Generation Of Vortex Beams Research Articles

Second harmonic generation of visible vortex laser based on a waveguide-grating emitter in LBO.

In this work, we propose a practical solution to visible vortex laser emission at 532 nm based on second harmonic generation (SHG) in a well-designed waveguide-grating structure. Such an integrated structure is fabricated by femtosecond laser direct writing (FsLDW) in an LBO crystal. Confocal micro-Raman spectroscopy is employed for detailed analysis of FsLDW-induced localized crystalline damage. By optical excitation at 1064 nm, the guiding properties, SHG performance, as well as vortex laser generation of the waveguide-grating hybrid structure are systematically studied. Our results indicate that FsLDW waveguide-grating emitter is a reliable design holding great promise for nonlinear vortex beam generation in integrated optics.

Dual-channel polarization-modulated metasurface

Metasurfaces provide excellent design flexibility, allowing for the creation of versatile integrated designs with significant potential for practical applications. This paper proposes a dual-channel polarization-modulated metasurface, which realizes the modulation of line-polarized light (LP) to circularly polarized light (CP) with opposite rotation. The polarization state of the dual channels can be changed by adjusting the polarization angle of the line-polarized light. Through the reasonable selection of element atoms, the function of the quarter waveplate is combined with the wavefront control of the general metalens, and the spiral phase can be arbitrarily added to the two channels to realize the simultaneous generation of multi-mode vortex beams. This work achieves functional integration on a single-layer metasurface, enabling its application in polarization imaging and other areas. This work achieves functional integration on a single-layer metasurface, enabling its application in polarization imaging and other areas.

Underwater double vortex generation using 3D printed acoustic lens and field multiplexing

The generation of acoustic vortex beams has attracted an increasing amount of research attention in recent years, offering a range of functions, including acoustic communication, particle manipulation, and biomedical ultrasound. However, incorporating more vortices and broadening the capacity of these beams and associated devices in three dimensions pose challenges. Traditional methods often necessitate complex transducer arrays and are constrained by conditions such as system complexity and the medium in which they operate. In this paper, a 3D printed acoustic lens capable of generating a double vortex pattern with an optional focusing profile in water was demonstrated. The performance of the proposed lens was evaluated through computational simulations using finite element analysis and experimental tests based on underwater measurements. The results indicate that by altering the positioning of the vortices’ axes, it is possible to control both the intensity and the location of the pressurized zone. The proposed approach shows promise for enhancing the effectiveness and versatility of various applications by generating a larger number of vortices and freely tailoring the focal profile with a single lens, thereby expanding the practical uses of acoustic vortex technology.

Bi-directional high-order orbital angular momentum mode generation using gratings in high numerical aperture fiber

We propose a novel design and theoretically analyse it for bi-directional orbital angular momentum (OAM) mode generation in high numerical aperture (NA) optical fibers using the combination of a long period grating (LPG), a short-period (Bragg) grating and a three-port optical circulator. The proposed design consists only of standard fiber gratings rather than specially designed fibers, such as ring-shaped or other types of fibers, making our model relatively simple. Full-vector true-mode analysis has been used to study the modal characteristics of the supported modes in the high-NA fiber. High-NA optical fibers can effectively relieve the degeneracy of the linearly polarized modes. A circularly polarized (CP) light is injected into a single mode fiber, the output end of which is axially spliced into a high-NA fiber. An appropriately designed raised-cosine apodized tilted LPG (TLPG) is used for broad bandwidth coupling of the fundamental HE11 mode to the co-propagating HE21 mode. The employed TLPG converts the CP fundamental core mode (HE 11x ± iHE 11y ) to ±1 order OAM modes (HE 21even ± iHE 21odd ). Both the CP mode and the generated OAM pass through the circulator in the direction of port 1 to port 2. A second fiber is connected at the output of port 2 and a tilted fiber Bragg grating (TFBG) is used to couple the forward-propagating HE11 core mode with the counter-propagating HE21, EH11 and HE31 core modes. The TFBG reflected higher order (±1 and ±2) OAM modes are transmitted through port 3. We observe that the TFBG has a mode-conversion efficiency of more than 95 % for each mode conversion. The generated vortex beam topological charges have been verified using the coaxial interference method.

