scholarly journals The near-axis backflow of energy in a tightly focused optical vortex with circular polarization

2018 ◽  
Vol 42 (3) ◽  
pp. 392-400 ◽  
Author(s):  
V. V. Kotlyar ◽  
A. G. Nalimov ◽  
S. S. Stafeev
Keyword(s):  
Energy Flow ◽  
Focal Plane ◽  
Topological Charge ◽  
Optical Axis ◽  
Optical Vortex ◽  
Diffractive Lens ◽  
Circularly Polarized ◽  
Left Hand ◽  
Maximum Value ◽  
Airy Disk

Using the Richards-Wolf formulae for a diffractive lens, we show that in the focal plane of a sharply focused left-hand circularly polarized optical vortex with the topological charge 2 there is an on-axis backflow of energy (as testified by the negative axial projection of the Poynting vector). The result is corroborated by the FDTD-aided rigorous calculation of the diffraction of a left-hand circularly polarized plane wave by a vortex zone plate with the topological charge 2 and the NA≈1. Moreover, the back- and direct flows of energy are comparable in magnitude. We have also shown that while the backflow of energy takes place on the entire optical axis, it has a maximum value in the focal plane, rapidly decreasing with distance from the focus. The length of a segment along the optical axis at which the modulus of the backflow drops by half (the depth of backflow) almost coincides with the depth of focus, and the transverse circle in which the energy flow is reversed roughly coincides with the Airy disk.

scholarly journals Backward flow of energy for an optical vortex with arbitrary integer topological charge

2018 ◽  
Vol 42 (3) ◽  
pp. 408-413
Author(s):  
V. V. Kotlyar ◽  
A. A. Kovalev ◽  
A. G. Nalimov
Keyword(s):  
Energy Flow ◽  
Topological Charge ◽  
Optical Vortex ◽  
Radial Coordinate ◽  
Arbitrary Integer ◽  
Absolute Value ◽  
Left Hand ◽  
Electric And Magnetic Fields ◽  
Sharp Focusing ◽  
Focus Intensity

We analyze the sharp focusing of an arbitrary optical vortex with the integer topological charge m and circular polarization in an aplanatic optical system. Explicit formulas to describe all projections of the electric and magnetic fields near the focal spot are derived. Expressions for the near-focus intensity (energy density) and energy flow (projections of the Pointing vector) are also derived. The expressions derived suggest that for a left-hand circularly polarized optical vortex with m > 2, the on-axis backward flow is equal to zero, growing in the absolute value as a power 2(m – 2) of the radial coordinate. These relations also show that upon the negative propagation, the energy flow rotates around the optical axis.

scholarly journals An orbital energy flow and a spin flow at the tight focus

2021 ◽  
Vol 45 (4) ◽  
pp. 520-524
Author(s):  
S.S. Stafeev
Keyword(s):  
Energy Flow ◽  
Optical Axis ◽  
Polarized Light ◽  
Orbital Energy ◽  
Circularly Polarized Light ◽  
Circularly Polarized ◽  
Left Hand ◽  
Left Handed ◽  
Sharp Focus ◽  
Positive Projection

We have shown that a reverse energy flow (negative projection of the Poynting vector onto the optical axis) at the sharp focus of an optical vortex with topological charge 2 and left-hand circular polarization arises because the axial spin flow has a negative projection onto the optical axis and is greater in magnitude than positive projection onto the optical axis of the orbital energy flow (canonical energy flow). Also, using the Richards-Wolf formulas, it is shown that when focusing a left-handed circularly polarized light, in the region of the on-axis reverse energy flow, the light is right-handed circularly polarized.

scholarly journals Inversion of the longitudinal component of spin angular momentum in the focus of a left-handed circularly polarized beam

2020 ◽  
Vol 44 (5) ◽  
pp. 699-706
Author(s):  
A.G. Nalimov ◽  
E.S. Kozlova
Keyword(s):  
Angular Momentum ◽  
Energy Flow ◽  
Longitudinal Component ◽  
Angular Momentum Vector ◽  
Spin Angular Momentum ◽  
Momentum Vector ◽  
Circularly Polarized ◽  
Left Hand ◽  
Left Handed ◽  
Polarized Beam

It has been shown theoretically and numerically that in the sharp focus of a circularly polarized optical vortex, the longitudinal component of the spin angular momentum vector is inverted. Moreover, if the input light to the optical system is left-hand circularly polarized, it has been shown to be right-hand polarized in the focus near the optical axis. Since this effect occurs near the focus where a backward energy flow takes place, such an inversion of the spin angular momentum can be used to detect the backward energy flow.

scholarly journals Linear to circular polarization conversion in the sharp focus of an optical vortex

2021 ◽  
Vol 45 (1) ◽  
pp. 13-18
Author(s):  
A.G. Nalimov ◽  
S.S. Stafeev
Keyword(s):  
Energy Flow ◽  
Transverse Energy ◽  
Optical Axis ◽  
Center Of Mass ◽  
Polarization Vector ◽  
Optical Vortex ◽  
Spin Orbital ◽  
Theoretical Predictions ◽  
Linearly Polarized ◽  
The Right

We have shown that when sharply focusing a linearly polarized optical vortex with topological charge 2, in the near-axis region of the focal plane, not only does a reverse energy flow (the negative on-axis projection of the Poynting vector) occur, but also the right-handed circular polariza-tion of light. Moreover, due to spin-orbital angular momentum conversion, the on-axis polarization vector and the transverse energy flow rotate around the optical axis in the same direction (counter-clockwise). If an absorbing spherical microparticle is put in the focus on the optical axis, it will rotate around the axis and around its center of mass counterclockwise. Numerical simulation results confirms the theoretical predictions.

