Atomic optical spatial mode extractor for vector beams based on polarization-dependent absorption

Vector beams with spiral phase and spatially varying polarization profiles have many applications from optical micromanipulation to materials processing. Here, we propose and demonstrate an atomic spatial mode extracting scheme for the vector beam based on polarization-dependent absorption in the atom vapor. By employing the linear polarization pump beam which induces polarization sensitive absorption in the atomic ensemble, a counter-propagated weak probe vector beam is extracted by spatial absorption, and extracted part still maintains the original polarization and the vortex phase.The topological charges of the extracted mode are verified by interfering with the Gaussian beam, and it can be found that the orbital angular momentum is conserved in the extracting process. Our work will have potential applications in non-destructive spatial mode identification, and is also useful for studying higher-dimensional quantum information based on atomic ensembles.

Propagation of cylindrical vector beams in a turbulent atmosphere

Based on the extended Huygens-Fresnel principle, the propagation of cylindrical vector beams in a turbulent atmosphere is investigated. The intensity distribution and the polarization degree of beams on propagation are studied. It is found that the beam profile has a Gaussian shape under the influence of the atmospheric turbulence, and the polarization distribution shows a dip in the cross section as the beam propagates in the turbulent atmosphere. It is also found that the beam profile and the polarization distribution are closely related to beam parameter and atmospheric turbulence.

Polarized photoluminescence spectroscopy in WS_(2),WSe_(2) atomic layers and heterostructures by cylindrical vector beams

Due to the large exciton binding energy,two-dimensional(2D)transition metal dichalcogenides(TMDCs)provide an ideal platform for studying excitonic states and related photonics and optoelectronics.Polarization states lead to distinct light-matter interactions which are of great importance for device applications.In this work,we study polarized photoluminescence spectra from intralayer exciton and indirect exciton in WS_(2) and WSe_(2) atomic layers,and interlayer exciton in WS_(2)/WSe_(2) heterostructures by radially and azimuthally polarized cylindrical vector laser beams.We demonstrated the same in-plane and out-of-plane polarization behavior from the intralayer and indirect exciton.Moreover,with these two laser modes,we obtained interlayer exciton in WS_(2)/WSe_(2) heterostructures with stronger out-of-plane polarization,due to the formation of vertical electric dipole moment.

Hybrid vector beams with non-uniform orbital angular momentum density induced by designed azimuthal polarization gradient

Based on angular amplitude modulation of orthogonal base vectors in common-path interference method, we propose an interesting type of hybrid vector beams with unprecedented azimuthal polarization gradient and demonstrate in experiment. Geometrically, the configured azimuthal polarization gradient is indicated by intriguing mapping tracks of angular polarization states on Poincaré sphere, more than just conventional circles for previously reported vector beams. Moreover, via tailoring relevant parameters, more special polarization mapping tracks can be handily achieved. More noteworthily, the designed azimuthal polarization gradients are found to be able to induce azimuthally non-uniform orbital angular momentum density, while generally uniform for circle-track cases, immersing in homogenous intensity background whatever base states are. These peculiar features may open alternative routes for new optical effects and applications.

A method for generating double-ring-shaped vector beams

We propose a method for generating double-ring-shaped vector beams. A step phase introduced by a spatial light modulator（SLM） first makes the incident laser beam have a nodal cycle. This phase is dynamic in nature because it depends on the optical length. Then a Pancharatnam–Berry phase（PBP） optical element is used to manipulate the local polarization of the optical field by modulating the geometric phase. The experimental results show that this scheme can effectively create double-ring-shaped vector beams. It provides much greater flexibility to manipulate the phase and polarization by simultaneously modulating the dynamic and the geometric phases.

Toroidal dipole response in rectangular waveguide:used to generate vector beams and vector vortex beams

Toroidal multipole is a special current distribution that has many different characteristics from electric multipole and magnetic multipole distributions.Because of its special properties,the toroidal dipole is a research hotspot in the field of metamaterials and nanophotonics.However,the low scattering of the toroidal dipole moment makes its excitation a challenging task.At present,there are relatively few studies on its specific engineering applications.In this paper,by slotting in the rectangular cavity,the excitation of an equivalent toroidal dipole is successfully achieved over a wide frequency range of 53-58 GHz.Results indicate that under the action of the toroidal dipole,the TE_(10)mode electromagnetic waves transmitted in the rectangular waveguide are converted into vector beams and are radiated outwards.Further adjusting the spatial distribution of the magnetic dipoles in the toroidal dipoles yields results that indicate that the resonance mode in the slot is still dominated by the magnetic toroidal dipole moment,and the electromagnetic waves radiating outward are vortex beams carrying vector polarization.The scattered energy of each dipole moment inside the antenna is calculated.This calculation verifies that the mass of the vector beam and vector vortex beam is closely related to the toroidal dipole supported by this antenna.The proposed structure can be applied to explorations in vortex filtering,in photon entanglement,and in the photonic spin Hall effect.

