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15 pages, 15053 KiB

Open AccessArticle

Simple Direct Measurement of the Orbital Stokes Parameters in Structured Vortex Beams

by Alexander Volyar, Mikhail Bretsko, Server Khalilov and Yana Akimova

Photonics 2024, 11(11), 1095; https://doi.org/10.3390/photonics11111095 - 20 Nov 2024

Viewed by 360

Abstract

An analogy with the polarization Stokes parameters and symplectic methods of the second-order intensity moment matrix allowed us to develop a simple technique for measuring the orbital Stokes parameters followed by mapping the structured beam states onto the orbital Poincaré sphere. The measurement [...] Read more.

An analogy with the polarization Stokes parameters and symplectic methods of the second-order intensity moment matrix allowed us to develop a simple technique for measuring the orbital Stokes parameters followed by mapping the structured beam states onto the orbital Poincaré sphere. The measurement process involves only two shots of the beam intensity patterns in front of a cylindrical lens and in its double focus. Such a simple measurement approach is based on the reciprocity effect between the experimentally measured cross-intensity element

W_{x y}

and the orbital angular momentum of the intensity moment matrix. For experiments, we chose two types of two-parameter structured beams, namely, structured Laguerre–Gaussian beams and binomial beams. We obtained a good agreement between our theoretical background and the experiments, as well as the results of other authors. Full article

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

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23 pages, 59448 KiB

Open AccessArticle

Interference Generation of a Reverse Energy Flow with Varying Orbital and Spin Angular Momentum Density

by Andrey V. Ustinov, Alexey P. Porfirev and Svetlana N. Khonina

Photonics 2024, 11(10), 962; https://doi.org/10.3390/photonics11100962 - 14 Oct 2024

Viewed by 770

Abstract

This paper presents a novel method for generating and shaping reverse energy flow through the interference of light fields from a minimal number of point light sources. Until now, reverse energy flow has only been observed using complex light fields, such as optical [...] Read more.

This paper presents a novel method for generating and shaping reverse energy flow through the interference of light fields from a minimal number of point light sources. Until now, reverse energy flow has only been observed using complex light fields, such as optical vortices or cylindrical vector beams, limiting the formation of reverse energy flow near the optical axis. We demonstrate both analytically and numerically that unbounded regions of reverse energy flow can be achieved with just two point light sources, positioned asymmetrically at specific angles (e.g., 90 or 45 degrees) and with particular polarization states. The results indicate that the relative reverse energy flow can be enhanced by increasing the number of sources to three or four, adjusting their polarization, or introducing a vortex phase singularity. The presence of an initially embedded asymmetry in the fields under consideration leads to the formation of a non-uniform distribution of spin and orbital angular momentum density. Variations in the polarization state, as well as the introduction of a vortex phase singularity, allow for changing the distribution of angular momentum density while maintaining the presence of a reverse energy flow. We also explore the feasibility of implementing the obtained results using sectional phase diffractive optical elements, which will enhance the energy efficiency of the generated fields compared to point sources. Full article

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

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27 pages, 52145 KiB

Open AccessArticle

Polarization-Mode Transformation of the Light Field during Diffraction on Amplitude Binary Gratings

by Pavel A. Khorin, Mariia P. Mamaeva, Yury V. Kapitonov and Svetlana N. Khonina

Photonics 2024, 11(9), 848; https://doi.org/10.3390/photonics11090848 - 6 Sep 2024

Viewed by 756

Abstract

In this paper, a comparative analysis and numerical simulation of operation of two types of amplitude binary gratings (conventional and fork), both in the focal plane and near-field diffraction under illumination by mode beams with different polarization states, were performed. The simulation of [...] Read more.

In this paper, a comparative analysis and numerical simulation of operation of two types of amplitude binary gratings (conventional and fork), both in the focal plane and near-field diffraction under illumination by mode beams with different polarization states, were performed. The simulation of the field formation in the focal plane was performed using the Richards–Wolf formalism. The diffraction calculation in the near-field diffraction was performed based on the FDTD method, considering the 3D structure of optical elements. The possibility of multiplying the incident beam in different diffraction orders of binary gratings and the polarization transformation associated with spin–orbit interaction at tight focusing were shown. In this case, various polarization transformations were formed in ±1 diffraction orders of the fork grating due to different signs of the introduced vortex-like phase singularity. The obtained results can be useful for the laser processing of materials and surface structuring. Full article

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

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21 pages, 8555 KiB

Open AccessArticle

Measured and Predicted Speckle Correlation from Diffractive Metasurface Diffusers

by Sif Fugger, Jonathan Gow, Hongfeng Ma, Villads Egede Johansen and Ulrich J. Quaade

Photonics 2024, 11(9), 845; https://doi.org/10.3390/photonics11090845 - 5 Sep 2024

Viewed by 1062

Abstract

Speckles are inherent in structured laser-based light projection using diffractive optics such as metasurfaces or diffractive optical elements (DOEs). One application of structured light is to provide illumination for machine vision and depth sensing. This is particularly attractive for mobile or low-power applications, [...] Read more.

