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14 pages, 4641 KiB

Open AccessArticle

Polarization Strips in the Focus of a Generalized Poincaré Beam

by Victor V. Kotlyar, Alexey A. Kovalev, Alexey M. Telegin and Elena Sergeevna Kozlova

Photonics 2024, 11(5), 430; https://doi.org/10.3390/photonics11050430 (registering DOI) - 4 May 2024

Viewed by 435

Abstract

We analyze the tight focusing of a generalized Poincaré beam using a Richards–Wolf formalism. Conventional Poincaré beams are superpositions of two Laguerre–Gaussian beams with orthogonal polarization, while the generalized Poincaré beams are composed of two arbitrary optical vortices with rotationally symmetric amplitudes. Analytical [...] Read more.

We analyze the tight focusing of a generalized Poincaré beam using a Richards–Wolf formalism. Conventional Poincaré beams are superpositions of two Laguerre–Gaussian beams with orthogonal polarization, while the generalized Poincaré beams are composed of two arbitrary optical vortices with rotationally symmetric amplitudes. Analytical relationships for projections of the electric field in the focal plane are derived. Using the superposition of a right-handed circularly polarized plane wave and an optical vortex with a topological charge of −1 as an example, relationships for the intensity distribution and the longitudinal projection of the spin angular momentum vector are deduced. It is theoretically and numerically shown that the original beam has a topological charge of −1/2 and a C-point of circular polarization, and it is generated at the focal plane center, producing an on-axis C-line with a singularity index of −1/2 (a star). Furthermore, when making a full circle of some radius around the optical axis, the major axis vector of polarization ellipse is theoretically and numerically shown to form a one-sided polarization (Möbius) strip of order −3/2, which has three half-twists and a single ‘patching’ in which two oppositely directed vectors of the major axis of polarization ellipse occur close to each other. Full article

(This article belongs to the Special Issue Recent Advances in Diffractive Optics)

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10 pages, 2754 KiB

Open AccessArticle

Scattering over Varying Amplification Grating

by Er’el Granot

Photonics 2024, 11(3), 244; https://doi.org/10.3390/photonics11030244 - 8 Mar 2024

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Abstract

The scattering pattern from a narrow absorbing/amplifying grating is investigated. A simple model of a narrow amplifying grating is solved exactly numerically and approximately analytically for the regime where the beam’s wavelength is much shorter than the grating’s wavelength. The main result is [...] Read more.

The scattering pattern from a narrow absorbing/amplifying grating is investigated. A simple model of a narrow amplifying grating is solved exactly numerically and approximately analytically for the regime where the beam’s wavelength is much shorter than the grating’s wavelength. The main result is that the incident angle divides the scattering pattern into two regimes: below and above the incident angles. The former regime has a weak dependence on the incident angle but has a strong dependence on the scattering one. In this regime, a new grating formula is derived. The opposite occurs in the latter regime, which is very sensitive to the incident angle but has only weak dependence on the scattering angle. Consequently, at certain incident angles, all of the scattering is concentrated in the first regime, i.e., all scattering angles are lower than the incident angle. Full article

(This article belongs to the Special Issue Recent Advances in Diffractive Optics)

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15 pages, 3725 KiB

Open AccessArticle

Creating an Array of Parallel Vortical Optical Needles

by Paulius Šlevas and Sergej Orlov

Photonics 2024, 11(3), 203; https://doi.org/10.3390/photonics11030203 - 24 Feb 2024

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Abstract

We propose a method for creating parallel Bessel-like vortical optical needles with an arbitrary axial intensity distribution via the superposition of different cone-angle Bessel vortices. We analyzed the interplay between the separation of individual optical vortical needles and their respective lengths and introduce [...] Read more.

We propose a method for creating parallel Bessel-like vortical optical needles with an arbitrary axial intensity distribution via the superposition of different cone-angle Bessel vortices. We analyzed the interplay between the separation of individual optical vortical needles and their respective lengths and introduce a super-Gaussian function as their axial profile. We also analyzed the physical limitations to observe well-separated optical needles, as they are influenced by the mutual interference of the individual beams. To verify our theoretical and numerical results, we generated controllable spatial arrays of individual Bessel beams with various numbers and spatial separations by altering the spectrum of the incoming laser beam via the spatial light modulator. We demonstrate experimentally how to implement such beams using a diffractive mask. The presented method facilitates the creation of diverse spatial intensity distributions in three dimensions, potentially finding applications in specific microfabrication tasks or other contexts. These beams may have benefits in laser material processing applications such as nanochannel machining, glass via production, modification of glass refractive indices, and glass dicing. Full article

