Open Access
Terajets produced by dielectric cuboids
(AIP Publishing, 2014) Pacheco-Peña, Víctor; Beruete Díaz, Miguel; Minin, Igor V.; Minin, Oleg V.; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
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.
Open Access
On the performance of the zoned fishnet metamaterial lens with positive and negative reference phase
(IEEE, 2016) Pacheco-Peña, Víctor; Minin, Igor V.; Minin, Oleg V.; Beruete Díaz, Miguel; Ingeniaritza Elektrikoa eta Elektronikoa; Institute of Smart Cities - ISC; Ingeniería Eléctrica y Electrónica
In this letter, several converging fishnet metalenses are designed using both the zoning and reference phase techniques. They are engineered with a focal length of 1.5λ0 at the design frequency of 55 GHz (λ0 = 5.45 mm) at which the fishnet metamaterial has an effective refractive index of nlens = ∼0.68. Three metalenses are analyzed—with positive, negative, and without reference phase—in order to compare their performance. The focal properties are evaluated both numerically and experimentally, demonstrating a good agreement between them. The best performance is achieved for the zoned metalens with positive reference phase,with an experimental power enhancement at the focal length of 6.2 dB, better axial resolution (0.65λ0 ), and reduced lateral lobes compared to other designs
Open Access
Phase reversal technique applied to fishnet metalenses
(Hindawi, 2018) Pacheco-Peña, Víctor; Minin, Igor V.; Minin, Oleg V.; Beruete Díaz, Miguel; Ingeniaritza Elektrikoa eta Elektronikoa; Institute of Smart Cities - ISC; Ingeniería Eléctrica y Electrónica
In this work, the fishnet metamaterial is applied to several converging metalenses by combining the zoning, reference phase, and phase reversal techniques. First, the zoning and reference phase techniques are implemented in several metalenses at 55 GHz ( λ 0 = 5.45 m m ) with a short focal length of 1.5 λ 0 . Then, the phase reversal technique is applied to these metalenses by switching from a concave to a convex profile in order to change the phase distribution inside of them. The designs are evaluated both numerically and experimentally demonstrating that chromatic dispersion (the shift of the position of the focus at different frequencies) is reduced when using the phase-reversed profiles. It is shown how the position of the focus remains at the same location within a relatively broadband frequency range of ~4% around the design frequency without affecting the overall behaviour of the metalenses. The best performance is achieved with the design that combines both reference phase and phase reversal techniques, with an experimental position of the focus of 1.75 λ 0 , reduced side lobes, and a power enhancement of 6.5 dB. The metalenses designed here may find applications in situations where a wideband response and low side lobes are required because of the reduced chromatic aberrations of the focus.
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
Doubling the propagation distance of surface plasmon polaritons
(SPIE, 2016) Pacheco-Peña, Víctor; Minin, Igor V.; Minin, Oleg V.; Beruete Díaz, Miguel; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
A novel passive repeater, based on a chain of 3D dielectric particles, has been proposed and numerically simulated.
Open Access
All-dielectric periodic terajet waveguide using an array of coupled cuboids
(AIP Publishing, 2015) Minin, Igor V.; Minin, Oleg V.; Pacheco-Peña, Víctor; Beruete Díaz, Miguel; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
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.
Open Access
Multifrequency focusing and wide angular scanning of terajets
(Optical Society of America, 2015) Pacheco-Peña, Víctor; Beruete Díaz, Miguel; Minin, Igor V.; Minin, Oleg V.; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
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.
Open Access
Comprehensive analysis of photonic nanojets in 3D dielectric cuboids excited by surface plasmons
(Wiley, 2016) Pacheco-Peña, Víctor; Minin, Igor V.; Minin, Oleg V.; Beruete Díaz, Miguel; Institute of Smart Cities - ISC
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.
Open Access
Increasing surface plasmons propagation via photonic nanojets with periodically spaced 3D dielectric cuboids
(MDPI, 2016) Pacheco-Peña, Víctor; Minin, Igor V.; Minin, Oleg V.; Beruete Díaz, Miguel; Ingeniaritza Elektrikoa eta Elektronikoa; Institute of Smart Cities - ISC; Ingeniería Eléctrica y Electrónica
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.
Open Access
Localized photonic jets from flat, three-dimensional dielectric cuboids in reflection mode
(Optical Society of America, 2015) Minin, Igor V.; Minin, Oleg V.; Pacheco-Peña, Víctor; Beruete Díaz, Miguel; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
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.