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
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
Exploiting the dispersion of the double-negative-index fishnet metamaterial to create a broadband low-profile metallic lens
(Optical Society of America, 2015) Orazbayev, Bakhtiyar; Pacheco-Peña, Víctor; Beruete Díaz, Miguel; Navarro Cía, Miguel; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
Metamaterial lenses with close values of permittivity and permeability usually display low reflection losses at the expense of narrow single frequency operation. Here, a broadband low-profile lens is designed by exploiting the dispersion of a fishnet metamaterial together with the zoning technique. The lens operates in a broadband regime from 54 GHz to 58 GHz, representing a fractional bandwidth ~7%, and outperforms Silicon lenses between 54 and 55.5 GHz. This broadband operation is demonstrated by a systematic analysis comprising Huygens-Fresnel analytical method, full-wave numerical simulations and experimental measurements at millimeter waves. For demonstrative purposes, a detailed study of the lens operation at two frequencies is done for the most important lens parameters (focal length, depth of focus, resolution, radiation diagram). Experimental results demonstrate diffraction-limited ~0.5λ transverse resolution, in agreement with analytical and numerical calculations. In a lens antenna configuration, a directivity as high as 16.6 dBi is achieved. The different focal lengths implemented into a single lens could be potentially used for realizing the front end of a non-mechanical zoom millimeter-wave imaging system.
Open Access
Experimental demonstration of a millimeter-wave metallic ENZ lens based on the energy squeezing principle
(IEEE, 2015) Torres Landívar, Víctor; Orazbayev, Bakhtiyar; Pacheco-Peña, Víctor; Teniente Vallinas, Jorge; Beruete Díaz, Miguel; Navarro Cía, Miguel; Sorolla Ayza, Mario; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
The performance of an epsilon-near zero (ENZ) plano-concave lens is experimentally demonstrated and verified at the D-band of the millimeter-waves. The lens is comprised of an array of narrow metallic waveguides near cut-off frequency, which effectively behaves as an epsilon-near-zero medium at 144 GHz. A good matching with free space is achieved by exploiting the phenomenon of energy squeezing and a clear focus with a transmission enhancement of 15.9 dB is measured. The lens shows good radiation properties with a directivity of 17.6 dBi and low cross-polar components of -34 dB. All results are supported by numerical simulations.
Open Access
Terahertz epsilon-near-zero graded-index lens
(Optical Society of America, 2013) Torres Landívar, Víctor; Pacheco-Peña, Víctor; Rodríguez Ulibarri, Pablo; Navarro Cía, Miguel; Beruete Díaz, Miguel; Sorolla Ayza, Mario; Engheta, Nader; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa; Gobierno de Navarra / Nafarroako Gobernua, 055/01/11
An epsilon-near-zero graded-index converging lens with planar faces is proposed and analyzed. Each perfectly-electric conducting (PEC) waveguide comprising the lens operates slightly above its cut-off frequency and has the same length but different cross-sectional dimensions. This allows controlling individually the propagation constant and the normalized characteristic impedance of each waveguide for the desired phase front at the lens output while Fresnel reflection losses are minimized. A complete theoretical analysis based on the waveguide theory and Fermat’s principle is provided. This is complemented with numerical simulation results of two-dimensional and three-dimensional lenses, made of PEC and aluminum, respectively, and working in the terahertz regime, which show good agreement with the analytical work.
Open Access
ε-near-zero (ENZ) graded index quasi-optical devices: steering and splitting millimeter waves
(IOP Publishing, 2014) Pacheco-Peña, Víctor; Torres Landívar, Víctor; Beruete Díaz, Miguel; Navarro Cía, Miguel; Engheta, Nader; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Graded index ε near-zero (GRIN-ENZ) quasi-optical components such as beam steerers and power splitters are designed, simulated and analyzed. The GRIN-ENZ medium is realized using stacked narrow hollow waveguides whose infinite array shows the first transmission peak at 1.0002 THz. Several GRIN-ENZ beam steerers to channel a normal incident plane wave to different output angles (15, 45, 65 and 80 deg) with good impedance matching (low reflection) are analytically and numerically demonstrated using planar structures with a thickness of 5λ0 = 1500 μm along z-axis. Moreover, symmetrical and asymmetrical power splitters are designed with output angles (plus/minus 45 deg) and (-80, +35 deg), respectively.
Open Access
All-metallic ε-near-zero (ENZ) lens based on ultra-narrow hollow rectangular waveguides: experimental results
(IEEE, 2014) Orazbayev, Bakhtiyar; Torres Landívar, Víctor; Pacheco-Peña, Víctor; Falcone Lanas, Francisco; Teniente Vallinas, Jorge; Beruete Díaz, Miguel; Sorolla Ayza, Mario; Navarro Cía, Miguel; Engheta, Nader; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
Here we perform numerical and experimental investigation of plano-concave all-metallic ε-near-zero (ENZ) lens with operational frequency f = 144 GHz. The ENZ lens is achieved by stacking an array of narrow hollow rectangular waveguides working near cut-off frequency. Focusing and radiation properties are numerically analyzed and measured. The enhancement of 5.61 dB and directivity of 17.6 dBi are shown. Good agreement between experimental and numerical results is demonstrated.