Imperial College London

Summary

Faculty of EngineeringDepartment of Electrical and Electronic Engineering

Visiting Researcher
 
 
 
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Contact

 

+44 (0)20 7594 6242m.navarro

 
 
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Assistant

 

Ms Susan Brace +44 (0)20 7594 6215

 
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Location

 

706Electrical EngineeringSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

337 results found

Cojocari M, Ospanova AK, Chichkov V, Navarro-Cia M, Gorodetsky A, Basharin AAet al., 2021, Pseudo-anapole regime in terahertz metasurfaces, PHYSICAL REVIEW B, Vol: 104, ISSN: 2469-9950

Journal article

Freer S, Sui C, Hanham SM, Grover LM, Navarro-Cia Met al., 2021, Hybrid reflection retrieval method for terahertz dielectric imaging of human bone, BIOMEDICAL OPTICS EXPRESS, Vol: 12, Pages: 4807-4820, ISSN: 2156-7085

Journal article

Sabery SM, Bystrov A, Navarro-Cia M, Gardner P, Gashinova Met al., 2021, Study of low terahertz radar signal backscattering for surface identification, Sensors, Vol: 21, Pages: 1-17, ISSN: 1424-8220

This study explores the scattering of signals within the mm and low Terahertz frequency range, represented by frequencies 79 GHz, 150 GHz, 300 GHz, and 670 GHz, from surfaces with different roughness, to demonstrate advantages of low THz radar for surface discrimination for automotive sensing. The responses of four test surfaces of different roughness were measured and their normalized radar cross sections were estimated as a function of grazing angle and polarization. The Fraunhofer criterion was used as a guideline for determining the type of backscattering (specular and diffuse). The proposed experimental technique provides high accuracy of backscattering coefficient measurement depending on the frequency of the signal, polarization, and grazing angle. An empirical scattering model was used to provide a reference. To compare theoretical and experimental results of the signal scattering on test surfaces, the permittivity of sandpaper has been measured using time-domain spectroscopy. It was shown that the empirical methods for diffuse radar signal scattering developed for lower radar frequencies can be extended for the low THz range with sufficient accuracy. The results obtained will provide reference information for creating remote surface identification systems for automotive use, which will be of particular advantage in surface classification, object classification, and path determination in autonomous automotive vehicle operation.

Journal article

Nekovic A, Camacho M, Freer S, Penchev P, Boix RR, Dimov S, Navarro-Cia Met al., 2021, Taming extraordinary THz transmission through sub-λ slot arrays via array truncation, slot rotation, polarization and angle of incidence, 2020 45th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz), Publisher: IEEE, Pages: 1-2

Accurate and time-effective simulation and design optimization of quasi-optical (QO) systems is an extremely challenging electromagnetic problem given the multi-scale dimension of QO components and the need to consider the finite size of such components to account for effects like diffraction. To show that the Method of Moments (MoM) provides an elegant solution for these problems, truncated rectangular arrays of tilted slots are measured in a QO Terahertz (THz) time-domain setup and comparison with MoM is carried out. The extraordinary transmission peaks are modulated by the size of the array and the orientation of the slots with respect to the incident electric field.

Conference paper

Gorodetsky A, Freer S, Navarro-Cia M, 2021, Continuous wave sub-Terahertz lensless holographic reflective imaging, 2020 45th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz), Publisher: IEEE, Pages: 1-1

We propose a simple setup involving standard commercially available sub-terahertz electronic source and camera in reflection layout. The setup is designed for imaging amplitude and phase objects. The construction allows for quick installation and potentially almost-realtime operation. Initial reconstruction results demonstrate resolution of about three wavelengths.

Conference paper

Freer S, Martinez R, Perez-Quintana D, Beruete M, Hanham SM, Attallah MM, Navarro-Cia Met al., 2021, Metal 3D printed D-band waveguide to surface wave transition, 2020 45th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz), Publisher: IEEE, Pages: 1-2

The coupling efficiency between free space waves and surface waves is low, narrowband, or both. Highly efficient broadband (better than 20% fractional bandwidth) coupling from waveguide modes can be achieved through sophisticated transitions whose fabrication can be enabled through additive manufacturing (e.g. selective laser melting). Here, we present alternative metallic transitions designed to couple the fundamental mode of a D-band waveguide to the fundamental transverse-magnetic surface mode supported by a periodic metal corrugated grating. Simulations of the coupling process and initial measurements have been undertaken.

