Suchergebnisse

This is a peer-reviewed, un-copyedited version of an article accepted for publication/published in Journal of Physics D: Applied Physics. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at https://doi.org/10.1088/1361-6463/aae3a5. ; The arbitrary control of surface plasmon (SP) propagation has become an intense research topic for several decades. This is due to the fact that they can be used in a variety of fields such as optical trapping, nanoantennas and medical applications. In this communication, the graded index technique is applied in the design of several steerers able to tailor the direction of propagation of the incident SPs by simply changing the height of a dielectric block on top of a semi?infinite metal slab. The design procedure is shown and the structures are numerically evaluated demonstrating a good agreement with the analytical calculations, with the SPs deflected at the design angles (θ ranging from 10° to 60°) with a wide bandwidth steering of 60 nm around the design value (633 nm) ; V.P.-P. is supported by the Newcastle University (Newcastle University Research Fellow). M. B. acknowledges support by the Spanish Ministerio de Economía y Competitividad with European Union FEDER funds [TEC2014-51902-C2-2-R].

In this paper, we design and numerically demonstrate an ultra-thin super-oscillatory metalens with a resolution below the diffraction limit. The zones of the lens are implemented using metasurface concepts with hexagonal unit cells. This way, the transparency and, hence, efficiency is optimized, compared to the conventional transparent–opaque zoning approach that introduces, inevitably, a high reflection in the opaque regions. Furthermore, a novel two-step optimization technique, based on evolutionary algorithms, is developed to reduce the side lobes and boost the intensity at the focus. After the design process, we demonstrate that the metalens is able to generate a focal spot of 0.46λ0 (1.4 times below the resolution limit) at the design focal length of 10λ0 with reduced side lobes (the side lobe level being approximately −11 dB). The metalens is optimized at 0.327 THz, and has been validated with numerical simulations. ; This research was funded by the Spanish Ministerio de Economía y Competitividad with European Union Fondo Europeo de Desarrollo Regional (FEDER) funds, grant number TEC2014-51902-C2-2-R.

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 l0 = 474.9nm (f = 631.67THz) with a focal length of 10.75l0. 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. ; This work was supported by the Spanish Ministerio de Economía y Competitividad under contract TEC2014-51902-C2-2-R. V.P.-P. is sponsored by Spanish Ministerio de Educación, Cultura y Deporte under grant FPU AP-2012-3796. M. N.-C. is supported by the Birmingham Fellowship. M.B. is sponsored by the Spanish Government via RYC-2011-08221.

This is the peer reviewed version of the following article: M. Navarro-Cía, V. Pacheco-Peña, S. A. Kuznetsov, M. Beruete: Extraordinary THz Transmission with a Small Beam Spot: The Leaky Wave Mechanism. Advanced Optical Materials 2018, 1701312, which has been published in final form at https://doi.org/10.1002/adom.201701312. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving. ; 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. ; This work was partially supported by the Spanish Ministerio de Economía y Competitividad with European Union Fondo Europeo de Desarrollo Regional (FEDER) funds [TEC2014-51902-C2-2-R]. M.N.-C. acknowledges support from University of Birmingham [Birmingham Fellowship]. V.P.-P. was sponsored by Spanish Ministerio de Educación, Cultura y Deporte [formación de profesorado universitario (FPU) AP-2012-3796]. S.A.K. acknowledges support from the Novosibirsk State University (NSU) program 5-100 established by the Russian Ministry of Education and Science.

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. ; This work was supported in part by the Spanish Government under contract Consolider Engineering Metamaterials CDS2008-00066 and contract TEC2011-28664-C02-01. B. O. is sponsored by Spanish Ministerio de Economía y Competitividad under grant FPI BES-2012-054909. V.P.-P. is sponsored by Spanish Ministerio de Educación, Cultura y Deporte under grant FPU AP-2012-3796. M. B. is sponsored by the Spanish Government via RYC-2011-08221. M. N.-C. is supported by the Imperial College Junior Research Fellowship.

A structure based on periodically arranged 3D dielectric cuboids connected by photonic nanojets (PNJs) is proposed with the aim of increasing the propagation distance of surface plasmon polaritons (SPPs) at the telecom wavelength of 1550 nm. The performance of the structure is evaluated and compared with the case without the cuboids demonstrating that the SPPs propagation length is enhanced by a factor greater than 2, reaching a value of approximately 190, when the gap between the cuboids is 2.50. Also, the dependence of the propagation length with the height of the cubes is evaluated, showing that this parameter is critical for a good performance of the chain. A subwavelength resolution is obtained for all the jets generated at the output of the cuboids. ; This work was supported by the Spanish Ministerio de Economía y Competitividad under contract TEC2014-51902-C2-2-R and partially was supported by the Mendeleev scientific fund of Tomsk State University No 8.2.48.2015. V.P.-P. is sponsored by Spanish Ministerio de Educación, Cultura y Deporte under grant FPU AP-2012-3796. M.B. is sponsored by the Spanish Government via RYC-2011-08221.

