Diversity combining in hybrid RF/FSO systems with PSK modulation

We present a novel architecture for hybrid radio frequency (RF)/ free space optical (FSO) wireless systems without feedback or channel state information (CSI) at the transmitter. Under the assumption that 60 GHz RF and FSO systems support the same data rates, the proposed implementation transmits the same data over both links, using phase shift keying (PSK) as a common modulation scheme, and combines the signals from each individual link at the receiver on a symbol-by-symbol basis. Two popular diversity combining schemes are considered, namely, selection combining (SC) and maximal ratio combining (MRC), while tractable analytical approximations for the bit error rate (BER) are obtained. Investigations over various weather conditions and link distances revealed that the proposed implementation fully exploits the complementary nature of RF and FSO channels, even when one of the two available links fails. Furthermore, the comparison of the combining schemes demonstrates MRC as the optimum combining scheme, offering link distance gains compared to SC

All-dielectric toroidal metasurfaces for angular-dependent resonant polarization beam splitting

An all-dielectric metasurface exhibiting a strong toroidal resonance is theoretically designed and experimentally demonstrated as an angular-dependent resonant polarization beam-splitter in the microwave K-band. The metasurface is fabricated by embedding a square periodic array of high-permittivity ceramic cuboid resonators in a 3D-printed substrate of polylactic acid. It is demonstrated that by properly selecting the resonator geometry and by tuning the angle of incidence through mechanical rotation, the metasurface can switch between a polarization beam splitting and bandpass or bandstop operation. Such performance is achieved by exploiting the highly asymmetric Fano spectral profile of the toroidal resonance and the very low (high) dispersion of the associated p-(s-) polarized mode resulting from the resonant toroidal dipole mode's field profile, as evidenced by both full-wave and band structure simulations. Theoretically infinite extinction ratios are achievable for polarization beam splitting operation with very low insertion losses and adjustable bandwidth. The experimental demonstration of such a compact, all-dielectric metasurface expands the research portfolio of resonant metasurfaces toward not only the investigation of the intriguing physics of toroidal modes but also to the engineering of functional millimeter-wave components for polarization control, for instance, in the context of 5G wireless communication networks.This research was co-financed by the European Union and Greek national funds through the Operational Program Competitiveness, Entrepreneurship and Innovation, under the call RESEARCH CREATE INNOVATE (Project code: No. T1EDK-02784) and by the Comunidad de Madrid and FEDER Program (S2018/NMT-4326), the Ministerio de Economía y Competitividad of Spain (TEC2016-77242-C3-1-R and TEC2016-76021-C2-2-R), and the FEDER/Ministerio de Ciencia, Innovación y Universidades and Agencia Estatal de Investigación (RTC2017-6321-1, PID2019-107270RB-C21 and PID2019-109072RB-C31)

Chapter Merging Plasmonics and Silicon Photonics Towards Greener and Faster “Network-on-Chip” Solutions for Data Centers and High-Performance Computing Systems

Endocrinolog

Merging Plasmonics and Silicon Photonics Towards Greener and Faster “Network-on-Chip” Solutions for Data Centers and High-Performance Computing Systems

Endocrinolog

Tunable one-dimensional photonic crystal slabs based on preferential etching of silicon-on-insulator

We design and assess a one-dimensional photonic crystal slab fabricated by preferential etching of a silicon-on-insulator substrate. The etched grooves are considered to be infiltrated by a highly-birefringent nematic liquid crystalline material. A detailed analysis of the nematic director response within the grooves is presented. We investigate different configurations and demonstrate large band gap shifting when switching the liquid crystal with an applied voltage. Furthermore, we assess this type of device as an efficient alternative for compact refractometric optical sensing application

Tunable optical properties of silicon-on-insulator photonic crystal slab structures

A photonic crystal slab structure with one-dimensional periodicity, obtained by preferential etching of a silicon-on-insulator wafer, is numerically investigated in 3-D. The etched grooves are considered to be filled either with an isotropic or with a Nematic Liquid Crystal (NLC) material. The molecular director is calculated using a consistent model of NLC reorientation under an external voltage. Different structures together with a broad range of voltage values are numerically simulated by means of a three-dimensional finite-difference timedomain method. The shifting of the photonic bandgap induced by the applied voltage, as well as its sensitivity in terms of refractometric applications, are discussed for a range of different structure geometries