1 Introduction Much recent interest in the field of plasmonics has been driven by the prospect of highbandwidth, nanoscale data transport and processing systems based on surface plasmon-polaritons (SPPs) as information carriers and an enhanced plasmonic synergy between today's microelectronic and photonic technologies. 'Active plasmonic' devices able to dynamically switch and modulate SPP signals will be crucial to such applications and a range of functional media have been investigated for this purpose in recent years [1]. With proof-of-principle demonstrations pushing performance limits into technologically competitive terahertz modulation frequency [2] and femtojoule switching energy [3] domains, increasing attention is being given to practical issues like CMOS (complementary metal-oxide semiconductor) and/or SOI (silicon-on-insulator) process compatibility and the longterm performance characteristics of switching media.

Non-volatile, bidirectional, all-optical switching in a phase-change metamaterial delivers high-contrast transmission and reflection modulation at near- to mid-infrared wavelengths in device structures down to ≈1/27 of a wavelength thick.

According to Huygens' superposition principle, light beams traveling in a linear medium will pass though one another without mutual disturbance. Indeed, it is widely held that controlling light signals with light requires intense laser fields to facilitate beam interactions in nonlinear media, where the superposition principle can be broken. We demonstrate here that two coherent beams of light of arbitrarily low intensity can interact on a metamaterial layer of nanoscale thickness in such a way that one beam modulates the intensity of the other. We show that the interference of beams can eliminate the plasmonic Joule losses of light energy in the metamaterial or, in contrast, can lead to almost total absorbtion of light. Applications of this phenomenon may lie in ultrafast all-optical pulse-recovery devices, coherence filters and THz-bandwidth light-by-light modulators

We demonstrate an innovative concept for nanoscale electro-optic switching. It exploits the frequency shift of a narrow-band Fano resonance mode in a plasmonic planar metamaterial induced by a change in the dielectric properties of an adjacent chalcogenide glass layer. An electrically stimulated transition between amorphous and crystalline forms of the glass brings about a 150 nm shift in the near-infrared resonance providing transmission modulation with a contrast ratio of 4:1 in a device of subwavelength thickness. © 2010 American Institute of Physics. ͓doi:10.1063/1.3355544͔ Nanophotonic applications, in particular, photonic data processing circuits, require active devices of subwavelength dimensions. However, electro-optic modulation of light in a device of nanoscale thickness is not a trivial problem. In conventional modulators exploiting the Pockels or Kerr effects, the polarization switching involved requires the interference of two propagating modes to develop over distances far in excess of the wavelength of light. The dimensions of such modulators in the propagation direction are often in the centimeter range. Signal modulation via control of the waveguide absorption coefficient or refractive index is another possibility. However, this approach also requires substantial propagation lengths over which an amplitude or phase change accumulates, or it involves interferometric arrangements that are inherently longer than the wavelength of light. It has been suggested that strong signal modulation may be achieved in nanophotonic devices, despite very short propagation lengths, through the use of materials that show a substantial change in absorption or refraction in response to a control excitation: the relative change in the real and/or imaginary parts of the refractive coefficient must be of the order of unity and this can only be achieved in metals, where phase changes can bring about significant changes in optical properties. Such functionality has been extensively demonstrated with elemental gallium, which can exist in phases with radically different optical properties. In this case, phase changes lead to a modification of the plasmon and interband absorption to provide a platform for nanoscale active devices. 1-3Here we demonstrate another approach to nanoscale electro-optic modulation that relies not on absorption modulation but rather on a change in the refraction of a material associated with a control-input-induced phase change. In a layer of nanoscale thickness, such a refractive index change would be insufficient to noticeably modulate the intensity or phase of a transmitted wave. However, we demonstrate that by combining a nanoscale layer of phase-change material with a planar plasmonic metamaterial ͑Fig. 1͒ one can exploit the fact that the position of narrow resonant absorption lines in certain metamaterials are strongly dependent on the dielectric environment; switching the dielectric layer in contact with such a metamaterial produces a massive change in its resonance frequency. Importantly, ...

Plasmonics is a rapidly developing field at the boundary of physical optics and condensed matter physics. It studies phenomena induced by and associated with surface plasmons-elementary polar excitations bound to surfaces and interfaces of nanostructured good metals. This Roadmap is written collectively by prominent researchers in the field of plasmonics. It encompasses selected aspects of nanoplasmonics. Among them are fundamental aspects such as quantum plasmonics based on quantum-mechanical properties of both underlying materials and plasmons themselves (such as their quantum generator, spaser), plasmonics in novel materials, ultrafast (attosecond) nanoplasmonics, etc. Selected applications of nanoplasmonics are also reflected in this Roadmap, in particular, plasmonic waveguiding, practical applications of plasmonics enabled by novel materials, thermo-plasmonics, plasmonic-induced photochemistry and photo-catalysis. This Roadmap is a concise but authoritative overview of modern plasmonics. It will be of interest to a wide audience of both fundamental physicists and chemists and applied scientists and engineers.