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1
Content available Subpixel localization of optical vortices using artificial neural networks
Popiołek-Masajada Agnieszka, Frączek Ewa, Burnecka Emilia
Metrology and Measurement Systems
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2021
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Vol. 28, nr 3
497--508
EN
Optical vortices are getting attention in modern optical metrology. Because of their unique features, they can be used as precise position markers. In this paper, we show that an artificial neural network can be used to improve vortex localization. A deep neural network with several hidden layers was trained to find subpixel vortex positions on the spiral phase maps. Several thousand training samples, differing by spiral density, its orientation, and vortex position, were generated numerically for teaching purposes. As a result, Best Validation Performance of the order of 10-5 pixel has been reached. To verify the usefulness of the proposed method, a related experiment in the setup of an optical vortex scanning microscope has been reported. It is shown that the vortex can be localized with subpixel accuracy also on experimental phase maps.
2
Content available Focusing of linearly polarized helico-conical Lorentz beam with sine-azimuthal variation wavefront
Bao Y., Lan J., Miao Y., Zhang D., Gao X.
Optica Applicata
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2018
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Vol. 48, nr 3
373--387
EN
In this article a theoretical research is described into focusing of a linearly polarized helico-conical Lorentz beam with a sine-azimuthal variation wavefront. The simulation results show the vortex charge on the axis, which has an obvious modulation effect on the focal modes of the Lorenz beam under certain beam parameters and phase parameters. Both the phase parameter and the vortex charge are zero, the focal spot appears round. The focal spot is symmetric about y axis when the charge is 0 and the phase parameter is adjusted. And the focal evolution patterns vary remarkably under different beam parameters and the phase parameters. In the process of focus evolution, there appears some novel focal patterns, such as a circle, a “T”, a butterfly, a small running humanoid, a whale tail, a flower of four leaves, a serpentine, a goldfish, a Chinese knot and an octopus, which indicates that the focus mode of the optical vortex Lorentz beam can be altered by changing the phase parameters and vortex charge.
3
Content available Dynamic evolution of mixed circular edge-screw dislocations
Gao P., Li J., Cheng K., Duan M.
Optica Applicata
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2017
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Vol. 47, nr 3
471--481
EN
Based on the extended Huygens–Fresnel principle, the analytical expressions for the cross-spectral density function of mixed circular edge-screw dislocations beams propagating through atmospheric turbulence have been derived, and used to study the dynamic evolution of mixed circular edge-screw dislocations in free space and atmospheric turbulence. It is shown that the radius of circular edge dislocations increases with increasing propagation distance, and both the positions of the optical vortex and the center of circular edge dislocations are located at the point (0, 0) when mixed circular edge-screw dislocations propagate in free space. When mixed circular edge-screw dislocations propagate in the atmospheric turbulence, the position of optical vortices varies with increasing propagation distance, the circular edge dislocation evolves into a pair of optical vortices with the opposite topological charge ±1, and the pair of optical vortices will annihilate as soon as the propagation distance becomes large enough.
4
Content available Polygonal micro-whirlpools induced in ferrofluids
Bacia M, Lamperska W, Masajada J, Drobczynski S, Marc M
Optica Applicata
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2015
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Vol. 45, nr 3
309--316
EN
We report on the observation of the polygonal whirlpools in the thin layer of ferrofluid under illumination with a laser beam carrying optical vortex and in the presence of a vertical magnetic field. This kind of structures have attracted attention after discovering a hexagonal storm in Saturn’s atmosphere. Our polygonal whirlpools were created in a closed system (no free surfaces) in micro-scale (whirlpool diameter <20 μm) by the use of holographic optical tweezers. The polygonal shape was changed by varying the magnetic field strength or value of the optical vortex topological charge.
5
Content available Theory of evanescent Bessel beams with a metallic sheet
Al-Awfi S.
Optica Applicata
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2013
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Vol. 43, nr 3
539--550
EN
We explain how a surface optical vortex can be created when a Bessel beam is totally reflected internally at the planar surface of a dielectric on which a metallic sheet has been deposited. A two-dimensional patterning on the surface, the strongly localized intensity distribution decays with distance vertical to the surface. The characteristics of this surface optical vortex depend on the incident beam parameters and the dielectric mismatch of the media.
