Increasing Surface Plasmons Propagation via Photonic Nanojets with Periodically Spaced 3D Dielectric Cuboids

Generation of Photonic Nanojet Using Gold Film Dielectric Microdisk Structure

Due to their narrow beam waist size, high intensity, and long propagation distance, photonic nanojets (PNJs) can be used in various fields such as nanoparticle sensing, optical subwavelength detection, and optical data storage. In this paper, we report a strategy to realize an SPP-PNJ by exciting a surface plasmon polariton (SPP) on a gold-film dielectric microdisk. In detail, an SPP is excited by the grating-coupling method, then it irradiates the dielectric microdisk to form an SPP-PNJ. The characteristics of the SPP-PNJ, including maximum intensity, full width at half maximum (FWHM), and propagation distance, are studied by using finite difference time domain (FDTD) numerical solutions. The results demonstrate that the proposed structure can produce a high-quality SPP-PNJ, the maximum quality factor of which is 62.20, and the propagation distance of the SPP-PNJ is 3.08 λ. Furthermore, the properties of the SPP-PNJ can be modified flexibly by changing the thickness and refractive index of the dielectric microdisk.

On-fiber high-resolution photonic nanojets via high refractive index dielectrics

In this manuscript, we present high spatial resolution focusing of electromagnetic waves at telecommunication wavelengths (λ₀ = 1.55 µm) by using high-refractive index mesoscale dielectrics placed at the end of an optical fiber. Our approach exploits photonic nanojets (PNJs) to achieve high-intensity, spatially narrow focal spots. The response of the device is evaluated in detail considering 2-dimensional (2D) and 3-dimensional (3D) configurations using high-index mesoscale cylindrical and spherical dielectrics, respectively, placed on top of an optical fiber. It is shown how the PNJs can be shifted towards the output surface of the mesoscale high-index dielectric by simply truncating its 2D/3D cylindrical/spherical output profile. With this setup, a PNJ with a high transversal resolution is obtained using the 2D/3D engineered mesoscale dielectric particles achieving a Full-Width at Half-Maximum of FWHM = 0.28λ₀ (2D truncated dielectric), and FWHMy = 0.17λ₀ and FWHMx = 0.21λ₀ (3D truncated dielectric). The proposed structure may have potential in applications where near-field high spatial resolution is required, such as in sensing and imaging systems.

Plasmonic meniscus lenses

Controlling and manipulating the propagation of surface plasmons has become a field of intense research given their potential in a wide range of applications, such as plasmonic circuits, optical trapping, sensors, and lensing. In this communication, we exploit classical optics techniques to design and evaluate the performance of plasmonic lenses with meniscus-like geometries. To do this, we use an adapted lens maker equation that incorporates the effective medium concepts of surface plasmons polaritons travelling in dielectric-metal and dielectric-dielectric-metal configurations. The design process for such plasmonic meniscus lenses is detailed and two different plasmonic focusing structures are evaluated: a plasmonic lens with a quasi-planar output surface and a plasmonic meniscus lens having a convex-concave input–output surface, respectively. The structures are designed to have an effective focal length of 2λ₀ at the visible wavelength of 633 nm. A performance comparison of the two plasmonic lenses is shown, demonstrating improvements to the power enhancement, with a 22% and 16.5% increase when using 2D (ideal) or 3D (realistic plasmonic) meniscus designs, respectively, compared to the power enhancement obtained with convex-planar lenses. It is also shown that the depth of focus of the focal spot presents a 19.8% decrease when using meniscus lenses in 2D and a 34.3% decrease when using the proposed 3D plasmonic meniscus designs. The broadband response of a plasmonic meniscus lens (550–750 nm wavelength range) is also studied along with the influence of potential fabrication errors on the generated effective focal length. The proposed plasmonic lenses could be exploited as alternative focusing devices for surface plasmons polaritons in applications such as sensing.

Optical Phenomena in Mesoscale Dielectric Particles

During the last decade, new unusual physical phenomena have been discovered in studying the optics of dielectric mesoscale particles of an arbitrary three-dimensional shape with the Mie size parameter near 10 (q~10). The paper provides a brief overview of these phenomena from optics to terahertz, plasmonic and acoustic ranges. The different particle configurations (isolated, regular or Janus) are discussed, and the possible applications of such mesoscale structures are briefly reviewed herein in relation to the field enhancement, nanoparticle manipulation and super-resolution imaging. The number of interesting applications indicates the appearance of a new promising scientific direction in optics, terahertz and acoustic ranges, and plasmonics. This paper presents the authors’ approach to these problems.

Diffraction limited photonic hook via scattering and diffraction of dual-dielectric structures

Photonic hooks have demonstrated to be great candidates for multiple applications ranging from sensing up to optical trapping. In this work, we propose a mechanism to produce such bent structured light beams by exploiting the diffraction and scattering generated by a pair of dielectric rectangles immersed in free space. It is shown how the photonic hooks are generated away from the output surface of the dielectrics by correctly engineering each individual dielectric structure to generate minimum diffraction and maximum scattering along the propagation axis. Different scenarios are studied such as dual-dielectric structures having different lateral dimensions and refractive index as well as cases when both dielectrics have the same lateral dimensions. The results are evaluated both numerically and theoretically demonstrating an excellent agreement between them. These results may open new avenues for optical trapping, focusing and sensing devices via compact and simple dual-dielectric structures.

Plasmonic nanojet: an experimental demonstration

We propose and study a microstructure based on a dielectric cuboid placed on a thin metal film that can act as an efficient plasmonic lens allowing the focusing of surface plasmons at the subwavelength scale. Using numerical simulations of surface plasmon polariton (SPP) field intensity distributions, we observe high-intensity subwavelength spots and formation of the plasmonic nanojet (PJ) at the telecommunication wavelength of 1530 nm. The fabricated microstructure was characterized using amplitude and phase-resolved scattering-type scanning near-field optical microscopy. We show the first experimental observation of the PJ effect for the SPP waves. Such a novel, to the best of our knowledge, and simple platform can provide new pathways for plasmonics, high-resolution imaging, and biophotonics, as well as optical data storage.