Open Access
Extraordinary THz transmission with a small beam spot: the leaky wave mechanism
(Wiley, 2018) Navarro Cía, Miguel; Pacheco-Peña, Víctor; Kuznetsov, Sergei A.; Beruete Díaz, Miguel; Institute of Smart Cities - ISC
The discovery of extraordinary optical transmission (EOT) through patterned metallic foils in the late 1990s was decisive for the development of plasmonics and cleared the path to employ small apertures for a variety of interesting applications all along the electromagnetic spectrum. However, a typical drawback often found in practical EOT structures is the large size needed to obtain high transmittance peaks. Consequently, practical EOT arrays are usually illuminated using an expanded (mimicking a plane wave) beam. Here, it is shown with numerical and experimental results in the THz range that high transmittance peaks can be obtained even with a reduced illumination spot exciting a small number of holes, provided that the structure has a sufficient number of lateral holes out of the illumination spot. These results shed more light on the prominent role of leaky waves in the underlying physics of EOT and have a direct impact on potential applications.
Open Access
Zoned fishnet lens antenna with reference phase for side lobe reduction
(IEEE, 2015) Pacheco-Peña, Víctor; Navarro Cía, Miguel; Orazbayev, Bakhtiyar; Minin, Igor V.; Minin, Oleg V.; Beruete Díaz, Miguel; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
Reduction of first side lobe level and nulls in artificial fishnet metalenses is accomplished here by applying the reference phase concept along with the zoning technique. Higher focusing efficiency is achieved for a specific reference phase when comparing numerically and experimentally four different designs. For such best design, an improvement of the first side lobe level (2.4 dB), first null (13 dB) and gain (1.77dB) is achieved experimentally compared to the design without reference phase.
Open Access
Strong lateral displacement in polarization anisotropic extraordinary transmission metamaterial
(IOP Publishing Ltd, 2010) Beruete Díaz, Miguel; Navarro Cía, Miguel; Sorolla Ayza, Mario; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
In this paper, a deep numerical as well as experimental study of the anisotropy response of extraordinary transmission metamaterials constructed by stacking subwavelength hole arrays is presented. Two-dimensional (2D) dispersion diagrams for S- and P-polarization were obtained from simulation. From them, it was found that negative refraction can be obtained for the latter case for small angles of incidence. Additionally, it was found that double periodic and dielectric loaded hole arrays are optimal to enlarge the numerical aperture that leads to negative refraction. Several experiments are then presented in the V-band of the millimetre-wave range that show excellent agreement with the numerical calculations. Moreover, the richness of the anisotropic characteristic exhibited by the stacked hole array structure allows for designing structures with complex electromagnetic response other than solely negative refraction. Thus, the results presented here could be taken as a novel route to achieve exotic behaviour, such as negative refraction at other frequency ranges, like terahertz or the visible.
Open Access
New regimes to achieve enhanced transmission through subwavelength hole arrays
(2011) Navarro Cía, Miguel; Beruete Díaz, Miguel; Sorolla Ayza, Mario; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
In this communication we present millimetre- and THz-waves experimental confirmation of enhanced transmission through subwavelength hole arrays with rectangular lattice when the incident electric field is parallel to the short periodicity.
Open Access
Description of bow-tie nanoantennas excited by localized emitters using conformal transformation
(American Chemical Society, 2016) Pacheco-Peña, Víctor; Beruete Díaz, Miguel; Fernández Domínguez, Antonio I.; Luo, Yu; Navarro Cía, Miguel; Ingeniaritza Elektrikoa eta Elektronikoa; Institute of Smart Cities - ISC; Ingeniería Eléctrica y Electrónica
The unprecedented advance experienced by nano- fabrication techniques and plasmonics research over the past few years has made possible the realization of nanophotonic systems entering into the so-called strong coupling regime between localized surface plasmon (LSP) modes and quantum emitters. Unfortunately, from a theoretical point of view, the field is hindered by the lack of analytical descriptions of the electro- magnetic interaction between strongly hybridized LSP modes and nanoemitters even within the Markovian approximation. This gap is tackled here by exploiting a conformal transformation where a bow-tie nanoantenna excited by a dipole is mapped into a periodic slab−dipole framework whose analytical solution is available. Solving the problem in the transformed space not only provides a straightforward analytical explanation for the original problem (validated using full-wave simulations) but also grants a deep physical insight and simple design guidelines to maximize the coupling between localized dipoles and the bow-tie LSP modes. The results presented here therefore pave the way for a full analytical description of realistic scenarios where quantum dots or dye molecules (modeled beyond a two-level system) are placed near a metallic bow-tie nanoantenna.
