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In turbid water, target reflected lidar signal is easily buried in “clutter” due to scattering. We proposed an underwater laser ranging model applying an optical vortex in the receiver to separate the scattering clutter from the target reflected signal. A spiral phase plate (SPP) was placed in front of the detector to convert the target reflected Gaussian beam to an optical vortex. While the scattering clutters were not able to be converted due to the loss of spatial coherence. Therefore, the target reflected signal and scattering clutters were spatially separated by the SPP. An underwater laser detection simulation using Zemax software was carried out. The numerical simulation showed that when the SPP was placed in front of the receiver, the contrast of signal to clutter of the detection was improved by blocking the scattering clutters which had a Gaussian distribution at the center on the detection plane. The effects of beam divergence and orbital angular momentum (OAM) order to the lidar performance were also analyzed.

We report, to the best of our knowledge, the first visible-wavelength all-fiber passively mode-locked vortex laser by a figure-9 cavity in combination with 635 nm mode selective coupler, which can deliver picosecond optical vortex pulses with topological charges of OAM±1. The mode-locked vortex laser emits stable rectangular pulses with pulse duration tunable range from 85 to 510 ps and a 0.16-nm narrow linewidth at 634.36 nm. The maximum output power of the vortex laser reaches 1.3 mW with a high purity 97.2%. This work demonstrated the generation of picosecond pulsed vortex in visible passively mode-locked fiber laser, showing their potential for applications in particle trapping, optical tweezers, and high-resolution microscopy.

Atoms moving in an optical vortex beam are subjected to the azimuthal Doppler effect in addition to the usual longitudinal Doppler effect. This fact extends the capabilities of plasma flow measurement using laser-induced fluorescence to the direction perpendicular to the laser path by employing optical vortex beams. Furthermore, by assuming a uniform flow traversing the beam, the LIF spectrum undergoes deformation due to the spatial dependence of the resonant absorption condition. Preliminary experiments were performed for metastable argon ions in the vicinity of a negatively biased electrode immersed in a plasma. An increase in the standard deviation of the spectrum was observed when a negative voltage was applied to the electrode, which qualitatively agrees with our previous numerical study.

Optical vortices with tunable properties in multiple dimensions are highly desirable in modern photonics, particularly for broadly tunable wavelengths and topological charges at the micrometer scale. Compared to solid-state approaches, here we demonstrate tunable optical vortices through the fusion of optofluidics and vortex beams in which the handedness, topological charges, and lasing wavelengths could be fully adjusted and dynamically controlled. Nanogroove structures inscribed in Fabry-Pérot optofluidic microcavities were proposed to generate optical vortices by converting Hermite-Gaussian laser modes. Topological charges could be controlled by tuning the lengths of the nanogroove structures. Vortex laser beams spanning a wide spectral band (430-630 nm) were achieved by alternating different liquid gain materials. Finally, dynamic switching of vortex laser wavelengths in real-time was realized through an optofluidic vortex microlaser device. The findings provide a robust yet flexible approach for generating on-chip vortex sources with multiple dimensions, high tunability, and reconfigurability. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) All the authors would like to thank A*STAR for support. This research is supported by A*STAR under its AME IRG Grant (project no. A20E5c0085). M.K. is also thankful for the support from ACRF Tier 2 (Grant T2EP50120-0003).

Dynamic control of motion at the molecular level is a core issue in promoting the bottom-up programmable modulation of sophisticated self-organized superstructures. Self-assembled artificial nanoarchitectures through subtle noncovalent interactions are indispensable for diverse applications. Here, the active solar renewable energy is used to harness cholesteric liquid crystal (CLC) superstructure devices via delicate control of the dynamic equilibrium between the concentrations of molecular motor molecules with opposite handedness. Thus, the spectral position and handedness of a photonic superstructure can be tuned continuously, bidirectionally, and reversibly within the entire working spectrum (from near-ultraviolet to the thermal infrared region, over 2 μm). With these unique horizons, three advanced photoresponsive chiroptical devices, namely, a mirrorless laser, an optical vortex generator, and an encrypted contactless photorewritable board, are successfully demonstrated. The sunlight-fueled chirality inversion prompts facile switching of functionalities, such as free-space optical communication, stereoscopic display technology, and spin-to-orbital angular momentum conversion. Motor-based chiroptic devices with dynamic and versatility controllability, fast response, ecofriendly characteristics, stability, and high efficiency have potential to replace the traditional elements with static functions. The inexhaustible natural power provides a promising means for outdoor-use optics and nanophotonics.

