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A special issue of Photonics (ISSN 2304-6732).

Deadline for manuscript submissions: closed (31 May 2022) | Viewed by 12126

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Special Issue Editor

Prof. Dr. Enrique J. Galvez

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Guest Editor

Department of Physics and Astronomy, Colgate University, 13 Oak Drive Hamilton, NY 13346, USA
Interests: geometric phase in optics; optical beams in high-order modes; singular optics; photon entanglement; quantum interference with correlated photons

Special Issue Information

Dear Colleagues,

We invite submissions to the Special Issue “Singular Optics”. The aim of this Special Issue is to present research works relating to the creation, manipulation, propagation, and detection of complex light beams that contain optical singularities. These may include optical vortices, caustics, knots, c-points, c-lines, Mobius polarization, or other related phenomena. This also includes works on the interaction of complex light with media via novel optical forces or interactions such as exchange of linear, spin, or orbital angular momentum and the manipulation of matter with light patterns.

Prof. Dr. Enrique J. Galvez
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Photonics is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Published Papers (6 papers)

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Research

9 pages, 9903 KiB

Open AccessArticle

Dynamics of Fractional Vortex Beams at Fraunhofer Diffraction Zone

and

Photonics 2022, 9(7), 479; https://doi.org/10.3390/photonics9070479 - 09 Jul 2022

Cited by 1 | Viewed by 1142

Abstract

Fractional vortex beams (FVBs) possess unique topological properties that are manifested in the vortex distribution. However, there are still discrepancies in the value of the vortex strength of FVBs at the far field. In this work we present a complete picture of the behavior of the phase singularities of non-integer (commonly known as fractional) beams in the Fraunhofer diffraction region and demonstrate a very good correspondence between experiments and simulations. As shown in the text, the original beam waist

ω_{0}

was found to be a key factor relating to the beam profile topology. This variable was measured in the process of calibrating the experiment. Finally, an experimental method to obtain the non-integer topological charge is proposed. This method only requires an analysis of the intensity, knowledge of the transition behaviors, and the beam waist. Full article

(This article belongs to the Special Issue Singular Optics)

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Graphical abstract

13 pages, 14296 KiB

Open AccessArticle

Generation and Detection of Optical Vortices with Multiple Cascaded Spiral Phase Plates

and

Photonics 2022, 9(5), 354; https://doi.org/10.3390/photonics9050354 - 18 May 2022

Cited by 3 | Viewed by 1795

Abstract

Spiral phase plate (SPP) is the widely used method in the generation of vortex beam (VB) with fixed topological charges (TCs) for specific wavelength. Although VB with large TCs can be directly generated by using the SPP with high vortex order. The fabrication of high-quality SPPs with high vortex orders usually requires complex manufacturing process and high machining accuracy. An alternative method to generate VBs with large TCs is cascaded multiple SPPs with low order. In this study, we numerically calculate the transmitted light field of cascaded multiple SPPs according to the Huygens–Fresnel diffraction integral, and perform the experimental verifications. Based on cascading 6 SPPs (3 SPPs with TCs of 2, and 3 SPPs with TCs 4, respectively), an VB with TCs as high as 18 is generated. Furthermore, The TCs of the generated VB are detected by coaxial and off-axis interfering with fundamental Gaussian beam or its conjugate beam, respectively. The generated fork and spiral patterns allow us to distinguish the value and sign of TCs carried by the VB. The experimental results coincide well with the theoretical simulations. The fork pattern shows better resolution than the spiral one, and the petal pattern with small spiral allows us to distinguish large TCs with a higher resolution. Full article

(This article belongs to the Special Issue Singular Optics)

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9 pages, 2950 KiB

Open AccessArticle

Singular Warped Beams Controlled by Tangent Phase Modulation

Gustavo Funes

Eduardo Peters

and

Jaime Anguita

Photonics 2021, 8(8), 343; https://doi.org/10.3390/photonics8080343 - 23 Aug 2021

Cited by 1 | Viewed by 1756

Abstract

We analyze the effect of spatial phase modulation using non-linear functions applied to singular warped beams to control their topological states and intensity distribution. Such beams are candidates for optical trapping and particle manipulation for their controllable pattern of intensities and singularities. We first simulate several kinds of warped beams to analyze their intensity profiles and propagation characteristics. Secondly, we experimentally validate the simulations and investigate the far-field profiles. By calculating the intensity gradients, we describe how these beams are qualified candidates for optical manipulation and trapping. Full article

