The novel frequency shifting reconfigurable intel-ligent surface (FS-RIS) is built by a new generation of meta-materials and circuits, which is able to perform an operation that changes the frequency spectrum of the signal that was originally transmitted. The use of this FS- RIS for communication is still in its infancy. In this work, a millimeter wave (mmWave) communication link aided by FS-RIS is proposed. The FS-RIS is able to down-convert the carrier frequency of the mm Wave signal and spread the control information to the cell by using a more reliable and stable link, due to the fact that lower bands have a lower attenuation. A novel multi-frequency beam-management procedure (BMP) relying on FS-RIS is given. The proposed method is faster than existing methods since it makes use of wider beams without suffering from range penalization thanks to the better propagation in sub-6 GHz bands, unlike the hierarchical BMP. Overall, this paper provides a new way to exploit FS-RIS in wireless communications, which has the potential to change the way we look at spectrum and interference management.

Frequency shifting-reconfigurable intelligent surfaces (FS-RISs) can be built by a new generation of meta-materials and circuits, which can perform an operation that changes the original frequency spectrum of the transmitted signal. Its exploitation for wireless communications is still in its infancy. In this work, a millimetre wave (mmWave) cellular network aided by FS-RIS is proposed to satisfy the new challenging communication services. The FS-RIS is able to down-convert the carrier frequency of the mmWave signal and spread the control information to the cell by using a more reliable and stable link, relying on better propagation within the lower bands, and a novel multi-frequency beam-management procedure is given. The proposed method can rapidly discover all users in the entire cell by using different sizes of beams. It avoids range penalization due to the better propagation in sub-6 GHz bands, unlike the hierarchical BMP. Additionally, the proposed technique only requires one base station (BS), and hence the delay overhead caused by the information exchange among several BSs is fully avoided, unlike the case of coordinated multi-point (CoMP). Overall, this paper provides a new way to exploit FS-RIS in wireless systems, which can potentially change the way we look at spectrum and interference management for the efficient exploitation of communication applications.

N-path commutated capacitive networks provide a practical solution to implement highly sought on-chip high-Q filtering applications in which the use of lumped inductors is undesirable due to their significant footprints and low Q-factors. Recently, it has been also revealed that N-path networks can also exhibit other interesting functionalities, such as nonreciprocal phase-shifting and ultra-wideband true time delay, providing a path to miniaturization of various reciprocal and nonreciprocal devices. The analytical treatment of these networks, however, remains challenging, because their operation involves frequency mixing produced by the time modulation. In this article, we present a highly accurate frequency-domain approach for the analysis of N-path networks based on perturbation theory. Our method compares favorably to the state-of-the-art polyphase analysis by being much simpler mathematically, yet providing results essentially indistinguishable from numerical simulations, while offering physical insights into the N-path filter operation. We particularize the solution for the high-Q operation regime and obtain simple closed-form analytical expressions for harmonic transfer functions, scattering parameters and baseband impedance.

Electromagnetic waves, from radio signals to light, generally obey a strict symmetry in transmission: if they can travel from point A to point B, they can also travel backward from B to A with the same properties. This general symmetry, rooted in the fact that Maxwell’s equations are symmetric with respect to time and known as reciprocity, has profound implications on a variety of technologies and device functionalities. On the one hand, we count on reciprocity when we operate an antenna, in a variety of measurement schemes, and in analytical/numerical techniques to study the response of electromagnetic systems. On the other hand, reciprocity inherently limits the degree of control in manipulating electromagnetic waves and hence the overall functionality of many devices. For instance, breaking reciprocity enables the possibility of transmitting a signal without having to worry about backreflections, which may harm sensitive equipment or interfere with incoming data streams, and of transmitting and receiving signals through the same transducer at the same frequency and at the same time—the holy grail of full-duplex communication schemes. Fields as diverse as radar technologies, wireless communications, and optical and quantum computing all require nonreciprocal signal routing to enable reception of signal echoes while transmitting, data transmission without worrying about jammers, and to guarantee one-way streams of data that can be robustly processed.

Being able to manipulate and control light flows at small scales holds the promise to open groundbreaking opportunities for a variety of technologies. Consider, for instance, the challenges currently faced in the world of computing: as data rates and processing demands increase worldwide at an exponential rate, we are facing unsustainable increases in energy consumption associated with data centers and streaming providers. To address these challenges, optical computing and communications offer an interesting alternative to electronic-based systems. Using light for these purposes, however, is hindered by the fact that photons are not easily squeezed to volumes beyond the diffraction limit, i.e., below the wavelength scale, which would be required both to enable lowenergy computation at sufficiently high speeds and to match the degree of integration density available in electronic systems. Today, the field of optoelectronics, which combines highdensity electronic devices to process the data and low-energy data transport enabled by light, is growing at a very fast pace.

