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Epsilon near zero metamaterials for ultra low power nonlinear applications

Epsilon near zero metamaterials for ultra low power nonlinear applications

Epsilon-near-zero metamaterial samples, composed of five alternating bi-layers of silica and silver, are fabricated using the electron-beam evaporator. Nonlinear properties of samples are measured using a pulsed Ti:sapphire laser by the z-scan technique. It is observed that the real part of the nonlinear Kerr index is one order of magnitude higher than the values expected from a naive averaging of the corresponding coefficients of metal and dielectric layers (the correct averaging should be performed with respect to the nonlinear susceptibility), so that its value is actually of the same order of magnitude as that of a single silver layer. At the same time, the transmission of our samples is remarkably higher than that of a single silver layer of the same thickness. These characteristics have a great impact on the amount of optical energy which can be pumped into the structure, thus allowing its nonlinear properties to be accumulated over long propagation distance along the sample. This property is very promising for applications, which are based on the modulation of phase, amplitude or frequency of light, especially those which require low-power operations, such as all-optical switching and memory elements.
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Optically induced metal to dielectric transition in Epsilon Near Zero metamaterials

Optically induced metal to dielectric transition in Epsilon Near Zero metamaterials

Epsilon-Near-Zero materials exhibit a transition in the real part of the dielectric permittivity from positive to negative value as a function of wavelength. Here we study metal-dielectric layered metamaterials in the homogenised regime (each layer has strongly subwavelength thickness) with zero real part of the permittivity in the near-infrared region. By optically pumping the metamaterial we experimentally show that close to the Epsilon-Near-Zero (ENZ) wavelength the permittivity exhibits a marked transition from metallic (negative permittivity) to dielectric (positive permittivity) as a function of the optical power. Remarkably, this transition is linear as a function of pump power and occurs on time scales of the order of the 100 fs pump pulse that need not be tuned to a specific wavelength. The linearity of the permittivity increase allows us to express the response of the metamaterial in terms of a standard third order optical nonlinearity: this shows a clear inversion of the roles of the real and imaginary parts in crossing the ENZ wavelength, further supporting an optically induced change in the physical behaviour of the metamaterial.
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One dimensional chirality : strong optical activity in epsilon near zero metamaterials

One dimensional chirality : strong optical activity in epsilon near zero metamaterials

tude of the magnetoelectric coupling term relative to the local dielectric contribution from the y component of the first of Eq. (3) and evaluated at z ¼ L − in the same situation of Figs. 2(a) – 2(b), and ρ shows a marked peak around λ ¼ 0 . 51 μ m reaching the maximum of 1.2. The same mechanism can also be grasped from the expression of the extraordinary eigenwaves where it is evident that the first order parameter ruling the effect of 1D chirality on the electromagnetic field is κ=ϵ ⊥ rather than κ and this produces the enhancement of optical activity in the epsilon-near-zero regime. In Fig. 3(d), we plot the percentage difference Δ and δΦ as functions of the angle θ for λ ¼ 0 . 5 μ m. Note that the circular dichroism and birefringence are completely absent for θ ¼ 0 deg [black
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Gain Enhancement of a Millimeter Wave Antipodal Vivaldi Antenna by Epsilon-Near-Zero Metamaterial

Gain Enhancement of a Millimeter Wave Antipodal Vivaldi Antenna by Epsilon-Near-Zero Metamaterial

In this section, the design of the proposed ENZ metamaterial is discussed. The ENZ metamaterial in the present case is composed of periodic patches printed on a dielectric slab with a periodicity which is much smaller than the operating wavelength. By controlling the shape of these patches and the spacing between them, it is possible to control the resulting equivalent dielectric permittivity. In the present case, the epsilon near zero has only one component of permittivity tensor close to zero. Fig. 1 shows the geometry of the proposed unit cell obtained from [25]. The dimensions of this unit cell are presented in Table 1. Two dimensions, a and b, are varied to tune this unit cell for the required operating frequency range. These cells are periodic in the x-direction, and the proposed epsilon near zero is obtained in the y-direction [26]. This unit cell corresponds to an equivalent LC circuit. The quasi mender line in the x-direction corresponds to the inductive part while the parallel y-arms corresponds to the capacitive effect between the adjacent cells. The dimensions of the unit cell are optimized here to operate in the Ka frequency band. The substrate is assumed to be Rogers RO4003C with a dielectric constant ε r = 3.38,
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Large optical nonlinearity of nanoantennas coupled to an epsilon near zero material

