Fishnet Metamaterials Research Articles

Dual-Band Terahertz Left-Handed Metamaterial with Fishnet Structure

We present the design of a dual-band left-handed metamaterial with fishnet structure in the terahertz regime. Its left-handed properties are described by the retrieved effective electromagnetic parameters. We introduce an equivalent circuit which offers a theoretical explanation for the left-handed behavior of the dual-band fishnet metamaterial, and investigate its losses receiving higher figure of merit. The design is beneficial to the development of frequency agile and broadband THz materials and devices. The dual-band fishnet metamaterial can be extended to infrared and optical frequency ranges by regulating the structural parameters.

Loss optimization in double fishnet metamaterials at telecommunication wavelengths

A hole shape optimization study was made for a double fishnet metamaterial producing a negative index of refraction within 1.4 - 1.5 µm. It is found that within these wavelengths, elliptical holes offer lower losses as compared to rectangular ones and theoretically produce the best figure of merit (FOM) of approximately 6.

Overcoming Losses with Gain in a Negative Refractive Index Metamaterial

On the basis of a full-vectorial three-dimensional Maxwell-Bloch approach we investigate the possibility of using gain to overcome losses in a negative refractive index fishnet metamaterial. We show that appropriate placing of optically pumped laser dyes (gain) into the metamaterial structure results in a frequency band where the nonbianisotropic metamaterial becomes amplifying. In that region both the real and the imaginary part of the effective refractive index become simultaneously negative and the figure of merit diverges at two distinct frequency points.

Self-consistent calculations of loss-compensated fishnet metamaterials

We present a computational approach, allowing for a self-consistent treatment of three-dimensional (3D) fishnet metamaterial coupled to a gain material incorporated into the nanostructure. We show numerically that one can compensate the losses by incorporating gain material inside the fishnet structure. The pump rate needed to compensate the loss is much smaller than the bulk gain and the figure of merit (FOM = |Re(n)/Im(n)|) increases dramatically with the pump rate. Transmission, reflection, and absorption data, as well as the retrieved effective parameters, are presented for the fishnet structure with and without gain material. Kramers-Kronig relations of the effective parameters are in excellent agreement with the retrieved results with gain.

Fishnet Metamaterials - Rules for refraction and limits of homogenization

The perfectly conducting stacked fishnet metamaterial is studied in this paper. The analysis is based on a combination of the mode matching method together with the generalized eigenvalue problem, and takes into account wave propagation along all three Cartesian axes. The analysis has been developed for a fishnet of square lateral periodicity and for two particular polarizations, namely TE and TM, corresponding to the two most common excitations. The 1D and 2D dispersion characteristics are calculated for both polarizations, showing that the TM waves undergo negative refraction in a narrow frequency band just below Wood's anomaly, whereas TE polarized waves exhibit ordinary positive refraction. Finally, possible homogenization of the fishnet metamaterial is considered, showing that only for small angles of incidence and in the immediate vicinity of Wood's anomaly can the fishnet be seen as homogenizable uniaxial medium.

Influence of the substrate on negative index fishnet metamaterials

We analyze numerically the influence of the dielectric substrate on the optical response and effective macroscopic parameters of fishnet metamaterials. We show that the substrate can suppress the region of the negative refractive index due to the weakening of the gap plasmon associated with the magnetic resonance of the structure. We also demonstrate that the effect of substrate vanishes when the number of the functional layers increases.

Tunable fishnet metamaterials infiltrated by liquid crystals

We analyze numerically the optical response and effective macroscopic parameters of fishnet metamaterials infiltrated with a nematic liquid crystal. We show that even a small amount of liquid crystal can provide tuning of the structures due to reorientation of the liquid crystal director. This enables switchable optical metamaterials, where the refractive index can be switched from positive to negative by an external field. This tuning is primarily determined by the shift in the cut-off wavelength of the holes, with only a small influence due to the change in plasmon dispersion.

Tilted response of fishnet metamaterials at near-infrared optical wavelengths

We study experimentally the transmission properties of ${\text{Au-TiO}}_{2}\text{-Au}$ fishnet metamaterials in the near-infrared spectral range and analyze the change in the transmission resonances at varying angles of incidence and different input polarizations. The results show that the main transmission peak through the fishnet is due to the excitation of hole modes. This high-transmission region is significantly influenced by surface plasmon coupling when the incident electric field has a component normal to the metal plates, while little change with respect to tilt is observed when the electric field is parallel to the two metal films of the fishnet.

Validity of effective material parameters for optical fishnet metamaterials

Although optical metamaterials that show artificial magnetism are mesoscopic systems, they are frequently described in terms of effective material parameters. But due to intrinsic nonlocal (or spatially dispersive) effects it may be anticipated that this approach is usually only a crude approximation and is physically meaningless. In order to study the limitations regarding the assignment of effective material parameters, we present a technique to retrieve the frequency-dependent elements of the effective permittivity and permeability tensors for arbitrary angles of incidence and apply the method exemplarily to the fishnet metamaterial. It turns out that for the fishnet metamaterial, genuine effective material parameters can only be introduced if quite stringent constraints are imposed on the wavelength/unit cell size ratio. Unfortunately they are only met far away from the resonances that induce a magnetic response required for many envisioned applications of such a fishnet metamaterial. Our work clearly indicates that the mesoscopic nature and the related spatial dispersion of contemporary optical metamaterials that show artificial magnetism prohibits the meaningful introduction of conventional effective material parameters.