6
Content available Sieć neuronowa lokalizująca wiry optyczne rozmieszczone w regularnej strukturze
Guszkowski T., Frączek E.
Pomiary Automatyka Kontrola
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2010
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R. 56, nr 9
1074-1076
PL
Praca prezentuje opartą na sztucznej sieci neuronowej metodę określania położenia wirów optycznych rozmieszczonych w regularnej strukturze i powstałych w wyniku interferencji trzech fal płaskich. Do uczenia i oceny jakości działania sieci neuronowej wykorzystano zestaw symulowanych obrazów, na które dodatkowo nałożono szum pomiarowy oraz zniekształcenia geometryczne wynikające z symulowanych drgań układu pomiarowego. W wyniku uczenia sieci neuronowej uzyskano neuronowy lokalizator wirów optycznych o medianie błędu lokalizacji poniżej 0,4 piksela.
EN
The paper presents a short introduction to the optical vortices localization problem and an Artificial Neural Network (ANN) for localization of the optical vortices positioned in a regular structure of honeycomb. The analyzed vortices form as an effect of interference of three planar waves. A set of 1800 simulated images with added noise and geometric distortions modelling experimental setup vibrations was used for ANN learning and evaluation. As a result an unidirectional ANN with 100 inputs which correspond with pixels in a 10x10 image matrix; one non-linear hidden layer of 5 neuron and 2 outputs representing the coordinates of the vortex were created. The learning criterion was Mean Square Error (MSE) and the net was taught with Levenberg-Marquardt algorithm implemented in MATLAB. Final tests were performed with 180 images excluded from ANN learning. As a result a neuronal localizator of optical vortices was obtained with the worst-case localization error less than 2.1 pixel and localization error median less than 0.4 pixel.
7
Content available remote Optical vortex sign determination using self-interference methods
Kurzynowski P., Borwińska M., Masajada J.
Optica Applicata
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2010
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Vol. 40, nr 1
165--175
EN
We have proposed a simple method for determining the sign of optical vortex seeded in optical beam. Our method can be applied to any single optical vortex, also the one with topological charge magnitude higher than 1, as well as to the whole vortex lattice. The proposed method has been verified experimentally for all the cases.
8
Content available remote An analysis of an optical vortices interferometer with focused beam
Frączek E., Budzyń G.
Optica Applicata
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2009
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Vol. 39, nr 1
91--99
EN
In recent years a lot of effort was put into testing and improving the idea of a three-beam interferometer known as an optical vortices interferometer (OVI). Devices based on the idea of the OVI allow measuring small rotation angles and small shifts with a superb resolution. Unfortunately, there are still many problems that have to be solved before an OVI-based device can go into production. In this paper, theoretical calculations and experimental results of using another type of OVI, OVI with focused beam, are presented. The results of measuring small displacements and small rotation angles of reflecting areas are also shown.
9
Content available remote An accuracy analysis of small angle measurement using the Optical Vortex Interferometer
Frączek E., Mroczka J.
Metrology and Measurement Systems
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2009
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Vol. 16, nr 2
249-257
EN
In recent years a lot of effort has been put into testing and improving the idea of a three-beam interferometer known as Optical Vortex Interferometer (OVI). Devices based on the idea of an OVI allow, among other things, measuring small rotation angles of the wave [1]. In this paper complex statistical analysis has been used for the results of the small-angle rotation wave measuring method. The authors of this paper claim that the presented analysis of data handling error in a new measurement method increases the accuracy of the measured angle by better choice of random triplets.
10
Content available remote Interferometria na wirach optycznych
Masajda J., Kurzynowski P.
Przegląd Elektrotechniczny
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2008
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R. 84, nr 5
165-168
PL
Artykuł zawiera omówienie obecnego stanu badań nad interferometrią na wirach optycznych. Przedstawione są wyniki dotyczące rozwoju samych interferometrów oraz metod obróbki danych pomiarowych. Przedyskutowane są również niektóre potencjalne zastosowania interferometrii na wirach optycznych.