Bi‐Layer Reflection‐Transmission Dual‐Mode Metasurface with Flexible Bandwidth Control

AbstractA general strategy for designing bi‐layer reflection‐transmission integrated dual‐mode metasurfaces is presented with flexible bandwidth control. The design of such metasurfaces is enlightened by introducing a cutting hole in the ground plane, which not only acts as a filter for reflection and transmission but also has an eloquent role for bandwidth control. For proof of concept, a bi‐layer metasurface consisting of split ring resonators (SRRs) is designed on the top side and I‐shaped resonators on both sides. The proper adjustment of ground cut/hole shifts the two co‐polarized resonances (initial resonances of the SRRs) close to each other, and in addition, converts wideband cross‐polarized reflection (in between the two initial co‐polarized resonances of SRR) to co‐polarized reflection. This results in a broadband response by shifting two co‐polarized resonances close to each other and converting cross‐polarized reflection into co‐polarized reflection. It is demonstrated that a simple SRR can be responsible for broadband (7.9–12 GHz) reflection while an I‐shaped structure is used for transmission with central frequency at 17.58 GHz with independent phase controls. To endorse the proposed strategy, a metasurface prototype is fabricated and tested for the generation of vortex beams and focusing.

Elliptical spiral zone plate fabrication using direct laser writing for generating an elliptical perfect vortex beam.

We report and fabricate a novel, to our knowledge, vortex beam generator called elliptical spiral zone plate (ESZP) using direct laser writing (DLW), which can generate the elliptical perfect vortex beam (EPVB). It is shown that the radius of the EPVB can be adjusted by tuning the control parameters of the ESZP. It is verified through the interference experiment and the Hermitian-Gaussian light field that the topological charge of the EPVB is consistent with the design. In addition, we integrate the ESZP at the tip of the single-mode fiber. Our work may set the scene for applications in fiber optical tweezers, optical communications, and integrated optics.

MEMS-integrated metasurfaces for dynamic linear polarizers

Optical metasurfaces (OMSs), planar arrays of meticulously designed meta-atoms, are renowned for remarkable capabilities in manipulating the polarization state of light at subwavelength scales. Nevertheless, most OMS-empowered polarization optics remain static, featuring well-defined optical responses determined by their configurations set during fabrication. Here, we demonstrate a MEMS-OMS-based dynamic linear polarizer (DLP) with an electrically controlled extinction ratio, which is tunable in a fast and reversible fashion, by combining an anisotropic plasmonic OMS with a thin-film piezoelectric MEMS mirror. Capitalizing on the MEMS-OMS DLP, we further implement voltage-controlled grayscale imaging and vector vortex beam generation under linearly and circularly polarized excitations, respectively. Our MEMS-OMS DLP design could enable adaptive photonic systems for advanced applications in optical image encryption, displays, and beyond.

Nonlinear spin-orbit coupling in optical thin films

Tunable generation of vortex beams holds relevance in various fields, including communications and sensing. In this paper, we demonstrate the feasibility of nonlinear spin-orbit interactions in thin films of materials with second-order nonlinear susceptibility. Remarkably, the nonlinear tensor can mix the longitudinal and transverse components of the pump field. We observe experimentally our theoretical predictions in the process of second-harmonic generation from a thin film of aluminum gallium arsenide, a material platform widely spread for its role in the advancement of active, nonlinear, and quantum photonic devices. In particular, we prove that a nonlinear thin film can be used to produce vector vortex beams of second-harmonic light when excited by circularly-polarized Gaussian beams.

Direct generation of vortex beams from an off-axis pumped all-solid-state laser

Direct generation of vortex beams from an off-axis pumped all-solid-state laser

Quarter-Wave Plate Metasurfaces for Generating Multi-Channel Vortex Beams.

Metasurfaces of quarter-wave plate (QWP) meta-atoms have exhibited high flexibility and versatile functionalities in the manipulation of light fields. However, the generation of multi-channel vortex beams with the QWP meta-atom metasurfaces presents a significant challenge. In this study, we propose dielectric metasurfaces composed of QWP meta-atoms to manipulate multi-channel vortex beams. QWP meta-atoms, systematically arranged in concentric circular rings, are designed to introduce the modulations via the propagation phase and geometric phase, leading to the generation of co- and cross-polarized vortex beams in distinct channels. Theoretical investigations and simulations are employed to analyze the modulation process, confirming the capability of QWP meta-atom metasurfaces for generating the multi-channel vortex beams. This study presents prospective advancements for the compact, integrated, and multifunctional nanophotonic platforms, which have potential applications in classical physics and quantum domains.

