Losses In Metamaterials Research Articles

Dispersed and Encapsulated Gain Medium in Plasmonic Nanoparticles: a Multipronged Approach to Mitigate Optical Losses

The performance of all metamaterial-based applications is significantly limited by the inherent and strong energy dissipation present in metals, especially in the visible range. In fact, these materials suffer from rather strong damping of the plasmon fields which can become obstructive for most optical and photonic applications. Therefore, eliminating losses in optical metamaterials is critical for enabling their numerous potential applications. We experimentally demonstrate that the incorporation of gain material (fluorophores) in the high-local-field areas of a metamaterial subunits (gold core/silica shell nanoparticles) makes it possible to induce resonant energy transfer processes from gain units to plasmonic nanoparticles. A comparison between gain-assisted (nanoparticle-dye dispersion) and gain-functionalized (dye encapsulated into the shell) systems is reported. Fluorescence quenching and time-resolved spectroscopy along with modification of Rayleigh scattering and transmission of a probe beam as a function of impinging energy are key evidence of the strong coupling occurring between NPs and gain medium. The multipronged approach used to compensate losses in these metal-based subunits permits one to obtain important advances in materials science and paves the way toward further promising scientific research aimed to enable the wide range of electromagnetic properties of optical metamaterials.

Photonic gap vanishing in one-dimensional photonic crystals with single-negative metamaterials

The properties of photonic band gap in one-dimensional photonic crystals composed of single-negative metamaterials are studied theoretically. Our study shows that the photonic gap will vanish at a certain incident angle when both the phase-match and impedance-match conditions are satisfied simultaneously, suggesting that the bandwidth and location of the photonic gap are strongly dependent on the incident angle and polarization. However, the photonic gap will not vanish and may become insensitive to the incident angle when the two match conditions cannot be met. Our study also shows that losses in metamaterials have little effect on the properties of the photonic gap.

Sub-Wavelength Elliptical Patch Antenna Loaded With <formula formulatype="inline"><tex Notation="TeX">$\mu$</tex></formula>-Negative Metamaterials

Following our recent findings on the possibility of squeezing the resonant dimensions of circular patch antennas by using negative-permeability loadings, here we theoretically and numerically analyze sub-wavelength elliptical patch antennas partially loaded with magnetic metamaterials. First, we formulate a general theory for inhomogeneously loaded subwavelength elliptical patch antennas, deriving a closed-form solution for the modes supported by this geometry in the long wavelength limit. Our theory proves that their resonant size may be in principle squeezed to any arbitrarily small dimension, provided that the properties of the loading metamaterial are properly tailored. Then, we highlight several advantages offered by the elliptical shape: two orthogonal modes may be independently excited within a subwavelength volume, providing large flexibility in the design, and more degrees of freedom compared to the circular geometry. In particular, the odd mode is shown to provide better gain than the circular case, due to larger aperture efficiency. Full-wave simulations, considering a finite ground plane, realistic feed and the influence of metamaterial loss, prove that the elliptical geometry presents great potentials for a variety of electrically small low-profile antenna applications.

Loss and gain in metamaterials

Results of studies in the influence of losses on the superresolution achievability are presented. The studies involve modeling and realization of superresolution devices. It is found that rigorous electrodynamic models that are not based on homogenization of composites can be effectively used in modeling devices with metamaterials. The possibilities to compensate losses in near-optic metamaterials by means of active inclusions or active medium are discussed and the active material design is presented. Alternatively, what we believe to be new designs are suggested for applications where losses are desirable.

Losses in metamaterials: Restrictions and benefits

Results of studies in the influence of losses on the superresolution achieveability are presented. The studies involve modeling and realization of superresolution devices. It is found that rigorous electrodynamic models that are not based on homogenization of composites can be effectively used in modeling devices with metamaterials. The possibilities to compensate losses in near-optic metamaterials by means of “active” inclusions are discussed; they appear to be rather doubtful. Alternatively, new designs are suggested for applications where losses are desirable.

