Open Access
Photonic nanojets with mesoscale high-index dielectric particles
(AIP Publishing, 2019) Pacheco-Peña, Víctor; Beruete Díaz, Miguel; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Institute of Smart Cities - ISC; Ingeniería Eléctrica, Electrónica y de Comunicación
In this work, we demonstrate the ability of high-index dielectric particles immersed in air to generate photonic nanojets with extreme resolution (∼0.06λ0). Both 2D (cylindrical) and 3D (spherical) particles are analyzed, and their profile is truncated using the Weierstrass formulation for solid immersion lenses to produce a photonic nanojet at the output surface under plane wave illumination. Their focusing capability is evaluated in terms of the spatial resolution achieving subwavelength values of ∼0.14λ0 and ∼0.06λ0 for a truncated cylinder and sphere, respectively. The capability of the truncated sphere to enhance the backscattering produced by two small metallic spherical scatterers placed near the photonic nanojet is evaluated by using a scanning-probe microscopy configuration. The imaging capabilities of this technique are also analyzed by moving the metallic spheres in the transversal plane where the photonic nanojet is produced. The results presented here improve greatly the typical resolution of photonic nanojets generated with dielectric particles with a small index contrast. In addition, the high-index material allows using mesoscale particles, leading to a more compact setup. These results may find applications in areas such as microscopy, imaging, and sensing devices where a subwavelength resolution below the diffraction limit is needed.
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
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
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
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.
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
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.