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Journal ArticleDOI

Helical core optical fibers maintaining propagation of a solitary optical vortex

09 Jul 2008-Physical Review A (American Physical Society)-Vol. 78, Iss: 1, pp 013813
TL;DR: In this article, the authors studied the mode structure of few-mode core optical fibers with small (up to a wavelength order) values of the helix pitch and showed that 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.
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.
Citations
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Journal ArticleDOI
TL;DR: In this paper, the authors proposed an effective method to generate high-order optical vortices (OVs) using H-FBG written in a multimode fiber with conversion efficiency as high as 97%.
Abstract: Helical fiber Bragg grating (H-FBG) induced by UV-side exposure exhibits wavelength-dependent coupling between different modes. In this paper, we propose an effective method to generate high-order optical vortices (OVs) using H-FBG written in a multimode fiber. We simulate the conversion of OVs with different topological charges: 0 → ± 1, ±1 → 0, 0 → ± 2, 0 → ± 3 with conversion efficiency as high as 97%. We prove that higher order topological charge can be obtained simply by changing the parameters of the fiber to increase the number of modes in the fiber. We also analyze the conversion of H-FBG under various conditions of the induced asymmetric index profile and the length of H-FBG.

59 citations


Cites background from "Helical core optical fibers maintai..."

  • ...For examples, inverse parabolic graded-index fiber [3], ring-design fiber [18], [19], chiral long-period gratings [20]– [22] and helical core optical fibers [23] have been reported for...

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Journal ArticleDOI
TL;DR: In this paper, the authors theoretically study the generation and conversion of optical vortices in long-period helical core fibers (HCFs) produced by drawing from a perform with an eccentric core.
Abstract: We theoretically study generation and conversion of optical vortices (OVs) in long-period helical core fibers (HCFs) produced by drawing from a perform with an eccentric core. Solving scalar waveguide equation in the helical coordinates we demonstrate that in such fibers topologically induced corrections to scalar propagation constants lead to convergence of spectral curves. At their intersection points a resonance coupling takes place between the fundamental and the vortex modes, as well as the coupling between OVs, whose topological charges differ by unity. This coupling leads to energy exchange between the coupled modes, which is manifested either in conversion of the input fundamental mode into an OV or transformation of an OV into the OV with higher by 1 (or lower, depending on core's helicity) value of the topological charge. This effect can be used for creation of all-fiber generators of singular beams from regular input beams. We also study effect of ellipticity of the core's form on transformation properties of HCFs and show that this leads to splitting of resonance fiber's parameters, at which conversion of left and right circularly polarized input regular beams into OVs occurs. We prove that in long-period HCFs one can neglect this effect due to reduction of polarization mode dispersion in twisted fibers.

56 citations

Journal ArticleDOI
TL;DR: In this article, the authors proposed a method of generation, conversion, and exchange of fiber-guided OAM modes using helical gratings (HGs), which is flexible and well compatible with OAM fibers, featuring a high conversion efficiency close to 100% and a conversion bandwidth about 10nm in transmission spectra, while less than 1nm in reflection spectra.
Abstract: By exploiting helical gratings (HGs), we propose and simulate flexible generation, conversion, and exchange of fiber-guided orbital angular momentum (OAM) modes. HGs can enable the generation of OAM modes, and the OAM conversion between two arbitrary modes guided in fibers. A specific HG can exchange the OAM states of a couple of OAM modes, i.e., OAM exchange. In addition, a Fabry-Perot (F-P) cavity cascaded with two identical reflective HGs can reflect converted OAM modes with a comb spectrum. The HG-based generation/conversion/exchange of OAM modes are dependent on helix period, orientation, and the fold number of helical fringes. The proposed method of generation, conversion, and exchange of fiber-guided OAM modes using HGs is flexible and well compatible with OAM fibers, featuring a high conversion efficiency close to 100% and a conversion bandwidth about 10 nm in transmission spectra, while less than 1 nm in reflection spectra.

51 citations

Journal ArticleDOI
TL;DR: In this article, the authors investigated the possibility of using optical vortices with different values of topological charge l, and hence with different value of the orbital angular momentum (OAM), for mode-division multiplexing in optical fibres.
Abstract: The possibility of using optical vortices with different values of topological charge l, and hence with different values of the orbital angular momentum (OAM), for mode-division multiplexing in optical fibres is here investigated. Two OAM modes with l equal to 0 and 1, respectively, are multiplexed in a few-mode fibre and then demultiplexed after a fibre propagation of 200 m. Such modes are spatially separated at the two output ports of a Mach–Zehnder interferometer with mutually 90°-rotated Dove prisms in the two arms. It is also shown how to generalize this demultiplexing scheme, which is all-optical, passive and in principle without splitting losses, in order to deal with a higher number of vortices propagating in the fibre. Therefore the proposed mode-division multiplexing technique based on OAM modes is very promising for increasing the capacity of fibre-optic transmission systems in an energy-saving efficient way, without the high power consumption of modal demultiplexing exploiting real-time electronic post-processing.