We experimentally generate cylindrically polarized wavepackets with transverse orbital angular momentum, demonstrating the coexistence of spatiotemporal optical vortex with spatial polarization singularity. The results in this paper extend the study of spatiotemporal wavepackets to a broader scope, paving the way for its applications in various areas such as light-matter interaction, optical tweezers, spatiotemporal spin-orbit angular momentum coupling, etc., 5 pages, 5 figures

The perfect optical vortex (POV) beam with the characteristic of the topological charge (TC)- independence radial profile is first considered to improve the spatial-mode-based underwater wireless optical communication (UWOC) performance. The evolution model of POV beams is proposed on the basis of Rytov approximation and the mutual coherence function to explore the impact of wave parameters on the orbital angular momentum (OAM) detection probability spectrum. The instantaneous crosstalk coefficients describing the POV-based UWOC systems are simulated by the multiple phase screen method with the signal coefficient modeled by a mixture Gamma-Gamma and normal distribution. A discrete and memoryless channel and a set of noncollaborative channels are modeled to obtain the capacity performances of the spatial-mode modulating and multiplexing systems, respectively. Results show the transmission quality of POV beams in oceanic turbulence is most related to the beam radius, while it is nearly free from the wavelength, TC, and radius-thickness ratio. Enjoying the advantage of the TC-independence beam radius, POV beams-based UWOC systems could achieve better bit error rate and capacity performances than the widely used Laguerre-Gauss beams when the higher-order TCs are adopted to modulate and multiplex information, which also confirms the superiority of POV beams in spatial-mode-based UWOC systems.

An optical vortex possesses a ring-shaped spatial profile and orbital angular momentum (OAM) owing to its helical wavefront. This form of structured light has garnered significant attention in recent years, and it has enabled new investigations in fundamental physics and applications. One such exciting application is laser-based material transfer for nano-/micro-fabrication. In this work, we demonstrate the application of a single-pulse optical vortex laser beam for direct printing of ring-shaped structures composed of hexagonal close-packed, mono-/multi-layered nanoparticles which exhibit ‘structural color’. We compare and contrast the interaction of the vortex beam with both dielectric and metallic nanoparticles and offer physical insight into how the OAM of vortex beams interacts with matter. The demonstrated technique holds promise for not only photonic-based nano-/micro-fabrication, but also as a means of sorting particles on the nanoscale, a technology which we term ‘optical vortex nanoparticle sorting’.

Terahertz (THz) vortex beams carrying orbital angular momentum (OAM) with high purity and tunable topological charge (TC) will undoubtedly bring extraordinary capacities for advanced imaging or communication systems. We propose a convenient and efficient method to generate a tunable and broadband vortex beam that is excited by superradiant Smith Purcell radiation (SSPR) on a helical grating. This scheme fully explores the advantages of natural broadband evanescent wave carried by the electron beam and the Bloch’s theorem regulated helical periodic systems. An explicit relation is established between the index of the spatial harmonic wave on the grating and the topological charge of the vortex beam. The electron energy in the SSPR can be customized to ignite the specific spatial harmonics and manipulate the OAM beam, accordingly. The separated radiation region also promises the high purity of the OAM spectrum. The harmonic excitation reduces the communality between the wavelength and the device size and alleviates the difficulty of device fabrication in the THz band. The proposed vortex scheme can not only be handily scaled to microwave and mid‑infrared regions, but also bring possibilities to applications based on compact tunable vortex beam sources.

Recently, orbital angular momentum (OAM) has been adopted to measure the shape of static objects and the translation motion of moving objects in optical remote sensing. Most of these studies rely on measuring the intensity variation of OAM beams. However, the OAM intensity does not change with the rotation of the spinning object, but its phase changes. The phase variation is proved to be proportional to the object’s angular velocity. Since a rotating object will cause the OAM phase dependent on time, the OAM phase needs to be measured instantaneously, to support the OAM-based angular velocity measurement. In this work, we report a scheme to measure the angular velocity of a spinning object using a photonic OAM phase spectrum. A phase-to-intensity strategy is implemented to enable the real-time multi-OAM phase measurement, in which the phase can be determined with the intensities of four focal spots in a two-dimensional array generated by a phase-only spatial light modulator. The experimental results show that the average error of the measured angular velocity could be under 2.45% by detecting the phase of two OAM modes. This OAM-based angular velocity detection method provides a complementary approach to characterize the rotational Doppler effect, especially for slow angular motion.

Optical vortex beams have attracted significant research interest owing to their potential for application in optical communication and imaging. In this study, we demonstrated devices with electric...

