Programmable time-domain digital-coding metasurface for non-linear harmonic manipulation and new wireless communication systems

Optical non-linear phenomena are typically observed in natural materials interacting with light at high intensities, and they benefit a diverse range of applications from communication to sensing. However, controlling harmonic conversion with high efficiency and flexibility remains a major issue in modern optical and radio-frequency systems. Here, we introduce a dynamic time-domain digital-coding metasurface that enables efficient manipulation of spectral harmonic distribution. By dynamically modulating the local phase of the surface reflectivity, we achieve accurate control of different harmonics in a highly programmable and dynamic fashion, enabling unusual responses, such as velocity illusion. As a relevant application, we propose and realize a novel architecture for wireless communication systems based on the time-domain digital-coding metasurface, which largely simplifies the architecture of modern communication systems, at the same time yielding excellent performance for real-time signal transmission. The presented work, from new concept to new system, opens new pathways in the application of metamaterials to practical technology

Ultrafast cryptography with indefinitely switchable optical nanoantennas

Bistability is widely exploited to demonstrate all-optical signal processing and light-based computing. The standard paradigm of switching between two steady states corresponding to '0" and '1" bits is based on the rule that a transition occurs when the signal pulse intensity overcomes the bistability threshold, and otherwise, the system remains in the initial state. Here, we break with this concept by revealing the phenomenon of indefinite switching in which the eventual steady state of a resonant bistable system is transformed into a nontrivial function of signal pulse parameters for moderately intense signal pulses. The essential nonlinearity of the indefinite switching allows realization of well-protected cryptographic algorithms with a single bistable element in contrast to software-assisted cryptographic protocols that require thousands of logic gates. As a proof of concept, we demonstrate stream deciphering of the word 'enigma' by means of an indefinitely switchable optical nanoantenna. An extremely high bitrate ranging from ~0.1 to 1 terabits per second and a small size make such systems promising as basic elements for all-optical cryptographic architectures.Comment: Light: Science & Applications, to appea

1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface

A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance

Beam scanning by liquid-crystal biasing in a modified SIW structure

A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium

Wave Engineering in Time Modulated, Nonlinear, and Anisotropic Metamaterials

Leveraging wave matter interactions is central to a myriad of electromagnetic wave-based applications. During the past decades, research on extreme wave manipulation has been revolutionized by artificially engineered materials (metamaterials) and by adding new aspects to the wave-matter interactions that showed intriguing results inaccessible in conventional linear, time invariant (LTI), passive and isotropic media. In this work, I will explore, numerically and experimentally, the possibility of realizing devices that perform beyond or close to their fundamental LTI limitations by adding periodic modulation, nonlinearity, and gain. I will demonstrate these concepts at radio frequencies (RF) and at optical frequencies. Specifically, at RF I will show that small periodic temporal modulation of nonlinear matching network can enhance the radiation of electrically small antennas by boosting unbalanced energy exchange between the wave and the modulating pump. I will show how large modulation ratios can be exploited to build novel compact phase conjugator, time reversal devices. In harnessing the role of nonlinearity, I will show the experimental demonstration of a single unit cell of parametric frequency divider-by-3 that enable phase tri-stability– an important feature needed to realize computational platform for combinatorial optimization problems. Extending RF modulation schemes to optical frequencies is hindered by current technologies, which only allow small modulation ratios and speeds. I will demonstrate how weak optical nonlinearities can replace temporal modulation at RF to efficiently achieve similar effects, for instance realizing nonlinearity-based nonreciprocity, in which the wave itself modulates the medium, overcoming speed limitations. To further increase the efficiency, I will show how nonlinear generation and wave mixing can be obtained in thin 2D periodic structures based on multi-quantum-wells, and in parallel I demonstrate how to enhance nonlinearity from 2D materials, as well as show the possibility to engineer the dispersion of hyperbolic surface wave propagation on judiciously designed metasurfaces that leverage enhanced wave-matter interactions, opening new avenues for compact imaging and sensing devices. TRANSLATE with x English Arabic Hebrew Polish Bulgarian Hindi Portuguese Catalan Hmong Daw Romanian Chinese Simplified Hungarian Russian Chinese Traditional Indonesian Slovak Czech Italian Slovenian Danish Japanese Spanish Dutch Klingon Swedish English Korean Thai Estonian Latvian Turkish Finnish Lithuanian Ukrainian French Malay Urdu German Maltese Vietnamese Greek Norwegian Welsh Haitian Creole Persian TRANSLATE with COPY THE URL BELOW Back EMBED THE SNIPPET BELOW IN YOUR SITE Enable collaborative features and customize widget: Bing Webmaster Portal Bac

An experimental investigation into smart radio environments

The potential for dynamically manipulating the wireless channel introduces a revolutionary concept in wireless communication systems known as the smart radio environment (SRE). Recent works have suggested that SREs hold the promise of delivering unprecedented performance benefits to wireless networks. However, a notable gap exists as the overwhelming majority of published works on this subject lack a robust data-driven approach. This investigation into SREs sets out to bridge the chasm between theory and reality. Novel reconfigurable intelligent surface (RIS) prototypes have been developed, whose electromagnetic properties have been designed to efficiently reshape the wireless propagation environment to our advantage. Two extensive field measurement campaigns have been undertaken. A series of measurements obtained within RISaided wireless communication setups throughout an indoor environment reveal that substantial increases in channel gain are possible through strategic placement and configuration of these smart reflectors. Furthermore, frequency domain measurements obtained throughout an existing multi-antenna urban macrocell reveal the potential for contemporary networks to benefit from the SRE concept. The benefits RISs can bring to multiple-input multiple-output (MIMO) outdoor networks are revealed, alongside potentially detrimental impacts in the form of a reduced effective rank and increased interference. This works sheds a light on a number of practical issues, from design and implementation, to real-world deployment of RISs