309 results found
Ma M, Wang Y, Navarro-Cía M, et al., 2019, The dielectric properties of some ceramic substrate materials at terahertz frequencies, Journal of the European Ceramic Society, ISSN: 0955-2219
The terahertz (THz) dielectric constant (εr') and dielectric loss tangent (tanδ) of the commercial LTCC materials (Ferro A6M and DuPont 951), Al2O3 (ceramic and single crystal), AlN and β-Si3N4 ceramics were measured using a vector network analyzer (VNA) over the frequency range of 140–220 GHz and a time-domain spectrometer (TDS) from 0.2 to 1.0 THz. The results from the two instruments are compared with the literature and show good agreement and consistency. For Ferro A6M, εr' = 6.06, tanδ = 0.012 at 1.0 THz. For DuPont 951, εr' = 7.67, tanδ = 0.097 at 1.0 THz. For Al2O3 ceramic and single crystal, the measured THz dielectric properties are consistent with the reported works. The dielectric constant of AlN (εr' = 8.85) and β-Si3N4 (εr' = 8.41) ceramics in the THz region is a little lower than those reported for the MHz to GHz region. These results provide valuable and much needed reference information for device designers and material scientists.
Razavizadeh SM, Sadeghzadeh R, Ghattan Z, et al., 2019, Compact THz waveguide filter based on periodic dielectric-gold rings, The Fifth International Conference on Millimeter Wave & Terahertz Technologies, Publisher: IEEE, Pages: 42-44, ISSN: 2157-0965
A band pass filter based on hollow circular waveguide loaded with axially periodic dielectric and gold rings is demonstrated for THz frequencies. The presence of coaxial gold rings can introduce the single mode operation due to a high rejection values at the both-sides of pass-band, and an acceptable confinement for the proposed structure. The presented numerical results show that the influences of the gold rings on the propagation properties are significant.
Aznabet M, El Mrabet O, Beruete M, et al., 2019, Chiral SRR metasurfaces for circular polarisation conversion, 18th Mediterranean Microwave Symposium (MMS), Publisher: IEEE, Pages: 404-406, ISSN: 2157-9822
A circular polarization dual band metamaterial polarization rotator composed of two double split ring resonators rotated 90° with respect to each other is presented. Asymmetric transmission between T xx and T yy and symmetric transmission between T xy and T yx has been achieved. The circular polarization is caused by the symmetric transmission between T xy and T yx . The design has been demonstrated numerically at microwaves frequency. The structure holds promise for ultra-compact polarizing devices for any frequency range given the scalability of the approach.
Camacho M, Boix RR, Kuznetsov SA, et al., 2019, Far-Field and Near-Field Physics of Extraordinary THz Transmitting Hole-Array Antennas, IEEE Transactions on Antennas and Propagation, ISSN: 0018-926X
CCBY Despite three decades of effort, predicting accurately extraordinary transmission through subwavelength hole arrays has proven challenging. This lack of quantitative design and modelling able to take into account the inherent complexity of high frequency instrumentation has prevented the development of practical high-performance components based on this phenomenon. This manuscript resorts to the Method of Moments to provide, not only such missing quantitative prediction, but also a theoretical framework to understand and shed more light on the far-field and near-field physics of the extraordinary terahertz (THz) transmission through subwavelength hole arrays under different illumination and detection conditions. An excellent agreement between numerical and experimental results with various illumination and detection setups is obtained, demonstrating the suitability of this computationally efficient modelling tool to predict the response of extraordinary transmission structures in practical situations.
