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.

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

An innovative microstructured flat optical fiber is designed to obtain a multiaxial strain sensor for composite material monitoring. The sensing regions are constituted by the two eyelets where Bragg gratings are written. To achieve multiaxial sensing, a suitable microstructure is designed close to only one of the eyelets. The effect of the strain field, evaluated via a 3D finite element method approach, is considered to obtain the change of the refractive index distribution. The electromagnetic modal analysis and the coupled mode theory are exploited to evaluate the Bragg wavelength shift for the slow and fast axis fundamental modes, guided in the two eyelets and affecting the sensor response. The designed microstructured flat optical fiber is technologically feasible and promises sensing performance higher than that obtainable with the conventional optical fibers. In addition, flat optical fiber can be embedded in composite materials reducing the drawbacks related to both orientation and excess resin.

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.

In this work, a novel metamaterial lens (metalens) is designed and optimized to improve the radiation performance of an antipodal Vivaldi antenna for wideband applications. The metalens is integrated into the antenna substrate, and placed close to the tapered slot in the end-fire direction, allowing the preservation of the lightweight and compactness of the antenna. The prototype has been fabricated and characterized, demonstrating good agreement with the simulations. The insertion of the metalens allows, with respect to the pristine Vivaldi, a measured maximum gain of $G_{max}=14.2 \mathrm{d}\mathrm{B}$, increased by about $\Delta G_{max}=4.8 \mathrm{d}\mathrm{B};$ an operating bandwidth of $f=3÷14.7 \mathrm{G}\mathrm{H}\mathrm{z}$, increased by $\Delta f=1.2 \mathrm{G}\mathrm{H}\mathrm{z}$; and a radiation pattern with a maximum reduction in half-power beamwidth of $\Delta HPB{W}_{max}=31.3°$, more symmetrical in the E and H planes.

This manuscript illustrates the design and characterization of the first fiber-based photonic lantern, tailored for an efficient operation in the Mid-Infrared spectral range. The design and fabrication of the proposed device involve the use of three distinct indium fluoride optical fibers into a surrounding low refractive index glass capillary. An adiabatic transition is achieved through a controlled manufacturing process based on heating and drawing. The modal behavior of the photonic lantern is investigated along the transition via electromagnetic modal analysis, at the wavelength ${\bm{\lambda}} \ = \ \text{3.34}\ {\bm{\mu} \mathbf{m}}$ . Mode-group selectivity is obtained through the use of optical fibers with different characteristics. This implies that the light launched into a particular optical fiber evolves into specific mode groups at the photonic lantern multi-mode end. Experimental results demonstrate the possibility to excite the LP ₀₁ mode and two, odd and even, LP ₁₁ propagation modes, with losses below 1.3 dB and 1.7 dB, respectively. These results emphasize the feasibility of the proposed photonic lantern based on indium fluoride glass, with potentials for diverse applications, e.g., in communications, astrophotonics, remote sensing and spectroscopy.