EN
The paper gives a short overview of the current research work on the optical vortex interferometry. The progress in the development of optical vortex interferometers and methods for interferograms analysis are presented. The possible applications of the optical vortex interferometry are discussed in brief.
11
Content available remote The interferometry based on regular lattice of optical vortices
Masajada J.
Optica Applicata
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2007
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Vol. 37, nr 1-2
167-185
EN
The optical vortices are point phase dislocations. The point where the phase is undetermined is called a vortex point. The lattice of optical vortices can be generated by the interference of three or more plane waves, but the optical vortex lattice generated by interference of three plane waves is regular and posses a number of special properties, which are discussed in this paper. The basic geometrical features of such a regular lattice of optical vortices are also presented. The regular lattice of optical vortices is a base for optical vortex interferometer (OVI). The OVI takes advantages of special properties of three plane wave interference field. The relations between OVI advantages and special features of the vortex lattice are discussed in brief.
12
Content available remote Optical vortices and their application to interferometry
Masajada J.
Prace Naukowe Instytutu Fizyki Politechniki Wrocławskiej. Monografie
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2004
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Vol. 36, nr 25
1--104
EN
Regular net of optical vortices can be generated by three plane waves interference. Such a net has a number of unique properties and its geometry is very sensitive to phase and amplitude disturbances introduced to any of the three interfering waves. The Optical Vortex Interferometer (OVI) is a new instrument which takes advantage of special properties of optical vortex net. The OVI can be set up in various configurations fitted to specific needs of measurements. The key problem for OVI accuracy is localization of vortex points. A number of localization methods, which work with subpixel resolution have been proposed and tested. These methods are fast and enable real time measurements. In this monograph, the basic physical and technical features of OVI are discussed. The possible applications of OVI are: small-angle rotations and small linear shift measurement, determination of wavefront geometry, 3-D scanning interferometry, superresolution microscopy. The measurement of small-angle rotations is presented in detail. The monograph contains also an introduction to the theory of optical vortices.
PL
Regularna sieć wirów optycznych może powstać w wyniku interferencji trzech fal płaskich. Sieć taka charakteryzuje się unikatowymi własnościami i jest bardzo wrażliwa na zaburzenia wprowadzone do jednej z interferujących fal. Własności sieci wirów optycznych wykorzystano w interferometrze, którego działanie jest oparte na wirach optycznych. Interferometr można skonfigurować na wiele sposobów. Jest więc on instrumentem, którego budowę można przystosować do specyficznych warunków pomiarowych. Kluczowym zagadnieniem decydującym o dokładności tego interferometru jest lokalizacja wirów optycznych. Aby rozwiązać ten problem, zaproponowano i przetestowano kilka metod ich lokalizacji. Metody te zapewniają rozdzielczość większą niż odległość między punktami pomiarowymi (pikselami) i są jednocześnie wystarczająco szybkie, aby umożliwić pomiar w czasie rzeczywistym. Przedstawiono też podstawowe własności fizyczne i zagadnienia techniczne związane z interferometrem opartym na wirach optycznych. Omówiono jego możliwe zastosowania, w tym: pomiar małych kątów obrotu, pomiar małych przesuwów liniowych, rekonstrukcję geometrii frontu falowego, interferometrię 3-D, zastosowania w mikroskopii nadrozdzielczej. Zagadnieniu pomiaru małych kątów obrotu poświęcono szczególną uwagę. Monografia zawiera również krótkie wprowadzenie do teorii wirów optycznych.
13
Content available remote Gaussian beams with optical vortex of charge 2- and 3-diffraction by a half-plane and slit.
Masajda J.
Optica Applicata
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2000
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Vol. 30, nr 2-3
247-256
EN
In the paper, the half-plane diffraction of the Gaussian light beam containing double and triple optical vortex is examined. The analysis is based on the scalar theory of diffraction in the Fresnel-Kirchhoff approximation. Special attention is paid to the dynamics of the optical vortex within the diffracted beam. Some results for the case of diffraction by a single slit are also presented.
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