Pacheco-Pena V, Navarro-Cia M, 2018, Understanding quantum emitters in plasmonic nanocavities with conformal transformation: Purcell enhancement and forces, Nanoscale, Vol: 10, Pages: 13607-13616, ISSN: 2040-3364
Nanogaps supporting cavity plasmonic modes with unprecedented small mode volume are attractive platforms for tailoring the properties of light–matter interactions at the nanoscale and revealing new physics. Hitherto, there is a concerning lack of analytical solutions to divide the complex interactions into their different underlying mechanisms to gain a better understanding that can foster enhanced designs. Bowtie apertures are viewed as an effective and appealing nanocavity and are studied here within the analytical frame of conformal transformation. We show how the non-radiative Purcell enhancement of a quantum emitter within the bowtie nanocavity depends strongly not only on the geometry of the nanocavity, but also on the position and orientation of the emitter. For a 20 nm diameter (∅ 20 nm) bowtie nanocavity, we report a change of up to two orders of magnitude in the maximum non-radiative Purcell enhancement and a shift in its peak wavelength from green to infra-red. The changes are tracked down to the overlap between the emitter field and the gap plasmon mode field distribution. This analysis also enables us to understand the self-induced trapping potential of a colloidal quantum dot inside the nanocavity. Since transformations can be cascaded, the technique introduced in this work can also be applied to a wide range of nanocavities found in the literature.
Liu Y, Guo Q, Liu H, et al., 2018, Circular-polarization-selective transmission induced by spin orbit coupling in a helical tape waveguide, Physical Review Applied, Vol: 9, ISSN: 2331-7019
Spin-orbit coupling of light, describing the interaction between the polarization (spin) and spatial degrees of freedom (orbit) of light, plays an important role in subwavelength scale systems and leads to many interesting phenomena, such as the spin Hall effect of light. Here, based on the spin-orbit coupling, we design and fabricate a helical tape waveguide (HTW), which can realize a circular-polarization-selective process. When the incident circularly polarized wave is of the same handedness as the helix of the HTW, a nearly complete transmission is observed; in contrast, a counterrotating circular polarization of incident wave results in a much lower transmission or is even totally blocked by the HTW. Indeed, both simulations and experiments reveal that the blocked component of power leaks through the helical aperture of the HTW and forms a conical beam analogous to helical Cherenkov radiation due to the conversion from the spin angular momentum to the orbital angular momentum. Our HTW structure demonstrates its potential as a polarization selector in a broadband frequency range.
Navarro-Cia M, Pacheco-Pena V, Kuznetsov SA, et al., 2018, Extraordinary THz transmission with a small beam spot: the leaky wave mechanism, Advanced Optical Materials, Vol: 6, ISSN: 2195-1071
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.
Rodriguez-Ulibarri P, Navarro-Cia M, Rodriguez-Berral R, et al., 2017, Annular Apertures in Metallic Screens as Extraordinary Transmission and Frequency Selective Surface Structures, IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, Vol: 65, Pages: 4933-4946, ISSN: 0018-9480
A 2-D periodic array of annular apertures (or ring slots) is studied using an accurate circuit model. The model accounts for distributed and dynamic effects associated with the excitation of high-order modes operating above or below cutoff but not far from their cutoff frequencies. This paper allows to ascertain the substantial differences of the underlying physics when this structure operates as a classical frequency selective surface or in the extraordinary-transmission (ET) regime. A discussion of two different designs working at each regime is provided by means of the equivalent circuit approach (ECA), full wave simulation results, and experimental characterization. The agreement between the equivalent circuit calculation applied here and the simulation and experimental results is very good in all the considered cases. This validates the ECA as an efficient minimal-order model and a low computational-cost design tool for frequency selective surfaces and ET-based devices. Additional scenarios such as oblique incidence and parametric studies of the structural geometry are also considered.
Pacheco-Pena V, Beruete M, Fernandez-Dominguez AI, et al., 2017, Understanding Bowtie Nanoantennas Excited by a Localized Emitter, International Symposium of IEEE-Antennas-and-Propagation-Society / USNC/URSI National Radio Science Meeting, Publisher: IEEE, Pages: 693-694, ISSN: 1522-3965
A full analytical description of a bowtie nanoantenna excited by a localized emitter is presented using the transformation electromagnetic technique. By applying the conformal mapping, the bowtie nanoantenna is transformed into a periodic multi-parallel plate transmission line problem which can be easily evaluated analytically providing physical insight of the coupling between the dipole nanoemitter and the bowtie nanoantenna. The non-radiative Purcell enhancement spectrum is evaluated both analytically and numerically for different lengths, arm angles and metals, demonstrating a good agreement between both approaches. The method here presented fills the gap of the design techniques for optical nanoantennas.
