Convention of Optical Vortices in Two-Helix Long-Period Fiber Gratings

An effective method to fabricate two-helix long-period fiber gratings （TH-LFGs） is presented. Based on the coupling mode theory, the conversion of optical vortices （OVs） in TH-LFGs are analyzed in detail. The conversions of OVs with different topological charges： 0 → ±2 and 1 → 3 are simulated as three examples and the conversion efficiency higher than 98% can be realized.

Advances in communications using optical vortices

An optical vortex having an isolated point singularity is associated with the spatial structure of light waves.A polarization vortex(vector beam) with a polarization singularity has spatially variant polarizations. A phase vortex with phase singularity or screw dislocation has a spiral phase front. The optical vortex has recently gained increasing interest in optical trapping, optical tweezers, laser machining, microscopy, quantum information processing, and optical communications. In this paper, we review recent advances in optical communications using optical vortices. First, basic concepts of polarization/phase vortex modulation and multiplexing in communications and key techniques of polarization/phase vortex generation and(de)multiplexing are introduced. Second, free-space and fiber optical communications using optical vortex modulation and optical vortex multiplexing are presented. Finally, key challenges and perspectives of optical communications using optical vortices are discussed. It is expected that optical vortices exploiting the space physical dimension of light waves might find more interesting applications in optical communications and interconnects.

Non-probe compensation of optical vortices carrying orbital angular momentum

In this paper, we demonstrate a scheme for compensating distorted optical vortex beams carrying orbital angular momentum. By inputting the intensity profile into the Gerchberg–Saxton algorithm [Optik 35, 237(1972)], the pre-compensation phase mask can be acquired. No additional probe beams are introduced, and all the computing is aiming at the transmitted vortex beams. The distorted vortex beams are investigated experimentally before and after pre-compensation, showing favorable compensation performance. This scheme will find applications in the areas of rotation detection, optical communications, and so on.

Propagation dynamics of ring Airy Gaussian beams with cosine modulated optical vortices

We numerically investigate the propagation properties of ring Airy Gaussian beams （RAGBs） with cosine modulated optical vortices （CMOV）. In comparison to the common RAGBs without any modulation, the dynamic propagation of RAGBs with CMOV exhibits a unique feature： the rings of RAGBs with CMOV will gradually shrink into several main lobes with the increase of the propagation distance. The number of lobes and the peak intensity of each lobe are determined by the factors of cosine modulated function. By designing the initial phase, we can easily change the transversal location of the peak intensity. Our results may find potential applications in optical manipulations.

Compression and stretching of ring vortex in a bulk nonlinear medium

We explore the nonlinear gain coupled Schrödinger system through the utilization of the variables separation method and ansatz technique.By employing these approaches,we generate hierarchies of explicit dissipative vector vortices(DVVs)that possess diverse vorticity values.Numerous fundamental characteristics of the DVVs are examined,encompassing amplitude profiles,energy fluxes,parameter effects,as well as linear and dynamic stability.

Propagation of optical vortex solitons due to the Gouy phase in strongly nonlocal nonlinear media

In this paper, we present a study on the propagation of the symmetrical optical vortices formed by two collinear Laguerre-Gauss solitons in strongly nonlocal nonlinear media. The optical vortices, which move along the beam axis as the light propagates, result in a rotation of the beam＇s transverse profile. This physical reason of the rotation is the Gouy phase acquired by the component beams.

Superposition of orbital angular momentum of photons by a combined computer-generated hologram fabricated in silica glass with femtosecond laser pulses

This paper introduces a novel method to realize the superposition of orbital angular momentum of photons by combined computer-generated hologram （CCGH） fabricated in silica glass with femtosecond laser pulses. Firstly, the two computer-generated holograms （CGH） of optical vortex were obtained and combined as a CCGH according to the design. Then the CCGH was directly written inside glass by femtosecond laser pulses induced microexplosion without any preor post-treatment of the material. The vortex beams with different vortex topological charges （including new topological charges） have been restructured using a collimated He-Ne laser beam incidence to the CCGH normally. A theoretical and experimental explanation has been presented for the generations of the new topological charges.

Propagation properties and radiation force of circular Airy Gaussian vortex beams in strongly nonlocal nonlinear medium

We study the abruptly autofocusing and autodefocusing properties of the circular Airy Gaussian vortex(CAi GV)beams in strongly nonlocal nonlinear medium for the first time through numerical simulations.The magnitude of topological charges and the position of the vortex could change not only the light spot pattern but also the intensity contrast.Meanwhile,we can change the position of the autofocusing and autodefocusing planes by changing the parameter of the incident beam.Furthermore,we can control the peak intensity contrast through choosing properly the truncation factor.As for the radiation force,we study the gradient and the scattering forces of CAi GV beams on Rayleigh dielectric sphere.Our analyses demonstrate that the radiation force can be enhanced by choosing proper parameters of CAi GV beams.