Flexible manipulation terahertz beam based on an all-dielectric metasurface by utilizing addition and convolution algorithms.

The flexibly manipulated terahertz wave is currently a hot research topic. To address this challenge, we proposed an all-dielectric coding metasurface for shaping the terahertz wave including beam splitting, beam deflection, vortex beam generators, and a vortex beam and multi-beam splitting combination by combining addition with the convolution theorem. This work represents what we believe to be a new method of combining terahertz wave regulation with digital signal processing and opens up the versatile design ideas of multifunctional metadevices.

Generation of arbitrary vector vortex beams on a higher-order Poincaré sphere using a double-exposure polarization-multiplexed hologram.

The existing methods for the generation of arbitrary vector vortex beams often involve complex optical setups or intricate fabrication methods. In this Letter, we propose a novel, to the best of our knowledge, and simplified approach for the efficient generation of vector vortex beams using a polarization-multiplexed hologram fabricated on an azo-carbazole polymer using a simple double-exposure technique. The hologram generates a vector vortex beam when simply illuminated by a collimated beam and also allows for a seamless traversal across the entire higher-order Poincaré sphere (arbitrary vortex beam generation) just by modulating the polarization of an illuminating beam.

Rapidly switchable x-ray orbital angular momentum from a free electron laser oscillator

X-ray vortices carrying tunable orbital angular momentum (OAM) are an emerging tool for x-ray characterization. However, in contrast to the generation of vortex beams in the visible wavelength region, the generation of x-ray vortices in a controlled manner has proved challenging. Here, we demonstrate an x-ray free-electron laser oscillator (XFELO) can adjust only the kinetic energy of the electron beam to produce vortex beams that can be programmed to dynamically change between different OAM modes, without the need for additional optical elements. With the nominal parameters of currently constructing 1 MHz repetition rate facility (i.e., Shanghai high-repetition-rate XFEL and Extreme Light Facility), the active formation of the OAM modes of l=±1 and l=±2 and the rapid switching between them by detuning the electron beam energy of the XFELO are numerically illustrated. The real-time switching can be achieved within 200 μs, while the output pulse energy can reach the 100 μJ level. This result extends the capabilities of XFELOs and paves the way for advanced at-source applications using x-ray vortex beams.

High-order optical vortex beam generation based on watt-class spatial phase plate-integrated photonic-crystal surface-emitting lasers.

We develop spatial phase plate (SPP)-integrated photonic-crystal surface-emitting lasers featuring double-lattice photonic-crystal structures embedded using a crystal regrowth technique. SPPs possessing eight segmentations per phase rotation number l are fabricated on the top surface to generate optical vortex beams (OVBs) with l = 1-3. The beams exhibit a high output power of ∼5 W and high mode purities of 85%, 78%, and 72% for l = 1-3, respectively. These purity values are comparable with those of a pure Gaussian mode passing through an SPP. The compact, high-power, and high-purity OVB sources can be used in the fields of material processing, optical manipulation, and microscopy.

Remotely Controlled Laser‐Programmable Microwave Metasurfaces

AbstractProgrammable metasurfaces have brought significant advance to electromagnetic (EM) and related fields, making it easier and more efficient to manipulate the EM waves and realize higher tuning flexibility and range. However, how to achieve independent control of each unit of the programmable metasurface in a low‐overhead and wireless manner remains a challenge. Here, a laser‐programmable microwave metasurface is proposed and constructed, in which each unit can be controlled remotely by laser intensity in real time. The key is to design an ultra‐compact photoelectric passive boost circuit and integrate it into the meta‐unit. In this case, the light sensing‐to‐power‐to‐control‐to‐microwave manipulation process can be fully realized on the highly integrated meta‐unit, and thus the metasurface can be completely programmed at the unit level by laser coding patterns, without any wire connections and external power suppliers. As experimental demonstration, a phase‐coding laser‐programmable microwave metasurface is presented using a laser array. To show the capabilities of the metasurface, 2D beam scanning and vortex beam generation are demonstrated using 1‐bit phase modulations under the laser illuminations. This approach offers an effective route for the space lasers to manipulate microwaves accurately, which is helpful in developing advanced functional devices, passive platforms, and photoelectric hybrid systems.