Speckles are inherent in structured laser-based light projection using diffractive optics such as metasurfaces or diffractive optical elements (DOEs). One application of structured light is to provide illumination for machine vision and depth sensing. This is particularly attractive for mobile or low-power applications, where metasurfaces provide a compact, customizable solution, which can furthermore reach extreme field of illuminations. However, the speckles might limit detection capabilities by, e.g., lowering the detection range or providing false results. In this work, we present a series of measurements with matching simulations on a 70 × 50 degrees diffractive diffuser using different light sources (varying divergence angles + VCSEL array) to quantify the impact of speckles. We observe a qualitative agreement in speckle correlation between the measurements and the simulations and explain, in part using cross-correlation for analysis, why we do not observe the same speckle pattern between the measurements and the simulations. By performing extra simulations, we conclude that by only changing the light source, there is a limit to the reduction of the speckle contrast which, we can achieve, and, to reduce it further, alternative approaches such as changing the design method of the diffractive diffuser must be harnessed. Full article

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

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14 pages, 9002 KiB

Open AccessArticle

Design of Cascaded DOEs for Focusing Different Wavelengths to Different Points

by Leonid L. Doskolovich, Daniil V. Soshnikov, Georgy A. Motz, Egor V. Byzov, Evgeni A. Bezus, Dmitry A. Bykov and Nikolay L. Kazanskiy

Photonics 2024, 11(9), 791; https://doi.org/10.3390/photonics11090791 - 23 Aug 2024

Viewed by 719

Abstract

We propose a task-specific method for calculating cascaded phase diffractive optical elements (DOEs) for focusing Q incident beams with different wavelengths to Q given points. Due to the utilization of a special optimization criterion, the proposed method makes it possible to calculate the [...] Read more.

We propose a task-specific method for calculating cascaded phase diffractive optical elements (DOEs) for focusing Q incident beams with different wavelengths to Q given points. Due to the utilization of a special optimization criterion, the proposed method makes it possible to calculate the elements of the cascaded DOE in a sequential way. In addition, the calculation of the diffractive microrelief of each DOE in the cascade is reduced to solving a set of independent and computationally simple “pointwise” optimization problems. Using the proposed method, cascades of two DOEs were designed to focus radiation of 11 different wavelengths to 11 different points. The presented numerical simulation results demonstrate good performance of the method. The chosen operating wavelengths correspond to a set of widely used vegetation indices enabling monitoring the vegetation status conditions and tracking the environmental stresses. This makes the obtained results promising for the application in remote sensing and smart agriculture. Full article

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

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13 pages, 1250 KiB

Open AccessArticle

Super-Oscillating Diffractive Optical Spot Generators

by Markus E. Testorf, Praneeth Gadamsetti, Paolo Batoni and Menelaos K. Poutous

Photonics 2024, 11(9), 790; https://doi.org/10.3390/photonics11090790 - 23 Aug 2024

Viewed by 535

Abstract

The prior discrete Fourier transform (PDFT) is applied to the design of super-oscillating diffractive optical elements with rotational symmetry. Numerical simulations of the filter response are used to demonstrate the potential of the PDFT-based approach, which includes a regularization method for improved numerical [...] Read more.

The prior discrete Fourier transform (PDFT) is applied to the design of super-oscillating diffractive optical elements with rotational symmetry. Numerical simulations of the filter response are used to demonstrate the potential of the PDFT-based approach, which includes a regularization method for improved numerical and functional stability of the filter design. For coherent monochromatic illumination, the Strehl ratio of spot generators as a function of the spot radius is compared to the theoretical upper bound. It is shown that the performance of the PDFT design varies significantly depending on the aperture function and the encoding as a phase-only diffractive element. Experimental results are in good agreement with simulations and demonstrate the moderate demands to implement super-oscillating diffractive optical elements. Full article

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

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15 pages, 4455 KiB

Open AccessArticle

Design of Diffractive Neural Networks for Solving Different Classification Problems at Different Wavelengths

by Georgy A. Motz, Leonid L. Doskolovich, Daniil V. Soshnikov, Egor V. Byzov, Evgeni A. Bezus, Nikita V. Golovastikov and Dmitry A. Bykov

Photonics 2024, 11(8), 780; https://doi.org/10.3390/photonics11080780 - 22 Aug 2024

Viewed by 739

Abstract

We consider the problem of designing a diffractive neural network (DNN) consisting of a set of sequentially placed phase diffractive optical elements (DOEs) and intended for the optical solution of several given classification problems at different operating wavelengths, so that each classification problem [...] Read more.

