scholarly journals Sharp Focusing of a Hybrid Vector Beam with a Polarization Singularity

Photonics ◽  
2021 ◽  
Vol 8 (6) ◽  
pp. 227
Author(s):  
Victor V. Kotlyar ◽  
Sergey S. Stafeev ◽  
Anton G. Nalimov
Keyword(s):  
Focal Plane ◽  
Topological Charge ◽  
Light Field ◽  
Stokes Vector ◽  
Elliptical Polarization ◽  
Intensity Pattern ◽  
Singularity Index ◽  
Sharp Focusing ◽  
New Type ◽  
Local Polarization

The key result of this work is the use of the global characteristics of the polarization singularities of the entire beam as a whole, rather than the analysis of local polarization, Stokes and Poincare–Hopf indices. We extend Berry’s concept of the topological charge of scalar beams to hybrid vector beams. We discuss tightly focusing a new type of nth-order hybrid vector light field comprising n C-lines (circular polarization lines). Using a complex Stokes field, it is shown that the field polarization singularity index equals n/2 and does not preserve in the focal plane. The intensity and Stokes vector components in the focal plane are expressed analytically. It is theoretically and numerically demonstrated that at an even n, the intensity pattern at the focus is symmetrical, and instead of C-lines, there occur C-points around which axes of polarization ellipses are rotated. At n = 4, C-points characterized by singularity indices 1/2 and ‘lemon’-type topology are found at the focus. For an odd source field order n, the intensity pattern at the focus has no symmetry, and the field becomes purely vectorial (with no elliptical polarization) and has n V-points, around which linear polarization vectors are rotating.

scholarly journals Sharp focusing of beams with V-point polarization singularities

2021 ◽  
Vol 5 (45) ◽  
pp. 643-653
Author(s):  
V.V. Kotlyar ◽  
A.G. Nalimov ◽  
S.S. Stafeev ◽  
A.A. Kovalev
Keyword(s):  
Intensity Distribution ◽  
Linear Polarization ◽  
Light Field ◽  
Focal Spot ◽  
Polarization Direction ◽  
Intensity Pattern ◽  
Singularity Index ◽  
Local Maxima ◽  
Sharp Focus ◽  
Sharp Focusing

It is theoretically and numerically shown that when tightly focusing an n-th order vector light field that has the central V-point (at which the linear polarization direction is undetermined), the polarization singularity index n, and a "flower"-shaped intensity pattern with 2(n-1) lobes it forms a transverse intensity distribution with 2(n-1) local maxima. At the same time, a vector light field with the polarization singularity index -n, which has the form of a "web" with 2(n+1) cells generates at the sharp focus a transverse intensity distribution with 2(n+1) local maxima. In the focal spot, either 2(n-1) or 2(n+1) V-point polarization singularities with alternating indices +1 or -1 are formed at the intensity zero.

scholarly journals Comparison of the focused optical vortices produced by high-aperture phase conventional and spiral zone plates

2021 ◽  
Vol 2103 (1) ◽  
pp. 012175
Author(s):  
A A Savelyeva ◽  
E S Kozlova ◽  
V V Kotlyar
Keyword(s):  
Gaussian Beam ◽  
Focal Plane ◽  
Topological Charge ◽  
Focal Spot ◽  
Zone Plate ◽  
Fdtd Simulation ◽  
Optical Vortices ◽  
Phase Zone ◽  
Linearly Polarized ◽  
Sharp Focusing

Abstract Using the FDTD simulation, sharp focusing of a linearly polarized Gaussian beam with an embedded topological charge m = 3 by a phase zone plate and focusing of a Gaussian beam by a phase spiral zone plate with topological charge m = 3 were studied. The obtained results showed that proposed elements formed different patterns of intensity at a focal plane. The spiral zone plate forms a focal spot with three petals. At a distance of 13.5 μm from the focus, the lobe structure of the intensity (and energy flux) is replaced by an annular distribution.

scholarly journals A Flexible Coding Scheme Based on Block Krylov Subspace Approximation for Light Field Displays with Stacked Multiplicative Layers

Sensors ◽  
2021 ◽  
Vol 21 (13) ◽  
pp. 4574
Author(s):  
Joshitha Ravishankar ◽  
Mansi Sharma ◽  
Pradeep Gopalakrishnan
Keyword(s):  
Light Field ◽  
Krylov Subspace ◽  
Motion Parallax ◽  
Low Rank ◽  
Coding Scheme ◽  
Krylov Subspace Approximation ◽  
New Type ◽  
Value Decomposition ◽  
Subspace Approximation ◽  
Inter Frame

To create a realistic 3D perception on glasses-free displays, it is critical to support continuous motion parallax, greater depths of field, and wider fields of view. A new type of Layered or Tensor light field 3D display has attracted greater attention these days. Using only a few light-attenuating pixelized layers (e.g., LCD panels), it supports many views from different viewing directions that can be displayed simultaneously with a high resolution. This paper presents a novel flexible scheme for efficient layer-based representation and lossy compression of light fields on layered displays. The proposed scheme learns stacked multiplicative layers optimized using a convolutional neural network (CNN). The intrinsic redundancy in light field data is efficiently removed by analyzing the hidden low-rank structure of multiplicative layers on a Krylov subspace. Factorization derived from Block Krylov singular value decomposition (BK-SVD) exploits the spatial correlation in layer patterns for multiplicative layers with varying low ranks. Further, encoding with HEVC eliminates inter-frame and intra-frame redundancies in the low-rank approximated representation of layers and improves the compression efficiency. The scheme is flexible to realize multiple bitrates at the decoder by adjusting the ranks of BK-SVD representation and HEVC quantization. Thus, it would complement the generality and flexibility of a data-driven CNN-based method for coding with multiple bitrates within a single training framework for practical display applications. Extensive experiments demonstrate that the proposed coding scheme achieves substantial bitrate savings compared with pseudo-sequence-based light field compression approaches and state-of-the-art JPEG and HEVC coders.

