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.

/pdf/far-field-optical-nanoscopy-3qevt2g1wp.pdf

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.

/pdf/optical-negative-index-metamaterials-2q5qafgl3m.pdf

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.

/pdf/planar-photonics-with-metasurfaces-1sfd62lis7.pdf

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.

/pdf/science-and-technology-roadmap-for-graphene-related-two-4q9m7czlkc.pdf

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

F. Javier Garcia de Abajo opened a general discussion of the two papers by Jeremy Baumberg and Javier Aizpurua.

Surface plasmon enhanced spectroscopies and time and space resolved methods: General discussion

We have developed a new mode matching technique capable of accurate numerical computation of wave coupling in arrays of planar structures. The algorithm is illustrated on several examples of plasmonic and volumetric waveguides.

Quasi-planar optics: computing light propagation and scattering in planar waveguide arrays

Computationally designed multi-scale gratings demonstrating both diffractive and effective medium properties can dramatically increase optical coupling out of a high-index dielectric. Typical results show increase of transmission on the order of 20%.

Multiscale metasurfaces for enhanced light extraction

We analyze the behavior of group and phase velocities in optical waveguides supporting strongly confined propagating modes. We discuss the implications of material absorption for electromagnetic properties of nanoguides and develop an analytical description of the interplay between geometry-induced and materials-induced dispersions. In the limit of strong confinement, the phase velocity of waveguide modes becomes vanishingly small, while group velocity can be modulated from negative to positive values. The modulation of group velocity is enhanced by the factor of λ2/R2 with respect to macroscopic systems. Both slow- and fast-light regimes can be achieved in the same nanoguiding structure, and dynamical switching between the two regimes is possible. Applications of the developed formalism lie in the field of ultrafast active nanophotonics.

Enhancement of dispersion modulation in nanoscale waveguides

In random metal-dielectric composites near the percolation threshold surface plasmons are localized in small nanometer-sized areas, hot spots, where the local field can exceed the applied field by several orders of magnitude. The high local fields result in dramatic enhancement of optical responses, especially, nonlinear ones. The local-field distributions and enhanced optical nonlinearities are described using the scale renormalization. A theory predicts that the local fields consist of spatially separated clusters of sharp peaks representing localized surface plasmons. Experimental observations are in good accord with theoretical predictions. The localization of plasmons maps the Anderson localization problem described by the random Hamiltonian with both on- and off-diagonal disorder. A feasibility of nonlinear surface-enhanced spectroscopy of single molecules and nanocrystals on percolation films is shown.

Viktor A. Podolskiy

Papers

Surface plasmon enhanced spectroscopies and time and space resolved methods: General discussion

Quasi-planar optics: computing light propagation and scattering in planar waveguide arrays

Multiscale metasurfaces for enhanced light extraction

Enhancement of dispersion modulation in nanoscale waveguides

Percolation Composites: Localization of Surface Plasmons and Enhanced Optical Nonlinearities