B. P. Lapin

Bio: B. P. Lapin is an academic researcher from Tavrida National V.I. Vernadsky University. The author has contributed to research in topics: Optical vortex & Optical fiber. The author has an hindex of 9, co-authored 43 publications receiving 315 citations.

Spin-orbit-interaction-induced generation of optical vortices in multihelicoidal fibers

Abstract: We have studied the effect of the spin-orbit interaction on generation and conversion of optical vortices in multihelicoidal fibers, that is, the fibers possessing a multihelical refractive index profile. On the basis of a fully analytical approach we have obtained the spectra of coupled modes and their structure. Specifically, we have established selection rules, under which the spin-orbit interaction mediates the conversion of optical vortices into vortices with the topological charge changed by $\ifmmode\pm\else\textpm\fi{}(\ensuremath{\ell}\ifmmode\pm\else\textpm\fi{}2)$, $\ensuremath{\ell}$ being the number of helical branches in refractive index distribution. Also, we have shown that the spin-orbit interaction can lead to generation of radially and azimuthally polarized TE and TM modes from optical vortices. We have also demonstrated that if such generation is mediated by a scalar-type perturbation of the fiber's form, it is possible only for weakly deformed fibers. For strongly deformed fibers such perturbation can result only in generation of vortices with zero total angular momentum. Additionally, we have studied the possibility of polarization control over the orbital angular momentum of the generated state in such a system.

Twisted anisotropic fibers for robust orbital-angular-momentum-based information transmission

Abstract: We study the light propagation in the twisted anisotropic optical fibers endowed with torsional mechanical stress by obtaining the analytical solution of the vector wave equation. We show that at certain interplay between fiber parameters optical vortex beams of topological charge $\ensuremath{\ell}=0,\ifmmode\pm\else\textpm\fi{}1,\ifmmode\pm\else\textpm\fi{}2,...$ become the modes of the fibers in question. To explain the splitting of the optical vortex propagation constants we introduce the notions of orbital birefringence and optical Zeeman effect. Moreover, we unveil that induced by torsional stress circular birefringence makes the vortex beams with the well-defined orbital angular momentum robust against small perturbations characterized by both constant and spatially varying orientation of a director. We believe that such fibers can be successfully utilized for the long-range robust transmission of information encoded in the light's orbital degrees of freedom.

Generation of optical vortices in layered helical waveguides

Abstract: We study the possibility of changing the topological charge of incident beams by layered helical structures consisting of planar layers. We show that such structures can effectively change the topological charge of the incoming beam by unity. The problem of the fundamental mode and optical vortex passage through such a layered helical waveguide of a finite length is solved. The spectral characteristics of these processes are obtained. It is shown that such a waveguide can operate as a broadband compact generator of optical vortices from both regular and singular beams.

Generation and conversion of optical vortices in long-period twisted elliptical fibers.

Abstract: We theoretically demonstrate that long-period twisted elliptical fibers have the ability to change in a certain wavelength range the topological charge of the incoming field by two units. We also show that such fibers can generate charge-2 optical vortices from the incoming Gaussian beams.

Helical core optical fibers maintaining propagation of a solitary optical vortex

Abstract: We study theoretically the mode structure of few-mode helical core optical fibers with small (up to a wavelength order) values of the helix pitch. We demonstrate that in such fibers, at certain values of pitch the fundamental $H{E}_{11}$ mode strongly hybridizes with $l=1$ optical vortices and the forbidden zone appears in the spectra of such hybrid modes, which results in their attenuation. We have shown that within the spectrum gap, the only forward-propagating guiding modes are represented by two circularly polarized optical vortices with opposite polarization and the same topological charge so that upon excitation of such a fiber with a circularly polarized beam, only a solitary optical vortex could be excited in it. Such ``monovortex'' fibers are found to be analogous to conventional monomode fibers that maintain the propagation of the $H{E}_{11}$ mode.

4 × 20 Gbit/s mode division multiplexing over free space using vector modes and a q-plate mode (de)multiplexer

Abstract: Vector modes are spatial modes that have spatially inhomogeneous states of polarization, such as, radial and azimuthal polarization. In this work, the spatially inhomogeneous states of polarization of vector modes are used to increase the transmission data rate of free-space optical communication via mode division multiplexing. A mode (de)multiplexer for vector modes based on a liquid crystal q-plate is introduced. As a proof of principle, four vector modes each carrying a 20-Gbit/s quadrature phase shift keying signal (aggregate 80 Gbit/s) on a single wavelength channel (λ∼1550 nm) were transmitted ∼1 m over the lab table with <−16.4 dB mode crosstalk. Bit error rates for all vector modes were measured at the 7% forward error correction threshold with power penalties <3.41 dB.

Using the nonseparability of vector beams to encode information for optical communication

Abstract: In this work, it is experimentally demonstrated that the nonseparability of vector beams (e.g., radial and azimuthal polarization) can be used to encode information for optical communication. By exploiting the nonseparability of a vector beam's space and polarization degrees of freedom using conventional wave plates, it is shown that 2 bits of information can be encoded when applying the identity and three Pauli operators to its polarization degree of freedom. It is also shown that vector beams can be efficiently decoded with as low as 2.7% cross talk using a Mach-Zehnder interferometer that exploits a higher-order Pancharatnam-Berry phase and liquid crystal q-plates.

Geometrodynamics of polarized light: Berry phase and spin Hall effect in a gradient-index medium

Abstract: We review the geometrical-optics evolution of an electromagnetic wave propagating along a curved ray trajectory in a gradient-index dielectric medium. A Coriolis-type term appears in Maxwell equations under transition to the rotating coordinate system accompanying the ray. This term describes the spin–orbit coupling of light which consists of (i) the Berry phase responsible for trajectory-dependent polarization variations and (ii) the spin Hall effect representing polarization-dependent trajectory perturbations. These mutual phenomena are described within universal geometrical structures underlying the problem and are explained by the dynamics of the intrinsic angular momentum carried by the wave. Such close geometrodynamical interrelations illuminate a dual physical nature of the phenomena.

Orbital-angular-momentum-preserving helical Bloch modes in twisted photonic crystal fiber

Abstract: In optical fiber telecommunications, there is much current work on the use of orbital angular momentum (OAM) modes for increasing channel capacity. Here we study the properties of a helically twisted photonic crystal fiber (PCF) that preserves the chirality of OAM modes of the same order, i.e., it inhibits scattering between an order +1 mode to an order −1 mode. This is achieved by thermally inducing a helical twist in a PCF with a novel three-bladed Y-shaped core. The effect is seen for twist periods of a few millimeters or less. We develop a novel scalar theory to analyze the properties of the twisted fiber, based on a helicoidal extension to Bloch wave theory. It yields results that are in excellent agreement with full finite element simulations. Since twisted PCFs with complex core structures can be produced in long lengths from a fiber drawing tower, they are of potential interest for increasing channel capacity in optical telecommunications, but the result is also of interest to the photonic crystal community, where a new kind of guided helical Bloch mode is sure to excite interest, and among the spin–orbit coupling community.