Pacheco-Pena V, Fernandez-Dominguez AI, Luo Y, et al., 2017, Aluminum nanotripods for light-matter coupling robust to nanoemitter orientation, Laser and Photonics Reviews, Vol: 11, ISSN: 1863-8880
Nanoantennas enable the concentration and manipulation of light at the (sub‐)nanoscale. This ability offers novel strategies to strengthen light‐matter interactions in a controlled fashion. However, most nanoantennas are highly sensitive to light polarization and emitter orientation, which is disadvantageous for many applications (e.g., Raman and fluorescence spectroscopy depend strongly on molecular symmetry and orientation, as well as on the local optical field gradient). It is also unfortunate that analytical descriptions, essential to bridge experimental observations to knowledge and future design guidelines, have lagged behind. Here, resorting to conformal transformation, aluminum nanotripods excited by a nanoemitter of arbitrary orientation are studied analytically. Our results, corroborated with full‐wave simulations, show that aluminum nanotripods are robust not only to emitter orientation, but also to its position. Hence, this work exemplifies the effectiveness and efficiency of transformation optics to analytically describe and optimize light‐matter interaction in complex plasmonic nanoantennas.
Rodriguez-Ulibarri P, Beruete M, Navarro-Cia M, et al., 2017, Equivalent Circuit for Double Annular Aperture Frequency Selective Surfaces, IEEE-MTT-S International Conference on Numerical Electromagnetic and Multiphysics Modeling and Optimization for RF, Microwave, and Terahertz Applications (NEMO), Publisher: IEEE, Pages: 100-102
In this work a double annular aperture frequency selective surface is analyzed from an equivalent circuit perspective. A comparison between full wave numerical solution and the proposed equivalent circuit results is provided for different examples. A very good agreement is obtained endowing the equivalent circuit with great potential as a very powerful and efficient design tool for advanced space filters.
Beaskoetxea U, Maci S, Navarro-Cia M, et al., 2017, Additive Manufactured Millimeter Wave Off-Axis Bull's-Eye Antenna, 11th European Conference on Antennas and Propagation (EUCAP), Publisher: IEEE, ISSN: 2164-3342
Despite their low profile and competitive radiation characteristics, most of the devices in the corrugated leaky wave antenna family feature an unnecessary excess weight which result detrimental for current innovative applications, such as unmanned aerial vehicles (UAV), aircrafts or satellite antennas. Stereolitography, accompanied by plating, is presented as an economic and fast solution for the manufacturing of lightweight devices, which at the same time is able to overcome traditional metal drilling/spark erosion manufacturing limitations, like the impossibility of eroding extremely narrow grooves. Here we present an elliptical Bull's-Eye antenna operating at 96 GHz fabricated following a 3D-printing and copper coating process. Due to its off-centered grooves distribution, a tilted beam pointing at 16.5° is obtained, presenting a gain of 17 dB and 3.5 beamwidth. The theoretical analysis conducted to obtain the equations which govern the grooves distribution and shape is also presented. This prototype results of interest for point-to-point communications where direct front side view is not possible, as well as for applications where lightweight and cost-effective antennas are needed, such as satellite communications or deployed in UAV's
Beaskoetxea U, Maci S, Navarro-Cia M, et al., 2017, 3-D-Printed 96 GHz Bull's-Eye Antenna With Off-Axis Beaming, IEEE Transactions on Antennas and Propagation, Vol: 65, Pages: 17-25, ISSN: 0018-926X
Reducing the profile, footprint and weight of antennas embarked on aircrafts, drones or satellites has been a long pursued objective. Here we tackle this issue by developing a millimeter-wave 96 GHz elliptical Bull's-Eye antenna with off-axis radiation at 16.5° that has been fabricated by low cost 3-D printing stereolithography, followed by metal coating. The theoretical basis for optimum off-axis operations is explained. Measurement results show an overall good agreement with simulations, displaying a gain of 17 dB and a 3.5° beamwidth (E-plane) at the operational frequency. The off-axis beaming enlarges the potential applicability of this technology with respect to the broadside beam solution.