Large optical nonlinearity of nanoantennas coupled to an epsilon near zero material

Over the years several approaches have been ex- plored to enhance the intrinsic nonlinear optical re- sponse of materials, including local field enhance- ment using composite structures [3, 4, 5], plasmonic structures [6, 7], and metamaterials [8, 9, 10, 11]. However, these techniques offer only limited control over the magnitude (and sign when applicable) of the wavelength-dependent nonlinear response, and typi- cally involve a trade-off between the strength of the nonlinearity and the spectral position of the peak nonlinear response. It has been reported recently that materials with vanishingly small permittivity – commonly known as epsilon-near-zero or ENZ mate- rial – exhibit intriguing linear [12, 13, 14, 15, 16] and large nonlinear responses [17, 18, 19, 20, 21]. How- ever, an ENZ material has a large nonlinear response over only a relatively narrow spectral range. Fur- thermore, the zero-permittivity wavelength, strength of the nonlinear response, and the losses depend on the optical properties of the ENZ material. In com- parison to previous works [17, 18] where strong non- linear responses were reported in ENZ materials, here we show that many of these constraints can be over- come by incorporating engineered nanostructures on an ENZ host material. Specifically, we report a new approach to engineer an optical medium with an un- precedentedly large intensity-dependent refractive in- dex using nanoantennas coupled to a thin ENZ mate- rial. The simple design concepts presented here pro- vide an exquisite control to engineer the sign and the magnitude of the nonlinear refractive index, and can be used in an all-dielectric CMOS-compatible fabrica- tion process to miniaturize non-linear optical devices
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Enhanced nonlinear effects in pulse propagation through epsilon near zero media

Enhanced nonlinear effects in pulse propagation through epsilon near zero media

During the last decade the metamaterial route for achiev- ing unusual electromagnetic properties has attracted a great deal of interest in both theoretical and applied research, since it has brought to light novel electromagnetic regimes [1–6], and has suggested a number of remarkable devices for extreme manipulation of the radiation [7–9]. Structures exhibiting very small dielectric permittivity, or epsilon- near-zero (ENZ) metamaterials [10–15], belong to the fam- ily of media able to affect electromagnetic radiation in a very unconventional way because the medium’s effective wavelength is much larger than the vacuum wavelength, and because they host a regime where both field amplitude and phase are slowly-varying over relatively large portions of the bulk, which is quite opposite to geometrical optics. Such key feature has been exploited to conceive setups where ultra-narrow ENZ channels are able to ”squeeze” electromagnetic waves at will [16–19], and to develop new paradigms of devices for tailoring the antenna radiation pattern [20–22]. In addition, ENZ metamaterials have also been shown to support a rich phenomenology of surface waves [23–29], to achieve perfect absorption [30], to en- hance spatial dispersion effects [31], and to support novel cloaking mechanisms [32, 33].
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Design of a Reflectarray Antenna Using Graphene and Epsilon-Near-Zero Metamaterials in Terahertz Band

Design of a Reflectarray Antenna Using Graphene and Epsilon-Near-Zero Metamaterials in Terahertz Band

Abstract—In this paper, a graphene-based reflectarray antenna using ENZ (Epsilon-Near-Zero) metamaterial at terahertz (THz) band is proposed, and the performance of its unitcell is investigated. Then, the phase distribution and radiation pattern of the antenna are examined. Benefiting from exceptional complex surface conductivity of graphene which is a novel 2-d material, the size reduction of reflectarray has been facilitated as a result of plasmonic mode propagation within the structure which in turn leads to an increase in propagation constant. Moreover, tunneling phenomenon in ENZ material, a kind of metamaterial which has a relative permittivity under 1, helps reduce the loss. Taking advantage of these outstanding features of both materials, the proposed reflectarray is designed to function at 1 THz and is composed of 150 × 150 elements with square-shape configuration. We have achieved 40 dB of gain using the combination of graphene and ENZ material in reflectarrays, and also it is the first time that they are used together in the reflectarray. This work mainly focuses on the impact of using ENZ material and graphene simultaneously which is not done before, then the results demonstrate that it has a considerable effect on increasing the reflectarray gain.
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Optically induced metal-to-dielectric transition in epsilon-near-zero metamaterials

Optically induced metal-to-dielectric transition in epsilon-near-zero metamaterials