Open Access
77-GHz high-gain bull’s-eye antenna with sinusoidal profile
(IEEE, 2015) Beaskoetxea Gartzia, Unai; Pacheco-Peña, Víctor; Orazbayev, Bakhtiyar; Akalin, Tahsin; Maci, Stefano; Navarro Cía, Miguel; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
A high-gain Bull’s-Eye leaky-wave horn antenna working at 77 GHz with sinusoidal profile has been designed, fabricated, and experimentally measured. The influence of the number of periods on the gain and beamwidth is numerically investigated. Experimental measurements show a high gain of 28.9 dB, with low sidelobe level and a very narrow beamwidth in good agreement with results obtained from simulations.
Open Access
Zoned near-zero refractive index fishnet lens antenna: steering millimeter waves
(AIP Publishing, 2014) Pacheco-Peña, Víctor; Orazbayev, Bakhtiyar; Beaskoetxea Gartzia, Unai; Beruete Díaz, Miguel; Navarro Cía, Miguel; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
A zoned fishnet metamaterial lens is designed, fabricated, and experimentally demonstrated at millimeter wavelengths to work as a negative near-zero refractive index lens suitable for compact lens antenna configurations. At the design frequency f=56.7GHz (wavelength = 5.29 mm), the zoned fishnet metamaterial lens, designed to have a focal length FL= 9 wavelengths, exhibits a refractive index n = 0.25. The focusing performance of the diffractive optical element is briefly compared with that of a non-zoned fishnet metamaterial lens and an isotropic homogeneous zoned lens made of a material with the same refractive index. Experimental and numerically-computed radiation diagrams of the fabricated zoned lens are presented and compared in detail with that of a simulated non-zoned lens. Simulation and experimental results are in good agreement, demonstrating an enhancement generated by the zoned lens of 10.7 dB, corresponding to a gain of 12.26 dB. Moreover, beam steering capability of the structure by shifting the feeder on the xz-plane is demonstrated.
Open Access
Lensing system and Fourier transformation using epsilon-near-zero metamaterials
(American Physical Society, 2012) Navarro Cía, Miguel; Beruete Díaz, Miguel; Sorolla Ayza, Mario; Engheta, Nader; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
Metamaterials and metastructures with effective relative permittivity near zero exhibit unusual wave properties such as uniform phase distributions across such domains. Here we discuss the possibility of using ε-near-zero (ENZ) metamaterials for lensing and Fourier transforming. Owing to the possibility of having ENZ metamaterials in different wavelength regimes, the concepts shown here can be utilized at any frequency bands in which such materials can be constructed.
Open Access
Polarization-tunable negative or positive refraction in self-complementariness-based extraordinary transmission prism
(EMW Publishing, 2010) Navarro Cía, Miguel; Beruete Díaz, Miguel; Falcone Lanas, Francisco; Sorolla Ayza, Mario; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
Here we report a prism made of stacked quasi-selfcomplementary extraordinary transmission surfaces which allows simultaneously left- and right-handed propagation within the V-band for vertical and horizontal polarizations, respectively and righthanded propagation within the W-band for both polarizations. The numerical dispersion diagram of the infinite structure and effective indexes of refraction retrieved from S-parameters under normal incidence together with the finite integration time domain simulations predict single negative and double positive birefringence. The unusual type of birefringence single negative and regular double positive birefringence are afterwards demonstrated experimentally at the millimeter-waves (V- and W-bands) by the wedge experiment which lets us check, using a straightforward geometrical method, the refraction of each component. The effective index of refraction is retrieved via the Snell's law and compared to those obtained through the dispersion diagram and the retrieval method from S-parameters computed with the commercial software CST Microwave StudioTM.
Open Access
Comportamiento de propagacion electromagnetica en el apilamiento de agujeros sublambda y agujeros propagantes
(2009) Navarro Cía, Miguel; Beruete Díaz, Miguel; Falcone Lanas, Francisco; Campillo, Igor; Sorolla Ayza, Mario; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
In this work, we provide more insight on the physics underlying the transmission through subwavelength hole arrays metaprism by comparing it with propagating hole arrays prism. We show the critical role that the size of the holes plays in this electromagnetic propagation, changing the effective index of refraction from negative to positive values as the hole diameter increases. This causes negative refraction for the zero-th order emerging beam in the metaprism whereas positive refraction in the non-cut-off holes prism. Experimental results (co- and cross-polar measurements) performed at the V-band of the millimeter waves in the Fresnel zone are well supported by numerical analyses in terms of dispersion diagram, spatial electric field distribution and power flow within the prism along with in the output air zone. As expected, higher order diffracted outgoing beams are recorded for the classical prism but not for the metaprism.