Diffraction deep neural network-based classification for vector vortex beams

The vector vortex beam(VVB)has attracted significant attention due to its intrinsic diversity of information and has found great applications in both classical and quantum communications.However,a VVB is unavoidably affected by atmospheric turbulence(AT)when it propagates through the free-space optical communication environment,which results in detection errors at the receiver.In this paper,we propose a VVB classification scheme to detect VVBs with continuously changing polarization states under AT,where a diffractive deep neural network(DDNN)is designed and trained to classify the intensity distribution of the input distorted VVBs,and the horizontal direction of polarization of the input distorted beam is adopted as the feature for the classification through the DDNN.The numerical simulations and experimental results demonstrate that the proposed scheme has high accuracy in classification tasks.The energy distribution percentage remains above 95%from weak to medium AT,and the classification accuracy can remain above 95%for various strengths of turbulence.It has a faster convergence and better accuracy than that based on a convolutional neural network.

Stokes scintillations for vector beams in turbulence

We introduce the Stokes scintillation indices and the corresponding overall Stokes scintillations for quantitatively studying the fluctuations of both the intensity and polarization of an optical vector beam transmitting through the atmospheric turbulence.With the aid of the multiple-phase-screen method,we examine the Stokes fluctuations of a radially polarized beam in Kolmogorov turbulence numerically.The results show that the overall scintillation for the intensity distribution is always larger than the overall scintillation for the polarization-dependent Stokes parameters,which indicates that the polarization state of a vector beam is stabler than its intensity distribution in the turbulence.We interpret the results with the depolarization effect of the vector beam in turbulence.The findings in this work may be useful in free-space optical communications utilizing vector beams.

Controlled generation of order-switchable cylindrical vector beams from a Nd:YAG laser

We reporte and demonstrate a solid-state laser to achieve controlled generation of order-switchable cylindrical vector beams(CVBs).In the cavity,a group of vortex wave plates(VWPs)with two quarter-wave plates between the VWPs was utilized to achieve mode conversion and order-switch of CVBs.By utilizing two VWPs of first and third orders,the second and fourth order CVBs were obtained,with mode purities of 96.8%and 94.8%,and sloping efficiencies of 4.45%and 3.06%,respectively.Furthermore,by applying three VWPs of first,second,and third orders,the mode-switchable Gaussian beam,second,fourth,and sixth order CVBs were generated.

Spatial quantum coherent modulation with perfect hybrid vector vortex beam based on atomic medium

The perfect hybrid vector vortex beam(PHVVB)with helical phase wavefront structure has aroused significant concern in recent years,as its beam waist does not expand with the topological charge(TC).In this work,we investigate the spatial quantum coherent modulation effect with PHVVB based on the atomic medium,and we observe the absorption characteristic of the PHVVB with different TCs under variant magnetic fields.We find that the transmission spectrum linewidth of PHVVB can be effectively maintained regardless of the TC.Still,the width of transmission peaks increases slightly as the beam size expands in hot atomic vapor.This distinctive quantum coherence phenomenon,demonstrated by the interaction of an atomic medium with a hybrid vector-structured beam,might be anticipated to open up new opportunities for quantum coherence modulation and accurate magnetic field measurement.

Segmented cylindrical vector beams for massively-encoded optical data storage

The possibility to achieve unprecedented multiplexing of light-matter interaction in nanoscale is of virtue importance from both fundamental science and practical application points of view. Cylindrical vector beams(CVBs) manifested as polarization vortices represent a robust and emerging degree of freedom for information multiplexing with increased capacities. Here, we propose and demonstrate massivelyencoded optical data storage(ODS) by harnessing spatially variant electric fields mediated by segmented CVBs. By tight focusing polychromatic segmented CVBs to plasmonic nanoparticle aggregates, recordhigh multiplexing channels of ODS through different combinations of polarization states and wavelengths have been experimentally demonstrated with a low error rate. Our result not only casts new perceptions for tailoring light-matter interactions utilizing structured light but also enables a new prospective for ultra-high capacity optical memory with minimalist system complexity by combining CVB’s compatibility with fiber optics.

Generation of cylindrical vector beams in a mode-locked fiber laser using a mode-selective coupler

We experimentally obtain cylindrical vector beams（CVBs） in a passively mode-locked fiber laser based on nonlinear polarization rotation. A mode-selective coupler composed of both a single-mode fiber（SMF） and a twomode fiber（TMF） is incorporated into the cavity to act as a mode converter from LP01 mode to LP11 mode with broad spectral bandwidth. CVBs in different mode-locked states including single-pulse, multi-pulse, and bound pulse are obtained, for the first time to our best knowledge. The ultrafast CVBs with different operation states have potential applications in many fields such as laser beam machining, nanoparticle manipulation, and so on.

