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

Modern electronics based on semiconductors is meeting the fundamental speed limit caused by the interconnect delay and large heat generation when the sizes of components reach nanometer scale. Photons as a carrier of the information are superior to electrons in bandwidth, density, speed, and dissipation. More over, photons could carry intensity, polarization, phase, and frequency information which could break through the limitation of binary system as in electronic devices. But due to the diffraction limitation, the photonic components and devices can not be fabricated small enough to be integrated densely. Surface plasmon polariton is quanta of collective oscillations of free electrons excited by photons in metal nanostrucrures, which offers a promising way to manipulate light at the nanoscale and to realize the miniaturization of photonic devices. Hence, plasmonic circuits and devices have been proposed for some time as a potential strategy for advancing semiconductor-based computing beyond the fundamental performance limitations of electronic devices, as epitomized by Moore's law. A variety of individual plasmonic nanodevices have been intensively studied recently, but the crucial and necessary step to enable nanophotonic circuits for future information technology, namely cascade logics integrated on-chip, has not been achieved. Here we demonstrate that a nanophotonic binary logic NOR gate can be realized by cascading plasmonic OR and NOT gates in four-terminal nanowire networks. We explain the operating principle for the device based on quantum dot luminescence imaging, which reveal the interferences for different logic functions between propagating plasmon wave packets in the nanowire network in great detail. Since the NOR gate is logic complete, i.e. any Boolean logic gate can be constructed from it, our results could have a key role in defining a viable path for the development of novel subwavelength optical processor architectures.

Cascaded Logic Gates in Nanophotonic Plasmon Networks

Broadband electromagnetic wave absorbers are highly desirable in numerous applications such as solar-energy harvesting, thermo-photovoltaics, and photon detection. The aim to efficiently achieve ultrathin broadband absorbers with high-yield and low-cost fabrication process has long been pursued. Here, we theoretically propose and experimentally demonstrate a unique broadband plasmonic-metamaterial absorber by utilizing a sub-10 nm meta-surface film structure to replace the precisely designed metamaterial crystal in the common metal–dielectric–metal absorbers. The unique ultrathin meta-surface can be automatically obtained during the metal film formation process. Spectral bandwidth with absorbance above 80% is up to 396 nm, where the full absorption width at half-maximum is about 92%. The average value of absorbance across the whole spectral range of 370–880 nm reaches 83%. These super absorption properties can be attributed to the particle plasmon resonances and plasmon near-field coupling by the automati...

Automatically acquired broadband plasmonic-metamaterial black absorber during the metallic film-formation.

Active metamaterials and metadevices: a review

In this paper, a multi-mode surface plasmon resonance absorber based on dart-type single-layer graphene is proposed, which has the advantages of polarization independence, tunability, high sensitivity, high figure of merit, etc. The device consists of a top layer dart-like patterned single-layer graphene array, a thicker silicon dioxide spacer layer and a metal reflector layer, and has simple structural characteristics. The numerical results show that the device achieves the perfect polarization-independent absorption at the resonance wavelengths of λI = 3369.55 nm, λII = 3508.35 nm, λIII = 3689.09 nm and λIV = 4257.72 nm, with the absorption efficiencies of 99.78%, 99.40%, 99.04% and 99.91%, respectively. The absorption effect of the absorber can be effectively regulated and controlled by adjusting the numerical values such as the geometric parameters and the structural period p of the single-layer graphene array. In addition, by controlling the chemical potential and the relaxation time of the graphene layer, the resonant wavelength and the absorption efficiency of the mode can be dynamically tuned. And can keep high absorption in a wide incident angle range of 0° to 50°. At last, we exposed the structure to different environmental refractive indices, and obtained the corresponding maximum sensitivities in four resonance modes, which are SI = 635.75 nm RIU−1, SII = 695.13 nm RIU−1, SIII = 775.38 nm RIU−1 and SIV = 839.39 nm RIU−1. Maximum figure of merit are 54.03 RIU−1, 51.49 RIU−1, 43.56 RIU−1, and 52.14 RIU−1, respectively. Therefore, this study has provided a new inspiration for the design of the graphene-based tunable multi-band perfect metamaterial absorber, which can be applied to the fields such as photodetectors and chemical sensors.

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Multi-mode surface plasmon resonance absorber based on dart-type single-layer graphene

Ultra-broadband perfect solar absorber by an ultra-thin refractory titanium nitride meta-surface

Near-unity, full-spectrum, nanoscale solar absorbers and near-perfect blackbody emitters

Multispectral light perfect absorption is desired for many applications. Herein, we propose and demonstrate a novel multi-band light perfect absorber (MLPA) scheme based on a triple-layer dielectric meta-material structure coupled with a metal substrate. Four absorption bands with the maximal absorbance up to 98.9% and the narrow bandwidth down to 2 nm are achieved in the visible range. Optical cavity resonances and the plasmon-like dipolar resonance of the high-index dielectric resonators and their hybridization effects contribute to the observed absorption behaviors. Moreover, the obtained MLPA is with high scalability in the frequency range by tuning the structural parameters. These features pave a new and feasible way for multispectral light absorption and hold applications in the optoelectronic detection, filtering and imaging.

Multi-band light perfect absorption by a metal layer-coupled dielectric metamaterial.

Quantitatively optical and electrical-adjusting high-performance switch by graphene plasmonic perfect absorbers

Metal structures with high optical transparency and conductivity are of great importance for practical applications in optoelectronic devices. Here we investigate the transparency response of a continuous metal film sandwiched by double plasmonic nanoparticle arrays. The upper nanoparticle array shows efficient light trapping of the incident field, acting as a light input coupler, and the lower nanoparticle array shows a light release gate opening at the other side, acting as the light output coupler. The strong near-field light–matter interactions of the nano-scale separated plasmonic nanoparticles, the excitation of surface plasmon waves of the metal film, and their cooperative coupling effects result in broadband scattering cancellation and near-unity transparency (up to 96%) in the optical regime. The transparency response in such a structure can be efficiently modified by varying the gap distance of adjacent nanoparticles, dielectric environments, and the distance between the plasmonic array and the metal film. This motif may provide a new alternative approach to obtain transparent and highly conducting metal structures with potential applications in transparent conductors, plasmonic filters, and highly integrated light input and output components.

https://iopscience.iop.org/article/10.1088/0957-4484/24/15/155203/pdf

Guolan Fu

Papers

Ultra-broadband perfect solar absorber by an ultra-thin refractory titanium nitride meta-surface

Near-unity, full-spectrum, nanoscale solar absorbers and near-perfect blackbody emitters

Multi-band light perfect absorption by a metal layer-coupled dielectric metamaterial.

Quantitatively optical and electrical-adjusting high-performance switch by graphene plasmonic perfect absorbers

Near-unity transparency of a continuous metal film via cooperative effects of double plasmonic arrays.