Conference paper

Freer S, Gorodetsky A, Navarro-Cia M, 2021, Beam profiling of a commercial lens-assisted terahertz time domain spectrometer, IEEE Transactions on Terahertz Science and Technology, Vol: 11, Pages: 90-100, ISSN: 2156-342X

To undertake THz spectroscopy and imaging, and accurately design and predict the performance of quasi-optical components, knowledge of the parameters of the beam (ideally Gaussian) emitted from a THz source is paramount. Despite its proliferation, relatively little work has been done on this in the frame of broadband THz photoconductive antennas. Using primarily pinhole scanning methods, along with stepwise angular spectrum simulations, we investigate the profile and polarization characteristics of the beam emitted by a commercial silicon-lensintegrated THz photoconductive antenna and collimated by a TPX (polymethylpentene) lens. Our study flags the limitations of the different beam profiling methods and their impact on the beam Gaussianity estimation. A non-Gaussian asymmetric beam is observed, with main lobe beam waists along x and y varying from 8.4 ± 0.7 mm and 7.7±0.7 mm at 0.25THz,to1.4±0.7 mm and 1.4 ± 0.7 mm at 1 THz, respectively. Additionally, we report a maximum cross-polar component relative to the ON-axis co-polar component of -11.6 dB and -21.2 dB, at 0.25 THz and 1 THz, respectively.

Journal article

Pacheco-Pena V, Alves RA, Navarro-Cia M, 2020, Plasmonic nanoantennas and nanocavities: a transformation electromagnetics perspective, 2020 XXXIIIrd General Assembly and Scientific Symposium of the International Union of Radio Science (URSI GASS), Publisher: IEEE, Pages: 1-4

Here, we apply the transformation electromagnetics technique to study the performance of plasmonic bowtie and diabolo nanoantennas as well as nanocavities. The nanoparticles are illuminated by a nanoemitter and their response is evaluated in terms of the non-radiative Purcell enhancement. The influence of the polarization of the emitter, metals and aperture of the arms is analyzed. Moreover, hidden symmetries between diabolo nanoantennas and nanocavities are unveiled and explained by means of the transformation electromagnetics approach.

Conference paper

Gorodetsky AA, Freer S, Navarro-Cía M, 2020, Assessment of cameras for continuous wave sub-terahertz imaging, Terahertz Emitters, Receivers, and Applications XI, Publisher: SPIE, Pages: 1-9

In this contribution, we present the direct comparison between Ophir Pyrocam IV and Terasense Tera-1024 cameras used for imaging of terahertz (THz) and sub-THz signals. We compare general properties, such as frequency dependent and polarisation dependent sensitivity, angle dependent sensitivity essential for holographic and noncollinear interferometric measurements, and draw a conclusion about the most suitable camera for the discussed imaging approaches. Both cameras show acceptable performance and sensitivity at imaging both 0.14 THz and 0.3 THz signals. The Terasense camera, expectedly, shows stronger polarisation dependent properties, however, is significantly more angle independent, showing an acceptable performance at all tested incident angles up to 50 degrees. At the same time, although the angle dependence is stronger for the Ophir camera, it has smaller pixel pitch and more extended post-processing features, thus making it somewhat better suited for noncollinear interferometric and holographic sub THz imaging.