Optical vortex is of great value in optical trapping, manipulating, and arranging. Here, we propose a dual-helical dielectric cone to generate a dual-vortex beam which can be used to manipulate and arrange dielectric microparticles in three-dimensional space. With the finite-difference time-domain simulation, we calculate the electromagnetic field intensity distribution, phase, and Poynting vector during the propagation of the dual-vortex beam, the optical force and optical torque on the microparticles in the range of dual-vortex beam is also considered. In the experiment, we use the phase mask projected on spatial light modulator to generate a dual-vortex beam, which can trap, manipulate, and arrange the fluorescent microparticles to a specific and stable shape, which is consistent with the results of our simulation calculations. The dual-vortex beam generated by the dual-helical dielectric cone provides a feasible method three-dimensional optical manipulation, which is significant in biophotonical researches.

The key information about any nanoscale system relates to the orientations and conformations of its parts. Unfortunately, these details are often hidden below the diffraction limit, and elaborate techniques must be used to optically probe them. Here we present imaging of the 3D rotation motion of metal nanorods, restoring the distinct nanorod orientations in the full extent of azimuthal and polar angles. The nanorods imprint their 3D orientation onto the geometric phase and space-variant polarization of the light they scatter. We manipulate the light angular momentum and generate optical vortices that create self-interference images providing the nanorods’ angles via digital processing. After calibration by scanning electron microscopy, we demonstrated time-resolved 3D orientation imaging of sub-100 nm nanorods under Brownian motion (frame rate up to 500 fps). We also succeeded in imaging nanorods as nanoprobes in live-cell imaging and reconstructed their 3D rotational movement during interaction with the cell membrane (100 fps).

Monolayer transition metal dichalcogenides have intrinsic spin-valley degrees of freedom, drawing broad interests due to their potential applications in information storage and processing. Here, we demonstrate the possibility of using cylindrical vector pumped beams, which are nonseparable in their polarization and spatial modes, to manipulate nonlinear valley-locked twisted-vortex emissions in monolayer tungsten disulfide (WS2). The second-harmonic (SH) photons from K and K' valleys are encoded with opposite optical vortices, thus allowing the SH beams to emerge as cylindrical vector beams with doubled topological orders compared to the fundamental beams. The conically refracted pumped beams allow us to generate the first-order SH cylindrical vector and full Poincare beams via tuning the valley-locked emitted light field profiles. With fanshaped WS2 films breaking the axial symmetry of SH beams, the SH valley photons are routed to opposite directions. Our results pave the way to develop atomically thin nonlinear photonic devices and valleytronic nanodevices.

With the development of optical communication technology based on orbital angular momentum (OAM), more and more OAM modes are employed in communication systems, which puts forward higher requirements for the capacity of OAM state detection at the receiving end. In this work, we reported a scheme to measure and demultiplex OAM beams with topological charges from −32 to +32 by using a specially engineered two-dimensional 64-focus vortex demultiplexing array. The phase mask for generating this array was calculated by dense phase stitching algorithm which integrates four candidate phase masks that can generate four 16-focus arrays respectively. The first step of the algorithm is to extract sector phase areas from the four phase masks successively by using rotationally symmetric sector apertures whose total angular aperture is π/2. The second step of the algorithm is to form a stitched phase mask with the extracted sector phase areas. Consequently, the 64-focus vortex array can be generated by using the stitched phase mask, which is almost equivalent to generating four 16-focus arrays by four candidate phase masks simultaneously. Furthermore, by adjusting the number of sector apertures, the modal crosstalk in the OAM detection range can be greatly reduced. With the help of this scheme, both single OAM mode and multiplexing OAM modes in the range from −32 to +32 can be effectively measured. According to this scheme, simple devices can be arranged to achieve both low modal crosstalk and wide detection range of vortex beams, which can support the advanced high-capacity OAM-based optical communication systems.

In optical data transmission with using vortex laser beams, data can be encoded by the topological charge, which is theoretically unlimited. However, the topological charge of a single separate vortex (screw dislocation) is limited by possibilities of its generating. Therefore, we investigate here three examples of multivortex Gaussian light fields (two beams are form-invariant and one beam is astigmatic) with an unbounded (countable) set of screw dislocations. As a result, such fields have an infinite topological charge. The first beam has the complex amplitude of the Gaussian beam, but multiplied by the cosine function with a squared vortex argument. Phase singularity points of such a beam reside in the waist plane on the Cartesian axes and their density grows with increasing distance from the optical axis. The transverse intensity distribution of such a beam has a shape of a four-pointed star. All the optical vortices in this beam has the same topological charge of +1. The second beam also has the complex amplitude of the Gaussian beam, multiplied by the vortex-argument cosine function, but the cosine is raised to an arbitrary power. This beam has a countable number of the optical vortices, which reside in the waist plane uniformly on one Cartesian axis and the topological charge of each vortex equals to power, to which the cosine function is raised. The transverse intensity distribution of such beam consists of two light spots residing on a straight line, orthogonal to a straight line with the optical vortices. Finally, the third beam is similar to the first one in many properties, but it is generated with a tilted cylindrical lens from a 1D parabolic-argument cosine grating.