Ultrahigh Purcell factors and Lamb shifts in slow-light metamaterial waveguides

Employing a medium-dependent quantum optics formalism and a Green function solution of Maxwell's equations, we study the enhanced spontaneous emission factors (Purcell factors) and Lamb shifts from a quantum dot or atom near the surface of a %embedded in a slow-light metamaterial waveguide. Purcell factors of approximately 250 and 100 are found at optical frequencies for $p-$polarized and $s-$polarized dipoles respectively placed 28\thinspace nm (0.02\thinspace $\lambda_{0}$) above the slab surface, including a realistic metamaterial loss factor of $\gamma /2\pi =2 \mathrm{THz}$. For smaller loss values, we demonstrate that the slow-light regime of odd metamaterial waveguide propagation modes can be observed and related to distinct resonances in the Purcell factors. Correspondingly, we predict unusually large and rich Lamb shifts of approximately -1 GHz to -6 GHz for a dipole moment of 50 Debye. We also make a direct calculation of the far field emission spectrum, which contains direct measurable access to these enhanced Purcell factors and Lamb shifts.

Reducing ohmic losses in metamaterials by geometric tailoring

Losses in metamaterials render the applications of such exotic materials less practical unless an efficient way of reducing them is found. We present two different techniques to reduce ohmic losses at both lower and higher frequencies, based on geometric tailoring of the individual magnetic constituents. We show that an increased radius of curvature, in general, leads to the least losses in metamaterials. Particularly at higher THz frequencies, bulky structures outperform the planar structures.

A Method of Analyzing Transmission Losses in Left-Handed Metamaterials

A method of analyzing transmission loss in left-handed metamaterials (LHMs) is proposed. As a demonstration of this method, transmission loss of LHMs composed of split-ring resonators (SRR) and conducting wires is studied. By means of retrieving and analyzing the effective constitutive parameters, different transmission losses as well as their origins are studied. The results show that the left-handed bandwidth is narrowed because of high loss caused by the non-zero high imaginary parts of the effective permeability and permittivity. In the effective left-handed band, the radiation loss is very low and can be neglected, and the transmission losses are the sum of the substrate loss and the ohmic loss. Moreover, when the dielectric loss tangent of the substrate is greater than 0.003, the substrate loss is higher than the ohmic loss.

Manipulating the loss in electromagnetic cloaks for perfect wave absorption

We examine several ways to manipulate the loss in electro-magnetic cloaks, based on transformation electromagnetics. It is found that, by utilizing inherent electric and magnetic losses of metamaterials, perfect wave absorption can be achieved based on several popular designs of electromagnetic cloaks. A practical implementation of the absorber, consisting of ten discrete layers of metamaterials, is proposed. The new devices demonstrate super-absorptivity over a moderate wideband range, suitable for both microwave and optical applications. It is corroborated that the device is functional with a subwavelength thickness and, hence, advantageous compared to the conventional absorbers.

AN EXTERNAL CLOAK WITH ARBITRARY CROSS SECTION BASED ON COMPLEMENTARY MEDIUM

Electromagnetic cloak is a device which makes an object \invisible for electromagnetic irradiation in a certain frequency range. Material parameters for the complementary medium-assisted external cylindrical cloak with arbitrary cross section are derived based on combining the concepts of complementary media and transformation optics. It can make the object with arbitrary shape outside the cloaking domain invisible, as long as an \antiobject is embedded in the complementary layer. The external cloaking efiect has been verifled by full-wave simulation. Moreover, the efiect of metamaterial losses is studied, and small losses less than or equal to 0.01 do not disturb the cloaking efiect.

Can light be stopped in realistic metamaterials?

Arising from: K. L. Tsakmakidis, A. D. Boardman & O. Hess , 397–401 (2007)10.1038/nature06285 ; Tsakmakidis et al. reply Tsakmakidis et al.1 extend earlier work (for example, refs 2, 3) in proposing a novel metamaterial waveguide structure that can stop broadband light, producing so-called “trapped rainbows”. The authors make the bold assumption that metamaterial loss can be ignored: but material loss, with dispersion, is an inherent feature of negative-index metamaterials (for example, refs 4, 5); any realistic model must include loss and dispersion to satisfy the fundamental principle of causality6. Here we revisit the authors’ predictions1 and show that even when an arbitrarily small metamaterial loss is introduced, it is impossible to stop the light; moreover, we find that all slow-light modes in such structures give impractically large propagation losses.