38 citations

Journal ArticleDOI
TL;DR: In this article, a method of generation, conversion, and exchange of fiber-guided orbital angular momentum (OAM) modes using helical gratings (HGs) is proposed.
Abstract: By exploiting helical gratings (HGs), we propose and simulate flexible generation, conversion and exchange of fiber guided orbital angular momentum (OAM) modes. HGs can enable the generation of OAM modes, and the OAM conversion between two arbitrary modes guided in fibers. A specific HG can exchange the OAM states of a couple of OAM modes, i.e, OAM exchange. In addition, a Fabry Perot cavity cascaded with two identical reflective HGs can reflect converted OAM modes with a comb spectrum. The HGs based generation conversion and exchange of OAM modes are dependent on helix period, orientation, and the fold number of helical fringes. The proposed method of generation, conversion, and exchange of fiber guided OAM modes using HGs is flexible and well compatible with OAM fibers, featuring a high conversion efficiency close to 100% and a conversion bandwidth about 10 nm in transmission spectra, while less than 1 nm in reflection spectra.

30 citations

References
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Journal ArticleDOI
TL;DR: The transfer of information encoded as orbital angular momentum states of a light beam is demonstrated, which is resistant to eavesdropping and gives an experimental insight into the effects of aperturing and misalignment of the beam on the OAM measurement and demonstrates the uncertainty relationship for OAM.
Abstract: We demonstrate the transfer of information encoded as orbital angular momentum (OAM) states of a light beam. The transmitter and receiver units are based on spatial light modulators, which prepare or measure a laser beam in one of eight pure OAM states. We show that the information encoded in this way is resistant to eavesdropping in the sense that any attempt to sample the beam away from its axis will be subject to an angular restriction and a lateral offset, both of which result in inherent uncertainty in the measurement. This gives an experimental insight into the effects of aperturing and misalignment of the beam on the OAMmeasurement and demonstrates the uncertainty relationship for OAM.

2,230 citations

Journal ArticleDOI
TL;DR: In this paper, it was shown that dislocations are to be expected whenever limited trains of waves, ultimately derived from the same oscillator, travel in different directions and interfere -for example in a scattering problem.
Abstract: When an ultrasonic pulse, containing, say, ten quasi-sinusoidal oscillations, is reflected in air from a rough surface, it is observed experimentally that the scattered wave train contains dislocations, which are closely analogous to those found in imperfect crystals. We show theoretically that such dislocations are to be expected whenever limited trains of waves, ultimately derived from the same oscillator, travel in different directions and interfere - for example in a scattering problem. Dispersion is not involved. Equations are given showing the detailed structure of edge, screw and mixed edge-screw dislocations, and also of parallel sets of such dislocations. Edge dislocations can glide relative to the wave train at any velocity; they can also climb, and screw dislocations can glide. Wavefront dislocations may be curved, and they may intersect; they may collide and rebound; they may annihilate each other or be created as loops or pairs. With dislocations in wave trains, unlike crystal dislocations, there is no breakdown of linearity near the centre. Mathematically they are lines along which the phase is indeterminate; this implies that the wave amplitude is zero.

1,984 citations

Journal ArticleDOI
01 Jun 1996
TL;DR: This work is, to their knowledge, the first demonstration of three-dimensional trapping of a spherical low-index particle using a single, stationary beam using a stationary, focused Gaussian beam containing an optical vortex.
Abstract: Summary form only given. We demonstrate that a low-index dielectric particle can be stably trapped in three-dimensions using a stationary, focused Gaussian beam containing an optical vortex. This work is, to our knowledge, the first demonstration of three-dimensional trapping of a spherical low-index particle using a single, stationary beam. Vortex traps allow the trapping of low- and high-index particles with less risk of damage and better isolation.

829 citations

Book ChapterDOI
TL;DR: In this paper, an isolated dark ring is created within a light beam, with an analytical description of the field, and a screw wave-front dislocation has a feature that the spatial structure of the wave front has the form of a helicoid around the dislocation axis.
Abstract: Singular optics is a branch of modern physical optics that involves a wide class of effects associated with the phase singularities in wave fields and with the topology of wave fronts. Optical singularities (optical vortices) exhibit some fundamental features absent in the "usual" fields with smooth wave fronts. Namely, optical vortices possess orbital angular momentum, topological charge for helical wave front of beams with well-defined direction of propagation. As a result, an interesting spatial evolution can be generated such as optical vortices "nucleation" and "annihilation" by pairs with participation of phase saddles, often called "optical chemistry." To study the structure of the circular edge dislocation, an isolated dark (zero-amplitude) ring is created within a light beam, with an analytical description of the field. A screw wave-front dislocation has a feature that the spatial structure of the wave front has the form of a helicoid around the dislocation axis. The chapter also describes reflection, refraction, interference and diffraction of OVs. Both frequency up- and down-conversion processes possess essential peculiarities for light beams with OVs. The chapter discusses the topology of wave fronts and vortex trajectories. Gouy phase shift in singular optics is also described in the chapter.

725 citations

Journal ArticleDOI
TL;DR: It is shown that suitable light vortex pancakes allow the add-drop of specific vector projections and it is suggested that such photons might allow the generation of engineered quNits in multidimensional quantum information systems.
Abstract: We put forward schemes to prepare photons in multidimensional vector states of orbital angular momentum. We show realizable light distributions that yield prescribed states with finite or infinite normal modes. In particular, we show that suitable light vortex pancakes allow the add-drop of specific vector projections. We suggest that such photons might allow the generation of engineered quNits in multidimensional quantum information systems.

548 citations