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Simferopol', Ukraine

Alexeyev C.N.,Taurida National University
Applied Optics

We have theoretically studied long-period spun l-helicoidal fibers and their ability to generate singular beams from regular ones. On the basis of perturbation theory in the presence of degeneracy, applied to the scalar waveguide equation, we obtained the structure of coupled modes of such fibers and their spectra. It is shown that the coupled modes consist of the fields, which taken separately bear topological charges that differby l units. We have numerically studied the process of the passage of a Gaussian beam through such a fiber and demonstrated that long-period l-helicoidal fibers have the ability to change - in a certain wavelength range - the topological charge of the incoming Gaussian beam by l units, generating in this way charge-l optical vortex. © 2012 Optical Society of America. Source

Alexeyev C.N.,Taurida National University
Physical Review A - Atomic, Molecular, and Optical Physics

In this paper, we have studied the propagation of light in a p array, that is, a circular array of strongly anisotropic fibers, orientation of whose anisotropy axes linearly depends on the angular position of the fiber in the array and makes an integer number of full rotations p while tracing along its contour. We have obtained the spectrum and the structure of supermodes for such a system and have shown that they consist of two discrete optical vortices nestled in the opposite circular polarizations. We have found the expressions for topological charges of such vortices. We have also studied the angular momentum carried by these supermodes. We have obtained the expression for the evolution of an arbitrary excitation created at the array's input upon its discrete diffraction in the array. As an example, we have examined the propagation of the set of circularly polarized fundamental modes excited at the input end with equal weights and phases. We have demonstrated that, in certain cross sections, the p array generates a discrete circularly polarized optical vortex, whose topological charge is determined by the array's index p. In this way, we have shown that the p arrays enable polarization control over phase singularities being a discrete analog of the q plates. © 2012 American Physical Society. Source

We have studied theoretically reflecting and transmitting properties of Bragg multihelicoidal spun fibers, in which refractive index distribution features l helical branches and possesses an l-fold symmetry in the transverse cross section. It is shown that for a special choice of the profile function modulation, such fibers in certain spectral ranges have the property to change the topological charge of the incoming Gaussian beam in the reflected field by l units. This property could be used for narrowband generation of optical vortices (OVs) from Gaussian beams and for changing the topological charge of incoming OVs. © 2013 Optical Society of America. Source

Volyar Alexander V.,Taurida National University
Ukrainian Journal of Physical Optics

We have considered a new type of singular beams called as optical quarks. They have fractional topological charges being equal to half an integer and they possess rather unique properties. There are four types of optical quarks, even and odd ones, which reveal the opposite signs of topological charges. The sums or differences of the even and odd quarks form standard vortex or non-vortex beams with the topological charges of integer order. All the quarks in the same beam annihilate and the beam vanishes. The analysis of angular spectra of the optical quarks shows that the latter represent structurally unstable forms of field under condition of free-space propagation. We have analysed their propagation properties for different types of beam envelope, including a symmetric beam array with discrete optical quarks. We have discussed the properties of possible structurally stable forms of the quarks and the media capable of maintaining the optical quarks. Source

Alexeyev C.N.,Taurida National University
Journal of Optics (United Kingdom)

We have studied the longitudinal evolution of spin angular momentum (SAM) in a system of two coupled anisotropic monomode optical fibres. On the basis of perturbation theory with degeneracy we have obtained the modes of such a system for various cases of mutual orientation of anisotropy axes and relations between anisotropy and exchange constants. We have provided their expressions in both local and global coordinate frames. We have studied the evolution of the SAM of individual fibres if one of the fibres is excited with linearly and circularly polarized light. We have shown that at certain points the specific SAM (SAM reduced to energy) suffers fast changing from +1 to -1, the spatial scale of such variations being small and determined by the ratio of the anisotropy constant to the inter-fibre exchange. © 2013 IOP Publishing Ltd. Source

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