We consider the problem of designing a diffractive neural network (DNN) consisting of a set of sequentially placed phase diffractive optical elements (DOEs) and intended for the optical solution of several given classification problems at different operating wavelengths, so that each classification problem is solved at the corresponding wavelength. The problem of calculating the DNN is formulated as the problem of minimizing a functional that depends on the functions of the diffractive microrelief height of the DOEs constituting the DNN and represents the error in solving the given classification problems at the operating wavelengths. We obtain explicit and compact expressions for the derivatives of this functional, and using them, we formulate a gradient method for the DNN calculation. Using this method, we design DNNs for solving the following three classification problems at three different wavelengths: the problem of classifying handwritten digits from the MNIST database, the problem of classifying fashion products from the Fashion MNIST database, and the problem of classifying ten handwritten letters from the EMNIST database. The presented simulation results of the designed DNNs demonstrate the high performance of the proposed method. Full article

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

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14 pages, 4139 KiB

Open AccessArticle

Design of Photonic Molecule-Based Multiway Beam Splitter/Coupler with Variable Division Ratio

by Yury E. Geints

Photonics 2024, 11(7), 600; https://doi.org/10.3390/photonics11070600 - 26 Jun 2024

Viewed by 1037

Abstract

An optical beam splitter is used for dividing an input optical beam into several separate beams with a specific power ratio. Usually, conventional optical beam splitters have bulky dimensions (many optical wavelengths) and a fixed dividing ratio, which significantly limit the design of [...] Read more.

An optical beam splitter is used for dividing an input optical beam into several separate beams with a specific power ratio. Usually, conventional optical beam splitters have bulky dimensions (many optical wavelengths) and a fixed dividing ratio, which significantly limit the design of new miniaturized optical devices and integrated optical circuits. We propose and investigate in detail a novel physical concept of a highly miniaturized (up to two working wavelengths) planar optical resonant splitter/coupler with a switching element comprising a photonic molecule (PM) pair dispersing input optical fluxes in multiple directions with a tailored power ratio. The structural design of the proposed splitter is based on a silicon-on-insulator (SOI) platform and composed of high-quality resonators in the form of electromagnetically coupled submicron-sized microcylinders. The control on the power division ratio and the selection of optical beam directions is realized by tuning the photonic splitter structure to the corresponding resonance of the PM supermode. Compared to known analogs, the proposed design is easy and cheap in fabrication. Because of its tiny dimensions, it is suitable for integration into a “System-on-a-chip” platform and can dynamically change the beam power division ratio by input wave-phase manipulation. Full article

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

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18 pages, 2319 KiB

Open AccessEditor’s ChoiceArticle

Propagation of a Partially Coherent Bessel–Gaussian Beam in a Uniform Medium and Turbulent Atmosphere

by Igor Lukin and Vladimir Lukin

Photonics 2024, 11(6), 562; https://doi.org/10.3390/photonics11060562 - 14 Jun 2024

Viewed by 1616

Abstract

In this paper, the coherent properties of partially coherent Bessel–Gaussian optical beams propagating through a uniform medium (free space) or a turbulent atmosphere are examined theoretically. The consideration is based on the analytical solution of the equation for the transverse second-order mutual coherence [...] Read more.

In this paper, the coherent properties of partially coherent Bessel–Gaussian optical beams propagating through a uniform medium (free space) or a turbulent atmosphere are examined theoretically. The consideration is based on the analytical solution of the equation for the transverse second-order mutual coherence function of the field of partially coherent optical radiation in a turbulent atmosphere. For the partially coherent Bessel–Gaussian beam, the second-order mutual coherence function of the source field is taken as a Gaussian–Schell model. In this approximation, we analyze the behavior of the coherence degree and the integral coherence scale of these beams as a function of the propagation pathlength, propagation conditions, and beam parameters, such as the radius of the Gauss factor of the beam, parameter of the Bessel factor of the beam, topological charge, and correlation width of the source field of partially coherent radiation. It was found that, as a partially coherent vortex Bessel–Gaussian beam propagates through a turbulent atmosphere, there appear not two (as might be expected: one due to atmospheric turbulence and another due to the partial coherence of the source field), but only one ring dislocation of the coherence degree (due to the simultaneous effect of both these factors on the optical radiation). In addition, it is shown that the dislocation of the coherence degree that significantly affects the beam coherence level is formed only for beams, for which the coherence width of the source field is larger than the diameter of the first Fresnel zone. Full article

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

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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 - 4 May 2024

Cited by 1 | Viewed by 1297

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

Viewed by 935

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

Cited by 3 | Viewed by 1473

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 AccessEditor’s ChoiceArticle

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

Viewed by 1225

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 1074

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 AccessEditor’s ChoiceArticle

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 2 | Viewed by 1440

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

Cited by 1 | Viewed by 997

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

Jump to: Research

77 pages, 9183 KiB

Open AccessEditor’s ChoiceReview

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 6166

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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