Current efforts in metamaterials research focus on attaining dynamic functionalities such as tunability, switching and modulation of electromagnetic waves. To this end, various approaches have emerged, including embedded varactors, phase-change media, the use of liquid crystals, electrical modulation with graphene and superconductors, and carrier injection or depletion in semiconductor substrates. However, tuning, switching and modulating metamaterial properties in the visible and near-infrared range remain major technological challenges: indeed, the existing microelectromechanical solutions used for the sub-terahertz and terahertz regimes cannot be shrunk by two to three orders of magnitude to enter the optical spectral range. Here, we develop a new type of metamaterial operating in the optical part of the spectrum that is three orders of magnitude faster than previously reported electrically reconfigurable metamaterials. The metamaterial is actuated by electrostatic forces arising from the application of only a few volts to its nanoscale building blocks-the plasmonic metamolecules-that are supported by pairs of parallel strings cut from a flexible silicon nitride membrane of nanoscale thickness. These strings, of picogram mass, can be driven synchronously to megahertz frequencies to electromechanically reconfigure the metamolecules and dramatically change the transmission and reflection spectra of the metamaterial. The metamaterial's colossal electro-optical response (on the order of 10(-5)-10(-6) m V(-1)) allows for either fast continuous tuning of its optical properties (up to 8% optical signal modulation at up to megahertz rates) or high-contrast irreversible switching in a device only 100 nm thick, without the need for external polarizers and analysers.

Abstract:We demonstrate the first temperature driven mechanically reconfigurable photonic metamaterials (RPMs) providing tunability at optical frequencies.OCIS codes: (160.3918) Metamaterials; (230.4685) Optical microelectromechanical devicesHere we introduce the first mechanically reconfigurable photonic metamaterials with tunable transmission and reflection characteristics provided by nanoscale movements of the components of the metamaterial structure. In the past control of electromagnetic response of metamaterials has only been possible in the terahertz part of the spectrum through micro-electro-mechanically activated motion.Using a sophisticated nanofabrication process on a multilayered metal-dielectric membrane we fabricated a two-dimensional array of C-shaped plasmonic resonators (meta-molecules). In our reconfigurable metamaterial alternating rows of the meta-molecules are supported by different gold-silicon nitride layered substrates of nanoscale thickness, see Fig. 1. Through the virtue of differential thermal expansion the mutual position of alternating rows can be controlled by temperature: we observed a substantial and reversible change of the metamaterial's transmission by tuning temperature within a 200K range, see Fig.2.The metamaterial's transmission spectrum shows several transmission resonances in the near infrared, which are sensitive to coupling between the plasmonic resonators and thus the mutual positions of the meta-molecules in neighboring rows, see Fig. 2. It illustrates the transmission change relative to a reference temperature of 270K. At the resonance frequencies the metamaterial transmission decreases by up to 35% when the sample is cooled to 76K. This large temperature-controlled change in the structure's transmission characteristics is reversible by heating the metamaterial back to its initial temperature We discuss possible improvements and limits of the technology and potential applications of mechanically reconfigurable photonic metamaterials.

We report that hybridizing semiconductor quantum dots with plasmonic metamaterial leads to a multi-fold intensity increase and narrowing of their photoluminescence spectrum. The luminescence enhancement is a clear manifestation of the cavity quantum electrodynamics Purcell effect that can be controlled by the metamaterial's design. This observation is an essential step towards understanding loss compensation in metamaterials with gain media and for developing metamaterial-enhanced gain media.Control of Joule losses is a key challenge for plasmonic and metamaterial technologies. Losses hamper the development of negative index media for super-resolution and optical cloaking devices, and plasmonic data processing circuits. Lowering losses is also crucially important for the performance of spectral filters, delay lines and, in fact, practically any other metamaterial and plasmonic applications [1]. Although using superconducting metamaterials can largely eliminate losses in THz and microwave metamaterials [2], Joule losses at optical frequencies are unavoidable. Recent works report compensation of losses with gain in metamaterials aggregated with semiconductor quantum dots (QDs) [3] and organic dyes [4] embedded into the metal nanostructures. Parametric metamaterials gain systems are also under investigation in theory [5][6][7]. Another grand goal of active metamaterials research is to improve laser gain media and to develop a 'lasing spaser' device: a 'flat' laser with emission fueled by plasmonic excitations in an array of coherently emitting meta-molecules [8]. An essential part of this development shall be the study of luminescence of active material hybridized with plasmonic nanostructures that could support collective, coherent plasmonic excitations in the lasing spaser. Here we report the first study of photoluminescence of semiconductor QDs hybridized with asymmetric split-ring plasmonic metamaterial. This type of metamaterial supports a closed-mode Fano-type excitation which has the key characteristics required for the lasing spaser application: the mode is formed by collective interactions between individual meta-molecules that shall ensure coherent laser action [9]. In this letter, we experimentally demonstrate that the photoluminescence properties of QDs can be greatly enhanced by the plasmonic metamaterial. Figure 1(a) schematically illustrates a plasmonic metamaterial combined with QDs. The metamaterials studied here consist of periodic arrays of asymmetrically split ring slits (negative structure), which have been successfully applied to switching, nonlinear and sensor applications [10]. The metamaterial arrays with a total size of 40 × 40 µm each were fabricated by focused ion beam milling in a 50nm-thick gold film on a glass substrate [see inset of Fig. 1(b)]. In order to systematically investigate the correlation between QD photoluminescence spectrum and the spectral position of the Fano plasmonic metamaterial resonance, we manufactured five metamaterial arrays with different unit cell sizes rangin...

The development of metamaterials, data processing circuits and sensors for the visible and ultraviolet parts of the spectrum is hampered by the lack of low-loss media supporting plasmonic excitations. This has driven the intense search for plasmonic materials beyond noble metals. Here we show that the semiconductor Bi 1.5 Sb 0.5 Te 1.8 Se 1.2 , also known as a topological insulator, is also a good plasmonic material in the blue-ultraviolet range, in addition to the already-investigated terahertz frequency range. Metamaterials fabricated from Bi 1.5 Sb 0.5 Te 1.8 Se 1.2 show plasmonic resonances from 350 to 550 nm, while surface gratings exhibit cathodoluminescent peaks from 230 to 1,050 nm. The observed plasmonic response is attributed to the combination of bulk charge carriers from interband transitions and surface charge carriers of the topological insulator. The importance of our result is in the identification of new mechanisms of negative permittivity in semiconductors where visible range plasmonics can be directly integrated with electronics.

Periodic nanostructuring can enhance the optical nonlinearity of plasmonic metals by several orders of magnitude. By patterning a gold film, the largest sub-100 femtosecond nonlinearity is achieved, which is suitable for terahertz rate all-optical data processing as well as ultrafast optical limiters and saturable absorbers.