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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.

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.

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.

It is theoretically and numerically shown that when tightly focusing an n-th order vector light field that has the central V-point (at which the linear polarization direction is undetermined), the polarization singularity index n, and a "flower"-shaped intensity pattern with 2(n-1) lobes it forms a transverse intensity distribution with 2(n-1) local maxima. At the same time, a vector light field with the polarization singularity index -n, which has the form of a "web" with 2(n+1) cells generates at the sharp focus a transverse intensity distribution with 2(n+1) local maxima. In the focal spot, either 2(n-1) or 2(n+1) V-point polarization singularities with alternating indices +1 or -1 are formed at the intensity zero.

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.

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.

In this paper, we calculated the radiation from the state where an electron in cyclotron motion under the uniform magnetic field Bex was accelerated by the externally applied circularly polarized wave with strong Ein and Bin. The electron was accelerated in the parallel direction by the term β⊥ × Bin (β⊥: perpendicular velocity of the electron) as well as in the perpendicular direction by the electric field of the wave Ein. Then, the electron can be resonantly accelerated when the Bex is set to the magnetic field strength which is equivalent to frequency of the externally applied circularly polarized wave. The radiation from such an accelerated electron was confirmed to have helical wavefront at harmonics cyclotron frequency.

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.

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.

The term Poincaré beam, which describes the space-variant polarization of a light beam carrying spin angular momentum (SAM) and orbital angular momentum (OAM), plays an important role in various optical applications. Since the radius of a Poincaré beam conventionally depends on the topological charge number, it is difficult to generate a stable and high-quality Poincaré beam by two optical vortices with different topological charge numbers, as the Poincaré beam formed in this way collapses upon propagation. Here, based on an all-dielectric metasurface platform, we experimentally demonstrate broadband generation of a generalized perfect Poincaré beam (PPB), whose radius is independent of the topological charge number. By utilizing a phase-only modulation approach, a single-layer spin-multiplexed metasurface is shown to achieve all the states of PPBs on the hybrid-order Poincaré Sphere for visible light. Furthermore, as a proof-of-concept demonstration, a metasurface encoding multidimensional SAM and OAM states in the parallel channels of elliptical and circular PPBs is implemented for optical information encryption. We envision that this work will provide a compact and efficient platform for generation of PPBs for visible light, and may promote their applications in optical communications, information encryption, optical data storage and quantum information sciences., Well-controlled Poincaré beams are potentially useful in optical communications applications. Here, the authors present phase-only metasurfaces that generate broadband, perfect Poincaré beams in the visible, with radius independent of the topological number.

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.

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.

Polarization measurement has found applications in many fields ranging from quantum science to our daily life. However, traditional polarization measurement systems suffer from large volume and high cost. To keep pace with the continued device miniaturization and system integration, new detection approaches and devices are desirable. The marriage between optical metasurfaces and superposition of optical vortex beams has offered a new idea method for polarization detection. We propose and experimentally demonstrate a single metasurface for polarization measurement based on the superposition of optical vortex beams. The relationship between the three parameters of the polarization state and the interference pattern of vortex beams is deduced theoretically. The major axis, ellipticity and handedness of a polarization state are determined by analyzing the intensity patterns of the superimposed vortex beams. Our method has provided a new approach for the development of compact optical devices for polarization measurement.

We propose and numerically verify a design approach to a grating coupler (GC) for in-plane generation and propagation of quasi-TE vortex modes with azimuthal order $\pm$1 within photonic integrated circuits (PICs). In the considered GC design example, silicon nitride waveguides with silica substrate and cladding are used. The shallowly etched grating is illuminated by the incident optical beam from a standard single-mode fiber. We optimize the GC design parameters to maximize the purity of orbital angular momentum (OAM) mode first for the case of a theoretical ideally fabricated grating, and then consider a more practical case of GC design, when the etching resolution is limited. The numerical modeling results show possibility of the vortex mode generation with >96% purity of the target OAM state $\pm$1 at the wavelength 1550 nm. The proposed design, compatible with the standard nanofabrication process, provides a simple, compact and robust solution for various potential PIC-based applications of OAM beams.

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.

Scientific reports 10(1), 21981 (2020). doi:10.1038/s41598-020-78613-7, Published by Macmillan Publishers Limited, part of Springer Nature, [London]

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.

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.

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.

In this work, a novel technique to create positive-negative tunable liquid crystal lenses is proposed and experimentally demonstrated. This structure is based on two main elements, a transmission line acting as a voltage divider and concentric electrodes that distribute the voltage homogeneously across the active area. This proposal avoids all disadvantages of previous techniques, involving much simpler fabrication process (a single lithographic step) and voltage control (one or two sources). In addition, low voltage signals are required. Lenses with switchable positive and negative focal lengths and a simple, low voltage control are demonstrated. Moreover, by using this technique other optical devices could be engineered, e.g. axicons, Powell lenses, cylindrical lenses, Fresnel lenses, beam steerers, optical vortex generators, etc. For this reason, the proposed technique could open new venues of research in optical phase modulation based on liquid crystal materials. This work was supported by Comunidad de Madrid and FEDER Program (S2018/NMT-4326), the Ministerio de Economía y Competitividad of Spain (TEC2016-77242-C3-1-R and TEC2016-76021-C2-2-R), the FEDER/ Ministerio de Ciencia, Innovación y Universidades and Agencia Estatal de Investigación (RTC2017-6321-1). Also, the Ministry of National Defense of Poland (GBMON/13-995/2018/WAT).

