Propagation Of Optical Vortices Research Articles

Structured light routing in CROW-endowed add-drop filters

In this paper, we study the propagation of optical vortices (OVs) through the add-drop filter that comprises a coupled resonator optical waveguide (CROW). We develop a fully vectorial theory not based on transfer matrix formalism and apply it to the description of CROWs based on multimode fibers. We study the transmission of higher-order OVs through a CROW-endowed add-drop filter and demonstrate the possibility of transmitting such OVs along the CROW chain. We show that during such transmission OVs may invert their topological charges and determine the condition under which an OV propagates without such charge inversion. We suggest that such a system can be used for the generation of OV frequency combs. We also study group delay time and show that this system may be used as a time delay line for OVs.

Propagation of optical vortices in an add-drop resonator based on a vertical array of ring resonators

Propagation of optical vortices in an add-drop resonator based on a vertical array of ring resonators

Vortex-frequency-comb generation assisted by PT -symmetric ring resonators

We study propagation of optical vortices (OVs) in coupled parity-time ($\mathcal{P}\mathcal{T}$) symmetric multimode fibers with equal gain and loss. We show that this system has two second-order exceptional points (EPs) of spectral branches confluence where the degenerate modes are odd and even Laguerre-Gaussian (LG) modes. We study the evolution of an arbitrary incoming superposition of LG modes with the same orbital index in such a coupler. We prove that if the loss parameter exceeds its value in the lowest-lying EP, in the limit of the large coupler's length the outcoming field tends to the same attractor state depicted on the orbital Poincar\'e sphere (PS) by the orbital ``black hole.'' We show that localization of such a ``black hole'' on the PS does not change with variations of loss parameter beyond its value at the lowest EP, which can be called the pinning of the orbital ``black hole.'' We also demonstrate that the fiber ring resonator based on such a coupler can generate an optical vortex frequency comb (FC) far from the EP. The mechanism of such generation is not connected with any nonlinearity in the system. We determine the coupler's parameters under which such generation is feasible. This property can be useful for optimizing fiber-based orbital angular momentum communications.

All-fiber SWAP-CNOT gate for optical vortices

We study the propagation of optical vortices in a system which consists of a tandem of a multi-helical and twisted anisotropic fiber. We show that at certain resonance regimes of the optical fibers such a system allows one to control sign flipping of the topological charge and the circular polarization of the input optical vortex. Moreover, parameters of the multihelical and the twisted anisotropic fibers are established for the implementation of a logical operation that corresponds to the sequential executing of two fundamental SWAP and CNOT gates over the states of circularly polarized optical vortices.

Parametric control of propagation of optical vortices through fibre ring resonators

In this paper, we have studied transmission of optical vortices (OVs) through ring resonators (RRs) based on multimode fibres. Using the formalism of transfer matrix we have obtained in the scalar approximation the analytical expressions for amplitudes of transmitted OVs with opposite topological charges (TCs) as functions of RR’s parameters. We have calculated the orbital angular momentum (OAM) of the outcoming field and shown that by changing such parameters one can efficiently control its TC and continuously change its OAM. We have established that TC and OAM feature wavelength-scale sensitivity to variations of the ring’s length. We have demonstrated that this ability of RRs to influence OAM is due to a multipass interference assisted with TC inversion in the coupling area. We have also studied the effect of losses on the transmission of OVs through RRs and established that by controlling the attenuation parameter one can also control the TC of the outcoming field. Finally, we have solved the problem of OV transmission within the frameworks of a fully vectorial approach that allows for the spin–orbit interaction (SOI) in fibres. We have shown that accounting the SOI does not alter the main properties of RRs established with the use of the scalar approximation theory. We have shown that RRs, which operate on OAM modes, can be used for emulation of the quantum logical X, Y, S, T and Z gates. This can be useful for optical simulation of quantum computations.

Optical vortices and orbital angular momentum in strongly coupled optical fibers.

We have studied the effect of strong coupling on the propagation of optical vortices (OVs) and evolution of their orbital angular momentum (OAM) in parallel multimode optical fibers. Based on the perturbation theory that goes beyond the limits of weak orthogonality approximation we have established that strong coupling does not lead to alteration of the structure of supermodes as compared to the case of weak coupling. The strong coupling affects only the propagation constants of such supermodes, which we have found analytical expressions for. We have also studied the evolution of OVs and emphasized the difference between the powers stored in partial OVs and powers located at the fiber cores. We have studied OAM in such fibers, as well as corrections to the total OAM due to interference effects and shown that the influence of such effects on forming the total OAM under strong coupling is negligible. We have also demonstrated that in such systems it is sufficient to take account only of the coupling of OVs with equal by modulus topological charges, whereas other types of coupling are negligible.

