scholarly journals Birth of optical vortices in propagating fields with an original fractional topological charge

2020 ◽  
Vol 44 (4) ◽  
pp. 493-500
Author(s):  
A.A. Kovalev ◽  
A.P. Porfirev
Keyword(s):  
Angular Momentum ◽  
Free Space ◽  
Topological Charge ◽  
Random Phase ◽  
Phase Variation ◽  
Optical Vortex ◽  
Optical Vortices ◽  
Integer Number ◽  
Weak Phase ◽  
Phase Distortions

In contrast to the orbital angular momentum (OAM), which is conserved on free space propagation, the topological charge (TC) of a paraxial optical vortex (OV) is not conserved in the general case. Here, we investigate a Gaussian beam with a fractional TC in the original plane and demonstrate both theoretically and numerically how the TC changes in the course of propagation. Depending on the proximity of the topological charge to an even or odd integer number, an optical vortex with the original fractional TC is shown to behave in a number of different ways. For simple OVs (Laguerre-Gaussian or Bessel-Gaussian modes), TC is conserved both in propagation and after weak phase distortions. An experiment shows that when scattered by a random phase screen, the integer TC of an OV is conserved right up to a random phase variation of π. Therefore, in the case of weak turbulences, it is expedient to measure a discretely varying TC instead of a continuously varying OAM.

scholarly journals Topological stability of optical vortices diffracted by a random phase screen

2019 ◽  
Vol 43 (6) ◽  
pp. 917-925 ◽  
Author(s):  
V.V. Kotlyar ◽  
A.A. Kovalev ◽  
A.P. Porfirev
Keyword(s):  
Intensity Distribution ◽  
Topological Charge ◽  
Random Phase ◽  
Optical Vortex ◽  
Phase Screen ◽  
Optical Vortices ◽  
Average Intensity ◽  
Vortex Identification ◽  
Topological Stability ◽  
Random Phase Screen

Here, we theoretically demonstrate that if a Gaussian optical vortex is distorted by a random phase screen (diffuser) then the average intensity distribution in the focus of a spherical lens has a form of a ring with a nonzero value on the optical axis. The radius of the average-intensity ring depends on both the topological charge of an optical vortex and on the diffusing power of the diffuser. Therefore, the value of the topological charge cannot be unambiguously determined from the radius of the average intensity ring. However, the value of the topological charge of the optical vortex can be obtained from the number of points of phase singularity that can be determined using a Shack-Hartmann wavefront sensor. It is also shown that if we use a linear combination of two optical vortices, then the average intensity distribution has local maxima, the number of which is equal to the difference of the topological charges of the two original vortices. The number of these maxima no longer depends on the scattering force of the diffuser and can serve as an indicator for optical vortex identification. Modeling and experiments confirm the theoretical conclusions.

scholarly journals Measurement of the orbital angular momentum of an astigmatic Hermite–Gaussian beam

2019 ◽  
Vol 43 (3) ◽  
pp. 356-367
Author(s):  
V.V. Kotlyar ◽  
A.A. Kovalev ◽  
A.P. Porfirev
Keyword(s):  
Angular Momentum ◽  
Gaussian Beam ◽  
Orbital Angular Momentum ◽  
Topological Charge ◽  
Optical Axis ◽  
Optical Vortex ◽  
Cylindrical Lens ◽  
Optical Vortices ◽  
Special Choice ◽  
Different Types

