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9 pages, 1165 KB

Open AccessArticle

Nonparaxial Exploding Cylindrical Vector Beams

by Marcos G. Barriopedro, Manuel Holguín and Miguel A. Porras

Photonics 2025, 12(11), 1083; https://doi.org/10.3390/photonics12111083 - 2 Nov 2025

Viewed by 583

Exploding or concentrating beams, vortex beams, and cylindrical vector beams have a precisely shaped transversal amplitude profile such that they produce a continuously concentrating and intensifying focal spot upon focusing as the lens aperture is opened. This effect is the physical manifestation of the mathematical fact that Fresnel diffraction integral predicts an infinite intensity at the focus when the aperture effects are ignored. Here, using a full electromagnetic, nonparaxial focusing model, we show that the singularity in exploding cylindrical vector beams is an artifact of the paraxial approximation. Nevertheless, the exploding or concentrating effect, alien to any other light beam with finite power, keeps going up to unit numerical aperture, equivalent to infinite aperture radius. This unique feature enables a dynamic control of the focal intensity and spot size down to the sub-wavelength scale using a single light beam, imitating similar control when focusing an ideal plane wave, but requiring a finite amount of power. Full article

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28 pages, 3787 KB

Open AccessEditor’s ChoiceReview

Plasmonic Sensors Based on a Metal–Insulator–Metal Waveguide—What Do We Know So Far?

by Muhammad A. Butt

Sensors 2024, 24(22), 7158; https://doi.org/10.3390/s24227158 - 7 Nov 2024

Cited by 27 | Viewed by 8347

Abstract

Metal–insulator–metal (MIM) waveguide-based plasmonic sensors are significantly important in the domain of advanced sensing technologies due to their exceptional ability to guide and confine light at subwavelength scales. These sensors exploit the unique properties of surface plasmon polaritons (SPPs) that propagate along the metal–insulator interface, facilitating strong field confinement and enhanced light–matter interactions. In this review, several critical aspects of MIM waveguide-based plasmonic sensors are thoroughly examined, including sensor designs, material choices, fabrication methods, and diverse applications. Notably, there exists a substantial gap between the numerical data and the experimental verification of these devices, largely due to the insufficient attention given to the hybrid integration of plasmonic components. This disconnect underscores the need for more focused research on seamless integration techniques. Additionally, innovative light-coupling mechanisms are suggested that could pave the way for the practical realization of these highly promising plasmonic sensors. Full article

(This article belongs to the Special Issue Waveguide-Based Sensors and Applications)

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13 pages, 11012 KB

Open AccessArticle

Manipulating the Generation of Photonic Moiré Lattices Using Plasmonic Metasurfaces

by Zhanliang Mu, Yuqin Zhang, Jianshan An, Xuehui Zhang, Haoran Zhou, Hongsheng Song, Changwei He, Guiyuan Liu and Chuanfu Cheng

Nanomaterials 2024, 14(2), 230; https://doi.org/10.3390/nano14020230 - 20 Jan 2024

Cited by 2 | Viewed by 3642

Abstract

The generation of moiré lattices by superimposing two identical sublattices at a specific twist angle has garnered significant attention owing to its potential applications, ranging from two-dimensional materials to manipulating light propagation. While macroscale moiré lattices have been widely studied, further developments in manipulating moiré lattices at the subwavelength scale would be crucial for miniaturizing and integrating platforms. Here, we propose a plasmonic metasurface design consisting of rotated nanoslits arranged within N + N′ round apertures for generating focused moiré lattices. By introducing a spin-dependent geometric phase through the rotated nanoslits, an overall lens and spiral phase can be achieved, allowing each individual set of round apertures to generate a periodic lattice in the focal plane. Superimposing two sets of N and N′ apertures at specific twist angles and varying phase differences allows for the superposition of two sublattices with different periods, leading to the formation of diverse moiré patterns. Our simulations and theoretical results demonstrate the feasibility of our proposed metasurface design. Due to their compactness and tunability, the utilization of metasurfaces in creating nanoscale photonic moiré lattices is anticipated to find extensive applications in integrated and on-chip optical systems. Full article

(This article belongs to the Special Issue Nano-Photonics: Subwavelength Optical Elements, Metasurfaces, Plasmonics and Quantum Photonics)

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13 pages, 7252 KB

Open AccessArticle

Nonlocal Soft Plasmonics in Planar Homogeneous Multilayers

by Preethi Ramesh Narayan and Christin David

Photonics 2023, 10(9), 1021; https://doi.org/10.3390/photonics10091021 - 7 Sep 2023