Conference paper

Camacho M, Nekovic A, Freer S, Penchev P, Boix RR, Dimov S, Navarro-Cia Met al., 2020, Symmetry and finite-size effects in quasi-optical extraordinarily THz transmitting arrays of tilted slots, IEEE Transactions on Antennas and Propagation, Vol: 68, Pages: 6109-6117, ISSN: 0018-926X

Extraordinarily transmitting arrays are promising candidates for quasi-optical (QO) components due to their high frequency selectivity and beam scanning capabilities owing to the leaky-wave mechanism involved. We show here how by breaking certain unit cell and lattice symmetries, one can achieve a rich family of transmission resonances associated with the leaky-wave dispersion along the surface of the array. By combining 2-D and 1-D periodic method of moments (MoM) calculations with QO terahertz (THz) time-domain measurements, we provide physical insights, numerical, and experimental demonstration of the different mechanisms involved in the resonances associated with the extraordinary transmission peaks and how these evolve with the number of slots. Thanks to the THz instrument used, we are also able to explore the time-dependent emission of the different frequency components involved.

Journal article

Alves RA, Guerreiro A, Navarro-Cia M, 2020, Bridging the hydrodynamic Drude model and local transformation optics theory, PHYSICAL REVIEW B, Vol: 101, Pages: 1-9, ISSN: 2469-9950

The recent ability of plasmonic nanostructures to probe subnanometer and even atomic scales demands theories that can account for the nonlocal dynamics of the electron gas. The hydrodynamic Drude model (HDM) captures much of the microscopic dynamics of the quantum mechanical effects when additional boundary conditions are considered. Here, we revisit the HDM under the Madelung formalism to reexpress its coupled system of equations as a single nonlinear Schrödinger equation in order to have a natural quantum mechanical description of plasmonics. Specifically, we study the response of two overlapping nanowires with this formalism. We ensure that an proposed frame concurs with classical electrodynamics when the local response approximation holds in the plasmonic system by finding the correction needed.

Journal article

Razavizadeh SM, Kashani ZG, Sadeghzadeh R, Navarro-Cía Met al., 2020, Tunable compression of THz chirped pulses using a helical graphene ribbon-loaded hollow-core waveguide., Applied Optics, Vol: 59, Pages: 4247-4253, ISSN: 1559-128X

Pulse shaping is important for communications, spectroscopy, and other applications that require high peak power and pulsed operation, such as radar systems. Unfortunately, pulse shaping remains largely elusive for terahertz (THz) frequencies. To address this void, a comprehensive study on the dispersion tunability properties of THz chirped pulses traveling through a dielectric-lined hollow-core waveguide loaded with a helical graphene ribbon is presented. It is demonstrated that there is an optimal compression waveguide length over which THz chirped pulses reach the maximum compression. The optimal length is dependent on the chirp pulse duration. It is shown that by applying an electrostatic controlling gate voltage (Vg) of 0 and 30 V on the helical graphene ribbon, the temporal input pulses of width 8 and 12 ps, propagating through two different lengths, can be tuned by 5.9% and 8%, respectively, in the frequency range of 2.15-2.28 THz.

Journal article

Freer S, Camacho M, Kuznetsov SA, Boix RR, Beruete M, Navarro-Cia Met al., 2020, Revealing the underlying mechanisms behind TE extraordinary THz transmission, Photonics Research, Vol: 8, Pages: 430-439, ISSN: 2327-9125

Transmission through seemingly opaque surfaces, so-called extraordinary transmission, provides an exciting platform for strong light–matter interaction, spectroscopy, optical trapping, and color filtering. Much of the effort has been devoted to understanding and exploiting TM extraordinary transmission, while TE anomalous extraordinary transmission has been largely omitted in the literature. This is regrettable from a practical point of view since the stronger dependence of the TE anomalous extraordinary transmission on the array’s substrate provides additional design parameters for exploitation. To provide high-performance and cost-effective applications based on TE anomalous extraordinary transmission, a complete physical insight about the underlying mechanisms of the phenomenon must be first laid down. To this end, resorting to a combined methodology including quasi-optical terahertz (THz) time-domain measurements, full-wave simulations, and method of moments analysis, subwavelength slit arrays under s-polarized illumination are studied here, filling the void in the current literature. We believe this work unequivocally reveals the leaky-wave role of the grounded-dielectric slab mode mediating in TE anomalous extraordinary transmission and provides the necessary framework to design practical high-performance THz components and systems.

