Open Access
Highly efficient focusing of terahertz waves with an ultrathin superoscillatory metalens: experimental demonstration
(Wiley, 2021-05-06) Legaria Lerga, Santiago; Teniente Vallinas, Jorge; Kuznetsov, Sergei A.; Pacheco-Peña, Víctor; Beruete Díaz, Miguel; Institute of Smart Cities - ISC
The performance of an ultrathin (thickness < 0.04λ 0) metasurface superoscillatory lens (metaSOL) is experimentally demonstrated in the terahertz (THz) range. The metaSOL is designed using two different hexagonal unit cells to improve the efficiency and properties of the conventional transparent–opaque zoning approach. The focusing metastructure produces, at a frequency f exp = 295 GHz, a sharp focal spot 8.9λ exp away from its output surface with a transversal resolution of 0.52λ exp (≈25% below the resolution limit imposed by diffraction), a power enhancement of 18.2 dB, and very low side lobe level (−13 dB). Resolution below the diffraction limit is demonstrated in a broad fractional operation bandwidth of 18%. The focusing capabilities of the proposed metaSOL show its potential use in a range of applications such as THz imaging, microscopy, and communications.
Open Access
Labyrinth metasurface absorber for ultra-high-sensitivity terahertz thin film sensing
(Wiley, 2018) Jáuregui López, Irati; Rodríguez Ulibarri, Pablo; Urrutia Azcona, Aitor; Kuznetsov, Sergei A.; Beruete Díaz, Miguel; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Institute of Smart Cities - ISC; Ingeniería Eléctrica, Electrónica y de Comunicación
In this work, a labyrinth metasurface sensor operating at the low‐frequency edge of the THz band is presented. Its intricate shape leads to a high electric field confinement on the surface of the structure, resulting in ultrasensitive performance, able to detect samples of the order of tens of nanometers at a wavelength of the order of millimeters (i.e., five orders of magnitude larger). The sensing capabilities of the labyrinth metasurface are evaluated numerically and experimentally by covering the metallic face with tin dioxide (SnO2) thin films with thicknesses ranging from 24 to 345 nm. A redshift of the resonant frequency is observed as the analyte thickness increases, until reaching a thickness of 20 μm, where the response saturates. A maximum sensitivity of more than 800 and a figure of merit near 4500 nm−1 are achieved, allowing discriminating differences in the SnO2 thickness of less than 25 nm, and improving previous works by a factor of 35. This result can open a new paradigm of ultrasensitive devices based on intricate metageometries overcoming the limitations of classical metasurface sensor designs based on periodic metaatoms.
Open Access
Labyrinth absorber based on metageometries metasurface for fungi detection
(IEEE, 2020) Jáuregui López, Irati; Rodríguez Ulibarri, Pablo; Kuznetsov, Sergei A.; Beruete Díaz, Miguel; Ingeniería Eléctrica, Electrónica y de Comunicación; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren
In this paper a labyrinth metasurface based in the new paradigm of metageometries is designed to operate in the Terahertz (THz) band as a biosensor. First, a numerical study is carried out to study the performance of the metasurface as a refractometer when working in two different configurations: transmission and reflection. Then, its performance as a fungi detector is evaluated and a comparison with other devices is performed, showing that the sensitivity and Figure of Merit (FOM) can be enhanced by the use of these kind of devices, in comparison with the classical approach of metaatoms. Particularly, the designed structure is able to detect 5 fungi elements arbitrarily distributed on the unit cell, which is equivalent to a concentration of 0.004/μm 2 , improving the results available in the literature by a factor of more than 4.
Open Access
Ultrathin sub-terahertz half-wave plate with high conversion efficiency based on zigzag metasurface
(IEEE, 2020) Moreno-Peñarrubia, Alexia; Kuznetsov, Sergei A.; Beruete Díaz, Miguel; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Institute of Smart Cities - ISC; Ingeniería Eléctrica, Electrónica y de Comunicación; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
In this communication, an ultrathin transmissive half-wave plate (HWP) based on a bi-layered zigzag metasurface operating at the lower frequency edge of the terahertz (THz) spectrum is numerically and experimentally studied. The thickness of HWP is only 100 μm and less than λ /20 at the operation frequency, and it achieves an amplitude transmission efficiency over 90% and a cross-polarization discrimination around 30 dB within a fractional bandwidth near 9%. A detailed analysis of the device robustness with respect to layer misalignments is carried out by designing and fabricating two additional devices with the maximum possible shift between layers along both transverse directions. The results show that the device is extremely robust relative to a misalignment along x and exhibits a frequency shift with misalignments along y , while maintaining in all cases an excellent performance as a HWP. The communication ends with a final study to ascertain a physical mechanism that explains the robustness of the device in regard to misalignments. These results complement and extend the reach of metasurfaces in the emerging THz band.

Beruete Díaz, Miguel

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