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.

Two algorithms for the determination of optical vortex coordinates are considered. In the first one, the vortex is found by branching of interference pattern fringes; in the second one, as a result of processing of the wavefront gradient distribution. It is shown that both algorithms allow one to record the coordinates with a high accuracy; in addition, it is possible to determine shifts of singular points appearing as a result of radiation diffraction.

Focusing light beyond the diffraction limit is among the greatest challenges in optical sciences, which would revolutionize many optical technologies from imaging and optical trapping to light deli...

We study the propagation dynamics of bright optical vortex solitons in nematic liquid crystals with a nonlocal reorientational nonlinear response. We investigate the role of optical birefringence on the stability of these solitons. In agreement with recent experimental observations, we show that the birefringence-induced astigmatism can eventually destabilize these vortex solitons. However, for low and moderate birefringence, vortex solitons can propagate stably over experimentally relevant distances.

Systems of controllable orbital angular momentum (OAM) require more compact, higher conversion efficiency and more tolerable wavelength or polarization. We introduce an optical vortex switch based on a multiplexed volume grating (MVG). The MVG recorded in a piece of photo-thermo-refractive (PTR) glass exhibits high diffraction efficiency (DE, also known as conversion efficiency in transporting), sensitive angular selectivity, and polarization-insensitivity. The effects of the incident divergence angle and polarization on the DE and the far-field diffraction profiles are demonstrated and investigated. It turns out that the divergence angle of the probe beam can greatly affect the DE. The fluctuation of the DE caused by polarization variation is less than 1.59%. This switch can be potentially applied in vortex tweezers, optical communication, and high power systems.

We investigate in detail the azimuthal and radial modulation (i.e., the azimuthal order l j and radial order p j with j = 1, 2) of double-four-wave mixing (double-FWM) by use of two higher-order Laguerre-Gaussian (LG) beams in a Landau quantized graphene ensemble. A pair of weak probe pulses in the graphene ensemble interacts with two LG beams and thus two vortex FWM fields with the opposite vorticity are subsequently generated. In combination with numerical simulations, we reveal that (i) there appear l1 + l2 periods of phase jumps in the phase profiles under any conditions; (ii) p + 1 concentric rings emerge in the intensity profile and the strength is mainly concentrated on the inner ring when the two LG beams have the same radial orders (i.e., p1 = p2 = p); (iii) there are p raised narrow rings occurring in the phase profile in the case of p1 = p2 = p and l1 ≠ l2, and the raised narrow rings would disappear when p1 = p2 and l1 = l2; (iv) p max + 1 concentric rings appear in the intensity profile, meanwhile, |p1 − p2| convex discs and p min raised narrow rings emerge in the phase diagram in the case of p1 ≠ p2, here p max = max(p1, p2) and p min = min(p1, p2). Moreover, the two generated FWM fields have the same results, and the difference is that the phase jumps are completely opposite. These findings may have potential application in graphene-based nonlinear optical device by using LG beams with adjustable mode orders.

We design and experimentally demonstrate a simple, single-shot method for the generation of arbitrary composite vortex (CV) beams using hybrid binary fork gratings (hBFG). These gratings were computationally generated by removing the central region around the fork-dislocation of azimuthal charge ℓ1 and substituting it with a BFG of a different charge ℓ2. The geometrical parameters of hBFGs were optimized for the efficient generation of CV beams. The method was further extended to the generation of CV beams consisting of three different ℓ and of higher radial charges p. This simple generation method may be useful to generate complex beam shapes with engineered phase fronts without complicated interferometry based techniques.

Perfect optical vortex beams (POV) have attracted considerable attention in many novel applications because they have the advantage of a radial profile that is independent of the topological charge (TC). Nowadays, there are few effective methods to measure both the integer and the fractional TCs of the POV. In this paper, we achieve the precise measurement of arbitrary TCs through the approach of dynamic angular double slits (ADS), which performs the transformation from the POV to the interference intensity patterns at the angular bisector direction of the ADS. The information of the TC can be obtained from the periodically changing interference pattern. The deviation is less than 2% by comparing the theoretical values with the fitting results, therefore the detection method is effective and reasonable.