An efficient way to reduce losses of left-handed metamaterials

We propose a simple and effective way to reduce the losses in left-handed metamaterials by manipulating the values of the effective parameters R, L, and C. We investigate the role of losses of the short-wire pairs and the fishnet structures. Increasing the effective inductance to capacitance ratio, L/C, reduces the losses and the figure of merit can increase substantially, especially at THz frequencies and in the optical regime.

Creating stable gain in active metamaterials

The question of losses in metamaterials that are based upon magnetic resonances deriving from split-ring arrays is addressed through the use of active inclusions designed from diode arrays. A full discussion of the way in which the current-voltage characteristics of the inclusions are deployed to produce gain is given, and the question of the overall stability of the new material is investigated in a quantitative way that is linked to absolute and convective instability. It is shown that instability associated with the inclusion of negative resistance devices can be avoided through a scheme that is approximately scalable from gigahertz to at least the low terahertz regimes. Furthermore, absolute instabilities that potentially complicate any active gain media can be controlled through a suitable choice of the system parameters. The latter step reduces the working frequency window over which spatial gain is available, leading to the need for compromise. Full numerical details are given with the conclusion that construction of such arrays of diode inclusions is possible and that a practical gain window is accessible.

Ultra-smooth metal surfaces generated by pressure-induced surface deformation of thin metal films

We present a mechanical pressing technique for generating ultra-smooth surfaces on thin metal films by flattening the bumps, asperities, rough grains and spikes of a freshly vacuum deposited metal film. The method was implemented by varying the applied pressure from 100 MPa to 600 MPa on an e-beam evaporated silver film of thickness 1000 A deposited on double-polished (100)-oriented silicon surfaces, resulting in a varying degree of film smoothness. The surface morphology of the thin film was studied using atomic force microscopy. Notably, at a pressure of ∼600 MPa an initial silver surface with 13-nm RMS roughness was plastically deformed and transformed to an ultra-flat plane with better than 0.1 nm RMS. Our demonstration with the e-beam evaporated silver thin film exhibits the potential for applications in decreasing the scattering-induced losses in optical metamaterials, plasmonic nanodevices and electrical shorts in molecular-scale electronic devices.

Surface Deformation of Metal Films Under Controlled Pressure for Generating Ultra-flat Metal Surfaces

ABSTRACTWe present a technique to generate ultra-smooth surfaces and direct pattern imprinting on thin metal films by flattening the bumps and spikes of a freshly vacuum deposited metal film. The technique was implemented by using a small footprint mechanical imprint press that has the capability to vary the applied pressure from 100MPa to 600MPa. The mechanical press was incorporated with a tactile force sensor that enabled direct monitoring of the applied pressure. We demonstrated the feasibility of the technique on an e-beam evaporated silver (Ag) metal film with thickness ranging from 150Å (optically thin) to 1000Å (optically thick). The film was deposited on double-polished (100)-oriented silicon surface and double-polished borosilicate glass, resulting in a varying degree of film smoothness. The surface morphology of the pressed thin film was then studied using atomic force microscopy and SEM. Our demonstration with the e-beam evaporated silver thin film exhibits the potential for applications in decreasing the scattering-induced losses in optical metamaterials, plasmonic nanodevices and electrical shorts in molecular-scale electronic devices.

Compensating losses in negative-index metamaterials by optical parametric amplification

Optical parametric amplification controlled by the auxiliary electromagnetic field enables transparency, amplification, and oscillation with no cavity in strongly absorbing negative-index metamaterials. The opposite directions of the wave vector and the Poynting vector in such materials result in extraordinary optical properties, including "backward" phase matching and the generation of entangled pairs of left- and right-handed counterpropagating photons.