The following article appeared in Minin, I., Minin, O., Pacheco-Pena, V., & Beruete, M. (n.d). All-dielectric periodic terajet waveguide using an array of coupled cuboids. Applied Physics Letters, 106(25), and may be found at http://dx.doi.org/10.1063/1.4923186. ; In this paper, the recently proposed technique to produce photonic jets (terajets at terahertz (THz) frequencies) using 3D dielectric cuboids is applied in the design of a mesoscale cuboid-chain wave- guide. The chains are basically designed with several dielectric cubes with side 1 wavelength placed periodically along the axial z-axis and separated by an air-gap. Based on this, a systematic study of the focusing properties and wave guiding of this chain is performed when the air-gap between the dielectric cubes is changed from 0.25 wavelengths to 3 wavelengths with the best performance achieved at 2.5 wavelengths.An analysis when losses are included in the cubes is also done, demonstrating a robust performance. Finally, the wave guiding is experimentally demonstrated at sub-THz frequencies with a good agreement with numerical results. The simulation results of focusing and transport properties are carried out using Finite Integration Technique. The results here presented may be scaled to any frequency ranges such as millimeter, sub-millimeter, and optical frequencies. ; This work was supported in part by the Spanish Government under Contract No. TEC2011-28664-C02-01. V.P.-P. was sponsored by Spanish Ministerio de Educación, Cultura y Deporte under Grant No. FPU AP-2012-3796. M.B. was sponsored by the Spanish Government via RYC-2011-08221.

The following article appeared Pacheco-Pena, V., Beruete, M., Minin, I., & Minin, O. (n.d). Terajets produced by dielectric cuboids. Applied Physics Letters, 105(8), doi:10.1063/1.4894243, and may be found at http://dx.doi.org/10.1063/1.4894243 ; The capability of generating terajets using three-dimensional (3D) dielectric cuboids working at terahertz (THZ) frequencies (as analogues of nanojets in the infrared band) is introduced and studied numerically. The focusing performance of the terajets is evaluated in terms of the transversal full width at half maximum (FWHM) along x- and y-directions using different refractive indices for a 3D dielectric cuboid with a fixed geometry, obtaining a quasi-symmetric terajet with a subwavelength resolution of 0.46 wavelengths when the refractive index is n=1.41. Moreover, the backscattering enhancement produced when metal particles are introduced in the terajet region is demonstrated for a 3D dielectric cuboid and compared with its two-dimensional (2D) counterpart. The results of the jet generated for the 3D case are experimentally validated at sub-THZ waves, demonstrating the ability to produce terajets using 3D cuboids. ; This work was supported in part by the Spanish Government under Contract Consolider Engineering Metamaterials CSD2008-00066 and Contract TEC2011-28664-C02-01. V.P.-P. is sponsored by Spanish Ministerio de Educacion, Cultura y Deporte under Grant FPU AP-2012-3796. M.B. is sponsored by the Spanish Government via RYC-2011-08221.

In this paper we study the excitation of photonic nanojets (PNJ) in 3D dielectric cuboids by surface plasmons at telecommunication wavelengths. The analysis is done using the effective refractive index approach. It is shown that the refractive index contrast between the regions with and without cuboid should be roughly less than 2 in order to generate jets at the output of the cuboid. The best performance at λ0 = 1550 nm is obtained when the height of the cuboid is 160 nm producing a jet just at the output interface with a subwavelength resolution of 0.68λ0 and a high intensity enhancement (×5) at the focus. The multi‐wavelength response is also studied demonstrating that it is possible to use the proposed structure at different wavelengths. Finally, the backscattering enhancement is numerically evaluated by inserting a metal particle within the PNJ region, demonstrating a maximum value of ∼2.44 dB for a gold sphere of radius 0.1λ0. ; This work was supported by the Spanish Ministerio de Economía y Competitividad under contract TEC2014‐51902‐C2‐2‐R and partially was supported by the Mendeleev scientific fund of Tomsk State University № 8.2.48.2015. V.P.‐P. is sponsored by Spanish Ministerio de Educación, Cultura y Deporte under grant FPU AP‐2012‐3796. M.B. is sponsored by the Spanish Government via RYC‐2011‐08221.

A photonic jet (a terajet at terahertz frequencies) commonly denotes a specific, spatially localized region in the near field on the front side of a dielectric particle with a diameter comparable with the wavelength illuminated by a plane wave on its back side (i.e., the jet emerges from the shadow surface of a dielectric particle). In this Letter, the formation of a photonic jet is demonstrated using the recently proposed three-dimensional (3D) dielectric cuboids working in the "reflection" mode when the specific, spatially localized region is localized in the direction of the incident wavefront. The results of the simulations based on the Finite Integration Technique are discussed. All dimensions are given in wavelength units so that all results can be scaled to any frequency of interest, including optical frequencies, thus simplifying the fabrication process compared with spherical dielectrics. The results presented here may be of interest for novel applications, including microscopy techniques and sensors. ; This work was supported in part by the Spanish Government under contract TEC2011-28664-C02-01. V. P.-P. is sponsored by Spanish Ministerio de Educación, Cultura y Deporte under grant FPU AP-2012-3796. M. B. is sponsored by the Spanish Government via RYC- 2011-08221.