The energy and spectral conditions for single-stage holographic recording of a diffraction optical element based on the carbazole-containing azo polymer, that forms singular light beams (optical vortices), have been established. With the atomic-force microscopy (AFM), the surface morphology of the recorded relief holograms was studying, and their diffraction efficiency has been estimated. The topology of the generated optical phase singularities has been studied and the stability range of an optical vortex having the topological charge l = 2 has been found. The possibility of using the developed diffractive optical element in the scheme of optical tweezers for manipulating micro-objects is demonstrated.

Vortex beams have attracted much attention in recent years due to unique features of the phase or polarization singularity in the center part of beams. Various applications have been explored by the vortex beams including optical communication, optical tweezer, etc . Especially, the vortex beams for optical sensing applications have emerged. Compared with the traditional Gaussian beams, the vortex beams enable the optical sensing with the degree of freedom by controlling the spin and orbital phase and polarization. In this review article, we have discussed the theory of polarization and phase vortices, and then summarized the vortex beam generation in optical fiber and their sensing applications. It is hoped that the article can intrigue further research interest and development in fiber vortices for sensing applications.

Generally, an optical vortex lattice (OVL) is generated via the superposition of two specific vortex beams. Thus far, OVL has been successfully employed to trap atoms via the dark cores. The topological charge (TC) on each optical vortex (OV) in the lattice is only ±1. Consequently, the orbital angular momentum (OAM) on the lattice is ignored. To expand the potential applications, it is necessary to rediscover and exploit OAM. Here we propose a novel high-order OVL (HO-OVL) that combines the phase multiplication and the arbitrary mode-controllable techniques. TC on each OV in the lattice is up to 51, which generates sufficient OAM to manipulate microparticles. Thereafter, the entire lattice can be modulated to desirable arbitrary modes. Finally, yeast cells are trapped and rotated by the proposed HO-OVL. To the best of our knowledge, this is the first realization of the complex motion of microparticles via OVL. Thus, this work successfully exploits OAM on OVL, thereby revealing potential applications in particle manipulation and optical tweezers.

Application of four algorithms developed for detecting optical vortices in model problems of singular optics is considered. Computational schemes that should be constructed for the software implementation of the algorithms are presented and the input information required for the operation of the computer applications is specified. Special attention is paid to the accuracy in detecting the number and coordinates of singular points of a wavefront. Depending on the characteristic of the methods and input data volume, the areas of their possible use (experiments or purely numerical simulation) are determined.

In order to generate high quality regular optical vortex array (OVA), we present an experimental method for generating OVA using phase only liquid crystal spatial light modulator (LC-SLM) assisted two gratings. In the scheme, holograms of two grating are displayed on the screen of two LC-SLMs respectively; the diffraction optical fields are captured by a CCD camera. The simulated and experimental results show that the regular OVA can be generated by using double diffraction gratings. The generated OVAs have a constant topological charge of ±1. The method can provide a useful pathway to produce regular OVA for some applications in optical communication, particle trapping and optical metrology.

Recently, electrical sensing techniques of single small objects, such as nanoparticles, viruses, and biomolecules, have attracted much attention. However, fine-tuning of a sensing section is requir...

We present twisted spatiotemporal optical vortex (STOV) beams, which are partially coherent light sources that possess a coherent optical vortex and a random twist coupling their space and time dimensions. These beams have controllable partial coherence and transverse orbital angular momentum (OAM), which distinguishes them from the more common spatial vortex and twisted beams (known to carry longitudinal OAM) in the literature and should ultimately make them useful in applications such as optical communications and optical tweezing. We present the mathematical analysis of twisted STOV beams, deriving the mutual coherence function and linear and angular momentum densities. We simulate the synthesis of twisted STOV beams and investigate their free-space propagation characteristics. We discuss how to physically generate twisted STOV fields and lastly conclude with a summary and brief discussion of future research.

Third order optical limiting utilizes nonlinear absorption or scatter to preferentially reduce the optical throughput of intense light through a medium. While these processes are dependent on intensity, it is often the transmitted energy or power that needs to be limited to avoid eye, sensor or detector damage. This is problematic when the input is a vortex mode or other higher order Gaussian distributions such as Bessel-Gaussian modes where the relationship between optical power and the on axis intensity is more complicated than for the TEM00 Gaussian mode. Here we show that for higher order Bessel-Gaussian modes that beam power transmission is not equivalent to peak intensity transmission through intensity dependent absorption or scatter based optical limiters. We present a theoretical model and experimental data that demonstrates that the power throughput in these media, increases by 4 and 7 times for n = 1 and 2 Bessel-Gaussian modes, respectively, over that observed when a TEM00 mode is used.