Epsilon-Near-Zero materials exhibit a transition in the real part of the dielectric permittivity from positive to negative value as a function of wavelength. Here we study metal-dielectric layered metamaterials in the homogenised regime (each layer has strongly subwavelength thickness) with zero real part of the permittivity in the near-infrared region. By optically pumping the metamaterial we experimentally show that close to the Epsilon-Near-Zero (ENZ) wavelength the permittivity exhibits a marked transition from metallic (negative permittivity) to dielectric (positive permittivity) as a function of the optical power. Remarkably, this transition is linear as a function of pump power and occurs on time scales of the order of the 100 fs pump pulse that need not be tuned to a specific wavelength. The linearity of the permittivity increase allows us to express the response of the metamaterial in terms of a standard third order optical nonlinearity: this shows a clear inversion of the roles of the real and imaginary parts in crossing the ENZ wavelength, further supporting an optically induced change in the physical behaviour of the metamaterial.
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A Novel Epsilon Near Zero (Enz) Tunneling Circuit Using Microstrip Technology for High Integrability Applications

A Novel Epsilon Near Zero (Enz) Tunneling Circuit Using Microstrip Technology for High Integrability Applications

field confinement in narrow channels and tight bends using ε-near- zero metamaterials. Brain Edwards et al. [5], proved Epsilon-Near- Zero metamaterial coupling and energy squeezing effect experimentally using a microwave waveguide. To date, ENZ tunnels have been realized with waveguide feeds, which derive in cumbersome structures. For high integrability MMIC devices, different 2-D approaches should be used such as microstrip or coplanar feeds.

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Enhanced asymmetric transmission in hyperbolic epsilon near zero slabs

Enhanced asymmetric transmission in hyperbolic epsilon near zero slabs

Media with very small permittivity exhibit a number of unique electromagnetic features providing a platform for the radiation manipulation at subwavelenght scales [1]. Epsilon-near-zero (ENZ) condition supports a static-like regime at a given frequency arising from the “stretching” of the wavelength and this key ingredient has an enormous impact for nanophotonics applications shrinking, for example, the device size [3, 4]. Static-like features of the ENZ regime have been exploited to achieve an enormous variety of phenomena such as tunneling of electromagnetic waves through narrow channels [5], slow-light [6, 7], and several photonics devices such as highly directive emitters [8], geometry-invariant resonant cavities [9], ultrafast switching devices [10, 11] and ENZ modulators [12, 13].
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Analysis of Epsilon-Near-Zero Metamaterial Super-Tunneling Using Cascaded Ultra-Narrow Waveguide Channels

Analysis of Epsilon-Near-Zero Metamaterial Super-Tunneling Using Cascaded Ultra-Narrow Waveguide Channels

Metamaterials with permittivity or epsilon near zero (ENZ) have attracted much attention from academic and engineering areas due to their unconventional electromagnetic features which can lead to intriguing potential applications, e.g., transparency and cloaking devices and antenna patterning shaping [1–6]. Dispersion relation of rectangular waveguides was employed to realize an ENZ metamaterial at particular frequencies [7], because effective permittivity is approaching zero when frequency is near waveguide cutoff. With the method proposed by Engheta’s group [8], an ultra- narrow waveguide channel connecting two larger waveguide sections, equivalently viewed as a section of the waveguide filled with ENZ metamaterial, exhibits an intriguing phenomenon, which has been experimentally demonstrated that the wave is capable of propagating
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Degenerate optical nonlinear enhancement in epsilon-near-zero transparent conductive oxides

Degenerate optical nonlinear enhancement in epsilon-near-zero transparent conductive oxides

Following the idea of increasing optical nonlinearities even further, we notice that TCOs allow to engineer the material dielectric permittivity so that it approaches zero at fundamental operational wavelengths across the telecom band. This can be attained by altering fabrication parameters and material stoichiometry. These Epsilon-Near-Zero (ENZ) conditions bring the optical nonlinearities to unprecedented levels. In certain cases, for high pump intensity, the optically induced change in the complex refractive index can be fitted to a semi-empirical model accounting for the standard Taylor series expansion of the dielectric polarization density inclusive of higher-order nonlinear susceptibility terms up to χ (7) [12–14]. These
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Polarization Insensitive Surface Plasmon Polarization Electro Absorption Modulator Based on Epsilon Near Zero Indium Tin Oxide