Navarro-Cía M, Wu J, Liu H, et al., 2016, Generation of radially-polarized terahertz pulses for coupling into coaxial waveguides, Scientific Reports, Vol: 6, ISSN: 2045-2322
Coaxial waveguides exhibit no dispersion and therefore can serve as an ideal channel for transmission of broadband THz pulses. Implementation of THz coaxial waveguide systems however requires THz beams with radially-polarized distribution. We demonstrate the launching of THz pulses into coaxial waveguides using the effect of THz pulse generation at semiconductor surfaces. We find that the radial transient photo-currents produced upon optical excitation of the surface at normal incidence radiate a THz pulse with the field distribution matching the mode of the coaxial waveguide. In this simple scheme, the optical excitation beam diameter controls the spatial profile of the generated radially-polarized THz pulse and allows us to achieve efficient coupling into the TEM waveguide mode in a hollow coaxial THz waveguide. The TEM quasi-single mode THz waveguide excitation and non-dispersive propagation of a short THz pulse is verified experimentally by time-resolved near-field mapping of the THz field at the waveguide output.
Kuznetsov SA, Navarro-Cia M, Paulish AG, et al., 2016, Metasurface-enabled pyroelectric detection of 140 GHz radiation with strong polarization discrimination, 10th International Congress on Advanced Electromagnetic Materials in Microwaves and Optics (METAMATERIALS), Publisher: IEEE, Pages: 238-240
Despite the potential of the millimeter- and submillimeter-wave region for fundamental science and industrial applications, its technology is well behind microwaves and optics in terms of performance and cost. We propose to improve a millimeter-wave technology by engineering cost effective solutions from neighboring spectral regions. Specifically, a pyroelectric infrared sensor is transformed into a polarization-selective millimeter-wave detector of 140 GHz radiation by integrating to it a metasurface absorber, which is 136 times as thin as the operating wavelength λ and has the overall dimensions near λ. It is demonstrated that, due to the small thickness and hence the thermal capacity of the absorber, the novel detector keeps high values of the response speed and sensitivity to polarized mm-wave radiation changed insignificantly against the regime of IR detection.
Gennaro SD, Rahmani M, Giannini V, et al., 2016, The Interplay of Symmetry and Scattering Phase in Second Harmonic Generation from Gold Nanoantennas, Nano Letters, Vol: 16, Pages: 5278-5285, ISSN: 1530-6992
Nonlinear phenomena are central to modern photonics but, being inherently weak, typically require gradual accumulation over several millimeters. For example, second harmonic generation (SHG) is typically achieved in thick transparent nonlinear crystals by phase-matching energy exchange between light at initial, ω, and final, 2ω, frequencies. Recently, metamaterials imbued with artificial nonlinearity from their constituent nanoantennas have generated excitement by opening the possibility of wavelength-scale nonlinear optics. However, the selection rules of SHG typically prevent dipole emission from simple nanoantennas, which has led to much discussion concerning the best geometries, for example, those breaking centro-symmetry or incorporating resonances at multiple harmonics. In this work, we explore the use of both nanoantenna symmetry and multiple harmonics to control the strength, polarization and radiation pattern of SHG from a variety of antenna configurations incorporating simple resonant elements tuned to light at both ω and 2ω. We use a microscopic description of the scattering strength and phases of these constituent particles, determined by their relative positions, to accurately predict the SHG radiation observed in our experiments. We find that the 2ω particles radiate dipolar SHG by near-field coupling to the ω particle, which radiates SHG as a quadrupole. Consequently, strong linearly polarized dipolar SHG is only possible for noncentro-symmetric antennas that also minimize interference between their dipolar and quadrupolar responses. Metamaterials with such intra-antenna phase and polarization control could enable compact nonlinear photonic nanotechnologies.