Here we study three different types of astigmatic Gaussian beams, whose complex amplitude in the Fresnel diffraction zone is described by the complex argument Hermite polynomial of the order (n, 0). The first type is a circularly symmetric Gaussian optical vortex with and a topological charge n after passing through a cylindrical lens. On propagation, the optical vortex "splits" into n first-order optical vortices. Its orbital angular momentum per photon is equal to n. The second type is an elliptical Gaussian optical vortex with a topological charge n after passing through a cylindrical lens. With a special choice of the ellipticity degree (1: 3), such a beam retains its structure upon propagation and the degenerate intensity null on the optical axis does not “split” into n optical vortices. Such a beam has fractional orbital angular momentum not equal to n. The third type is the astigmatic Hermite-Gaussian beam (HG) of order (n, 0), which is generated when a HG beam passes through a cylindrical lens. The cylindrical lens brings the orbital angular momentum into the original HG beam. The orbital angular momentum of such a beam is the sum of the vortex and astigmatic components, and can reach large values (tens and hundreds of thousands per photon). Under certain conditions, the zero intensity lines of the HG beam "merge" into an n-fold degenerate intensity null on the optical axis, and the orbital angular momentum of such a beam is equal to n. Using intensity distributions of the astigmatic HG beam in foci of two cylindrical lenses, we calculate the normalized orbital angular momentum which differs only by 7 % from its theoretical orbital angular momentum value (experimental orbital angular momentum is –13,62, theoretical OAM is –14.76).

scholarly journals Orbital angular momentum and topological charge of a Gaussian beam with multiple optical vortices

2020 ◽  
Vol 44 (1) ◽  
pp. 34-39
Author(s):  
A.A. Kovalev ◽  
V.V. Kotlyar ◽  
D.S. Kalinkina
Keyword(s):  
Numerical Simulation ◽  
Angular Momentum ◽  
Gaussian Beam ◽  
Orbital Angular Momentum ◽  
Topological Charge ◽  
Optical Axis ◽  
Random Phase ◽  
Beam Power ◽  
Optical Vortices ◽  
Local Intensity

Here we study theoretically and numerically a Gaussian beam with multiple optical vortices with unitary topological charge (TC) of the same sign, located uniformly on a circle. Simple expressions are obtained for the Gaussian beam power, its orbital angular momentum (OAM), and TC. We show that the OAM normalized to the beam power cannot exceed the number of vortices in the beam. This OAM decreases with increasing distance from the optical axis to the centers of the vortices. The topological charge, on the contrary, is independent of this distance and equals the number of vortices. The numerical simulation corroborates that after passing through a random phase screen (diffuser) and propagating in free space, the beams of interest can be identified by the number of local intensity minima (shadow spots) and by the OAM.

scholarly journals Topological charge and angular momentum of light beams carrying optical vortices

2004 ◽  
Author(s):  
M S Soskin ◽  
V N Gorshkov ◽  
M V Vasnctsov ◽  
J T Malos ◽  
N R Heckenberg
Keyword(s):  
Angular Momentum ◽  
Topological Charge ◽  
Optical Vortices ◽  
Light Beams

scholarly journals Strongly Focused Circularly Polarized Optical Vortices Regulated by a Fractal Conical Lens

2019 ◽  
Vol 10 (1) ◽  
pp. 28
Author(s):  
Zhirong Liu ◽  
Kelin Huang ◽  
Anlian Yang ◽  
Xun Wang ◽  
Philip H. Jones
Keyword(s):  
Angular Momentum ◽  
Optical Tweezers ◽  
Numerical Aperture ◽  
Optical Element ◽  
Optical Vortex ◽  
Optical Vortices ◽  
Circularly Polarized ◽  
Strong Focusing ◽  
New Type ◽  
Vortex Beams

In this paper, a recently-proposed pure-phase optical element, the fractal conical lens (FCL), is introduced for the regulation of strongly-focused circularly-polarized optical vortices in a high numerical aperture (NA) optical system. Strong focusing characteristics of circularly polarized optical vortices through a high NA system in cases with and without a FCL are investigated comparatively. Moreover, the conversion between spin angular momentum (SAM) and orbital angular momentum (OAM) of the focused optical vortex in the focal vicinity is also analyzed. Results revealed that a FCL of different stage S could significantly regulate the distributions of tight focusing intensity and angular momentum of the circularly polarized optical vortex. The interesting results obtained here may be advantageous when using a FCL to shape vortex beams or utilizing circularly polarized vortex beams to exploit new-type optical tweezers.

scholarly journals Topological charge and angular momentum of light beams carrying optical vortices

