Nanoplasmonic Metamaterials Research Articles

Tunable multiband metamaterial coherent perfect absorber based on graphene and vanadium dioxide

In this paper, we propose a tunable multiband metamaterial coherent perfect absorber, where vanadium dioxide (VO2) square particles are periodically arranged on the two sides of polysilicon–silica–graphene–silica–polysilicon​ structure. The absorption spectrum of our absorber exhibits three peaks with high absorptivity which are originated from the plasmon resonance modes of graphene and VO2 particle. Benefitting from the tunable conductivity of graphene, the adjustment range of the absorption peak based on the first-order plasmon resonance mode of graphene is as much as 7.88μm when the Fermi level of graphene is increased from 0.3 to 1 eV. As VO2 is changed from metal phase to insulating phase, the absorption peak stemming from the plasmon resonance mode of VO2 particle disappears. The modulation depth of absorption peak can achieve up to 98.85% by tuning the relative phase of two coherent light beams. The resonance wavelengths and intensities of absorption peaks are also dependent on the array period, side length of VO2 particle and the thickness of silica layer. In addition, the change of surrounding refractive index causes a shift of the absorption peak corresponding to VO2 particle. Our findings are helpful for the engineering of actively tunable nano plasmonic devices and metamaterials.

On the voltage-controlled assembly of nanoparticle arrays at electrochemical solid/liquid interfaces

Research in the field of nanoplasmonic metamaterials is moving towards more and more interesting and, potentially useful, applications. In this paper we focus on a class of such metamaterials formed by voltage controlled self-assembly of metallic nanoparticale at electrochemical solid |liquid interfaces. We perform a simplified, comprehensive analysis of the stability of a nanoparticle arrays under different conditions and assembly. From the Poisson-Boltzmann model of electrostatic interactions between a metallic nanoparticle and the electrode and between the nanoparticles at the electrode, as well as the Hamaker-Lifshitz theory of the corresponding van der Waals interactions, we reach some conclusions regarding the possibility to build arrays of charged nanoparticles on electrodes and disassemble them, subject to variation of applied voltage. Since systems of this type have been shown, recently, to provide nontrivial electrotuneable optical response, such analysis is crucial for answering the question whether the scenarios of electrochemical plasmonics are feasible.

An electro-tunable Fabry–Perot interferometer based on dual mirror-on-mirror nanoplasmonic metamaterials

Abstract Mirror-on-mirror nanoplasmonic metamaterials, formed on the basis of voltage-controlled reversible self-assembly of sub-wavelength-sized metallic nanoparticles (NPs) on thin metallic film electrodes, are promising candidates for novel electro-tunable optical devices. Here, we present a new design of electro-tunable Fabry–Perot interferometers (FPIs) in which two parallel mirrors – each composed of a monolayer of NPs self-assembled on a thin metallic electrode – form an optical cavity, which is filled with an aqueous solution. The reflectivity of the cavity mirrors can be electrically adjusted, simultaneously or separately, via a small variation of the electrode potentials, which would alter the inter-NP separation in the monolayers. To investigate optical transmittance from the proposed FPI device, we develop a nine-layer-stack theoretical model, based on our effective medium theory and multi-layer Fresnel reflection scheme, which produces excellent match when verified against full-wave simulations. We show that strong plasmonic coupling among silver NPs forming a monolayer on a thin silver-film substrate makes reflectivity of each cavity mirror highly sensitive to the inter-NP separation. Such a design allows the continuous tuning of the multiple narrow and intense transmission peaks emerging from an FPI cavity via electro-tuning the inter-NP separation in situ – reaping the benefits from both inexpensive bottom-up fabrication and energy-efficient tuning.

Optical Properties of Ordered Self-Assembled Nanoparticle Arrays at Interfaces

Nanoplasmonic metamaterials are rapidly finding uses in optical devices. Self-assembled soft matter optical nanostructures are straightforward to manufacture and are low cost, self-healing, and tunable. The simplest way to self-assemble such structures is to bring nanoparticles to interfaces where they can build lattices. While being simple to manufacture, these systems are difficult to model analytically. Here we develop an analytical model that is suitable for interfacial systems, that takes account of interactions of the nanoplasmonic structures at various interfaces and electrodes. The model is applicable to both thin-film and bulk electrodes, and it compares well with numerical calculations. On the basis of our model we propose designs suitable for simple surface-enhanced Raman scattering and optical mirror devices.

Analytic theory of optical nanoplasmonic metamaterials

Recent advances in nanofabrication techniques allow for the manufacture of optical metamaterials, bringing their unique and extraordinary properties to the visible regime and beyond. However, an analytical description of optical nanoplasmonic metamaterials is challenging due to the characteristic optical behavior of metals. Here we present an analytical theory that allows us to bring established microwave metamaterials models to optical wavelengths. This method is implemented for nanoscaled plasmonic wire-mesh and trihelical metamaterials, and we obtain an accurate prediction for their dispersive behavior at optical and near-IR wavelengths.

