Plasmonic Devices

Terahertz (THz) waves, i.e., electromagnetic waves with frequencies ranging from 0.1 to 10 terahertz, present unique opportunities for advanced applications, including wireless communications with terabit-per-second rates, high-speed miniaturized processing systems, tagging, sensing the presence of specific chemical or biological processes, imaging systems for inspection, screening, and non-invasive identification of materials in real-time by spectroscopy, study of cosmic background radiation, or detection of gases in the Earth and in the atmosphere of other planets, among many others. These applications are not currently being fully-exploited by the information society due to the immature state of THz technology in terms of sources, detectors, basic components and devices. In fact, this frequency region is known as the “THz gap”, as it occupies a technology gap between the well-developed areas of electronics and photonics. It appears clear today that significant new concepts and approaches —rather than the ‘mere’ further optimization of existing solutions— are required to circumvent the issues found at THz and develop  novel mass-producible, reliable, and low cost technology able to provide society with all the bandwidth and applications that the THz band can offer. We are currently addressing these challenges by applying graphene, novel 2D materials, and artificial metamaterials and metasurfaces to overcome the limitations of current technology in terms of integration, miniaturization, dynamic reconfiguration, and performance. 

We proposed and experimentally demonstrated the concept of reconfigurable graphene stacks at terahertz, which are structures composed of several graphene layers able to bias each other without additional gating structure [3]. Panel (a) shows an artistic illustration of the device and a picture of the fabricated prototype. Panel (b) depicts measured results, demonstrating advanced reconfiguration possibilities that goes well beyond the capabilities of standard graphene-based structures.

We also proposed, modeled, designed and analyzed novel tunable devices and antennas, including resonant and leaky-wave antennas, waveguides, switches and filters, by combining fundamental –yet powerful– electrical engineering concepts with the unusual electromagnetic response of graphene and 2D materials. First, the concept of tuneable graphene-based patch antennas operating at terahertz frequencies was pioneered [4,5] (see Panel c). This structure behaves as a true interface between guided waves (or a source/detector like a photomixer) and space waves. It was shown that in addition to high miniaturization owing to the plasmonic nature of the resonances, graphene electrical field effect can be efficiently used to provide large and efficient frequency-tuning of the antenna. We also proposed novel reconfigurable leaky-wave antennas based on the sinusoidally-modulated reactance concept [6,7] (Panel d). Here, graphene electric field effect is exploited to dynamically modify the surface impedance and in turn enable electronic beam-scanning capabilities. Concerning guided-wave electromagnetic devices, we have proposed plasmonic switches [8] (Panel e) and low-pass filters [9] (Panel f) by adequately controlling the guiding properties of a strip through graphene’s field effect. Moreover, the effect of spatial dispersion (or non-locality), which can be understood as a dependence of the material intrinsic electromagnetic property to the wave propagating on it, have been rigorously investigated [10-11]. It has been found that spatial dispersion significantly affects the propagation of surface plasmons in graphene, and consequently, that it must be taken into account in the development of graphene devices at terahertz. A comprehensive, extensive, review of graphene-based antennas can be found in [1].

In collaboration with Prof. Hihath (Arizona State University), we exploited plasmonic cavities to explore single-molecule electronics, correlating in time-domain Raman signals and conductance responses.