Based on the angular spectrum of rotating elliptical Gaussian vortex beams (REGVBs), the Imbert Fedorov (IF) shift of REGVBs with the topological charge m = 1 is calculated analytically and numerically. The effects of the topological charge and the vortex position on the IF shift of REGVBs are discussed. By comparing the IF shifts of Gaussian beams, Airy beams with finite energy and REGVBs, we find that REGVBs have unique advantages in the control of the IF shift, that is, the IF shift of REGVBs is similar to the odd symmetry near the Brewster angle, and the rotation parameters can specially control the magnitude and the direction of the IF shift at the same time. Our discovery breaks the previous thinking barrier, that is, most of the control of the IF shift direction is based on materials, and provides a new perspective for controlling the IF shift based on the properties of beams.

High energy pulsed High-order Mode (HOM) beams has great potential in materials processing and particle acceleration. We experimentally demonstrate a high energy mode-locking Raman all-fiber laser with switchable HOM state. A home-made fiber mode-selective coupler (MSC) is used as the mode converter with a wide bandwidth of 60 nm. By combining advantages of MSC and stimulated Raman scattering, 1.1 μJ pulsed HOM beams directly emitting from the all-fiber cavity can be achieved. After controlling the category and phase delay of vector modal superposition, different pulsed HOM beams including cylindrical vector beams (CVBs) (radial and angular) and optical vortex beams (OVBs) are reasonably obtained with high purity (all over 95%), as well as arbitrary switching. Furtherly, the slope efficiency of HOM beams in the mode-locking and continuous wave operations are as much as 20.3% and 31.8%, respectively. It may provide an effective way to achieve high energy pulsed HOM beams.

Coherent vortex structures are fascinating physical objects that are widespread in nature: from large scale atmospheric phenomena, such as tornadoes and the Great Red Spot of Jupiter to microscopic size topological defects in quantum physics and optics. Unlike classical vortex dynamics in fluids, optical vortices feature new interesting properties. For instance, novel discrete optical vortices can be generated in photonic lattices, leading to new physics. In nonlinear optical media, vortices can be treated as solitons with nontrivial characteristics currently studied under the emerging field of topological photonics. Parallel to theoretical advances, new areas of the engineering applications based on light vortices have emerged. Examples include the possibility of carrying information coded in the vortex orbital angular momentum, understood as a spatial-division-multiplexing scheme, to the creation of optical tweezers for efficient manipulation of small objects. This report presents an overview highlighting some of the recent advances in the field of optical vortices with special attention on discrete vortex systems and related numerical methods for modeling propagation in multi-core fibers.

Numerous approaches have been developed to generate optical vortex beams carrying orbital angular momentum (OAM) over the past decades, but the direct intracavity generation of such beams with practical output powers in the femtosecond regime still remains a challenge. Here we propose and experimentally demonstrate the efficient generation of high-peak-power femtosecond optical vortex pulses from a Mamyshev oscillator (MO) based on few-mode polarization-maintaining (PM) ytterbium-doped fibers (YDFs). By employing an appropriate intracavity transverse spatial mode selection technique, ultrafast pulses carrying OAM with selectable topological charge of l = ±1 are successfully generated with an average output power of ∼5.72 W at ∼24.35 MHz repetition rate, corresponding to a single pulse energy of ∼235 nJ. The chirped pulses can be compressed to ∼76 fs outside the cavity, leading to a pulse peak power of ∼2.2 MW. To the best of our knowledge, this is by far the highest pulse energy and peak power for optical vortex pulses ever generated directly from a fiber oscillator. This unprecedented level of performance should be of great interest for a variety of applications including materials processing and imaging.

Partially coherent optical vortices have been applicated widely to reduce the influence of atmospheric turbulence, especially for free-space optical (FSO) communication. Furthermore, the beam array is an effective way to increase the power of the light source, and can increase the propagation distance of the FSO communication system. Herein, we innovatively report evolution properties of the radial phased-locked partially coherent vortex (RPLPCV) beam array in non-Kolmogorov turbulence. The analytical expressions for the cross-spectral density and the average intensity of an RPLPCV beam array propagated through non-Kolmogorov turbulence are obtained. The numerical results reveal that the intensity distribution of the RPLPCV array propagated in the non-Kolmogorov turbulence is gradually converted to a standard Gaussian distribution. In addition, the larger the radial radius, radial number and waist radius are, the smaller the coherence length is. Moreover, the longer the wavelength is, the shorter the propagation distance required for the intensity distribution of the RPLPCV beam array to be converted into a Gaussian distribution in the non-Kolmogorov turbulence. The research in this paper provides a theoretical reference for the selection of light sources and the suppression of turbulence effects in wireless optical communication.

Photonic spin-orbit interaction has attracted much attention in recent years. This talk first reports the efficient generation of ultra-compact optical vortex (OV) in achiral nanostructures, which has a radius of only 1 μm and possesses a signal-to-noise ratio larger than 6 dB. A spin-selective and phase-resolved scanning near-field optical microscope (SNOM) is employed to probe and visualize the OV generation process in the spin basis. Furthermore, a SNOM system is developed for probing and analyzing nonlinear optical signals in nanostructures with subwavelength resolution, which images the near-field third-harmonic generation from an anapole dark-mode state in a silicon nanodisk.