(This article belongs to the Special Issue Recent Advances in Diffractive Optics)

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16 pages, 4382 KiB

Open AccessArticle

Multispectral Narrowband Frustrated Total Internal Reflection Filter with Inclusions of Plasmonic Nanoparticles

by Nikolai I. Petrov

Photonics 2024, 11(2), 180; https://doi.org/10.3390/photonics11020180 - 16 Feb 2024

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Abstract

A spatial-frequency thin-film filter with inclusions of nanoparticles operating in the visible range of the spectrum is investigated. The effect of nanoparticles embedded in the central and lateral layers of the frustrated total internal reflection filter on the spectral characteristics, considering the frequency [...] Read more.

A spatial-frequency thin-film filter with inclusions of nanoparticles operating in the visible range of the spectrum is investigated. The effect of nanoparticles embedded in the central and lateral layers of the frustrated total internal reflection filter on the spectral characteristics, considering the frequency dispersion, is investigated. It is shown that plasmonic effects cause the splitting of the filter bandwidth into a set of narrow-band spectral lines and the angular splitting of the incident beam into a set of output beams. It is demonstrated that due to the difference in the resonance conditions for s- and p-polarization waves, the spectral lines of transparency do not coincide, which indicates the possibility of using the filter as a polarizer. Full article

(This article belongs to the Special Issue Recent Advances in Diffractive Optics)

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14 pages, 3100 KiB

Open AccessArticle

Vector Light Field Immediately behind an Ideal Spherical Lens: Spin–Orbital Conversion, Additional Optical Vortices, Spin Hall Effect, Magnetization

by Victor V. Kotlyar, Alexey A. Kovalev, Sergey S. Stafeev, Elena S. Kozlova and Alexey M. Telegin

Photonics 2023, 10(11), 1247; https://doi.org/10.3390/photonics10111247 - 9 Nov 2023

Cited by 1 | Viewed by 707

Abstract

The Richards–Wolf formulas not only adequately describe a light field at a tight focus, but also make it possible to describe a light field immediately behind an ideal spherical lens, that is, on a converging spherical wave front. Knowing all projections of light [...] Read more.

The Richards–Wolf formulas not only adequately describe a light field at a tight focus, but also make it possible to describe a light field immediately behind an ideal spherical lens, that is, on a converging spherical wave front. Knowing all projections of light field strength vectors behind the lens, the longitudinal components of spin and orbital angular momenta (SAM and OAM) can be found. In this case, the longitudinal projection of the SAM immediately behind the lens either remains zero or decreases. This means that the Spin–Orbital Conversion (SOC) effect where part of the “spin goes into orbit” takes place immediately behind the lens. And the sum of longitudinal projections of SAM and OAM is preserved. As for the spin Hall effect, it does not form right behind the lens, but appears as focusing occurs. That is, there is no Hall effect immediately behind the lens, but it is maximum at the focus. This happens because two optical vortices with topological charges (TCs) 2 and −2 and with spins of different signs (with left and right circular polarization) are formed right behind the lens. However, the total spin is zero since amplitudes of these vortices are the same. The amplitude of optical vortices becomes different while focusing and at the focus itself, and therefore regions with spins of different signs (Hall effect) appear. A general form of initial light fields which longitudinal field component is zero at the focus was found. In this case, the SAM vector can only have a longitudinal component that is nonzero. The SAM vector elongated only along the optical axis at the focus is used in magnetization task. Full article

(This article belongs to the Special Issue Recent Advances in Diffractive Optics)

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9 pages, 1280 KiB

Open AccessArticle

Genetic Optimization of the Y-Shaped Photonic Crystal NOT Logic Gate

by Vladimir Pavelyev, Yuliana Krivosheeva and Dimitriy Golovashkin

Photonics 2023, 10(10), 1173; https://doi.org/10.3390/photonics10101173 - 21 Oct 2023

Cited by 1 | Viewed by 997

Abstract

The present paper is devoted to the actual problem of photonic crystal (PhC) logic gate design. The development of components for photonic digital computing systems will provide opportunities for high-efficient information processing. The use of 2D photonic crystals is one of the most [...] Read more.

