Graphene plasmons were predicted to possess ultra-strong field confinement and very low damping at the same time, enabling new classes of devices for deep subwavelength metamaterials, single-photon nonlinearities, extraordinarily strong light-matter interactions and nano-optoelectronic switches. While all of these great prospects require low damping, thus far strong plasmon damping was observed, with both impurity scattering and many-body effects in graphene proposed as possible explanations. With the advent of van der Waals heterostructures, new methods have been developed to integrate graphene with other atomically flat materials. In this letter we exploit near-field microscopy to image propagating plasmons in high quality graphene encapsulated between two films of hexagonal boron nitride (h-BN). We determine dispersion and particularly plasmon damping in real space. We find unprecedented low plasmon damping combined with strong field confinement, and identify the main damping channels as intrinsic thermal phonons in the graphene and dielectric losses in the h-BN. The observation and in-depth understanding of low plasmon damping is the key for the development of graphene nano-photonic and nano-optoelectronic devices.

Highly confined low-loss plasmons in graphene-boron nitride heterostructures

https://iopscience.iop.org/article/10.1088/2040-8978/18/10/103001/pdf

Resonant dielectric nanostructures: a low-loss platform for functional nanophotonics

The field of metamaterials has opened landscapes of possibilities in basic science, and a paradigm shift in the way we think about and design emergent material properties. In many scenarios, metamaterial concepts have helped overcome long-held scientific challenges, such as the absence of optical magnetism and the limits imposed by diffraction in optical imaging. As the potential of metamaterials, as well as their limitations, become clearer, these advances in basic science have started to make an impact on several applications in different areas, with far-reaching implications for many scientific and engineering fields. At optical frequencies, the alliance of metamaterials with the fields of plasmonics and nanophotonics can further advance the possibility of controlling light propagation, radiation, localization and scattering in unprecedented ways. In this review article, we discuss the recent progress in the field of metamaterials, with particular focus on how fundamental advances in this field are enabling a new generation of metamaterial, plasmonic and nanophotonic devices. Relevant examples include optical nanocircuits and nanoantennas, invisibility cloaks, superscatterers and superabsorbers, metasurfaces for wavefront shaping and wave-based analog computing, as well as active, nonreciprocal and topological devices. Throughout the paper, we highlight the fundamental limitations and practical challenges associated with the realization of advanced functionalities, and we suggest potential directions to go beyond these limits. Over the next few years, as new scientific breakthroughs are translated into technological advances, the fields of metamaterials, plasmonics and nanophotonics are expected to have a broad impact on a variety of applications in areas of scientific, industrial and societal significance.

https://iopscience.iop.org/article/10.1088/1361-6633/aa518f/pdf

Metamaterial, plasmonic and nanophotonic devices.

Two-dimensional graphene monolayers and bilayers exhibit fascinating electrical transport behaviors. Using infrared spectroscopy, we find that they also have strong interband transitions and that their optical transitions can be substantially modified through electrical gating, much like electrical transport in field-effect transistors. This gate dependence of interband transitions adds a valuable dimension for optically probing graphene band structure. For a graphene monolayer, it yields directly the linear band dispersion of Dirac fermions, whereas in a bilayer, it reveals a dominating van Hove singularity arising from interlayer coupling. The strong and layer-dependent optical transitions of graphene and the tunability by simple electrical gating hold promise for new applications in infrared optics and optoelectronics.

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Gate-Variable Optical Transitions in Graphene

We study the potential of graphene plasmons for spectrometer-free sensing based on surface-enhanced infrared absorption and Raman scattering. The large electrical tunability of these excitations enables an accurate identification of infrared molecular resonances by recording broadband absorption or inelastic scattering, replacing wavelength-resolved light collection by a signal integrated over photon energy as a function of the graphene doping level. The high quality factor of graphene plasmons plays a central role in the proposed detection techniques, which we show to be capable of providing label-free identification of the molecular vibration fingerprints. We find an enhancement of the absorption and inelastic scattering cross sections by 3–4 orders of magnitude for molecules in close proximity to doped graphene nanodisks under currently feasible conditions. Our results pave the way for the development of novel cost-effective sensors capable of identifying spectral signatures of molecules without using ...

Molecular Sensing with Tunable Graphene Plasmons

Sensing is to date one of the most successful applications of surface plasmons thanks to the exceptional field amplification and sensitivity of these modes in metallic nanostructures. Here we introduce a promising detection scheme based on the propagation of strongly confined antibonding plasmons supported by graphene sandwiches. Instead of measuring changes in the refractive index or enhancing a restricted number of molecular absorption lines, the proposed device can recover an extended portion of the infrared spectrum of a molecule. Moreover, the extreme compression of light in graphene means that a diluted 2 nm-thick analyte can cause up to 3 dB intensity changes. The broadband capability and sensitivity also imply that one can easily identify different chemicals in a mixture and extract their respective concentration. We conclude by presenting a simple experimental setup based on this mechanism for infrared spectroscopy that could become a cheap Fourier transform infrared accessory and an alternative ...