Polarization Insensitive Surface Plasmon Polarization Electro Absorption Modulator Based on Epsilon Near Zero Indium Tin Oxide

CMOS-compatible plasmonic modulators operating at the telecom wavelength are significant for a variety of on-chip applications. Relying on the manipulation of the transverse magnetic (TM) mode excited on the metal-dielectric interface, most of the previous demonstrations are designed to response only for specific polarization state. In this case, it will lead to a high polarization dependent loss, when the polarization-sensitive modulator integrates to a fiber with random polarization state. Herein, we propose a plasmonic modulator utilizing a metal-oxide indium tin oxide (ITO) wrapped around the silicon waveguide and investigate its optical modulation ability for both the vertical and horizontal polarized guiding light by tuning electro-absorption of ITO with the field-induced carrier injection. The electrically biased modulator with electron accumulated at the ITO/oxide interface allows for epsilon-near-zero (ENZ) mode to be excited at the top or lateral portion of the interface depending on the polarization state of the guiding light. Because of the high localized feature of ENZ mode, efficient electro-absorption can be achieved under the “ OFF ” state of the device, thus leading to large extinction ratio (ER) for both polarizations in our proposed modulator. Further, the polarization-insensitive modulation is realized by properly tailoring the thickness of oxide in two different stacking directions and therefore matching the ER values for device operating at vertical and horizontal polarized modes. For the optimized geometry configuration, the difference between the ER values of two polarization modes, i.e., the Δ ER, as small as 0.01 dB/ μ m is demonstrated and, simultaneously with coupling efficiency above 74%, is obtained for both polarizations at a wavelength of 1.55 μ m. The proposed plasmonic-combined modulator has a potential application in guiding and processing of light from a fiber with a random polarization state.
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Epsilon near zero metamaterials for optoelectronic applications

Epsilon near zero metamaterials for optoelectronic applications

behaves as an effective medium with an average permittivity close to zero, and we show that this ENZ medium can enhance the emission of quantum dots. This approach generally requires nanofabrication techniques developed for flat and rigid substrates, for example, the electron beam evaporation, which are not always applicable to micro- and macroscopic devices with arbitrary shapes. To surpass these limitations, we design and experimentally demonstrate an optical free- standing and low-loss ENZ membrane in the visible range, by layering polymer (SU-8) and Ag nano-layers. Additionally, we propose a method to introduce both flexibility and electrical tunability into ENZ media by replacing the metal layer with a 2D material, graphene, in the multilayer model. The other way to obtain an ENZ response is using natural materials which operate in prox- imity of their plasma frequency, typically here the indium tin oxide (ITO) at the near-infrared range. The ITO thin films are deposited using radio frequency magnetron sputtering, and their permittivities are manipulated via controlling fabrication parameters. We succeed in sweeping the zero-permittivity frequency of ITO media by controlling the gas recipe and deposition temperature during the sputtering process. To obtain specific optical responses, the ENZ ITO thin films are designed to be combined with different photonic features, including nanoantenna on microsphere and nanohelix, associated with a direct fabrication approach based on electron beam induced deposition (EBID).
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Two Types of Localized States in a Photonic Crystal Bounded by an Epsilon Near Zero Nanocomposite

Two Types of Localized States in a Photonic Crystal Bounded by an Epsilon Near Zero Nanocomposite

Reflectance spectra of the PhC/nanocomposite structure at the normal incidence of light onto the sample at different nanocomposite filling factors.. The nanocomposite layer thickness is.[r]

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Enhanced nonlinear refractive index in ε near zero materials

Enhanced nonlinear refractive index in epsilon-near-zero materials

The linear properties of these “ϵ-near-zero” (ENZ) materials have been investigated [15–32] for applications ranging from controlling the radiation pattern of electro- magnetic sources to novel waveguiding regimes and perfect absorption. Similarly, the nonlinear properties have also been shown to be largely affected by the ENZ condition [33 – 40], and recently it has been theoretically predicted that the interplay between linear and nonlinear properties of ENZ bulk materials may allow three-dimensional self- trapping of light [41]. However, experimental evidence reported so far is limited to phase matching-free conditions in four-wave mixing [42], enhanced third and second har- monic generation[43 – 45], and ultrafast optical switching [46]. In order to illustrate how the nonlinear Kerr index may be enhanced as a result of the ENZ linear properties, we employed a 900 nm thick film of oxygen-deprived alu- minium-doped zinc oxide (AZO) [46,47]. The AZO 900 nm thick thin film was deposited by pulsed laser deposition (PVD Products, Inc.) [48,49] using a KrF excimer laser (Lambda Physik GmbH) operating at a wavelength of 248 nm for source material ablation (see Ref. [47] for more details).
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Prediction of Term Structure with Potentially Misspecified Macro Finance Models near the Zero Lower Bound