Modeling the directed transmission and reflection enhancements of the lasing surface plasmon amplification by stimulated emission of radiation in active metamaterials

Simultaneously enhanced reflectance and transmittance greater than 35 dB are demonstrated for the lasing spaser (or spasing) behavior in an active fishnet metamaterial. In mimicking a lasing cavity, an equivalent active slab with Lorentz dispersion for the index of refraction is established to model the spasing metamaterial through the Fabry-Perot effect. Numerical and theoretical results show good agreement in the equal enhancement of reflectance and transmittance as well as the nonmonotonic dependence of the spasing intensity on the gain coefficient. In addition, directed emission of the spasing beam is verified numerically.

Fishnet-Based Metamaterials: Spectral Tuning Through Adsorption Mechanism

In this work we consider the tuning of spectral reflectance of fishnet metamaterials with circular or elliptic apertures due to the presence of dielectric analyte adsorbed within the pores of the dielectric part. We simulated the electromagnetic response of the fishnet metamaterials for the optical range utilizing the finite element method. Our investigation is dedicated to ultrathin, freestanding laminated structures (metal‐dielectric‐metal self-supported nanomembrane sandwiches with nanometric thickness). We also investigated some issues connected with experimental fabrication of the freestanding fishnets for adsorbtion-based sensors.

Parametric investigation and analysis of fishnet metamaterials in the microwave regime

We study through experiments and associated simulations the electromagnetic response of microwave fishnet metamaterials and its dependence on the system's geometrical parameters. Our study verifies the validity of an earlier proposed inductor-capacitor (LC) circuit description of the fishnet design and reveals a left-handed response with high transmittance for a wide variety of geometrical structure parameters. This study paves the way to achieve optimized left-handed fishnet metamaterial designs.

Ultrafast modulation of optical metamaterials

We show by pump-probe spectroscopy that the optical response of a fishnet metamaterial can be modulated on the femtosecond time scale. The modulation dynamics is dominated by pump-induced changes in the constituting dielectric medium, but the strength of modulation is dramatically enhanced through the plasmon resonance. The pump-induced spectral responses of the metamaterial provide understanding on how the resonance is modified by pump excitation. Our study suggests that metamaterials can be used as high-speed amplitude/phase modulators with terahertz-bandwidth.

Analytical theory of wave propagation through stacked fishnet metamaterials

This work analyzes the electromagnetic wave propagation through periodically stacked fishnets from zero frequency to the first Wood's anomaly. It is shown that, apart from Fabry-Perot resonances, these structures support two transmission bands that can be backward under the appropriate conditions. The first band starts at Wood's anomaly and is closely related to the well-known phenomena of extraordinary transmission through a single fishnet. The second band is related to the resonances of the fishnet holes. In both cases, the in-plane periodicity of the fishnet cannot be made electrically small, which prevents any attempt of homogenization of the structure along the fishnet planes. However, along the normal direction, even with very small periodicity transmission is still possible. An homogenization procedure can then be applied along this direction, thus making that the structure can behave as a backward-wave transmission line for such transmission bands. Closed-form design formulas will be provided by the analytical formulation here presented. These formulas have been carefully validated by intensive numerical computations.

Double-negative polarization-independent fishnet metamaterial in the visible spectrum

We show that a second-order magnetic resonance present in the fishnet metamaterial can be enhanced so as to achieve simultaneous negative permittivity and permeability in the visible range. The double-negative behavior leads to reduced losses in this particular fishnet metamaterial. We also study the stacking of several functional layers, verifying the convergence of the refractive index.

Bi-anisotropy of multiple-layer fishnet negative-index metamaterials due to angled sidewalls

Simulation results of near infrared (100- to 200-THz) fishnet-structure negative-index metamaterials (NIMs) with single and multiple functional layers exhibit bi-anisotropy - inhomogeneous asymmetry - due to the presence of a sidewall-angle. The influence of sidewall-angle resulting from realistic fabrication processes is investigated through the retrieved effective parameters by both a three-dimensional finite-difference time-domain (FDTD) method and a rigorous coupled wave analysis (RCWA).

Multiband negative index metamaterials at optical frequencies

Based on the fishnet negative index metamaterials （NIMs） of circular-shaped holes operating at optical frequencies，the influence of modifying the hole shape is studied using the commercial software package CST Microwave studio. Numerical simulations show that，even a tiny modification may lead to broadening of the negative refractive band. So we designed two fishnet NIMs of the gradient holes and half-global holes. Compared with the fishnet NIMs of circular-shaped holes，these two structures can realize negative refraction at multi-frequency bands，and the resonance frequencies exhibit an obvious red-shift. We present a chemical technique for preparing the fishnet NIMs of half-global holes，which is a simple and feasible way to realize multiband negative index metamaterials at optical frequencies.

Numerical simulations of terahertz double-negative metamaterial with isotropic-like fishnet structure

The isotropic-like fishnet metamaterial with an array of cross-shaped holes penetrating through the multiple layers has been numerically studied in the terahertz regime. Its left-handed properties are described by the retrieved effect media parameters and validated by the simulation of a wedge-shaped model. The influences of the various geometrical parameters on the electromagnetic response and the left-handed performance are investigated. This isotropic-like fishnet metamaterial has the advantage of lower losses and higher transmission and holds potential for further applications at higher frequencies.

Light propagation in a fishnet metamaterial

We derive the dispersion relation of Bloch modes in a fishnet metamaterial in the optical frequency domain. The dependence of the longitudinal wave vector component on the transverse one and the frequency, which governs diffraction and dispersive spreading of localized light excitations, respectively, are analyzed. We show that this type of metamaterial exhibits an involved anisotropic behavior with diffraction changing the sign in passing even a zero diffraction point. For completeness we derive furthermore a formal angle-dependent effective refractive index which exhibits discontinuities. Thus we conclude that an effective refractive index tends to get meaningless and that only the dispersion relation predicts reliably light propagation in metamaterials. The results are double checked with those obtained from a retrieval algorithm based on angular resolved reflection/transmission data of a finite slab. Excellent agreement is observed.