Viewed by 1973

Abstract

Plasmonics is the study of resonant oscillations of free electrons in metals caused by incident electromagnetic radiation. Surface plasmons can focus and steer light on the subwavelength scale. Apart from metals, plasmonic phenomena can be observed in soft matter systems such as electrolytes which we study here. Resonant charge oscillations can be induced for ions in solution, however, due to their larger mass, they are plasmon-active in a lower frequency regime and on a larger wavelength scale. Our investigation focuses on spatial confinement which allows increasingly strong charge interactions and gives rise to nonlocality or spatial dispersion effects. We derive and discuss the nonlocal optical response of ionic plasmons using a hydrodynamic two-fluid model in a planar homogeneous three-layer system with electrolyte-dielectric interfaces. As in metals, we observe the emergence of additional longitudinal propagation modes in electrolytes which causes plasmonic broadening. Studying such systems enables us to identify and understand plasmonic phenomena in biological and chemical systems. Full article

(This article belongs to the Special Issue Electrolytes, Charged Fluids and Plasmas)

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13 pages, 6356 KB

Open AccessArticle

Mie Scattering Nanointerferometry for the Reconstruction of Tightly Focused Vector Fields by Polarization Decomposition

by Dong Yang, Haifeng Hu, Han Gao, Jian Chen and Qiwen Zhan

Photonics 2023, 10(5), 496; https://doi.org/10.3390/photonics10050496 - 26 Apr 2023

Cited by 4 | Viewed by 3176

Abstract

Tightly focused vector fields, which can be generated by focusing a light beam through a high-numerical-aperture objective, play an important role in nano-optics research. How to fully characterize this kind of field in the subwavelength scale is a challenging but important task. The Mie scattering nanointerferometry technique has been proposed to reconstruct the tightly focused vector field accurately. In this work, we theoretically demonstrate that the technique can be realized by collecting the transmitted light with two orthogonal polarization states simultaneously. Therefore, when nanoparticles are employed to scan the fields to be measured, more information of the scattering field can be acquired in the far field. This is helpful for solving the linear inverse scattering problem by reducing the number of scanning points, thus making the measurement more efficient. Full article

(This article belongs to the Special Issue Nanophotonics, Metasurface, and Topological Photonic Crystals: Physics and Applications)

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7 pages, 2345 KB

Open AccessArticle

Deep Subwavelength-Scale Light Focusing and Confinement in Nanohole-Structured Mesoscale Dielectric Spheres

by Yinghui Cao, Zhenyu Liu, Oleg V. Minin and Igor V. Minin

Nanomaterials 2019, 9(2), 186; https://doi.org/10.3390/nano9020186 - 1 Feb 2019

Cited by 37 | Viewed by 5281

Abstract

One of the most captivating properties of dielectric mesoscale particles is their ability to form a sub-diffraction limited-field localization region, near their shadow surfaces. However, the transverse size of the field localization region of a dielectric mesoscale particle is usually larger than λ/3. In this present paper, for the first time, we present numerical simulations to demonstrate that the size of the electromagnetic field that forms in the localized region of the dielectric mesoscale sphere can be significantly reduced by introducing a nanohole structure at its shadow surface, which improves the spatial resolution up to λ/40 and beyond the solid immersion diffraction limit of λ/2n. The proposed nanohole-structured microparticles can be made from common natural optical materials, such as glass, and are important for advancing the particle-lens-based super-resolution technologies, including sub-diffraction imaging, interferometry, surface fabrication, enhanced Raman scattering, nanoparticles synthesis, optical tweezer, etc. Full article

(This article belongs to the Special Issue Dynamics and Applications of Photon-Nanostructured Systems)

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8 pages, 2750 KB

Open AccessArticle

Broadband Ultra-Deep Sub-Diffraction-Limit Optical Focusing by Metallic Graded-Index (MGRIN) Lenses

by Yechuan Zhu, Weizheng Yuan, Hao Sun and Yiting Yu

Nanomaterials 2017, 7(8), 221; https://doi.org/10.3390/nano7080221 - 12 Aug 2017

Cited by 13 | Viewed by 5295

Abstract

The development of techniques for efficiently confining energy in the visible and infrared spectral regions to the deep subwavelength spatial scale with dimensions as small as a few nanometers would have great significance for scientific research and engineering practices. Such an ability to manipulate light is impossible for conventional dielectric lenses due to the diffraction limit. Here, we propose a metallic graded-index (MGRIN) lens formed by an array of coupled metallic waveguides with identical nanoscale widths embedded by index-varying dielectrics to enable the optical nanofocusing. The focusing mechanism of the MGRIN lens is theoretically investigated based on Hamiltonian optics, which are verified by the finite-difference time-domain (FDTD) method. Numerical results reveal that an ultra-deep subwavelength focus of 8 nm (λ/500) with a long focal depth (1.93λ) and enhanced field intensity can be achieved. Moreover, the nanofocusing capability of the MGRIN lens without redesigning the structure can be well kept when the incident wavelength changes over a broad range from visible to infrared. Our design of optical nanofocusing shows great potential for use in nano-optics and nanotechnology. Full article

(This article belongs to the Special Issue Multifunctional Metallic Nanomaterials)

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