainable with a holmium-heavily-doped fiber, having same fiber section geometry, same refractive indices and pumped at ${{\bm{\lambda }}}_{\bm{p}} = {\bm{\ }}888{\bm{\ nm}}$ . Slope efficiency ${\bm{\eta \ }} = {\bm{\ }}16.67{\bm{\% }}$ and input power threshold ${{\bm{P}}}_{{\bm{th}}} = {\bm{\ }}0.2{\bm{\ W}}$ are obtained for the fiber length ${{\bm{L}}}_{{\bm{fiber}}} = {\bm{\ }}0.4{\bm{\ m}}$ , dopants concentrations ${{\bm{N}}}_{{\bm{Ho}}} = {\bm{\ }}8 \times {10}^{26}{\bm{\ ions}}/{{\bm{m}}}^3$ and ${{\bm{N}}}_{{\bm{Nd}}} = {\bm{\ }}1 \times {10}^{26}{\bm{\ ions}}/{{\bm{m}}}^3$ , and output mirror reflectivity ${{\bm{R}}}_{{\bm{out}}} = {\bm{\ }}60{\bm{\% }}$ . This result encourages the fabrication of a continuous wave laser based on a Ho:Nd-codoped fluoroindate fiber.

A gain-switched pulsed laser based on a commercial, heavily holmium-doped fluoroindate glass (FIG) fiber, is designed to emit in the middle-infrared range, at the wavelength =3.92 μm. The laser, pumped at =888 nm, is modeled by a six-level system, by taking into account experimental spectroscopic parameters, to identify a feasible laser configuration. An output signal peak power of about P_s^peak=14.62 W with a full width at half maximum (FWHM) pulse duration less than _s=73 ns and pulse energy E_s=1.214 J is predicted, by considering an input peak power of P_p^peak=10 W, and pump repetition rate of f=100 kHz, by employing a 8 cm-long fluoroindate fiber with holmium concentration N_Ho=100 000 ppm. The obtained result encourages the construction of a pulsed laser based on commercially available optical fiber, for applications in different fields as sensing and biomedicine.

For the first time, a 2×2 optical fiber coupler based on indium fluoride optical fibers is designed via coupled mode theory, fabricated via fused biconical tapering technique, and characterized in the mid-infrared spectral range. A conventional glass processing system, Vytran GPX-2400, is employed for the 2×2 optical fiber coupler fabrication, overcoming the main limitation related to the narrow temperature range for indium fluoride optical fiber processing. Moreover, the fabricated device exhibits negligible surface crystallizations. The experimental results are in optimum agreement with the simulations, demonstrating that reproducible manufacturing of low-loss fused optical fiber components for the mid-infrared spectral range is possible. In particular, the fabricated 2×2 optical fiber coupler is characterized by a measured coupling ratio CR= 72.2:27.8 at the wavelengthλ = 3.34 μm with low excess loss E_L = 0.88 dB

A high curvature flexible Bragg grating, in planar technology, is designed, fabricated and experimentally characterized by employing silica glass. The curvature sensing mechanism for slightly off-axis core is theoretically explained and experimentally demonstrated. The electromagnetic behavior of the proposed sensor is investigated through conformal mapping, modal analysis, and coupled-mode theory. The experimental measurement reveals different sensitivities to positive and negative curvatures. The reflection spectrum of the planar Bragg grating sensor and the relationship between its resonant wavelengths and the curvature is measured for a large curvature range up to 1/ R = ± 33 m ^-1 . The interest toward off-axis core on planar flexible platform for curvature monitoring is due to the lateral stiffness and low Young's modulus of the substrate.

A metamaterial lens based on a split ring resonator (SRR) array has been designed and optimized to improve the focusing and the penetration depth in human biological tissue of a microwave beam irradiated by a substrate integrated waveguide (SIW) cavity backed patch antenna. The impedance matching of the antenna loaded with human tissue is strongly improved. The simulations have been performed by using CST Microwave Studio^®. A prototype of the device has been fabricated with the printed board circuits (PCB) process and has been characterized using a Network Analyzer and an antenna measurement system in anechoic chamber. A novel microwave applicator for hyperthermia therapy of skin cancer could be developed. The performances of the proposed applicator have been evaluated in terms of measured $S_{11}$ scattering parameter modulus and simulated power loss density. The obtained results indicate that an SRR-based metamaterial is a promising solution for external microwave applicators to employ in dermatology.

The employment of unconventional and very cheap materials is proposed for fabricating a complex radiating structure, with the aim to test the actual feasibility. A partially reflective surface (PRS) is designed to enhance the broadside directivity of an inkjet printed V-slot loaded patch antenna, by means of the Fabry-Pérot resonance effect. The proposed multilayer PRS is obtained by means of ultra-thin polyethylene terephthalate (PET) layers, conductive ink patterns and alldielectric 3D printed polyethylene terephthalate glycol (PETG) layers to achieve a positive reflection phase gradient as a function of frequency f. A prototype of the Fabry-Pérot antenna is fabricated for the first time with the described materials and lowcost technology. The measurements are in good agreement with the design, proving the intended performance. The measured maximum gain is G_M = 13.2 dBi, the 3dB gain bandwidth is BW_G = 24.5% within the impedance matched bandwidth BW_% = 31.3%. The obtained result promises low-cost fabrication for conformal antennas exhibiting good performance even when compared to high quality substrates and more sophisticated technologies.