Optical orbital angular momentum (OAM), carried by optical vortices, is a fundamental property of light that grabs broad interests. The detection of OAM modes, including fractional OAM is of great importance in diverse fields. Here, we firstly propose and develop the limited integer-component measurement method to determine the fractional topological charge (TC) of OAM states. This method indicates that a 2-integer-mode responsive device could be applied for the detection of fractional TC. An orthogonal long-period fiber grating (OLPFG) element is used as a fractional OAM TC probe to verify the Applicability. We experimentally demonstrate the fractional TC detection, ranging from −1 to 0, and recognize different fractional OAM modes with the minimum TC interval of 0.01. This scheme provides a concise, precise, continuous, and fiber-compatible fractional TC detection method that might have great potential in micro-detection, optical communication, quantum information, and chiral sensing applications.

A harmonic vortex beam is a typical vector beam with a helical wavefront at harmonic frequencies (e.g., second and third harmonics). It provides an additional degree of freedom beyond spin- and orbital-angular momentum, which may greatly increase the capacity for communicating and encoding information. However, conventional harmonic vortex beam generators suffer from complex designs and a low nonlinear conversion efficiency. Here, we propose and experimentally demonstrate the generation of a large second-harmonic (SH) vortex beam with quasi-nonlinear spin–orbit interaction (SOI). High-quality SH vortex beams with large topological charges up to 28 are realized experimentally. This indicated that the quasi-angular-momentum of a plasmonic spiral phase plate at the excitation wavelength (topological charge, q) could be imprinted on the harmonic signals from the attached WS2 monolayer. The generated harmonic vortex beam has a topological charge of ln=2nq (n is the harmonic order). The results may open new avenues for generating harmonic optical vortices for optical communications and enables novel multi-functional hybrid metasurface devices to manipulate harmonic beams.

Features of the spectral broadening of femtosecond optical vortices at self-action in a medium with the anomalous group velocity dispersion have been studied experimentally and numerically. It has been found that the broadening of the frequency–angular spectrum is accompanied by the appearance of localized maxima in the Stokes and anti-Stokes regions, which have a strip structure, near the nonlinear focus. It has been shown that in the medium with the anomalous group velocity dispersion the broadening of the spectrum in an optical vortex is smaller than that in a Gaussian beam at the same excess of the power above the critical value.

Unlike traditional symmetrical vortex beams, we demonstrate one kind of asymmetric spatial modes, namely Lommel-Gaussian (LMG) mode carrying orbital angular momentum (OAM) for optical communications, which possesses higher channel capacity through orthogonal multiplexing process. Some unique properties, such as better detection probabilities of high-order modes compared with low-order modes, are experimentally observed and well explained using theoretical models based on Rytov approximation method. An efficient scheme to generate LMG superposition states for OAM mode multicasting and multiplexing is proposed. Also, some critical issues, such as mode mismatching, still need further investigations. This work inspires us to explore more spatial multiplexing approaches, whose distinctive properties may open up new prospects for future communications systems.

A combined high-aperture metalens in a thin silicon nitride film that consists of two tilted sectored metalenses is considered. Each sector of the metalens consists of a set of binary subwavelength gratings. The diameter of the metalens is 14 μm. Using a time-domain finite difference method, we show that the metalens can simultaneously detect optical vortices with two topological charges −1 and −2, almost over the entire spectrum of visible wavelengths. The metalens can distinguish several wavelengths that are focused at different points in the focal plane due to a 1-nm change in wavelength resulting in a focal spot shift of about 4 nm. When the metalens is illuminated by a Gaussian beam with left-handed circular polarization, two optical vortices with topological charges 1 and 2 are simultaneously formed 6-μm apart at the focal distance of 6 μm.

We have experimentally studied the stable trapping and rotation of silica microspheres using canonical vortex (CV) beam and power-exponent-phase vortex (PEPV) beam. Numerical simulation was carried...

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.

We explain how quadrupole-active atomic interactions be able to be enhanced once the neutral atom interacts with an evanescent winding light modes. The optical system presented is a semi-bounded space based on neutral atoms situated close to the evanescent Bessel-Gaussian modes. The quadrupole Rabi frequency (and hence the optical quadrupole potential) generated by such evanescent modes is large enough to be exploited in atoms manipulation. In particular, the atomic states in which the dipole transitions are prohibited but the quadrupole transitions are permissible create the optical quadrupole potential of accessible value to play an important role. It is also shown how such optical system acts to create of evanescent modes with $ \ell \gt 0 $ having an orbital angular momentum $ \ell \hbar $ in which the intensity distribution is restricted in the vicinity of the dielectric surface.