Pacheco-Pena V, Beruete M, Fernandez-Dominguez AI, et al., 2016, Description of bow-tie nanoantennas excited by localized emitters using conformal transformation, ACS Photonics, Vol: 3, Pages: 1223-1232, ISSN: 2330-4022
The unprecedented advance experienced by nanofabrication 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 electromagnetic 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.
Orazbayev B, Beruete M, Pacheco-Pena V, et al., 2016, Soret lens-antenna based on the fishnet metamaterial, 10th European Conference on Antennas and Propagation (EuCAP), Publisher: IEEE, ISSN: 2164-3342
In this work we present the design, numerical and experimental results for an ultrathin Soret fishnet metamaterial lens working at fexp = 96.45 GHz. The fishnet metamaterial with effective refractive index close to zero (n = -0.06) is introduced on the back side of the classical Soret lens in order to improve its efficiency. The experimental results are in good agreement with simulation results and demonstrate half-wavelength focal length and spot size. In a lens antenna configuration a high gain of 10.64 dB was measured at the operation frequency. The presented lens has a low-cost compact design, and may find applications in integrated lens antenna systems.
Beaskoetxea U, Navarro-Cía M, Beruete M, 2016, Broadband frequency and angular response of a sinusoidal bull’s eye antenna, Journal of Physics D - Applied Physics, Vol: 49, ISSN: 0022-3727
A thorough experimental study of the frequency and beaming angle response of a metallic leaky-wave bull's eye antenna working at 77 GHz with a sinusoidally corrugated profile is presented. The beam scanning property of these antennas as frequency is varied is experimentally demonstrated and corroborated through theoretical and numerical results. From the experimental results the dispersion diagram of the n = −1 and n = −2 space harmonics is extracted, and the operation at different frequency regimes is identified and discussed. In order to show the contribution of each half of the antenna, numerical examples of the near-field behavior are also displayed. Overall, experimental results are in good qualitative and quantitative agreement with theoretical and numerical calculations. Finally, an analysis of the beamwidth as a function of frequency is performed, showing that it can achieve values below 1.5° in a fractional bandwidth of 4% around the operation frequency, which is an interesting frequency-stable broadside radiation.
Kuznetsov SA, Paulish AG, Navarro-Cía M, et al., 2016, Selective Pyroelectric Detection of Millimetre Waves Using Ultra-Thin Metasurface Absorbers., Scientific Reports, Vol: 6, ISSN: 2045-2322
Sensing infrared radiation is done inexpensively with pyroelectric detectors that generate a temporary voltage when they are heated by the incident infrared radiation. Unfortunately the performance of these detectors deteriorates for longer wavelengths, leaving the detection of, for instance, millimetre-wave radiation to expensive approaches. We propose here a simple and effective method to enhance pyroelectric detection of the millimetre-wave radiation by combining a compact commercial infrared pyro-sensor with a metasurface-enabled ultra-thin absorber, which provides spectrally- and polarization-discriminated response and is 136 times thinner than the operating wavelength. It is demonstrated that, due to the small thickness and therefore the thermal capacity of the absorber, the detector keeps the high response speed and sensitivity to millimetre waves as the original infrared pyro-sensor does against the regime of infrared detection. An in-depth electromagnetic analysis of the ultra-thin resonant absorbers along with their complex characterization by a BWO-spectroscopy technique is presented. Built upon this initial study, integrated metasurface absorber pyroelectric sensors are implemented and tested experimentally, showing high sensitivity and very fast response to millimetre-wave radiation. The proposed approach paves the way for creating highly-efficient inexpensive compact sensors for spectro-polarimetric applications in the millimetre-wave and terahertz bands.