scholarly journals Topological Charge and Asymptotic Phase Invariants of Vortex Laser Beams

Photonics ◽  
2021 ◽  
Vol 8 (10) ◽  
pp. 445
Author(s):  
Alexey A. Kovalev ◽  
Victor V. Kotlyar ◽  
Anton G. Nalimov
Keyword(s):  
Numerical Simulation ◽  
Data Transmission ◽  
Topological Charge ◽  
Light Field ◽  
Observation Point ◽  
Laser Beams ◽  
Optical Data ◽  
Optical Signals ◽  
Asymptotic Phase ◽  
Ring Approximation

It is well known that the orbital angular momentum (OAM) of a light field is conserved on propagation. In this work, in contrast to the OAM, we analytically study conservation of the topological charge (TC), which is often confused with OAM, but has quite different physical meaning. To this end, we propose a huge-ring approximation of the Huygens–Fresnel principle, when the observation point is located on an infinite-radius ring. Based on this approximation, our proof of TC conservation reveals that there exist other quantities that are also propagation-invariant, and the number of these invariants is theoretically infinite. Numerical simulation confirms the conservation of two such invariants for two light fields. The results of this work can find applications in optical data transmission to identify optical signals.

scholarly journals Terahertz Synthetic Aperture Imaging with a Light Field Imaging System

Electronics ◽  
2020 ◽  
Vol 9 (5) ◽  
pp. 830
Author(s):  
Nanfang Lyu ◽  
Jian Zuo ◽  
Yuanmeng Zhao ◽  
Cunlin Zhang
Keyword(s):  
Focal Plane ◽  
Light Field ◽  
Imaging System ◽  
Focal Plane Array ◽  
Terahertz Imaging ◽  
Image Distortion ◽  
Resolving Power ◽  
Synthetic Aperture ◽  
Array Detectors ◽  
Field Imaging

In terahertz imaging systems based on Gaussian beam active illumination and focal plane array detectors, severe image distortion has been observed, which significantly reduces the resolving power of the imaging system. To solve this problem, a novel computational method, Light Field Imaging (LFI), has been introduced for terahertz imaging. A conventional transmission-type terahertz imaging system based on a gas-pumped terahertz source and terahertz Focal Plane Array Detectors (FPA) arrays is established to analyze the problem of image distortion. An experimental virtual camera array terahertz LFI system is also established. With the acquisition and reconstruction of synthetic aperture terahertz light fields, the improvement on resolving power and SNR performance have been validated.

scholarly journals X-type vortex and its effect on beam shaping

2021 ◽  
Author(s):  
Xiaoyan Pang ◽  
Weiwei Xiao ◽  
Han Zhang ◽  
Chen Feng ◽  
Xinying Zhao
Keyword(s):  
Three Dimensional ◽  
Beam Shaping ◽  
Optical Fields ◽  
Intensity Pattern ◽  
Phase Gradient ◽  
Rotation Direction ◽  
3D Space ◽  
New Type ◽  
Gradient Parameter ◽  
3D Fields

Abstract In this article we propose a new type of optical vortex, the X-type vortex. This vortex inherits and develops the conventional noncanonical vortex, i.e., it no longer has a constant phase gradient around the center, while the intensity keeps invariant azimuthally. The strongly focusing properties of the Xtype vortex and its effect on the beam shaping in three-dimensional (3D) fields are analyzed. The interesting phenomena, which cannot be seen in canonical vortices, are observed, for instance the `switch effect' which shows that the intensity pattern can switch from one transverse axis to another in the focal plane by controlling the phase gradient parameter. It is shown that by adjusting the phase gradient of this vortex, the focal field can have marvelous patterns, from the doughnut shape to the shapes with different lobes, and the beam along propagation direction will form a twisting shape in 3D space with controllable rotation direction and location. The physical mechanisms underlying the rule of the beam shaping are also discussed, which generally say that the phase gradient of the X-type vortex, the orbital angular momentum, the polarization and the `nongeneric' characteristic contribute differently in shaping fields. This new type of vortex may supply a new freedom for tailoring 3D optical fields, and our work will pave a way for exploration of new vortices and their applications.

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 Recognition of wavefront aberrations types corresponding to single Zernike functions from the pattern of the point spread function in the focal plane using neural networks

2020 ◽  
Vol 44 (6) ◽  
pp. 923-930
Author(s):  
I.A. Rodin ◽  
S.N. Khonina ◽  
P.G. Serafimovich ◽  
S.B. Popov
Keyword(s):  
Neural Network ◽  
Neural Networks ◽  
Point Spread Function ◽  
Focal Plane ◽  
Prediction Errors ◽  
Intensity Pattern ◽  
Data Set ◽  
Point Spread ◽  
The Neural Network ◽  
Spread Function

In this work, we carried out training and recognition of the types of aberrations corresponding to single Zernike functions, based on the intensity pattern of the point spread function (PSF) using convolutional neural networks. PSF intensity patterns in the focal plane were modeled using a fast Fourier transform algorithm. When training a neural network, the learning coefficient and the number of epochs for a dataset of a given size were selected empirically. The average prediction errors of the neural network for each type of aberration were obtained for a set of 15 Zernike functions from a data set of 15 thousand PSF pictures. As a result of training, for most types of aberrations, averaged absolute errors were obtained in the range of 0.012 – 0.015. However, determining the aberration coefficient (magnitude) requires additional research and data, for example, calculating the PSF in the extrafocal plane.

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