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.

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, ...

The field of 'plasmonics' deals with the unique optical properties of metallic nanostructures, and is one of the most fascinating and fast-moving areas of photonics. It has grown rapidly in recent years, driven by parallel advances in micro-/nano-fabrication techniques, optical diagnostic systems and computational tools, as well as wide-ranging potential applications in areas from (bio)chemical sensing to solar power generation. Surface plasmon-polaritons (SPPs) -propagating bound oscillations of electrons and light at a metal surface -have attracted particular interest because, as potential information carriers for future highly-integrated devices, they offer to combine the nanoscale dimensions of today's electronic components with the speed and bandwidth of optical systems and an innate ability to interface with both.However, if such technologies are to be realized, efficient techniques for active manipulation of SPP signals will be required. Since this challenge was spelt out in a 2004 paper describing transient SPP modulation based on light-induced structural transitions in gallium [1], a wide range of material systems (including thermo-and electro-optic media, quantum dots, and photochromic molecules) have been investigated for plasmonic switching applications. We have recently demonstrated direct optical modulation of SPP propagation on the femtosecond timescale [2], while others have reported femtojoule switching energies in a field-effect plasmonic modulator [3].In this presentation I will review and compare key active plasmonic technologies, consider emerging approaches to SPP modulation -in a study based on structurally switchable chalcogenide glasses our current investigations return to the 'phase-change' roots of the active plasmonic concept, and assess future challenges and prospects for the field.With performance characteristics approaching those of current data transport and processing technologies, the race is now on to develop active plasmonic structures that are efficient, compact and compatible with existing CMOS and/or SOI fabrication processes. Indeed, in the first instance, plasmonic components are likely to augment rather than replace electronic or photonic systems, bridging the gap between the two to create powerful hybrid devices that capitalize on their respective strengths (Fig. 1). REFERENCES[1] A. V. Krasavin and N. I. Zheludev, "Active plasmonics: Controlling signals in Au/Ga waveguide using nanoscale structural transformations," Fig. 1. Artistic impression of a hybrid opto-/electro-plasmonic chip, wherein new and enhanced functionalities are achieved by close integration of photonic, electronic and plasmonic systems. 77 MJ1 (Invited) 15.30 -16.00 978-1-4244-3681-1/09/$25.00 ©2009 IEEE

1 Introduction Much recent interest in the field of plasmonics has been driven by the prospect of high-bandwidth, 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 long-term performance characteristics of switching media.

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We analyze ultrafast surface plasmon-polariton pulse reshaping effects and nonlinear propagation modes for metal/dielectric plasmon waveguides. It is found that group velocity and loss dispersion effects can substantially modify both pulse duration (broadening/narrowing) and intensity decay (acceleration/retardation) by as much as several tens of percentage points in the short-pulse regime and that metallic nonlinearities alone may support soliton, self-focusing, and self-compressing modes.

Abstract:The technology behind rewritable optical disks offers a new switching paradigm for metamaterials. A switch comprising resonant plasmonic metamaterial and electro-optic chalcogenide glass layers provides 75% optical transmission modulation in a device of subwavelength thickness. Photonic metamaterials -nanostructured media with extraordinary properties not found in nature -have recently become the subject of intense investigation for revolutionary applications across major industries from telecommunications and defence to renewable energy and healthcare.Here, we demonstrate a new dimension in metamaterial functionality: an active switching device achieved through the hybridization of metamaterials with functional electro-optic materials. For this purpose we have exploited the active properties of chalcogenide glasses. These phase-change media, which can be reversibly switched between amorphous and crystalline states on a nanosecond timescale by optical and electronic excitations, underpin the functionality of today's re-writable optical data storage media and are set to form the basis of nextgeneration electronic memory chips known as phase change memory.We studied an electro-optical device consisting of a planar metamaterial array, with resonant transmission features, sandwiched between a thin layer of Ga:La:S chalcogenide glass and a supporting silicon nitride membrane (Figs. 1a, b). The functionality of the asymmetric split-ring metamaterial structure, milled by focused ion beam in a gold film, depends on so-called 'trapped (closed) mode' plasmon resonant excitations.An electric signal to control the device was applied between the structured gold layer and an electrode on the surface of the chalcogenide film. Switching the structural phase of the Ga:La:S from amorphous to crystalline (a transition that can be reversed by another electrical or optical input) leads to a strong change in the refractive index of the glass layer (Δn ~ 0.35). This in turn drives a blue shift of ~130 nm in the device's resonant transmission spectrum. The device that is only 370 nm thick provides a 75% electro-optically controlled resonant transmission modulation at a wavelength of 1200 nm (Fig. 1c).We show that by changing the structural parameters of the metamaterial array the resonant frequency of the device may be shifted throughout the visible and near-infrared parts of the spectrum.

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