In the past, it has been demonstrated that it is possible to produce terajets with high resolution at its focus using 3D dielectric cuboids under plane-wave illumination. Here, a systematic study of the harmonic and angular response of terajets using cuboids is performed. Mutifrequency focusing is demonstrated at the fundamental frequency and two higher frequency harmonics showing an intensity enhancement of∼10, ∼18, and∼14 for each case. This capability to use 3D dielectric cuboids to produce terajets at the fundamental frequency and first harmonic is experimentally evaluated at sub-THz frequencies, with good agreement with numerical results. Moreover, a robust angular response is demonstrated numerically and experimentally showing that the intensity at the focal position is maintained in a wide angular range (from 0° to 45°), demonstrating the capability to work as a wide scanning terajet-focusing lens. The results here presented may be scaled at different frequency bands such as optical frequencies and may be used in microscopy techniques and sensors. ; This work was supported in part by the Spanish Government under contract Consolider Engineering Metamaterials CSD2008-00066 and contract TEC2011- 28664-C02-01. V. P.-P. is sponsored by Spanish Ministerio de Educación, Cultura y Deporte under grant FPU AP- 2012-3796. M. B. is sponsored by the Spanish Government via RYC-2011-08221.

The following article appeared Pacheco-Pena, V., Orazbayev, B., Torres, V., Beruete, M., & Navarro-Cia, M. (n.d). Ultra-compact planoconcave zoned metallic lens based on the fishnet metamaterial. Applied Physics Letters, 103(18), and may be found at http://dx.doi.org/10.1063/1.4827876. ; A 1.5λ0 -thick planoconcave zoned lens based on the fishnet metamaterial is demonstrated experimentally at millimeter wavelengths. The zoning technique applied allows a volume reduction of 60% compared to a full fishnet metamaterial lens without any deterioration in performance. The structure is designed to exhibit an effective refractive index n = -0.25 at f = 56.7GHz (λ0 = 5.29 mm) with a focal length FL = 47.62 mm = 9λ0. The experimental enhancement achieved is 11.1dB, which is in good agreement with simulation and also with previous full fishnet metamaterial lenses and opens the door for integrated solutions. ; This work was supported in part by the Spanish Government under contract Consolider Engineering Metamaterials CSD2008-00066 and contract TEC2011- 28664-C02-01. V.P.-P. was sponsored by Spanish Ministerio de Educacion, Cultura y Deporte under Grant No. FPU AP- 2012-3796. B.O. was sponsored by Spanish Ministerio de Economıa y Competitividad under Grant No. FPI BES-2012- 054909. V.T. is sponsored by the Universidad Publica de Navarra. M.B. is sponsored by the Spanish Government via RYC-2011-08221. M.N.-C. was supported by the Imperial College Junior Research Fellowship.

The following article appeared in Pacheco-Pena, V., Orazbayev, B., Beaskoetxea, U., Beruete, M., & Navarro-Cia, M. (n.d). Zoned near-zero refractive index fishnet lens antenna: Steering millimeter waves. Journal Of Applied Physics, 115(12), and may be found at http://dx.doi.org/10.1063/1.4869436. ; 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. ; This work was supported in part by the Spanish Government under contract Consolider Engineering Metamaterials CSD2008-00066 and Contract No. TEC2011- 28664-C02-01. V.P.-P. is sponsored by Spanish Ministerio de Educacion, Cultura y Deporte under Grant No. FPU AP- 2012-3796. B.O. is sponsored by Spanish Ministerio de Economıa y Competitividad under Grant No. FPI BES-2012- 054909. M.B. is sponsored by the Spanish Government via RYC-2011-08221. M. N.-C. is supported by the Imperial College Junior Research Fellowship.

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. ; This work was supported in part by the Spanish Government under contract Consolider Engineering Metamaterials CSD2008-00066 and contract TEC2011-28664-C02-01. V.P.-P. is sponsored by Spanish Ministerio de Educación, Cultura y Deporte under grant FPU AP-2012-3796. V.T. is sponsored by the Universidad Pública de Navarra. M.B. is sponsored by the Spanish Government via RYC-2011-08221. M. N.-C. is supported by the Imperial College Junior Research Fellowship.

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. ; This work was supported in part by the Spanish Government under contract TEC2014-51902-C2-2-R. V.P.-P. is sponsored by Spanish Ministerio de Educación, Cultura y Deporte under grant FPU AP-2012-3796. M.B. is sponsored by the Spanish Government via RYC-2011-08221. A.I.F.-D. acknowledges funding from EU Seventh Framework Programme under grant agreement FP7-PEOPLE-2013-CIG63099. Y.L. would like to acknowledge the funding support from Singapore Ministry of Education (MOE) under grant no. MOE2015-T2-1-145, and NTU-A*STAR Silicon Technologies Centre of Excellence under the program grant no. 11235150003. M.N.-C. was supported by an Imperial College Junior Research Fellowship and is now supported by a Birmingham Fellowship.