/pdf/graphene-sandwiches-as-a-platform-for-broadband-molecular-22yhk7s6ij.pdf

Graphene Sandwiches as a Platform for Broadband Molecular Spectroscopy

As the demand for wireless communication system grows, the need for radio spectrum increases accordingly. In this context, cognitive radio has emerged as a breakthrough for effective utilization of radio spectrum. In order to realize dynamic spectrum management in the future, it is imperative to possess a thorough understanding about how wireless spectrum behaves over time, frequency, and space, etc. In this paper, we report the spectrum occupancy measurement campaign conducted in the frequency range of 20–3000MHz based on the radio monitoring network in Yunnan Province. Spectrum occupancy with space and time dependent characteristic at six typical fixed stations are obtained. The measurement results show relatively low spectrum occupancy with great potential for dynamic usage of spectrum. Besides, the ambient noise has a great influence on the measurement results, thus its calibration is a key issue in radio monitoring which is based on energy detection.

Spectrum occupancy analysis based on radio monitoring network

Participatory sensing, leveraging on the ubiquity of cheap sensors in mobile devices, enables various promising applications of great social benefit. However, its ubiquitous sampling and openness results in serious privacy concerns. People's activity trajectories may reveal their private information such as home and work place and thus requires proper protection. In this paper, we propose a novel design scheme, called query logics detached storage (QLDS), for trajectory privacy protection. The core idea of QLDS is to extract the query logics for personal trajectory retrieval and make actual trajectory tuples not clustered to any route-identity or user-identity at server end, which introduces fine-granularity anonymity. The QLDS design scheme stores the extracted query logics at users own client devices and the un-clustered location tuples at the backend server, guaranteeing trajectory reconstruction at client-end and privacy preservation at server-end. Besides, integration of QLDS with other privacy protection approaches can further enhance the protection strength and bring flexible configurations to meet individuals’ variable privacy concerns. The theoretical analytics is provided for the privacy and utility evaluation. The data retrieval performance of QLDS is experimentally evaluated in real-world internet environment.

QLDS: A Novel Design Scheme for Trajectory Privacy Protection with Utility Guarantee in Participatory Sensing

Metamaterials are artificial media structured on a size scale smaller than the wavelength of external stimuli, that may provide novel tools to significantly enhance the sensitivity and resolution of the sensors. In this paper, we derive the dispersion relation of hollow cylindrical dielectric waveguide, and compute the resonant frequencies and Q factors of the corresponding Whispering-Gallery-Modes (WGM). A metamaterial sensor based on microring resonator operating in WGM is proposed, and the resonance intensity spectrum curves in the frequency range from 185 to 212 THz were studied under different sensing conditions. Full-wave simulations, considering the frequency shift sensitivity influenced by the change of core media permittivity, the thickness and permittivity of the adsorbed substance, prove that the sensitivity of the metamaterial sensor is more than 7 times that of the traditional microring resonator sensor, and the metamaterial layer loaded in the inner side of the microring doesn’t affect the high Q performance of the microring resonator.

Simulation and analysis of a metamaterial sensor based on a microring resonator.

In this paper, a cylindrical graphene plasmon waveguide (CGPW), which consists of two rolled graphene ribbons, a dielectric core and a dielectric interlayer is proposed, and its use for molecular sensing is investigated. First, an analytical model for the surface plasmon modes supported by this graphene geometry is presented and verified by finite element method simulations. Furthermore, we demonstrate a large tunability of the modes behavior by varying the Fermi level of the graphene, the coupling distance between the two sheets and the radius of the cylinder. Finally, a molecular sensing scheme based on the CGPW is proposed. Broadband spectroscopy of ethanol and toluene thin layers is realized by recording the changes in spectral intensity of the propagating mode. Due to the broadband localization capability of graphene plasmon mode which leads to a strong light-matter interaction in the midinfrared and terahertz regime, the proposed sensing scheme may provide an effective way for detecting nanometric-size molecules.

Jingjing Yang

Papers

Graphene Sandwiches as a Platform for Broadband Molecular Spectroscopy

Spectrum occupancy analysis based on radio monitoring network

QLDS: A Novel Design Scheme for Trajectory Privacy Protection with Utility Guarantee in Participatory Sensing

Simulation and analysis of a metamaterial sensor based on a microring resonator.

Transmission properties and molecular sensing application of CGPW.