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 Comparison of backward flow values in the sharp focus of light fields with polarization and phase singularity

2019 ◽  
Vol 43 (2) ◽  
pp. 174-183 ◽  
Author(s):  
V.V. Kotlyar ◽  
A.G. Nalimov ◽  
S.S. Stafeev
Keyword(s):  
Topological Charge ◽  
Fdtd Method ◽  
Polarized Light ◽  
Polar Angle ◽  
Optical Vortex ◽  
Circularly Polarized Light ◽  
Circularly Polarized ◽  
Linearly Polarized ◽  
Phase Converter ◽  
Axis Light

Using Jones matrices and vectors, we show that an optical metasurface composed of a set of subwavelength binary diffraction gratings and characterized by an anisotropic transmittance described by a polarization rotation matrix by the angle mφ, where φ is the polar angle, forms an m-th order azimuthally or radially polarized beam when illuminated by linearly polarized light, generating an optical vortex with the topological charge m upon illumination by circularly polarized light. Such a polarization-phase converter (PPC) performs a spin-orbit transformation, similar to that performed by liquid-crystal q-plates. Using a FDTD method, it is numerically shown that when illuminating the PPC by a uniformly (linearly or circularly) polarized field with topological charge m = 2 and then focusing the output beam with a binary zone plate, a reverse on-axis light flow is formed, being comparable in magnitude with the direct optical flow. Moreover, the reverse flows obtained when focusing the circularly polarized optical vortex with the topological charge m = 2 and the second-order polarization vortex are shown to be the same in magnitude.

scholarly journals Topological charge of optical vortices and their superpositions

2020 ◽  
Vol 44 (2) ◽  
pp. 145-154
Author(s):  
V.V. Kotlyar ◽  
A.A. Kovalev ◽  
A.V. Volyar
Keyword(s):  
Finite Number ◽  
Topological Charge ◽  
Optical Axis ◽  
Weight Coefficient ◽  
Optical Vortex ◽  
Optical Vortices ◽  
Vortex Center ◽  
Absolute Value ◽  
The Individual ◽  
Weight Coefficients

An optical vortex passed through an arbitrary aperture (with the vortex center found within the aperture) or shifted from the optical axis of an arbitrary axisymmetric carrier beam is shown to conserve the integer topological charge (TC). If the beam contains a finite number of off-axis optical vortices with different TCs of the same sign, the resulting TC of the beam is shown to be equal to the sum of all constituent TCs. For a coaxial superposition of a finite number of the Laguerre-Gaussian modes (n, 0), the resulting TC equals that of the mode with the highest TC (including sign). If the highest positive and negative TCs of the constituent modes are equal in magnitude, then TC of the superposition is equal to that of the mode with the larger (in absolute value) weight coefficient. If both weight coefficients are the same, the resulting TC equals zero. For a coaxial superposition of two different-amplitude Gaussian vortices, the resulting TC equals that of the constituent vortex with the larger absolute value of the weight coefficient amplitude, irrespective of the relation between the individual TCs.

Bilayer split-ring chiral metamaterial based reconfigurable antenna for polarization conversion

Frequenz ◽  
2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Preet Kaur ◽  
Pravin R. Prajapati
Keyword(s):  
Low Cost ◽  
Axial Ratio ◽  
Center Frequency ◽  
Impedance Bandwidth ◽  
Split Ring ◽  
Circularly Polarized ◽  
Left Hand ◽  
Rectangular Patch ◽  
Mode 2 ◽  
Chiral Metamaterial

Abstract A bilayer split-ring chiral metamaterial converts the linearly polarized wave, into a nearly perfect left or right-handed circularly polarized wave. The proposed antenna is intended to operate at center frequency of 5.80 GHz with switchable polarization capability. The polarization re-configurability is achieved by electronically switching of two PIN-diode pairs, which are embedded into bilayer split-ring Chiral Metamaterial. The optimized length of rectangular patch is 16 mm and width is 12.1 mm. Two types of radiation characteristics offered by the proposed antenna; left hand circularly polarized in mode 1 and right hand circularly polarized in mode 2. Measured results show that its impedance bandwidth is 155 MHz from 5.70 to 5.855 GHz for both mode 1 and mode 2. The measured axial-ratio bandwidth is 100 MHz from 5.75 to 5.85 GHz for mode 1 and 110 MHz from 5.73 to 5.84 GHz for mode 2. Antenna has LHCP gain of 2.52 dBi and RHCP gain of −23 dBi in mode 1. RHCP gain of 2 dBi and polarization purity of about −20 dBi is obtained in mode 2. The proposed antenna has simple structure, low cost and it has potential application in field of wireless communication (i.e., WiMax, WLAN etc.).

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