Multi-channel structured light with orbital angular momentum (OAM) can be applied in different applications. For example, OAM modulation and OAM multiplexing in fiber optics communications, high-dimensional quantum cryptography-based OAM states for transmitting secure information across free-space, and independent data streams through OAM beams multiplexed free-space optical links. Using a simple and efficient system consisting of a spiral phase element (SPE) and a multi-channel vortex filter (MVF), we have converted input Gaussian beams into multi-channel OAM-based vortex beams for infrared wavelengths. An SPE has been designed, which generates optical vortices with wavelength-dependent topological charge (including fractional values). The resulting complex fields are optically relayed on a binary MVF designed by modulo- $2\pi $ phase addition of multiple fork gratings with topological charges 1, 2, and 3 and azimuthal orientations. In this way, the MVF generates beams with different OAM states for different carrier waves with different angles and maps them at desired locations in the detector plane. In this study, both $3\times 3$ , as well as a hexagonal configuration, were used. Furthermore, the experimentally obtained OAM spectrum qualitatively agrees with the results of numerical simulations, thus verifying our approach. The presented approach opens a new pathway for developing an efficient multi-channel OAM beams generator designed for a specific wavelength and illuminated by an input beam of different wavelengths over a broad spectral range.

In the last two decades, optical vortices carried by twisted light wavefronts have attracted a great deal of interest, providing not only new physical insights into light-matter interactions, but also a transformative platform for boosting optical information capacity. Meanwhile, advances in nanoscience and nanotechnology lead to the emerging field of nanophotonics, offering an unprecedented level of light manipulation via nanostructured materials and devices. Many exciting ideas and concepts come up when optical vortices meet nanophotonic devices. Here, we provide a mini review on recent achievements made in nanophotonics for the generation and detection of optical vortices and some of their applications.

An array of optical waveguide fed 45° metal-coated mirrors are proposed and validated by simulation, for generating optical scalar and vector vortices. Subwavelength element-to-element spacings are achieved, which is not possible in traditional grating-based phased arrays. This vortex source can be superior over other methods like phase masks which are not planar process integrable with lasers and phase modulators. A simple plane wave reflection model is used to analyze the mirror and the results are matched with reasonable tolerance against simulation results. The spin and orbital angular momentum charges are directly calculated from the field values for quantifying the performance. Four- and eight-element arrays are studied. The matching of prediction with simulation has been good for linear, azimuthal and radial polarization. Good angular momentum conversion efficiencies are obtained for up to orbital angular momentum charges ${l}$ = ±2. Important aspects of generating vortices with circular polarization are brought out. Directional beams with >10 dB gains are achieved. This is the first report in which a planar dielectric optical waveguide array with subwavelength spacing has achieved good angular momentum control for linearly, azimuthally, radially and circularly polarized beams, in the same geometry.

Integrating multiple functionalities into one single device is of great importance for ever-growing demand of photonic device. Optical vortex beam contains orbital angular momentum (OAM) and spin angular momentum (SAM) associated with phase and polarization singularities respectively, which has contributed to various application including optical manipulation, optical trapping and high-speed optical communication. Traditional methods to detect its phase and polarization mostly focus on the functionality of single dimensional optical field. However, quite different from the previous reports, we here propose a novel approach to measure the phase and polarization state based on the full use of near and far-field light functionalities in one single metadevice, which supports spin-controlled surface plasmon polaritons (SPPs) and topological charge-dependent focus spot position. On the one hand, this design makes the most of multidimensional field optical scattering characteristics to rich the functions of metadevice. On the other hand, it provides a novel concept to recognize various angular momentum information of vortex beam. We believe that such design will have great potential for the integration of different sub-wavelength optical components.

In linear optics, the angular momentum of light can be easily manipulated through the optical spin-orbit interaction (SOI) in structured media such as liquid crystals, metasurfaces, and forked gratings. Similarly, metasurfaces can be used to generate nonlinear optical beams with both custom-defined spin angular momentum (SAM) and orbital angular momentum (OAM) states. However, it has been limited to a low-order process in which only a Gaussian-shaped fundamental wave is used. In this work, the high-order nonlinear optical SOI effect on metasurfaces is demonstrated through the generation of multiple angular momentum states in nonlinear waves. This is achieved by exploiting the degrees of freedom provided by both the SAM and the OAM states of the fundamental wave (FW) and the topological charges of the plasmonic metasurfaces. The mechanism of both intrinsic and extrinsic contributions to the OAM of the nonlinear waves is revealed. High-order nonlinear SOI on metasurfaces offers new opportunities for realizing ultracompact nonlinear vortex beams.

