Optical Memory and Neural Networks最新文献

The dynamics of the optical field in a resonator with cubic nonlinearity, delayed feedback and external injection is investigated. It is shown that the formation of square optical waves is possible in such a system. The mechanism of formation of such waves is found. Possible solutions in the form of square optical waves are numerically investigated. A diagram illustrating possible solutions is constructed.

This article is devoted to a new direction of modern singular optics—Erf-Gaussian (EG) beams that carry a fractional topological charge. It is shown that Erf-Gaussian beams were generated using an axicon and an anisotropic crystal, and the polarization characteristics of these beams with a fractional topological charge in the vicinity of the beam axis were experimentally studied. Theoretical calculations were confirmed and it was shown that Erf-Gaussian beams introduce changes into the original picture of the polarization distribution, and that the central spiral polarization umbilical splits into two polarization features of the “lemon” type. The method described in the article for generating and analyzing polarization singularity in Erf-Gaussian beams based on a fractional topological charge can be used in optical profilometry to analyze the polarization and phase properties of materials and surface roughness.

In this work, using the Richards-Wolf formalism, we assume the tight focusing of optical vortices with hybrid polarization, which combines the properties of azimuthal and circular polarizations. It is shown that these beams have a number of unique properties the intensity in such beams rotates with length from the focal spot, and the longitudinal component of the spin angular momentum has an asymmetric appearance.

We consider the inverse diffraction problem for a generalized spiral phase plate. For a given luminous curve in the focal plane, the transmission function of the plate forming this curve is calculated. It is assumed that the curve is specified analytically in polar coordinates in the form of an explicit dependence of the radius on the angle. We give the conditions imposed on the curve under which the problem certainly has a solution. Also there are examples of solving the direct problem when curves that do not satisfy these conditions are formed.

The sharp focusing of the superposition of a plane wave with the linear polarisation (LP) and an optical vortex with topological charge (TC) m and with the same LP directed along the horizontal axis is considered. Applying the Richards–Wolf formalism, analytical formulas are derived for the intensity and the spin angular momentum (SAM) lengthwise component in the focal plane. It is demonstated that for odd and even TCs m the SAM and the intensity have different symmetries: for even m they are symmetric about both Cartesian axes, and for odd m they are symmetric only about the vertical axis. The intensity pattern has 2m local maxima in the focal plane. The intensity on the optical axis for any TC m is nonzero. The pattern of the lengthwise SAM (spin density) in the focal plane has 2(m + 2) subwavelength areas in the half of which the SAM has positive value while in others it has negative value. The centers of these areas alternately lie on a circle of a certain radius with a center on the optical axis. This spin pattern with different signs shows the spin Hall effect in the focal plane. The total negative and positive spin in the focal plane are mutually compensated and equal to zero.

We have shown theoretically and experimentally that for defining the orbital angular momentum (OAM) of structured Laguerre-Gaussian (sLG) beams with a broken symmetry, it is sufficient to measure the only element of the symplectic intensity moment matrix. It looks like an intertwining of two elements belonging to two submatrices of the general symplectic matrix of intensity moments under the condition when the amplitude parameter of the sLG beam is equal to unity. But once slightly to deviate the amplitude parameter from this value, as the intertwining at once unravels. Besides, we revealed that by measuring such a matrix element of the sLG beam in free space enables us to exactly predict the OAM behavior of the sLG beam in a first-order optical system with an astigmatic element, without any measuring in the astigmatic system itself.

We derive the axial projection of the spin angular momentum (SAM) vector for a vector Gaussian beam with 1D periodic amplitude modulation. Such a beam has zero SAM in the source plane and its polarization is inhomogeneous linear. We demonstrate that when such a beam propagates, its periodic modulation effectively splits the beam into two, having elliptic polarization of opposite handedness. Therefore, the spin Hall effect is shown to arise, since the cross section of the beam contains alternating domains with nonzero spin of opposite sign. For generating such a field, a metasurface can be employed, whose transmittance is changing with one coordinate periodically.

The diffraction of a Gaussian beam by a stepped spiral phase plate (SPP) is studied for different wavelengths of laser radiation. Numerically, using the finite difference time domain method, the formation of a vortex beam by a SPP with different number of uniform sectors is shown. The diffraction of laser radiation with a wavelength in the range from 0.5 to 1.5 μm by a SPP with 20 sectors was calculated and the transformation of a Gaussian beam into a vortex beam with different topological charges due to variations in wavelength was shown. To determine the value of the orbital angular momentum (OAM) of the formed vortex beam, the weight spectrum is calculated on the basis of angular harmonics (AH). We estimated the vortex beam quality of an integer order using a multichannel diffractive optical element (DOE), which implements the optical decomposition of the light field according to the AH basis. The detection of vortex beams with 1st, 2nd and 3rd order is shown numerically by matched filtering.

This paper presents a study of astigmatic structured Laguerre-Gaussian beams (asLG) and their orbital angular momentum (OAM). The complex amplitude of the asLG beam is obtained, which takes into account the distance along the z-axis after the cylindrical lens, as well as the angle of inclination of the cylindrical lens. An expression for the OAM is obtained that depends only on the Hermite-Gaussian mode amplitudes. Computer modeling has been carried out, which is in good agreement with experiment.

In this study, experiments were conducted aimed at the formation of both standard Laguerre-Gaussian vector beams and more complex structured Laguerre-Gaussian vector beams using a spatial light modulator. The ability to measure the polarization structure of these beams using a differential Stokes polarimeter was experimentally demonstrated. The obtained measurement data on the polarization distribution successfully correspond to theoretical calculations, which confirms the effectiveness and accuracy of this method in the analysis of optical structures.