In this article, we provide a comprehensive review of past and present efforts in the field of microwave nonreciprocity with an emphasis on the most commonly used nonreciprocal devices, namely gyrators, isolators, and circulators. After discussing the origin and history of such efforts, we elaborate on the pros and cons of four distinct approaches to break reciprocity which include magnetic biasing of ferrite materials, intrinsic nonreciprocity of solid-state devices, nonlinearities with geometric asymmetries, and finally, periodic spatiotemporal variation. We subsequently pay due attention to the spatiotemporal approach and show that the recently emerging proposals to achieve magnet-free nonreciprocity with linear, periodically time-varying circuits can compete with traditional ferrite devices and even outperform them in several metrics, thus opening the door to exciting venues for miniaturized low-cost and high-performance nonreciprocal devices with numerous applications ranging from full-duplex communications and quantum computing to biomedical imaging and radar systems.

Recent progress in nanofabrication has led to tremendous technological developments for devices that rely on the interaction of light with nanostructured matter. Nanophotonics has hence experienced a large surge of interest in recent years, from basic research to applied technology. For instance, the increased importance of ultralow-energy data processing at fast speeds has been encouraging the use of light for signal transport and processing. Energy demands and interaction time scales become smaller with the physical size of the nanostructures, hence nanophotonics opens important opportunities for integrating a large number of devices that can generate, control, modulate, sense, and process light signals at ultrafast speeds and below femtojoule/bit energy levels. However, losses and diffraction pose fundamental challenges to the fundamental ability of nanophotonic structures to efficiently confine light in smaller and smaller volumes. In this framework, active nanophotonics, which combines the latest advances in nanotechnology with gain materials, has recently become a vital area of optics research, both from the physics, material science, and engineering standpoint. In this article, we review recent efforts in enabling active nanodevices for lasing and optical sources, loss compensation, and to realize new optical functionalities, like PT-symmetry, exceptional points, and nontrivial lasing based on suitably engineered distributions of gain and loss in nanostructures.

Leaky waves have been among the most active areas of research in microwave engineering over the second half of the 20th century. They have been shown to dominate the near-field of several open wave-guiding structures, of great interest to tailor their radiation, guidance and filtering properties. The elegant theoretical analyses and deep physical insights in this area, developed in an era in which computational resources were limited, represent a fundamental scientific legacy that is still extremely relevant in today's engineering society and beyond. In this regard, the relevance of leaky-wave concepts has been increasingly recognized in recent times over a broader scientific community, including optics and physics societies. In this paper, after revisiting the fundamental concepts of leaky-wave theory, we discuss and connect different relevant research activities in which leaky-wave concepts have been applied, with the goal of facilitating multidisciplinary interactions on these topics. In addition to the canonical microwave applications of leaky waves, particular attention is devoted to a few areas of interest in modern optics, such as directive optical antennas, extraordinary optical transmission, and embedded scattering eigenvalues, in which leaky waves play a fundamental role.

Here we review the application of the optical nanocircuit paradigm to design and characterize metamaterials with exotic optical properties. The interaction of small nanoparticles with light is equivalently described in terms of optical lumped circuit elements, which relate the equivalent optical voltage across the particles and the optical displacement field current circulating through them. This equivalence goes beyond a simple description of the interaction of an individual nanoparticle with the impinging optical signal, as collections of closely spaced particles may be tailored as complex nanocircuit connections with specific optical response. Inspired by the fascinating concept and potentials of transmission-line metamaterials at microwaves, in which networks of lumped radio-frequency (RF) and microwave circuit elements may provide exotic metamaterial properties, in this paper, we review and discuss how analogous concepts may be translated to optical frequencies at the nanoscale, by applying the nanocircuit paradigm. We present several designs of 0-D, 1-D, 2-D, and 3-D arrays of nanoparticles supporting subwavelength resonances, negative-index propagation, and other exotic optical effects, achieved by suitably combining and connecting nanoparticles operating as optical lumped nanocircuit elements. Fascinating applications of these concepts are proposed in a variety of optical scenarios, considering the influence of natural material dispersion and loss in optical materials.