Optical Vortices in Quadratic Nonlinear Media with Nonlinear Absorption

A study is performed for the propagation of optical vortices in quadratic nonlinear media with linear and nonlinear absorption. When such beams propagate in media with a quadratic nonlinearity without absorption, their vortex structure is destroyed and they break up into several nonvortex quasi-solitons. Nonlinear absorption allows the beam to keep its structure longer.

Generation of Vortex Optical Beams Based on Chiral Fiber-Optic Periodic Structures.

In this paper, we consider the process of fiber vortex modes generation using chiral periodic structures that include both chiral optical fibers and chiral (vortex) fiber Bragg gratings (ChFBGs). A generalized theoretical model of the ChFBG is developed including an arbitrary function of apodization and chirping, which provides a way to calculate gratings that generate vortex modes with a given state for the required frequency band and reflection coefficient. In addition, a matrix method for describing the ChFBG is proposed, based on the mathematical apparatus of the coupled modes theory and scattering matrices. Simulation modeling of the fiber structures considered is carried out. Chiral optical fibers maintaining optical vortex propagation are also described. It is also proposed to use chiral fiber-optic periodic structures as sensors of physical fields (temperature, strain, etc.), which can be applied to address multi-sensor monitoring systems due to a unique address parameter—the orbital angular momentum of optical radiation.

Topological resonances, superefficient orbital-angular-momentum control, and spin-orbit-interaction enhancement in fiber-loop resonators

In this paper we study the propagation of optical vortices (OVs) through the loop resonator (LR) on a multimode fiber. Within the framework of a fully vectorial treatment that allows for the spin-orbit interaction (SOI) we demonstrate the existence in such LRs of a special topological resonance, which is in the inversion of the topological charge (TC) of the transmitted OV. We study the angular momentum (AM) of the transmitted field and show that near resonance points the orbital and spin AMs of the output field are sensitive to wavelength-scale variations of the LR's length parameters. The mechanism that underlies such supersensitivity is the multipass interference assisted by topological charge inversion in the coupling area. We show that this property can be used for superefficient control of the output field's OAM. We also demonstrate that such LRs are suitable for creation of combined wavelength and mode comb filters on their basis. The effect of losses is also discussed. We show the existence in LRs of an additional resonance: the spin-orbit resonance. This type of topological resonance arises due to the effect of the SOI enhancement, which nature we also unveil.

Transmission of optical vortices through fiber loop resonators.

In this Letter, we study the propagation of optical vortices (OVs) through the loop resonator (LR) on a multimode fiber. We demonstrate the existence of a special resonance, which is in the inversion of the topological charge of the transmitted OV. Near the resonance, the output orbital angular momentum (OAM) is sensitive to wavelength-scale variations of the LR's optical path length, which can be used for super-efficient OAM control. We also show the feasibility of a combined wavelength and OAM division multiplexing in comb filters on such LRs.

Multifocus self-focusing of a femtosecond optical vortex

We analyze formation of multifocus structure during the propagation of optical vortex with topological charge m = 1 in fused silica at wavelength 1800 nm, which corresponds to region of anomalous group velocity dispersion. Propagation of pulse is accompanied by sequence of nonlinear focuses, where each focus is a high intensive ring.

Propagation of optical vortices in a nonlinear atomic medium with a photonic band gap.

We experimentally generate a vortex beam through a four-wave mixing (FWM) process after satisfying the phase-matching condition in a rubidium atomic vapor cell with a photonic band gap (PBG) structure. The observed FWM vortex can also be viewed as the reflected part of the launched probe vortex from the PBG. Further, we investigate the propagation behaviors, including the spatial shift and splitting of the probe and FWM vortices in the medium with enhanced Kerr nonlinearity induced by electromagnetically induced transparency. This Letter can be useful for better understanding and manipulating the applications involving the interactions between optical vortices and the medium.

Propagation properties of vortex beams in a ring photonic crystal fiber

In the last decade, the vortex beams have received lots of attention for their orbital angular momentum.When they are applied to optical fiber communication field,the data channels will increase and information propagation speed will be effectively improved. Recently, researchers have shown the capabilities of long length stably propagation, nonlinear frequency conversion and mode division multiplexing of vortex modes in a ring fiber. Due to the photonic crystal fiber(PCF) having very flexible design degrees of freedom, it will enable a wide range of propagation properties. In this paper, a SiO2 air-hole ring PCF is proposed for separation and propagation of optical vortex modes.By using COMSOL Multiphysics software,the vortex modes(TE01, HE21± and TM01) are simulated and calculated. The differences in effective refractive index between them are 4.59×10-4 and 3.62×10-4 respectively. One can analyze the propagation properties of vortex beams in the ring PCF by changing the size of first layer air hole radius and air hole pitch. When the incident light wavelength of TE01 mode ranges from 1650 nm to 1950 nm, this ring PCF can achieve a total dispersion variation between 44.18 to 45.83 ps·nm-1·km-1, which is tend to be flat. When incident light wavelength is 1550 nm, the nonlinear coefficient of TE01 mode vortex light is 1.37 W-1·km-1. Due to the fact that long wavelength light is easier to leakage through the cladding than the short wavelength light, the confinement loss increases with the wavelength. When incident light wavelength is 2000 nm, there is still an eight-orders-of-magnitude of the low confinement loss. Theoretically, flat dispersion and low loss vortex beams in this fiber can be beneficial to propagating stably, and the vortex modes lay the foundation for long distance propagation in the optical fiber. In the future, this ring PCF will be used in optical fiber communication field and applications in aspects such as continuous spectrum research, which can make it have immense advantage over traditional fibers.

