Recent years have seen a rapid expansion of research into nanophotonics based on surface plasmon–polaritons. These electromagnetic waves propagate along metal–dielectric interfaces and can be guided by metallic nanostructures beyond the diffraction limit. This remarkable capability has unique prospects for the design of highly integrated photonic signal-processing systems, nanoresolution optical imaging techniques and sensors. This Review summarizes the basic principles and major achievements of plasmon guiding, and details the current state-of-the-art in subwavelength plasmonic waveguides, passive and active nanoplasmonic components for the generation, manipulation and detection of radiation, and configurations for the nanofocusing of light. Potential future developments and applications of nanophotonic devices and circuits are also discussed, such as in optical signals processing, nanoscale optical devices and near-field microscopy with nanoscale resolution.

Plasmonics beyond the diffraction limit

In 1873, Ernst Abbe discovered what was to become a well-known paradigm: the inability of a lens-based optical microscope to discern details that are closer together than half of the wavelength of light. However, for its most popular imaging mode, fluorescence microscopy, the diffraction barrier is crumbling. Here, I discuss the physical concepts that have pushed fluorescence microscopy to the nanoscale, once the prerogative of electron and scanning probe microscopes. Initial applications indicate that emergent far-field optical nanoscopy will have a strong impact in the life sciences and in other areas benefiting from nanoscale visualization.

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Far-Field Optical Nanoscopy

Artificially engineered metamaterials are now demonstrating unprecedented electromagnetic properties that cannot be obtained with naturally occurring materials. In particular, they provide a route to creating materials that possess a negative refractive index and offer exciting new prospects for manipulating light. This review describes the recent progress made in creating nanostructured metamaterials with a negative index at optical wavelengths, and discusses some of the devices that could result from these new materials.

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Optical negative-index metamaterials

Metamaterials, or engineered materials with rationally designed, subwavelength-scale building blocks, allow us to control the behavior of physical fields in optical, microwave, radio, acoustic, heat transfer, and other applications with flexibility and performance that are unattainable with naturally available materials. In turn, metasurfaces-planar, ultrathin metamaterials-extend these capabilities even further. Optical metasurfaces offer the fascinating possibility of controlling light with surface-confined, flat components. In the planar photonics concept, it is the reduced dimensionality of the optical metasurfaces that enables new physics and, therefore, leads to functionalities and applications that are distinctly different from those achievable with bulk, multilayer metamaterials. Here, we review the progress in developing optical metasurfaces that has occurred over the past few years with an eye toward the promising future directions in the field.

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Planar Photonics with Metasurfaces

We present the science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems, targeting an evolution in technology, that might lead to impacts and benefits reaching into most areas of society. This roadmap was developed within the framework of the European Graphene Flagship and outlines the main targets and research areas as best understood at the start of this ambitious project. We provide an overview of the key aspects of graphene and related materials (GRMs), ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries. We also define an extensive list of acronyms in an effort to standardize the nomenclature in this emerging field.

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Science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems

Josephson Traveling Wave Parametric Amplifiers (J-TWPAs) are promising platforms for realizing broadband quantum-limited amplification of microwave signals. However, substantial gain in such systems is attainable only when strict constraints on phase matching of the signal, idler and pump waves are satisfied – this is rendered particularly challenging in the presence of nonlinear effects, such as selfand cross-phase modulation, which scale with the intensity of propagating signals. In this work, we present a simple J-TWPA design based on ‘left-handed’ (negative-index) nonlinear Josephson metamaterial, which realizes autonomous phase matching without the need for any complicated circuit or dispersion engineering. The resultant efficiency of four-wave mixing process can implement gains in excess of 20 dB over few GHz bandwidths with much shorter lines than previous implementations. Furthermore, the autonomous nature of phase matching considerably simplifies the J-TWPA design than previous implementations based on ‘right-handed’ (positive index) Josephson metamaterials, making the proposed architecture particularly appealing from a fabrication perspective. The left-handed JTL introduced here constitutes a new modality in distributed Josephson circuits, and forms a crucial piece of the unified framework that can be used to inform the optimal design and operation of broadband microwave amplifiers.

Self phase-matched broadband amplification with a left-handed Josephson transmission line

Dielectric spheres and cylinders can support high-Q modes due to internal reflection of the light. However, small deviations of the shape of these resonators away from symmetry lead to the onset of chaotic ray dynamics and the resulting suppression of the mode lifetimes. We demonstrate, that in such conditions even the regular modes are strongly affected by small deformations, due to the phenomenon of chaos-assisted tunneling, and develop a
quantitative theory of this effect.

Chaos-assisted tunneling in whispering-gallery resonators

Comment on: All-angle broadband negative refraction of metal waveguide arrays in the visible range : Theoretical analysis and numerical demonstration. Authors' reply

Materials with simultaneously negative values of effective dielectric permittivity and magnetic permeability have been shown to have negative phase velocity (and refractive index). We propose a new approach to constructing a system with negative refractive index. In contrast to all previous designs, our system is implicitly non-magnetic and homogeneous. The proposed material is based on EM wave propagation inside a strongly anisotropic dielectric material in waveguide geometry. This design is highly scalable from GHz to optical frequencies. We present the theoretical description of the EM properties of the proposed system and several realizations for different spectral ranges.

Nanostructured non-magnetic left-handed composites

We propose a new class of planar focusing and imaging systems capable of subwavelength focusing of radiation in the far field of the source and present the Fourier-optics applications of these structures.

Viktor A. Podolskiy

Papers

Self phase-matched broadband amplification with a left-handed Josephson transmission line

Chaos-assisted tunneling in whispering-gallery resonators

Comment on: All-angle broadband negative refraction of metal waveguide arrays in the visible range : Theoretical analysis and numerical demonstration. Authors' reply

Nanostructured non-magnetic left-handed composites

Design of hyper-gratings for far field subwavelength focusing in planar geometry