Journal article

Liu Y, Li M, Song K, Hu D, Liu H, Zhao X, Zhang S, Navarro-Cia Met al., 2020, Leaky-wave antenna with switchable omnidirectional conical radiation via polarization handedness, IEEE Transactions on Antennas and Propagation, Vol: 68, Pages: 1282-1288, ISSN: 0018-926X

Reconfigurable antennas capable of beam-steering offer an efficient solution to optimize the use of the crowded wireless medium and can serve as a multifunction antenna. Beam-steering is often achieved by antenna geometry switching at the expense of hardware complexity. Here, polarization is used to realize beam-steering without the need of antenna geometry modification. Depending on the handedness of the feed, backward or forward conical radiation is demonstrated in a ∼13λ0-long short-circuited helically slotted waveguide antenna. Tapering the slit width with a Taylor distribution reduces the measured sidelobe levels by ∼3 dB in average and results in a realized gain of 10-13 dB and 11-13 dB for right-handed (backward radiation) and left-handed circularly polarized (forward radiation) feeding, respectively, in the bandwidth from 8.5 to 9.5 GHz.

Journal article

Freer S, Gape J, Shalom E, Navarro-Cia M, Kuznetsov SA, Beruete Met al., 2020, Study of leaky waves responsible for terahertz TE extroardinary transmission, 2019 12th UK-Europe-China Workshop on Millimeter Waves and Terahertz Technologies (UCMMT), Publisher: IEEE

Extraordinary transmission (ET) via transverse electric (TE) modes through dielectric-backed periodic subwavelength slit arrays is largely owed to the leakage of energy from waves guided by the structure. This phenomenon is investigated in order to shed light on the leaky wave mechanism. Both angular transmission and temporal measurements are undertaken, revealing the origin of both the modes developed in the structures and the behaviour of the energy coupled to these modes.

Conference paper

Makarevich A, Makarevich O, Ivanov A, Sharovarov D, Eliseev A, Amelichev V, Boytsova O, Gorodetsky A, Navarro-Cía M, Kaul Aet al., 2020, Hydrothermal epitaxy growth of self-organized vanadium dioxide 3D structures with metal–insulator transition and THz transmission switch properties, CrystEngComm, Vol: 22, Pages: 2612-2620, ISSN: 1466-8033

The hydrothermal method is the most effective approach for the synthesis of VO2 metastable polymorphs with unique powder crystallite morphology. In this work, we expanded the capabilities of this method, directing it to the growth of oriented crystallites in self-organized systems on single crystal substrates. According to our investigations, a large variety of 3D structures of vanadium dioxide can be obtained using one single crystal substrate r-sapphire by fine tuning of synthesis parameters. The orientation growth of six-pointed vanadium dioxide crystallites fits into an epitaxial growth model describing unit cell relations between the VO2(M1) film and r-sapphire substrate. We describe the process of VO2(M1) phase stabilization in the films and the changes of resistivity and terahertz transparency of the films based on the metal–insulator transition (MIT).

Journal article

Pacheco-Peña V, Alves RA, Navarro-Cía M, 2020, From symmetric to asymmetric bowtie nanoantennas: electrostatic conformal mapping perspective, Nanophotonics, Vol: 0, ISSN: 2192-8606

Plasmonic nanoantennas have revolutionized the way we study and modulate light–matter interaction. Due to nanofabrication limitations, dimer-type nanoantennas always exhibit some degree of asymmetry, which is desirable in some cases. For instance, in sensing applications, asymmetry is sometimes induced by design in plasmonic nanoantennas to favor higher order nonradiative modes with sharp Fano line shapes. Regardless of the actual origin of the asymmetry, unintentional or intentional, an analytical frame that can deal with it in a seamless manner would be beneficial. We resort to conformal mapping for this task and we track the influence of the degree of asymmetry of the circular sectors composing gold bowtie nanoantennas on the nonradiative Purcell enhancement of a nearby nanoemitter. This manuscript reviews the contributions of conformal mapping to plasmonic nanoantennas and illustrates the advantages of the elegant analytical solution provided by conformal mapping to grasp physical insights, which can serve as a springboard for new plasmonic asymmetric nanoantenna designs.

