Sub-Gigahertz Path Loss Measurement Campaign in Marine Environment: A Case Study.

This paper focuses on the characterization of radio propagation, and data communication in a marine environment. More specifically, we consider signal propagation when three different sub-gigahertz industrial, scientific, and medical (ISM) bands, i.e., 169 MHz, 434 MHz, and 868 MHz, are used. The main focus of the paper is to evaluate the path loss (PL), i.e., the power loss that a propagation radio wave would experience when communication occurs between a sail boat and a buoy. We describe the measurement results obtained performing three different radio power measurement campaigns, at the three different aforementioned ISM sub-gigahertz bands. We also want to correlate the radio propagation quality with the weather conditions present in the measurement areas. The obtained results show that higher distances are achieved by transmitting at lower frequencies, i.e., 169 MHz, and, on average, the propagation is directly dependent from the dew point index.

Nano-antenna array for high efficiency sunlight harvesting.

Solar rectennas are promising devices for energy harvesting. Capability of rectennas to convert incident light into useful energy depends on the antenna efficiency, that is the ratio between the power transferred to the load vs the incoming power. In this work, we first emphasize that for the efficiency to be calculated accurately, antennas need to be treated as receiving devices, not as transmitting ones. Then, we propose an arrangement of antennas that differs from those published so far in three respects: (1) the proposed arrangement is formed by an array of nano-antennas with sub-wavelength inter-element spacing, (2) it comprises a reflecting mirror, and (3) it allows for dual polarization operation. Through numerical simulations, we show that the small lattice pitch we use is responsible for frequency flattening of the lattice impedance over the whole solar spectrum, eventually allowing for excellent matching with the antennas' loads. Also, the small pitch allows for a smooth dependence of the receiving efficiency on the angle of incidence of sunlight. Finally, we show numerically that the reflecting mirror also allows for an almost complete cancellation of light scattered by the receiving antennas. The final result is a polarization insensitive receiving theoretical efficiency larger than 70% over the whole 300-3000 nm spectral range, with a less than 10% energy wasting due to back-scattering of sunlight.

Waveguide-Integrated, Plasmonic Enhanced Graphene Photodetectors.

We present a micrometer-scale, on-chip integrated, plasmonic enhanced graphene photodetector (GPD) for telecom wavelengths operating at zero dark current. The GPD is designed to directly generate a photovoltage by the photothermoelectric effect. It is made of chemical vapor deposited single layer graphene, and has an external responsivity ∼12.2 V/W with a 3 dB bandwidth ∼42 GHz. We utilize Au split-gates to electrostatically create a p-n-junction and simultaneously guide a surface plasmon polariton gap-mode. This increases the light-graphene interaction and optical absorption and results in an increased electronic temperature and steeper temperature gradient across the GPD channel. This paves the way to compact, on-chip integrated, power-efficient graphene based photodetectors for receivers in tele- and datacom modules.

Design optimization of single and double layer Graphene phase modulators in SOI.

In this paper we report on an electro-refractive modulator based on single or double-layer graphene on top of silicon waveguides. The graphene layers are biased to the transparency condition in order to achieve phase modulation with negligible amplitude modulation. By means of a detailed study of both the electrical and optical properties of graphene and silicon, as well as through optimization of the geometrical parameters, we show that the proposed devices may theoretically outperform existing modulators both in terms of V(π)L and of insertion losses. The overall figures of merit of the proposed devices are as low as 8.5 and 2dB∙V for the single and double layer cases, respectively.

Method for characterization of Si waveguide propagation loss.

A new method for measuring waveguide propagation loss in silicon nanowires is presented. This method, based on the interplay between traveling ring modes and standing wave modes due to back-scattering from edge roughness, is accurate and can be used for on wafer measurement of test structures. Examples of loss measurements and fitting are reported.

Graphene sustained nonlinear modes in dielectric waveguides.

We discuss the existence of nonlinear modes sustained by graphene layers in dielectric waveguides. Taking advantage of the almost two dimensional nature of graphene, we introduce the nonlinear effect as a parameter in the continuity equations. We then apply our modeling to a simple slab waveguide to enlighten how graphene can be used to induce huge nonlinear phase shifts at easily accessible power levels.

Developing the next generation of renewable energy technologies: an overview of low-TRL EU-funded research projects.

A cluster of eleven research and innovation projects, funded under the same call of the EU's H2020 programme, are developing breakthrough and game-changing renewable energy technologies that will form the backbone of the energy system by 2030 and 2050 are, at present, at an early stage of development. These projects have joined forces at a collaborative workshop, entitled ' Low-TRL Renewable Energy Technologies', at the 10th Sustainable Places Conference (SP2022), to share their insights, present their projects' progress and achievements to date, and expose their approach for exploitation and market uptake of their solutions.

Graphene-assisted control of coupling between optical waveguides.

The unique properties of optical waveguides electrically controlled by means of graphene layers are investigated. We demonstrate that, thanks to tunable losses induced by graphene layers, a careful design of silicon on silica ridge waveguides can be used to explore passive PT-symmetry breaking in directional couplers. We prove that the exceptional point of the system can be probed by varying the applied voltage and we thus propose very compact photonic structures which can be exploited to control coupling between waveguides and to tailor discrete diffraction in arrays.

Graphene-assisted critically-coupled optical ring modulator.

Graphene's conductivity at optical frequencies can be varied upon injection of carriers. In the present paper, this effect is used to modulate losses of an optical wave traveling inside a ring cavity. This way an optical modulator based on the critical-coupling concept first introduced by Yariv can be realized. Through numerical simulations, we show that a modulator featuring a bandwidth as large as 100 GHz can be designed with switching energy in the order of few fJ per bit. Also, we show that operations with driving voltages below 1.2 volt could be obtained, thus making the proposed modulator compatible with requirements of low-voltage CMOS technology.

Modeling of enhanced field confinement and scattering by optical wire antennas.

We describe the application of full-wave and semi-analytical numerical tools for the modeling of optical wire antennas, with the aim of providing novel guidelines for analysis and design. The concept of antenna impedance at optical frequencies is reviewed by means of finite-element simulations, whereas a surface-impedance integral equation is derived in order to perform an accurate and efficient calculation of the current distribution, and thereby to determine the equivalent-circuit parameters. These are introduced into simple circuits models, directly borrowed from radio frequency, which are applied in order to model the phenomena of enhanced field confinement at the feed gap and light scattering by optical antennas illuminated by plane waves.

Compact polarization converter in InP-based material.

We present a polarization converter using one-dimensional grating principles. The device is based on slanted slots etched deeply into an InP/InGaAsP heterostructure. Almost complete polarization conversion, with a 14 dB extinction ratio, is observed for a device less than 2 microm long.

Compact polarization rotators for integrated polarization diversity in InP-based waveguides.

We present the design, fabrication, and operation of a polarization converter based on angled waveguides in the InP/InGaAsP material system. By combining design elements from mode evolution and birefringent devices, the total device length is kept short (less than 50 microm) and the insertion efficiency high at 81%+/-19%, which corresponds to an insertion loss of 1 dB. Devices operate broadband, i.e., the polarization conversion exceeds 15 dB over a 100 nm wavelength range. A polarization rotator with these specifications is a prime candidate for use in an integrated polarization diversity scheme.