Pacheco-Pena V, Navarro-Cia M, Beruete M, 2016, [Invited] Epsilon-near-zero metalenses operating in the visible: invited paper for the section: hot topics in metamaterials and structures, Optics and Laser Technology, Vol: 80, Pages: 162-168, ISSN: 1879-2545
Several converging lenses working in the permittivity near to zero (ENZ) regime at optical frequencies are designed using an array of metal-dielectric-metal plasmonic waveguides. These plasmonic waveguides show a dispersive nature that enable to mimic an effective ENZ medium when using the fast wave transverse electric (TE1) mode near its cut-off wavelength. By arranging multiple plasmonic waveguides with the correct engineered dimensions, several metalenses, including graded index (GRIN) ones, and diffractive optical elements (i.e., zoned metalenses) are proposed. The metalenses are designed at λ0=474.9 nm (f=631.67 THz) with a focal length of 10.75λ0. Numerical results demonstrate that the best performance is obtained for the case of the GRIN metalens in terms of the focal position, transversal resolution and thickness, reducing its volume up to ∼52.3% with respect to the smooth-profiled plano-concave metalens.
Khromova I, Navarro-Cia M, Brener I, et al., 2016, Plasmonic resonances in carbon fibers observed with terahertz near-field microscopy, Conference on Quantum Sensing and Nano Electronics and Photonics XIII, Publisher: SPIE-INT SOC OPTICAL ENGINEERING, ISSN: 0277-786X
Pacheco-Pena V, Navarro-Cia M, Orazbayev B, et al., 2016, Improving the Performance of the Zoned Fishnet Metalens Using the Reference Phase Technique, 10th European Conference on Antennas and Propagation (EuCAP), Publisher: IEEE, ISSN: 2164-3342
Alkaraki S, Gao Y, Parini C, et al., 2016, Linearly and Circularly Polarised Bull's Eye Antenna, Loughborough Antennas and Propagation Conference (LAPC), Publisher: IEEE
Pacheco-Pena V, Orazbayev B, Beruete M, et al., 2016, V-Band Reference-Phase-Based Zoned Fishnet Metalens, IEEE International Symposium on Antennas and Propagation / USNC-URSI Radio Science Meeting, Publisher: IEEE, Pages: 67-68, ISSN: 2572-3804
Beaskoetxea U, Beruete M, Navarro-Cia M, 2016, Millimeter Wave Bull's-Eye Antenna Frequency and Angular Response, IEEE International Symposium on Antennas and Propagation / USNC-URSI Radio Science Meeting, Publisher: IEEE, Pages: 53-54, ISSN: 2572-3804
Pacheco-Pena V, Navarro-Cia M, Beruete M, 2016, Focusing Optical Waves via Graded-Epsilon-Near-Zero Metalens, 10th International Congress on Advanced Electromagnetic Materials in Microwaves and Optics (METAMATERIALS), Publisher: IEEE, Pages: 265-267
Navarro-Cia M, Wu J, Liu H, et al., 2016, Bias-Free and Compact Mode-Matched Excitation of THz Coaxial Waveguides, 41st International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), Publisher: IEEE, ISSN: 2162-2027
Orazbayev B, Navarro-Cia M, Beruete M, 2016, W-band Hybrid Wood Zone Plate Fishnet Metalens, 10th International Congress on Advanced Electromagnetic Materials in Microwaves and Optics (METAMATERIALS), Publisher: IEEE, Pages: 247-249
Rahmani M, Gennaro SD, Giannini V, et al., 2016, Linearly Polarized Dipolar Second Harmonic Generation from Gold Nano-antennas by Controlling Their Radiation Phase, Progress in Electromagnetic Research Symposium (PIERS), Publisher: IEEE, Pages: 2292-2292
This data is extracted from the Web of Science and reproduced under a licence from Thomson Reuters. You may not copy or re-distribute this data in whole or in part without the written consent of the Science business of Thomson Reuters.