Andrea Galtarossa

Hollow-core antiresonant optical fibers (ARFs) have emerged as a contender to succeed standard solid-core single-mode fibers. Their polarization properties are of primary importance for the operation of polarization-sensitive optical systems. Appropriate models are therefore required to design ARFs that can deliver light with precise polarization performance. This work proposes a method based on coupled-mode theory to extract the local polarization properties, in terms of birefringence and dichroism, of bent and twisted ARFs. The method is applied to a 5-tube nested antiresonant nodeless hollow-core fiber (NANF), and the results are discussed, introducing a model for the behavior of birefringence and dichroism as a function of bending radius and twist rate. Once birefringence and dichroism are obtained, their model can be used to study the polarization evolution and the polarization-dependent loss of ARFs, where the equations involved are the same as those of standard fibers. The proposed method is not limited to bend and twist, and can be applied to any perturbed ARFs where the propagation is effectively single-mode.

This work introduces a metalens designed to focus electromagnetic power in a magnetized plasma, primarily applied in electrodeless space propulsion. The focusing capability relies on the misalignment between the wavevector and the Poynting vector in a magnetized plasma. The metalens is synthesized initially by approximating it as a sheet with an equivalent tensorial susceptibility. Its constituent elements are then engineered to achieve the desired theoretical behavior. Numerical simulations confirm the effectiveness of the proposed design. The key novelty of this work lies in developing a metalens specifically tailored to focus electromagnetic power in a magnetized plasma, an anisotropic medium, rather than in free space.

We present an investigation into the use of reflectometric measurements for characterizing modal dispersion in optical fibers that support space-division multiplexing. A theoretical framework is provided to relate the dispersion characteristics observed in round-trip propagation to those measured in standard forward transmission. The proposed model is experimentally validated using a reflective configuration of an optical vector network analyzer, which enables single-ended access to the fiber. Improved experimental data are obtained with a stabilized laser source, significantly enhancing the signal quality and confirming the theoretical predictions with higher accuracy. In addition, we discuss practical considerations related to system calibration, including the compensation of temporal skew introduced by optical circulators and receiver-side polarization imbalance. The results highlight the potential of reflectometric techniques for accurately characterizing quasi-distributed advanced fiber links.

This paper analyses electromagnetic (EM) wave propagation within a metasurface-cladded waveguide filled with magnetized plasma. First, an analytical model is developed to understand the governing dynamics of the system. Second, a realistic numerical design is presented to assess the feasibility of the proposed concept. This technology targets microwave-driven plasma production, with the cladding metasurface enabling control over the cut-off frequency of the waveguide. Results suggest that EM propagation can be triggered regardless of the value of the static magnetic induction field. This represents a significant advance over standard implementations, promoting system miniaturization and facilitating the integration of waveguides with plasma sources.

A new scheme for spatially resolved measurement of mode dispersion, modal birefringence and differential chromatic dispersion in few-mode fibers is presented and experimentally validated on a weakly-coupled, 4-mode-group fiber. The method relies on spectral correlation analysis between fiber's coherent Rayleigh backscattering traces generated by each of the supported mode groups, measured through optical frequency domain reflectometry. The presented technique provides a viable and effective way to measure modal and chromatic dispersion properties between arbitrary pairs of modes of the probed fiber, providing sub-picosecond delay resolution and centimeter-scale spatial resolution.

This work proposes a metasurface-cladded waveguide which may be filled with positive- or negative-epsilon materials. This design targets microwave plasma technology, particularly devices intended to be loaded with tenuous and dense plasma. Namely, the dielectric permittivity of the filling material is positive or negative, depending on the scenario. First, a theoretical model has been proposed to assess the electromagnetic propagation regime. Specifically, the cladding metasurface is treated as an anisotropic surface impedance imposed at the edge of the waveguide. Second, a possible design relying on a hollow dielectric substrate whose internal surface is coated with a lattice of metallic patches is numerically investigated. The results show that the waveguide propagates electromagnetic waves independently from the sign of the dielectric permittivity of the filling material. The latter parameter and the geometry of the metallic lattice are shown to be governing design parameters, in particular, in determining the cut-off frequency of the fundamental mode.

This paper investigates the persistence of Rayleigh signatures in optical sensing fibers installed in harsh environments. We show that the measurements taken from some fibers installed in rough conditions still retain the Rayleigh signature after more than six years, even though those measurements have been collected with different Optical Frequency Domain Reflectometry interrogators and setups. To this aim, we rely on the Spectral Correlation Analysis, which compares and spectrally correlates the fiber's Rayleigh-backscattered trace despite the usage of different interrogator and their spatial misalignment.

This paper aims to comprehensively review the literature on Gaseous Plasma Antennas (GPAs). These innovative devices transmit electromagnetic (EM) signals through ionized gas, known as plasma, instead of conventional metal structures. GPAs offer distinct advantages over their metallic counter-parts, particularly in performance reconfigurability. The paper begins by evaluating the EM properties of the plasma medium, exploring methodologies for its generation, measurement, and simulation. Subsequently, the prevalent GPA architectures are presented, distinguishing between active and passive concepts based on the plasma’s primary role: either emitting EM signals or manipulating them. Additionally, unconventional GPA implementations, such as explosive or laser-based technologies, are examined. Finally, the paper assesses the most promising applications for leveraging GPAs in various fields.

We explore the use of uncoupled multi-core fibers employed for telecommunications as a technological platform for implementing polarization-based distributed twist sensors. Through polarimetric-optical frequency domain reflectometry we assess the twist-induced birefringence along the cores of an uncoupled four-core fiber. By applying controlled twist, we show that the elasto-optic coefficient in each core is consistent with the value reported for single-mode fibers, and that the cores experience the same birefringence variations in response to the applied twist. Moreover, we leverage the distinctive birefringence properties of unspun uncoupled multi-core fibers to achieve long-range twist sensing, showing that the measured twist is in excellent agreement with the applied one even when the perturbed fiber location is 500-m away from the source. We achieve a remarkable accuracy of 4 degrees in measuring the angle by which the fiber is twisted, with a spatial resolution of 8 cm. These results support the potential of uncoupled multi-core fibers to realize twist sensors that are relevant for applications such as umbilical cable monitoring.

This work presents the theoretical and numerical design of a cylindrical waveguide that supports Spoof Surface Plasmon Polaritons (SSPP) at microwave frequencies. First, a theoretical model is proposed to assess the propagation of SSPPs in a cylindrical geometry and to estimate the surface impedance required to enable these wave modes. The reliability of the theoretical model is verified against numerical results. The proposed cylindrical waveguide embeds a cladding metasurface with a dielectric substrate covered by a lattice of square metallic patches. According to numerical estimations, the proposed design allows the propagation of SSPPs in the frequency range 2.2–5.7 GHz. Notably, the cut-off frequency is lowered by approximately 3.5 GHz with respect to conventional metallic solutions. The target application of the proposed waveguide is efficient plasma generation.