Full-polarization-locked vortex beam generator with time-varying characteristics

Abstract Vortex beams carrying orbital angular momentum (OAM) are considered to hold significant prospects in fields such as super-resolution imaging, high-capacity communications, and quantum optics. Therefore, the techniques of vortex beam generation have attracted extensive studies, in which the development of metasurfaces brings new vigor and vitality to it. However, the generation of reconfigurable vortex beams by metasurfaces at the incidence of arbitrary polarized electromagnetic (EM) waves holds challenges. In this study, an efficient and reconfigurable strategy utilizing PB phase-modulated circularly polarized waves and dynamic phase-modulated linearly polarized waves is proposed, enabling a polarization-locked fully polarization vortex beams generator. Based on this strategy, we designed and fabricated a prototype of the vortex beam generator for full polarization, which verifies the rotating Doppler effect and generates a time-varying vortex beam. All the results have been verified by simulation and measurements. In addition, the proposed strategy can be easily extended to other frequency regions and holds potential in areas such as information encryption, biosensing, and OAM multiplexing communication.

Reuleaux triangle core fiber with triple rotational symmetry.

A Reuleaux triangle core fiber (RTF) with triple rotational symmetry is proposed and fabricated. Then the RTF is twisted to form the chiral fiber grating, which converts the core mode into a vortex mode containing 3rd-order orbital angular momentum (OAM). Based on the Fourier expansion of the core boundary, the straight-sided and arc-sided triangular core profiles were analyzed, revealing the mechanism of high-efficiency OAM3 generation. The experimental results show a 3rd-order vortex mode with a high conversion efficiency and purity, and the polarization-independent characteristics endowed by the core shape are also confirmed. The proposed RTF provides a new, to the best of our knowledge, way for higher-order vortex beam generation, which can be used in optical fiber communication systems with OAM multiplexing.

Research and design of metasurface antennas based on composite dielectric materials

The metasurface has the ability to regulate electromagnetic waves, which is widely used for polarization state control, impedance bandwidth expansion, vortex beam generation, and high-directional antennas. Research shows that the substrate of the metasurface has a significant impact on the performance of the antenna. The equivalent dielectric constant of composite dielectric materials is investigated by using the characteristic mode analysis (CMA). A novel metasurface with composite dielectric substrate is proposed. The composite dielectric material consists of a substrate with a dielectric constant of 3.55 and an air gap. The calculation results of the effective dielectric constant of composite dielectric materials are basically consistent with the simulation results. Based on this composite dielectric material, a metasurface antenna is designed. S11 is less than-10 dB in the frequency range of 5.22–7.87 GHz. The peak boresight gain is 10.44 dBi at 6.5 GHz.

Propagation of integral and fractional perfect vortex beams in a gradient-index medium.

The analytical expressions for the complex amplitude of integral and fractional perfect vortex (PV) beams propagating in a gradient-index (GRIN) medium are derived. The intensity and phase distributions, propagation trajectories, Poynting vectors, and the effects of topological charge and refractive index at the medium axis on the intensity of both beams in the medium are numerically investigated. It is shown that both beams propagate periodically in the GRIN medium with alternating spot focusing and reconstruction. Unlike the integral PV beam, the fractional PV beam has a dark line in intensity profiles and a line edge dislocation in phase distributions along the positive x-axis. These properties persist during the beam propagation in the GRIN medium. Moreover, the topological charge and the refractive index at the medium axis have little effect on the intensity of the PV beam propagating in the GRIN medium. The results presented in this paper may be useful for the application of integral and fractional PV beams in optical guiding and optical communications.

Generation and 2D field imaging of THz vortex beams

Optical rectification along three-fold axis in zincblende-symmetry crystal is used to generate vector and scalar vortex beams in THz. 2D electro-optic imaging is used for frequency- resolved THz field amplitude and phase characterization.