Journal article

Pacheco-Pena V, Alves R, Navarro-Cia M, 2019, Conformal transformation in bowtie nanoantennas and nanocavities: unveiling hidden symmetries, 2019 Thirteenth International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials), Publisher: IEEE

In this work, bowtie nanoantennas and nanocavities are analyzed using the conformal transformation technique. Their performance is studied in terms of the non-radiative Purcell enhancement and self-induced optical forces experienced by quantum emitters. It is demonstrated how these two geometrically different plasmonic nanoparticles can share the same non-radiative Purcell spectra. This hidden symmetric response is unveiled by properly applying the conformal transformation technique, demonstrating that both nanoparticles share the same transformed geometry.

Conference paper

Ma M, Wang Y, Navarro-Cía M, Liu F, Zhang F, Liu Z, Li Y, Hanham SM, Hao Zet al., 2019, The dielectric properties of some ceramic substrate materials at terahertz frequencies, Journal of the European Ceramic Society, Vol: 39, Pages: 4424-4428, 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.

Journal article

Freer S, Camacho M, Kuznetsov SA, Shalom E, Gape J, Boix RR, Beruete M, Navarro-Cia Met al., 2019, Modes and pseudo-modes in TE extraordinary THz transmission, 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), Publisher: IEEE, ISSN: 2162-2027

Transverse electric (TE) transmission through dielectric-baked subwavelength slit arrays is inextricably linked to the grounded-dielectric slab TE1 mode, and thus, it depends highly on the electrical thickness of the substrate. We track the influence of the TE1 mode using both TDS measurements and the Method of Moments. For electrically thick dielectric samples, the TE1 mode is in propagation, and hence total transmission occurs (in excess of 0 dB, attributed to collimation), whereas in electrically thin samples, the TE1 mode is in cutoff. In this regime, the mode still contributes to transmission, and hence is referred to as a pseudo-mode.

Conference paper

Akalin T, Chahadih A, Turer I, Navarro-Cia M, Beruete M, Ghaddar Aet al., 2019, Combined UTC-PD integrated THz source and a leaky wave antenna with complementary split ring resonators along a planar Goubau line, 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), Publisher: IEEE, ISSN: 2162-2027

We have fabricated a terahertz source based on the combination of an integrated Uni-Travelling-Carrier Photodiode (UTC-PD) and a leaky wave antenna. The UTC-PD is a broadband source and we have used an efficient transition from CPW to Planar Goubau Line (PGL). In this PGL section, we have included complementary Split Ring Resonators (c-SRR) in order to obtain a leaky wave antenna (LWA). The broadband behavior of the source and of the transition allow us to design systems at a given frequency range by modifying only the c-SRR along the PGL.

Conference paper

Camacho M, Boix RR, Kuznetsov SA, Beruete M, Navarro-Cia Met al., 2019, Far-field and near-field physics of extraordinary THz transmitting hole-array antennas, IEEE Transactions on Antennas and Propagation, Vol: 67, Pages: 6029-6038, ISSN: 0018-926X

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.

Journal article

Pacheco-Peña V, Alves R, Navarro-Cía M, 2019, Hidden symmetries in bowtie nanocavities and diabolo nanoantennas, ACS Photonics, Vol: 6, Pages: 2014-2024, ISSN: 2330-4022

Symmetries play an important role in many branches of physics and enable simplification of the mathematical description of problems. In some cases, symmetries are hidden and are only evident under suitable coordinate systems. With the help of conformal transformation, it is shown analytically here how asymmetric-looking plasmonics diabolo nanoantennas and bowtie nanocavities display a hidden symmetry that justifies the unforeseen symmetric nonradiative Purcell enhancement of a nanoemitter in their immediacy. The conformal transformation also provides physical insight on the dissimilar self-induced trapping potential experienced by such nanoemitter nearby/inside the diabolo nanoantenna/bowtie nanocavity. The analytical results are confirmed with full-wave simulations. This work highlights the elegant and cost-effective (in terms of computational burden) solution that conformal transformation provides to understand the underlying physics of and to design/model plasmonic nanostructures that are becoming key elements in sensing, quantum optics, and so on.