On the Origin of Chirality in Nanoplasmonic Gyroid Metamaterials

Metallic single gyroids, a new class of self-assembled nanoplasmonic metamaterials, are analyzed on the basis of a tri-helical metamaterial model. The physical mechanisms underlying the chiral optical behavior of the nanoplasmonic single gyroid are identified and it is shown that the optical chirality in this metallic structure is primarily determined by structural chirality and the connectivity of helices along the main cubic axes.

Gain-enhanced nanoplasmonic metamaterials: ultrafast sub-wavelength emitters

Nanoplasmonics and optical metamaterials have in the last 10–15 years emerged as a new paradigm in condensed matter optics and nanoscience, offering a fresh perspective on the world of optics. They enable efficient coupling of electromagnetic fields to the nanoscale: the world of biological and nonbiological molecules.1 This tight localization of light to truly nanoscopic dimensions—well below the diffraction limit for visible light— enhances its interaction with matter, paving the way for a multitude of classical and quantum nano-optics applications. However, metal optics suffer from inherent dissipative losses, which have persistently hampered many of the envisaged uses. Advances in the theoretical understanding and experimental fabrication of gain-enhanced nanoplasmonic metamaterials now promise to overcome these hindrances, potentially leading to novel nanophotonic components and devices. Dissipative losses in nanoplasmonics arise from the interaction of incident photons with quasi-free conduction electrons in metals, and therefore constitute an inherent feature of the responses ofmetal-based nanodevices. For truly sub-wavelength plasmonic structures, these losses follow universal laws, i.e., they do not depend on a particular geometric configuration, but rather only on the type of (usually noble) metal used. Typical damping rates ( ) are of the order of 100ps 1, requiring gain coefficients =c 103–104s 1 to compensate for the losses. As an alternative strategy, optical metamaterials pave the way toward nanoscale control of light at the fabrication level. However, such control needs to be modulated dynamically, on-demand and in real time. Both of the abovementioned challenges can be met by metamaterials with gain incorporated directly into their fabric. Figure 1. Schematic of a gain-enhanced plasmonic nano-fishnet metamaterial together with example profiles of the inversion (lower left) and electric-field amplitude. hm, hc, and hd denote the height of the metal, cladding, and dielectric layers, respectively, ax and ay are the width of the rectangular holes in the x and y direction, and p is the periodicity of the material.

Active nanoplasmonic metamaterials

Optical metamaterials and nanoplasmonics bridge the gap between conventional optics and the nanoworld. Exciting and technologically important capabilities range from subwavelength focusing and stopped light to invisibility cloaking, with applications across science and engineering from biophotonics to nanocircuitry. A problem that has hampered practical implementations have been dissipative metal losses, but the efficient use of optical gain has been shown to compensate these and to allow for loss-free operation, amplification and nanoscopic lasing. Here, we review recent and ongoing progress in the realm of active, gain-enhanced nanoplasmonic metamaterials. On introducing and expounding the underlying theoretical concepts of the complex interaction between plasmons and gain media, we examine the experimental efforts in areas such as nanoplasmonic and metamaterial lasers. We underscore important current trends that may lead to improved active imaging, ultrafast nonlinearities on the nanoscale or cavity-free lasing in the stopped-light regime.

Control and dynamic competition of bright and dark lasing states in active nanoplasmonic metamaterials

Active nanoplasmonic metamaterials support bright and dark modes that compete for gain. Using a Maxwell-Bloch approach incorporating Langevin noise we study the lasing dynamics in an active nano-fishnet structure. We report that lasing of the bright negative-index mode is possible if the higher-Q dark mode is discriminated by gain, spatially or spectrally. The nonlinear competition during the transient phase is followed by steady-state emission where bright and dark modes can coexist. We analyze the influence of pump intensity and polarization and explore methods for mode control.

Coherent Amplification and Noise in Gain-Enhanced Nanoplasmonic Metamaterials: A Maxwell-Bloch Langevin Approach

Nanoplasmonic metamaterials are an exciting new class of engineered media that promise a range of important applications, such as subwavelength focusing, cloaking, and slowing/stopping of light. At optical frequencies, using gain to overcome potentially not insignificant losses has recently emerged as a viable solution to ultra-low-loss operation that may lead to next-generation active metamaterials. Maxwell-Bloch models for active nanoplasmonic metamaterials are able to describe the coherent spatiotemporal and nonlinear gain-plasmon dynamics. Here, we extend the Maxwell-Bloch theory to a Maxwell-Bloch Langevin approach-a spatially resolved model that describes the light field and noise dynamics in gain-enhanced nanoplasmonic structures. Using the example of an optically pumped nanofishnet metamaterial with an embedded laser dye (four-level) medium exhibiting a negative refractive index, we demonstrate the transition from loss-compensation to amplification and to nanolasing. We observe ultrafast relaxation oscillations of the bright negative-index mode with frequencies just below the THz regime. The influence of noise on mode competition and the onset and magnitude of the relaxation oscillations is elucidated, and the dynamics and spectra of the emitted light indicate that coherent amplification and lasing are maintained even in the presence of noise and amplified spontaneous emission.