Prediction of Term Structure with Potentially Misspecified Macro Finance Models near the Zero Lower Bound

Figure 6 shows the QTSM prediction of the macro factors and the bond yields during the corresponding two forecasting periods. For the in-sample prediction in 1992Q4 - 1998Q1, the QTSM produces a less accurate forecast as with the ATSM model as in Figure 6(a). Moreover, the prediction density is positively skewed because the bond yields are bounded below by zero due to the imposition of non-negative short rate in QTSM. The strength of the QTSM is found to be prominent during the period of 2003Q4 - 2008Q3 when the zero lower bound is binding: the prediction produces only positive bond yields even though the short-term interest rate is extremely close to zero as in Figure 6(b). From the fan chart of the QTSM predictive density, we can observe that the probability mass near zero is significant even for mediam-term to long-term forecasting horizons. This reflects the stickiness nature of the QTSM which allows one to capture the persistence of the zero interest rate policy (Kim and Singleton, 2012).
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Maintenance-energy requirements and robustness of Saccharomyces cerevisiae at aerobic near-zero specific growth rates

Maintenance-energy requirements and robustness of Saccharomyces cerevisiae at aerobic near-zero specific growth rates

of fermentative capacity has previously been observed during prolonged cultivation of S. cerevisiae in aero- bic, glucose-limited chemostat cultures (50  % after 100 generations) [61]. This loss was attributed to mutations that reduced the metabolic burden of synthesizing large amounts of glycolytic proteins. Although retentostat- grown cells retained a high glycolytic capacity, this decreased by ca. 40  % at extremely low specific growth rates. It is, however, unlikely that evolutionary adapta- tion caused this reduction in glycolytic capacity, since the average number of generations in the retentostat experi- ments was approximately three as a consequence of the biomass retention. Instead, the reduced mRNA levels of several glycolytic genes suggest a transcriptional down- regulation of this key pathway at extremely low growth rates. Furthermore, glycolytic genes PGK1 and PYK1 that are considered to be constitutively expressed at high lev- els [62], displayed ca. twofold reduced transcript levels at near-zero growth (Fig.  8), and shows that glycolytic promoters for the expression of (heterologous) proteins should be carefully selected.
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Simple  construction  of  epsilon-biased  distribution

Simple construction of epsilon-biased distribution

A restricted but common form of the identity polynomial testing problem is: given a degree n univariate binary polynomial m(x), check if m(x) is identically zero. This task is trivial if m(x) is explicitly given as a sum of monomials, however in many cases m(x) is given in an implicit form, including a product of many polynomials or an arithmetic circuit.

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Article Ablation-Dominated Arcs in CO2 Atmosphere - Part I: Temperature Determination near Current Zero

Article Ablation-Dominated Arcs in CO2 Atmosphere - Part I: Temperature Determination near Current Zero

Abstract: Wall–stabilized arcs dominated by nozzle–ablation are key elements of self–blast circuit breakers. In the present study, high–current arcs were investigated using a model circuit breaker (MCB) in CO2 as gas alternative to SF6 and in addition a long polytetrafluoroethylene nozzle under ambient conditions for stronger ablation. The assets of different methods for optical investigation were demonstrated, e.g. high-speed imaging with channel filters and optical emission spectroscopy. Particularly the phase near current zero (CZ) crossing was studied in two steps. In the first step using high-speed cameras, radial temperature profiles have been determined until 0.4 ms before CZ in the nozzle. Broad temperature profiles with a maximum of 9400 K have been obtained from analysis of fluorine lines. In the second step, the spectroscopic sensitivity was increased using an intensified CCD camera, allowing single-shot measurements until few microseconds before CZ in the MCB. Ionic carbon and atomic oxygen emission were analyzed using absolute intensities and normal maximum. The arc was constricted and the maximum temperature decreased from >18000 K at 0.3 ms to about 11000 K at 0.010 ms before CZ. The arc plasma needs about 0.5-1.0 ms after both the ignition phase and the current zero crossing to be completely dominated by the ablated wall material.
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