Existence of Optical Vortex Solitons in Pair Plasmas

Optical vortices arise as phase dislocations of light fields and they are of importance in modern optical physics.In this study,we employ the calculus of variations method to develop an existence theory for the steady state vortex solutions of a nonlinear Schr?dinger type equation to model light waves that propagate in a medium with a new focusing-defocusing nonlinearity.First,we demonstrate the existence of positive radially symmetric solutions by constrained minimization,where we give some interesting explicit estimates related to vortex winding numbers and the wave propagation constant.Second,we establish the existence of saddle-point solutions through a mountain-pass argument.

Spatiotemporal optical vortex wavepackets with phase singularities embedded in multiple domains[Invited]

Spatiotemporal optical vortex(STOV)wavepacket carrying transverse photonic orbital angular momentum(OAM)has been extensively studied in the past few years.In this Letter,we propose and study a novel STOV wavepacket with multiple phase singularities embedded in different space–time domains using analytical and numerical approaches.By tuning different parameters used for designing the wavepacket,it is possible to engineer both the magnitude and orientation of the photonic OAM in space–time.The vectorially controllable OAM will pave new avenues and facilitate applications such as novel optical communication,studying complicated quantum systems,and spin-and-OAM interactions.

Propagation of transverse photonic orbital angular momentum through few-mode fiber

Spatiotemporal optical vortex(STOV)pulses can carry transverse orbital angular momentum(OAM)that is perpendicular to the direction of pulse propagation.For a STOV pulse,its spatiotemporal profile can be significantly distorted due to unbalanced dispersive and diffractive phases.This may limit its use in many research applications,where a long interaction length and a tight confinement of the pulse are needed.The first demonstration of STOV pulse propagation through a few-mode optical fiber is presented.Both numerical and experimental analysis on the propagation of STOV pulse through a commercially available SMF-28 standard telecommunication fiber is performed.The spatiotemporal phase feature of the pulse can be well kept after the pulse propagates a few-meter length through the fiber even with bending.Further propagation of the pulse will result in a breakup of its spatiotemporal spiral phase structure due to an excessive amount of modal group delay dispersion.The stable and robust transmission of transverse photonic OAM through optical fiber may open new opportunities for transverse photonic OAM studies in telecommunications,OAM lasers,and nonlinear fiber-optical research.

Quantum digital spiral imaging

We demonstrate that the combination of digital spiral imaging with high-dimensional orbital angular momentum(OAM)entanglement can be used for efficiently probing and identifying pure phase objects,where the probing light does not necessarily touch the object,via the experimental,non-local decomposition of non-integer pure phase vortices in OAM-entangled photon pairs.The entangled photons are generated by parametric downconversion and then measured with spatial light modulators and single-mode fibers.The fractional phase vortices are defined in the idler photons,while their corresponding spiral spectra are obtained non-locally by scanning the measured OAM states in the signal photons.We conceptually illustrate our results with the biphoton Klyshko picture and the effective dimensionality to demonstrate the high-dimensional nature of the associated quantum OAM channels.Our result is a proof of concept that quantum imaging techniques exploiting high-dimensional entanglement can potentially be used for remote sensing.

Generation of single-focus phase singularity by the annulusquadrangle-element coded binary square spiral zone plates

Optical vortices(OVs) with unique square symmetry are widely used in various applications including particle manipulation,microscopy, and image processing. However, the undesired higher-order foci introduced by the conventional vortex lens such as square spiral zone plates(SSZPs) may lead to additional artifacts and thus degrade contrast sensitivity. In this endeavor, herein,we propose a methodology to combine the merit of SSZPs and the advantage of Gabor zone plates(GZPs) in establishing a specific single optical element, termed binary single focused square spiral zone plates(BSSZPs). In contrast to the abrupt transitions of the SSZPs, our central idea aims to realize the sinusoidal transmittance along the radial direction of SSZPs by a series of randomly distributed annulus-quadrangle-shaped nanometer structure apertures. The innovative design can simultaneously generate OVs with unique square symmetry, and eliminate the interference of higher-order foci along the propagation direction. Guided by our theoretical predication, the focusing property of such optics was further experimentally demonstrated.These findings are expected to direct new avenue towards improving the performance of optical image processing and alignment system.

Detection of cylindrical vector beams with chiral plasmonic lens

The cylindrical vector beam(CVB) has been extensively studied in recent years, but detection of CVBs with on-chip photonic devices is a challenge. Here, we propose and theoretically study a chiral plasmonic lens structure for CVB detection. The structure illuminated by a CVB can generate single plasmonic focus, whose focal position depends on the incident angle and the polarization order of CVB. Thus, the incident CVB can be detected according to the focal position and incident angle and with a coupling waveguide to avoid the imaging of the whole plasmonic field. It shows great potential in applications including CVB-multiplexing integrated communication systems.