1997 ◽  
Vol 56 (5) ◽  
pp. 4064-4075 ◽  
Author(s):  
M. S. Soskin ◽  
V. N. Gorshkov ◽  
M. V. Vasnetsov ◽  
J. T. Malos ◽  
N. R. Heckenberg
Keyword(s):  
Angular Momentum ◽  
Topological Charge ◽  
Optical Vortices ◽  
Light Beams

scholarly journals Phyllotaxis-inspired nanosieves with multiplexed orbital angular momentum

eLight ◽  
2021 ◽  
Vol 1 (1) ◽  
Author(s):  
Zhongwei Jin ◽  
David Janoschka ◽  
Junhong Deng ◽  
Lin Ge ◽  
Pascal Dreher ◽  
...  
Keyword(s):  
Free Space ◽  
High Capacity ◽  
Vortex Generator ◽  
Optical Vortex ◽  
Optical Vortices ◽  
Time Resolved ◽  
Optical Applications ◽  
On Chip ◽  
Pine Cones ◽  
Meta Atom

AbstractNanophotonic platforms such as metasurfaces, achieving arbitrary phase profiles within ultrathin thickness, emerge as miniaturized, ultracompact and kaleidoscopic optical vortex generators. However, it is often required to segment or interleave independent sub-array metasurfaces to multiplex optical vortices in a single nano-device, which in turn affects the device’s compactness and channel capacity. Here, inspired by phyllotaxis patterns in pine cones and sunflowers, we theoretically prove and experimentally report that multiple optical vortices can be produced in a single compact phyllotaxis nanosieve, both in free space and on a chip, where one meta-atom may contribute to many vortices simultaneously. The time-resolved dynamics of on-chip interference wavefronts between multiple plasmonic vortices was revealed by ultrafast time-resolved photoemission electron microscopy. Our nature-inspired optical vortex generator would facilitate various vortex-related optical applications, including structured wavefront shaping, free-space and plasmonic vortices, and high-capacity information metaphotonics.

Optical vortices in fiber

Nanophotonics ◽  
2013 ◽  
Vol 2 (5-6) ◽  
pp. 455-474 ◽  
Author(s):  
Siddharth Ramachandran ◽  
Poul Kristensen
Keyword(s):  
Angular Momentum ◽  
Optical Fibers ◽  
Orbital Angular Momentum ◽  
Optical Vortex ◽  
Optical Vortices ◽  
New Class ◽  
Phase Singularities ◽  
Vortex Beams ◽  
Exotic Beams

AbstractOptical vortex beams, possessing spatial polarization or phase singularities, have intriguing properties such as the ability to yield super-resolved spots under focussing, and the ability to carry orbital angular momentum that can impart torque to objects. In this review, we discuss the means by which optical fibers, hitherto considered unsuitable for stably supporting optical vortices, may be used to generate and propagate such exotic beams. We discuss the multitude of applications in which a new class of fibers that stably supports vortices may be used, and review recent experiments and demonstration conducted with such fibers.

scholarly journals Transformation of a high-order edge dislocation to optical vortices (spiral dislocations)

2021 ◽  
Vol 45 (3) ◽  
pp. 319-323
Author(s):  
V.V. Kotlyar ◽  
A.A. Kovalev ◽  
A.G. Nalimov
Keyword(s):  
Angular Momentum ◽  
Orbital Angular Momentum ◽  
Edge Dislocation ◽  
Topological Charge ◽  
Hermite Polynomial ◽  
High Order ◽  
Cylindrical Lens ◽  
Optical Vortices ◽  
Focal Distance ◽  
Straight Line

We theoretically show that an astigmatic transformation of an nth-order edge dislocation (a zero-intensity straight line) produces n optical elliptical vortices (spiral dislocations) with unit topological charge at the double focal distance from the cylindrical lens, located on a straight line perpendicular to the edge dislocation, at points whose coordinates are the roots of an nth-order Hermite polynomial. The orbital angular momentum of the edge dislocation is proportional to the order n.

Sign in / Sign up

Export Citation Format

Share Document