Polarization evolution of vector beams generated by q-plates

The polarization evolution of vector beams(VBs) generated by q-plates is investigated theoretically and experimentally.An analytical model is developed for the VB created by a general quarter-wave q-plate based on vector diffraction theory.It is found that the polarization distribution of VBs varies with position and the value q.In particular,for the incidence of circular polarization,the exit vector vortex beam has polarization states that cover the whole surface of the Poincarésphere,thereby constituting a full Poincarébeam.For the incidence of linear polarization,the VB is not cylindrical but specularly symmetric,and exhibits an azimuthal spin splitting.These results are in sharp contrast with those derived by the commonly used model,i.e.,regarding the incident light as a plane wave.By implementing q-plates with dielectric metasurfaces,further experiments validate the theoretical results.

Experimental realization to efficiently sort vector beams by polarization topological charge via Pancharatnam–Berry phase modulation

This paper reports the experimental realization of efficiently sorting vector beams by polarization topological charge （PTC）. The PTC of a vector beam can be defined as the repetition number of polarization state change along the azimuthal axis, while its sign stands for the rotating direction of the polarization. Here, a couple of liquid crystal Pancharatnam-Berry optical dements （PBOEs） have been used to introduce conjugated spatial phase modulations for two orthogonal circular polarization states. Applying these PBOEs in a 4-foptical system, our experiments show the setup can work for PTC sorting with a separation efficiency of more than 58%. This work provides an effective way to decode information from different PTCs, which may be interesting in many fields, especially in optical communication.

Generation of nanosecond cylindrical vector beams in two-mode fiber and its applications of stimulated Raman scattering

We present the generation of the nanosecond cylindrical vector beams(CVBs)in a two-mode fiber(TMF)and its applications of stimulated Raman scattering.The nanosecond(1064 nm,10 ns,10 Hz)CVBs have been directly produced with mode conversion efficiency of~18 d B(98.4%)via an acoustically induced fiber grating,and then the stimulated Raman scattering signal is generated based on the transmission of the nanosecond CVBs in a 100-m-long TMF.The transverse mode intensity and polarization distributions of the first-order Stokes shift component(1116.8 nm)are consistent with the nanosecond CVBs pump pulse.

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.

Vector dynamics of ultrafast cylindrical vector beams in a mode-locked fiber laser

The vector dynamics of solitons are crucial but easily neglected for realizing vortex solitons. In this Letter, we investigate the effect of vector dynamics on cylindrical vector beams(CVBs) implementation and propose a novel technical method to realize femtosecond CVBs based on vector-locked solitons, which are presented as group-velocity-locked vector solitons(GVLVSs) in the experiment. The outstanding vector properties of GVLVSs not only greatly improve the efficiency of solitons converted into CVBs and output power of CVBs(2.4 times and 4.1 times that of scalar solitons and vector change periodical solitons, with the purity of 97.2%), but also relax the obstacle of ultrafast CVBs from the fundamental frequency to the harmonic regime(up to 198 MHz) for the first time, to the best of our knowledge. This is the highest repetition rate reported for ultrafast CVBs based on passive mode-locking. The investigation of the influence of solitons vector dynamics evolution on the realization of CVBs provides guidance for the excellent performance of ultrafast CVBs.

Milli-Joule pulses post-compressed from 14 ps to 475 fs in bulk-material multi-pass cell based on cylindrical vector beam

A cylindrical vector beam is utilized to enhance the energy scale of the pulse post-compressed in a bulk-material Herriott multi-pass cell(MPC).The method proposed here enables,for the first time to the best of our knowledge,pulse compression from 14 ps down to 475 fs with throughput energy beyond 1 mJ,corresponding to a compression ratio of 30,which is the highest pulse energy and compression ratio in single-stage bulk-material MPCs.Furthermore,we demonstrate the characteristic of the vector polarization beam is preserved in the MPC.

Tight Focusing of Radially and Azimuthally Polarized Vortex Beams through a Dielectric Interface

Based on vectorial Debye theory, tight focusing of radially and azimuthally polarized vortex beams passing through a dielectric interface are studied. The intensity distribution in the focal region is illustrated by numerical calculations. We show the influence of numerical-aperture （NA） on the full-width at half maximum （FWHM） of the focal spot or the focal hole. It has been found that compared with the azimuthally polarized Besse^Gaussian （BG） beams, the longitudinal component in the z direction of the radially polarized BG beams has no influence on the FWHM of the focal spot and hole, but enhances the total light intensity.

Structural polarization properties of vector Gaussian beam in the far field

Based on the vector angular spectrum representation of optical beam and the method of stationary phase, the analytical TE and TM terms of vector Gaussian beam have been presented in the far field. By using the local polarization matrix, the polarization properties of the TE and TM terms in the far field are investigated, and it is found that the degree of their polarization is only determined by the spatial location. When the source is completely polarized, the TE and TM terms are both completely polarized in the far field. When the source is completely unpolarized, the TE and TM terms in the far field are partially polarized. The whole beam is also partially polarized except on the propagating axis. Moreover, the degrees of polarization of TE and TM terms are both larger than that of the whole beam.