The structure of hybrid higher order modes of two coupled weakly guiding identical optical fibres is studied. On the basis of perturbation theory with degeneracy for the vector wave equation expressions for modes with azimuthal angular number l ≥ 1 are obtained that allow for the spin–orbit interaction. The spectra of polarization corrections to the scalar propagation constants are calculated in a wide range of distances between the fibres. The limiting cases of widely and closely spaced fibres are studied. The obtained results can be used for studying the tunnelling of optical vortices in directional couplers and in matters concerned with information security.

http://iopscience.iop.org/article/10.1088/2040-8978/12/11/115704/pdf

Higher order modes of coupled optical fibres

We study the evolution of circularly polarized optical vortices (OVs) in the system of two coupled few-mode optical fibres. We demonstrate that upon propagation OVs tunnel into the adjacent fibre as a complex superposition of OVs that comprise also OVs of opposite polarization and topological charge. The initial OV may tunnel into the other fibre as the same vortex state of lesser energy. The evolution of the orbital angular momentum in coupled fibres is studied.

Tunnelling of orbital angular momentum in parallel optical waveguides

Generation of a cylindrically polarized light beam, and in particular, a hybrid-azimuthal-radial polarization beams, called HARP modes, generated from an input linearly polarized Gaussian beam using a spun optical waveguide device is taught. The HARP modes are comprised of hybrid-azimuthal polarization (HAP) and hybrid-radial polarization (HRP) superposition modes. These beams possess a non-zero local angular momentum density that is spatially varying and a zero total angular momentum.

cylindrical polarization beams

We present here an experimental demonstration of the wavelength dependence of the polarization singularities due to linear combination of the vector modes excited directly in a two-mode optical fiber. The coherent superposition of the vector modes excited by linearly polarized Gaussian beam as offset skew rays propagated in a helical path inside the fiber results in the generation of phase singular beams with edge dislocation in the fiber output. The polarization character of these beams is found to change dramatically with wavelength—from left-handed elliptically polarized edge dislocation to right-handed elliptically polarized edge-dislocation through disclinations. The measured behaviour is understood as being due to intermodal dispersion of the polarization corrections to the propagating vector modes, as the wavelength of the input beam is scanned.

/pdf/wavelength-dependence-of-the-polarization-singularities-in-a-3lg91df7b9.pdf

Wavelength Dependence of the Polarization Singularities in a Two-Mode Optical Fiber

Spun Optical Fiber for generating optical vortex modes

We have studied the process of separation of the dominant mode and guided vortices in a Y-shaped directional fiber beam splitter. It is shown that, under certain conditions, the dominant mode field is completely pumped to the second channel, leaving the optical vortex field in this channel unchanged. Based on such a splitter, a vortex fiber interferometer has been created and characterized with respect to linearity and temperature sensitivity.

T. A. Fadeeva

Papers

Tunneling selection of optical vortices