Journal article

Wang D, Yang B, Gao W, Jia H, Yang Q, Chen X, Wei M, Liu C, Navarro-Cía M, Han J, Zhang W, Zhang Set al., 2019, Photonic Weyl points due to broken time-reversal symmetry in magnetized semiconductor, Nature Physics, Vol: 15, Pages: 1150-1155, ISSN: 1745-2473

Weyl points are discrete locations in the three-dimensional momentum space where two bands cross linearly with each other. They serve as the monopoles of Berry curvature in the momentum space, and their existence requires breaking of either time-reversal or inversion symmetry. Although various non-centrosymmetric Weyl systems have been reported, demonstration of Weyl degeneracies due to breaking of the time-reversal symmetry remains scarce and is limited to electronic systems. Here, we report the experimental observation of photonic Weyl degeneracies in a magnetized semiconductor—InSb, which behaves as a magnetized plasma19 for electromagnetic waves at the terahertz band. By varying the magnetic field strength, Weyl points and the corresponding photonic Fermi arcs have been demonstrated. Our observation establishes magnetized semiconductors as a reconfigurable terahertz Weyl system, which may prompt research on novel magnetic topological phenomena such as chiral Majorana-type edge states and zero modes in classic systems.

Journal article

Rider MS, Sokolikova M, Hanham SM, Navarro-Cia M, Haynes P, Lee D, Daniele M, Guidi MC, Mattevi C, Lupi S, Giannini Vet al., 2019, Experimental signature of a topological quantum dot, Publisher: arXiv

Topological insulators (TIs) present a neoteric class of materials, whichsupport delocalised, conducting surface states despite an insulating bulk. Dueto their intriguing electronic properties, their optical properties havereceived relatively less attention. Even less well studied is their behaviourin the nanoregime, with most studies thus far focusing on bulk samples - inpart due to the technical challenges of synthesizing TI nanostructures. Westudy topological insulator nanoparticles (TINPs), for which quantum effectsdominate the behaviour of the surface states and quantum confinement results ina discretized Dirac cone, whose energy levels can be tuned with thenanoparticle size. The presence of these discretized energy levels in turnleads to a new electron-mediated phonon-light coupling in the THz range. Wepresent the experimental realisation of Bi$_2$Te$_3$ TINPs and strong evidenceof this new quantum phenomenon, remarkably observed at room temperature. Thissystem can be considered a topological quantum dot, with applications to roomtemperature THz quantum optics and quantum information technologies.

Working paper

Razavizadeh SM, Sadeghzadeh R, Ghattan Z, Navarro-Cia Met 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.

Conference paper

Aznabet M, El Mrabet O, Beruete M, Navarro-Cia M, Essaidi Met 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.

Conference paper

Gape J, Shalom E, Navarro-Cía M, 2019, Single-pixel imaging with a commercial THz time-domain spectrometer via compressive sensing

Raster scanning is currently the industry standard for THz imaging with time-domain spectrometers (TDS). However, it involves lengthy acquisition time and often requires movement of the sample, which is ill-advised for fragile/liquid biological samples. Here, we show our progress in implementing a single-pixel detection method underpinned by compressive sensing that eliminates the need for movement of the TDS system or sample thereby reducing the complexity of the setup, sample disruption, and data acquisition time.

Conference paper

Freer S, Kuznetsov SA, Beruete M, Navarro-Cía Met al., 2019, On the behaviour of leaky waves in TE extraordinary terahertz transmission

The study of the leaky modes responsible for transverse electric (TE) extraordinary transmission (ET) through periodic subwavelength slit arrays has largely been overshadowed by transverse magnetic (TM) ET. Here we demonstrate the behaviour of these leaky waves and their dependency on periodic arrays of sufficient length to enable efficient TE ET.

Conference paper

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.

Journal article

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