Inversion of the topological charge of optical vortices in a coil fiber resonator

In this Letter, we study the propagation of optical vortices (OVs) in a two-coil multimode fiber resonator. We suggest an analytical scheme of solving this problem based on its reduction to one of propagation of OVs in parallel evanescently coupled optical fibers. In the framework of the scalar approximation, we derive expressions for normal modes of the system and study evolution of an OV with an arbitrary topological charge excited at the input end of the resonator. We show that such a coil resonator is able to invert the topological charge of the incoming OV, provided the resonance condition is met.

Divergence of optical vortex beams.

We show, both theoretically and experimentally, that the propagation of optical vortices in free space can be analyzed by using the width [w(z)] of the host Gaussian beam and the inner and outer radii of the vortex beam at the source plane (z=0) as defined in [Opt. Lett.39, 4364 (2014)10.1364/OL.39.004364OPLEDP0146-9592]. We also studied the divergence of vortex beams, considered as the rate of change of inner or outer radius with the propagation distance (z), and found that it varies with the order in the same way as that of the inner and outer radii at z=0. These results may be useful in designing optical fibers for orbital angular momentum modes that play a crucial role in quantum communication.

Dynamic propagation of optical vortices embedded in full Poincaré beams with rotationally polarization symmetry

Dynamical propagation characteristics of optical vortices embedded in Full Poincaré (FP) beams with rotationally polarization symmetry are studied in this paper to illustrate that polarization map alone does not provide a unique description of electromagnetic field. It is shown that different combinations of optical vortices embedded in FP beams lead to different propagation dynamics, even though the polarization maps of electromagnetic fields are identical. We investigate the interaction between optical vortices and the background field by numerical methods. The rotation, reversion of rotation and annihilation behaviors of the optical vortices with the same and opposite topological charges embedded in the FP beams are investigated in details. Numerical results show that FP beams with stable optical vortices in the center maintain the polarization distribution better. Moreover, we find that whether or not equality between the map area of right hand and left hand polarization in the source plane can affect the distribution of polarization map. The results of this study may help to develop more intuitive understanding of optical vortices motion embedded in vector beams and offer a new perspective for analyzing polarization rotation in the process of propagation.

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

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.

Propagation of optical vortices embedded with multiple wavefront singularities

Optical vortices with the embedded wavefront singularities have attracted intensive attentions in many branches of modern physics, due to their important applications in optical tweezers, quantum entangles, optical testing, atmospheric propagations, etc. In this paper, optical vortices are generated by new types of custom designed wavefronts and their propagation in free-space is reported. Huygens–Fresnel diffraction integral is directly solved using the Gauss–Legendre quadrature method to estimate the diffraction pattern at some arbitrary plane. The variation of vorticity is demonstrated under diffraction. Evolution of phase singularities in wavefronts as the wavefront propagate is predicted for various near field distances. Simulations reveal that the exchange of the nature of topological charge occurs at a finite distance. Experimentally, the wavefronts have been generated using the phase-only spatial light modulator and their far-field diffraction patterns are recorded. The experimental result has been validated with the numerical simulation.

Optical vortices in anisotropic optical fibers with torsional stress

Analytical expressions for the higher-order modes with the azimuthal number equal to unity and for corresponding propagation constants of optical fibers with linear anisotropy of the fiber material and a circular anisotropy induced by torsional mechanical stress been obtained at practically important relationships between fiber parameters. The possibility of stable propagation of optical vortices in these fibers and the dependence of characteristics of sustained optical vortices on the fiber parameters are demonstrated.

Numerical simulation of optical vortex propagation and reflection by the methods of scalar diffraction theory

Using the equations of scalar diffraction theory we consider the formation of an optical vortex on a diffractive optical element. The algorithms are proposed for simulating the processes of propagation of spiral wavefronts in free space and their reflections from surfaces with different roughness parameters. The given approach is illustrated by the results of numerical simulations.