Although higher order Poincare (HOP) beams are attractive due to their unique advantages and various efforts have been made for the generation of HOP sphere beams, the current generation technologies suffer from both limited output power and narrow bandwidth, preventing further practical applications. In this paper, we report on a femtosecond optical parametric oscillator (OPO) which can deliver high average power, on-demand arbitrary HOP sphere beams tunable across a wide spectral range in the near-infrared. The desired beam mode can be achieved by manipulating the geometric phase inside the OPO cavity to map the polarization to orbital angular momentum (OAM). Pumped by a Gaussian beam from an Yb-fiber laser, the generalized vector vortex femtosecond signal beams with spectral coverage from 1367 to 1650 nm are obtained. The device can produce over 200 mW structured beam signal power cross the complete tuning range with as much as 377 mW at 1480 nm for 2 W of input pump power. The proposed configuration, which shows superiorities of high average output power, flexible wavelength tunability and complete mode controlling property, may have direct implications in applications such as quantum optics and material processing.

A plasmonic in-plane zone-plate (IPZP) is analytically proposed and numerically analyzed. The proposed scheme consists of several discretely metallic nano-slits, which couple incident vortices into SPP and form focal spots. Wave front information of incident beam is reflected in the field distribution along “focal plane” of IPZP, and therefore, the proposed structure can be used for topological charge detection. Besides, an orthogonal slit array IPZP achieving simultaneous spin and orbital angular momentum detection is elaborated. IPZP structure has relatively high fabrication tolerance and the parameters can be adjusted to fit various operating wavelength. The proposed structure is expected to find potential applications in orbital angular momentum communication and high-dimensional quantum entanglement.

This research demonstrates that the usually weak electric quadrupole transitions can be clearly enhanced once the atom interacts at near resonance with a surface optical vortex. The design shown here is a type of bounded space based on atoms positioned near the evanescent twisted beam due to total internal reflection. The resulting optical quadrupole potential acting on the atom will be significant enough to be exploited. The situation forbids dipole transitions but allows quadrupole transitions, making them available to play a role. The research also shows that the surface optical vortex can distinctly affect the manipulation of absorbed atoms congregating in places of high intensity on the surface.

Background: Optical Vortex (OV) has attracted attention amongst many researchers. Paper proposes a nonlinear scheme of image encryption based on Optical Vortex (OV) and Double Random Phase Encoding (DRPE) in the Gyrator Transform (GT) domain under phase truncation operations. Objective: The amplitude and phase truncation operation in the image encryption generates two decryption keys and convert the method to nonlinear. It has also been proposed opto-electronically. Original image can only be decrypted with correct values of OV, GT rotation angles and Decryption Keys (DKs). Methods: A novel asymmetric image encryption scheme, using optical vortex mask has been proposed in view of amplitude and phase truncation operation. The scheme becomes more strengthened by the parameters used in the Optical Vortex (OV) and by taking the (n)th power operation in the encryption path and (n)th root operation in the decryption path. Results: It shows that for each of the encryption parameters, binary image has greater sensitivity as compared to the grayscale image. This scheme inflates the security by making use of OV-based Structured Phase Mask (SPM) as it expands the key space. The scheme has also been investigated for its robustness and its sensitivity against various attacks such as noise and occlusion attacks under number of iterations. Conclusion: This scheme provides solution to the problem of key space with the use of GT rotational angles and OV phase mask thus enhances the security. The scheme has been verified based on various security parameters such as occlusion, noise attacks, CC, entropy etc.

Diffraction phenomenon describing method based on the topological objects set by means of system analysis was developed in the work. Diffraction field topological objects are maximum, minimum and zero intensity, which is identical to the phase singularity or optical vortex. Topological objects mathematical representation by standard extremum search function methods was considered. The algorithm for distinguishing the minimum has been developed and zero intensity at the experimental images due to the algorithm the diffractive optical images classification possibility by the number of phase singularities without further interference analysis was shown. To increase the speed of data analyses the image segmentation method is suggested. Otained results and recommendations applying is possible in various fields of medicine and technology, which use laser radiation.

An averaged variational procedure has been developed to study the propagation of light bullets in optical fibers using the propagation of light pulses in media with Kerr and quadratic nonlinearities as examples. Criteria for the correct choice of trial solutions are discussed. The condition under which the dispersion length is much greater than the length of diffraction spreading is called the diffraction limit. It is shown that, in this limit, the temporal and spatial dynamics of a bullet are independent of each other, while finding the dynamic parameters of a soliton is reduced to finding various solutions of the nonstationary linear Schrodinger equation for an imaginary quantum particle. The efficiency of the proposed approach is demonstrated by the example of finding solutions in the form of optical vortices in a waveguide for nonlinearities of both types.