The present paper is devoted to the actual problem of photonic crystal (PhC) logic gate design. The development of components for photonic digital computing systems will provide opportunities for high-efficient information processing. The use of 2D photonic crystals is one of the most promising approaches to designing interference logic gates. Photonic crystal band gap and use of lattice defects are giving opportunities for flexible control of waveguiding light. Interference logic gates of NOT, OR, AND, and XOR types based on the Y-shaped structure are well known. However, known realizations have limited energy efficiency. Earlier, a method for minimizing energy losses at the PhC waveguide bending based on genetic optimization of the PhC waveguide topology was proposed and investigated. In this paper, the genetic algorithm for optimization of the PhC interference logic gate of the NOT type was used. Optimization of the Y-shaped topology allowed for an increase in the energy efficiency of the logic gate to 95%. A description of the developed numerical procedure as well as computer simulation results are presented. The developed procedure includes the possibility of taking into account the limitations of the technology to be used for the realization of a designed 2D PhC structure. Full article

(This article belongs to the Special Issue Recent Advances in Diffractive Optics)

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12 pages, 5137 KiB

Open AccessArticle

Influence of High-Order Twisting Phases on Polarization States and Optical Angular Momentum of a Vector Light Field

by Baoyin Liu, Yingqi Huang, Caixia Liu, Shu-Dan Wu, Khian-Hooi Chew and Rui-Pin Chen

Photonics 2023, 10(10), 1099; https://doi.org/10.3390/photonics10101099 - 29 Sep 2023

Viewed by 658

Abstract

This study investigates the influence of high-order twisting phases on polarization states and optical angular momentum of a vector light field with locally linear polarization and a hybrid state of polarization (SoP). The twisted vector optical field (TVOF) is experimentally generated based on [...] Read more.

This study investigates the influence of high-order twisting phases on polarization states and optical angular momentum of a vector light field with locally linear polarization and a hybrid state of polarization (SoP). The twisted vector optical field (TVOF) is experimentally generated based on the orthogonal polarization bases with high-order twisting phases. The initial SoP of a TVOF modulated by the high-order twisting phase possesses various symmetric distributions. The propagation properties of a high-order TVOF with locally linear polarization and hybrid SoP are explored, including the intensity compression, expansion, and conversion between the linear and circular polarization components. In particular, orbital angular momentum (OAM) appears in a high-order TVOF during propagation where no OAM exists in the initial field. The variation of OAM distribution in cross-section becomes more frequent with the increase of the twisting phase order. In addition, a non-symmetric OAM distribution appears in a non-isotropic TVOF, leading to the rotation of the beam around the propagation axis during propagation. The optical energy flow distribution of a high-order TVOF provides a more profound understanding of the propagation dynamics of high-order TVOF. These results provide a new approach for optical field manipulation in a high-order TVOF. Full article

(This article belongs to the Special Issue Recent Advances in Diffractive Optics)

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Review

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77 pages, 9183 KiB

Open AccessReview

Synergy between AI and Optical Metasurfaces: A Critical Overview of Recent Advances

by Zoran Jakšić

Photonics 2024, 11(5), 442; https://doi.org/10.3390/photonics11050442 - 9 May 2024

Viewed by 695

Abstract

The interplay between two paradigms, artificial intelligence (AI) and optical metasurfaces, nowadays appears obvious and unavoidable. AI is permeating literally all facets of human activity, from science and arts to everyday life. On the other hand, optical metasurfaces offer diverse and sophisticated multifunctionalities, [...] Read more.

The interplay between two paradigms, artificial intelligence (AI) and optical metasurfaces, nowadays appears obvious and unavoidable. AI is permeating literally all facets of human activity, from science and arts to everyday life. On the other hand, optical metasurfaces offer diverse and sophisticated multifunctionalities, many of which appeared impossible only a short time ago. The use of AI for optimization is a general approach that has become ubiquitous. However, here we are witnessing a two-way process—AI is improving metasurfaces but some metasurfaces are also improving AI. AI helps design, analyze and utilize metasurfaces, while metasurfaces ensure the creation of all-optical AI chips. This ensures positive feedback where each of the two enhances the other one: this may well be a revolution in the making. A vast number of publications already cover either the first or the second direction; only a modest number includes both. This is an attempt to make a reader-friendly critical overview of this emerging synergy. It first succinctly reviews the research trends, stressing the most recent findings. Then, it considers possible future developments and challenges. The author hopes that this broad interdisciplinary overview will be useful both to dedicated experts and a general scholarly audience. Full article

(This article belongs to the Special Issue Recent Advances in Diffractive Optics)

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