(This article belongs to the Special Issue Singular Optics)

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9 pages, 7680 KiB

Open AccessCommunication

Toroidal Vortices of Energy in Tightly Focused Second-Order Cylindrical Vector Beams

Sergey S. Stafeev

Elena S. Kozlova

and

Victor V. Kotlyar

Photonics 2021, 8(8), 301; https://doi.org/10.3390/photonics8080301 - 28 Jul 2021

Cited by 1 | Viewed by 1794

Abstract

In this paper, we simulate the focusing of a cylindrical vector beam (CVB) of second order, using the Richards–Wolf formula. Many papers have been published on focusing CVB, but they did not report on forming of the toroidal vortices of energy (TVE) near the focus. TVE are fluxes of light energy in longitudinal planes along closed paths around some critical points at which the flux of energy is zero. In the 3D case, such longitudinal energy fluxes form a toroidal surface, and the critical points around which the energy rotates form a circle lying in the transverse plane. TVE are formed in pairs with different directions of rotation (similar to optical vortices with topological charges of different signs). We show that when light with a wavelength of 532 nm is focused by a lens with numerical aperture NA = 0.95, toroidal vortices periodically appear at a distance of about 0.45 μm (0.85 λ) from the axis (with a period along the z-axis of 0.8 μm (1.5 λ)). The vortices arise in pairs: the vortex nearest to the focal plane is twisted clockwise, and the next vortex is twisted counterclockwise. These vortices are accompanied by saddle points. At higher distances from the z-axis, this pattern of toroidal vortices is repeated, and at a distance of about 0.7 μm (1.3 λ), a region in which toroidal vortices are repeated along the z-axis is observed. When the beam is focused and limited by a narrow annular aperture, these toroidal vortices are not observed. Full article

(This article belongs to the Special Issue Singular Optics)

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11 pages, 1199 KiB

Open AccessArticle

Light Confinement with Structured Beams in Gold Nanoparticle Suspensions

Argelia Balbuena Ortega

Felix E. Torres-González

Valentin López Gayou

Raul Delgado Macuil

Gaetano Assanto

and

Karen Volke-Sepulveda

Photonics 2021, 8(6), 221; https://doi.org/10.3390/photonics8060221 - 15 Jun 2021

Cited by 3 | Viewed by 2120

Abstract

We carry out an experimental campaign to investigate the nonlinear self-defocusing propagation of singular light beams with various complex structures of phase and intensity in a colloidal suspension of gold nanoparticles with a plasmonic resonance near the laser wavelength (532nm). Studying optical vortices embedded in Gaussian beams, Bessel vortices and Bessel-cosine (necklace) beams, we gather evidence that while intense vortices turn into two-dimensional dark solitons, all structured wavepackets are able to guide a weak Gaussian probe of different wavelength (632.8 nm) along the dark core. The probe confinement also depends on the topological charge of the singular pump. Full article

(This article belongs to the Special Issue Singular Optics)

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11 pages, 2252 KiB

Open AccessCommunication

Propagation-Invariant Off-Axis Elliptic Gaussian Beams with the Orbital Angular Momentum

Alexey A. Kovalev

Victor V. Kotlyar

and

Darya S. Kalinkina

Photonics 2021, 8(6), 190; https://doi.org/10.3390/photonics8060190 - 28 May 2021

Cited by 2 | Viewed by 2696

Abstract

We studied paraxial light beams, obtained by a continuous superposition of off-axis Gaussian beams with their phases chosen so that the whole superposition is invariant to free-space propagation, i.e., does not change its transverse intensity shape. Solving a system of five nonlinear equations for such superpositions, we obtained an analytical expression for a propagation-invariant off-axis elliptic Gaussian beam. For such an elliptic beam, an analytical expression was derived for the orbital angular momentum, which was shown to consist of two terms. The first one is intrinsic and describes the momentum with respect to the beam center and is shown to grow with the beam ellipticity. The second term depends parabolically on the distance between the beam center and the optical axis (similar to the Steiner theorem in mechanics). It is shown that the ellipse orientation in the transverse plane does not affect the normalized orbital angular momentum. Such elliptic beams can be used in wireless optical communications, since their superpositions do not interfere in space, if they do not interfere in the initial plane. Full article

(This article belongs to the Special Issue Singular Optics)

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