Traditionally, optical vortices (OVs) were generated with diffractive optical elements (DOEs) such as spiral phase plate (SPP), fork grating, spatial light modulator (SLM), and liquid crystal display (LCD). Here, a method was proposed for generating OVs by employing all-dielectric polarization-insensitive metasurfaces with cylinder arrays, which have high transmission efficiency. The polarization insensitivity of the metasurfaces was illustrated with the incidence of two pairs of orthogonal polarization, both the phase and transmission efficiency were consistent for the cylinder unit cell, and similar OVs were generated with the cylinder array. The topological charges of the generated OVs can be adjusted through the design of the metasurfaces. OVs with additional characteristics as vector beams, focused beams and Bessel beams were further generated. This work has potential applications in beam shaping, optical tweezers, and optical communication.

We experimentally demonstrate excitation of orbital angular momentum states in an air-core fiber by a silicon integrated vortex beam emitter which is designed and fabricated to match the modes supported by the fiber. The coupling loss is measured to be ∼7.5 dB. Excitation of eigenmodes is confirmed by analyzing the fiber output.

We present a method for achieving the cylindrical vector beams (CVBs) and optical vortex generation in a solid-core ring fiber (SCRF) by using an acoustically induced fiber grating (AIFG). Theoretical analysis shows that the SCRF can introduce a refractive index difference of ∼10–5 between the first group of adjacent high-order degenerate vector modes. In the experiment, the transmission spectra of AIFG constructed with the SCRF depicts three separate resonance peaks with 3-dB bandwidth and resonance wavelength interval of 0.16 and 2.5 nm, respectively, revealing that the high-order degenerate vector modes have been effectively separated. On the basis of the separation of the degenerate vector mode, the CVBs and the ±1-order optical vortex are further experimentally generated at three separate wavelengths using the AIFG.

Measuring the topological charge(TC) of optical vortices is of great importance in applications of vortex beams. A flexible and convenient method to determine the TC of an optical vortex is proposed by using an elliptical airy phase mask (EAPM). The mask can be embedded into a typical vortex generation setup, in which no additional optical elements are required. The number and the sign of TC are respectively obtained by analyzing the number and the direction of dark stripes in the far-field diffraction patterns of the vortex beam companied with EAPM. It is experimentally demonstrated that this method is able to measure TCs of both conventional and perfect vortex up to ±120.

Pump phase modulation is an important method for signal group velocity control. By controlling the phase difference between pump and signal, the fast and slow light can be changed easily, and the degree of signal delay or advancement can be greatly improved. In this letter, the fast and slow light of a Gaussian signal with pump phase modulation is studied for the first time. The Gaussian pulse signal is similar to the actual network transmission signal, so it is significant to investigate it. Unlike a sinusoidal signal, the duty ratio of a Gaussian signal can be adjusted, leading to the difference in pump phase modulation of the Gaussian signal. The experimental and simulation results show that the smaller the duty ratio of the Gaussian signal is, the smaller the impact of the pump phase adjustment on the fractional delay and advancement will be. Moreover, it is also found that at a certain duty ratio, two signal peaks appear within a certain adjustment range of phase difference.

In this letter, we report the demonstration of terawatt (TW)-scale femtosecond vortex laser pulses based on noncollinear optical parametric chirped-pulse amplification (OPCPA) centered at 800 nm. To the best of our knowledge, this is the first experimental study of amplification for OPCPA-based vortex pulses to achieve a powerful ultrafast (TW-scale) vortex pulse output. In this experiment, a 0.5-mJ broadband chirped vortex pulse was amplified to 47 mJ with a 15-mm-long LiB3O5 crystal. The double-pass grating pair compressor with an efficiency of 65% maintained the beam vortex, and a pulse of width 30.1 fs was obtained, corresponding to a peak power of 1.02 TW. This laser can be used in studies on nonlinear optics and relativistic laser-plasma interactions, compact plasma-based accelerators, and light sources.

Perfect vortex beam has the characteristics of optical orbital angular momentum and is widely studied because of its advantages of a uniform ring profile and fixed radius. However, the current method of generating perfect vortex beam is mainly based on the phase modulation of spatial light modulator. We have proposed and demonstrated the fabrication of polymer-based phase plate to generate the first and higher-order perfect vortex beams by using maskless lithography exposure technique. According to the relationship of the lithographic depth of polymer and grayscale exposure, the phase plates with different topological charges and axicon parameters are fabricated. By using such polymer-based phase plate, the radius and ring width of perfect vortex beams are analyzed theoretically and experimentally. The fabricated phase plate shows high transmittance as well as perfect vortex beam generation with high quality in the bandwidth range from 1460 nm to 1640 nm. The obtained results prove the feasibility of the attempt of polymer to generate perfect vortex beams, showing great potential in the application of highly miniaturized and integrated optical vortex applications.