Generation Of Vortex Beams Research Articles

1645-nm single-frequency vortex laser from an Er:YAG nonplanar ring oscillator.

A 1645-nm single-frequency vortex beam with narrow linewidth from an Er:YAG nonplanar ring oscillator (NPRO) using an annular pump beam is demonstrated. The pump beam from a 1532-nm fiber laser is shaped to an annular beam by an axicon. The Er:YAG NPRO generates a 1.96-W single-frequency vortex beam under a pump power of 13 W. The linewidth of the 1645-nm vortex laser is measured as 6 kHz. This work provides a convenient way of single-frequency vortex beam generation.

Reconfigurable metasurface for generating flexibly tunable focusing Vortex Beams

As the vortex wave propagation distance increases, its dispersion increases, so its focus needs to be enhanced when performing information transmission. However, in order to expand the detection range, the dispersion needs to be increased in the detection scenario. Thus, it is important to dynamically adjust the focus dispersion of the vortex beam. Therefore, here we propose a novel programmable metasurface design to realize the generation of vortex beams and tune their near-field focusing dispersion performance. By introducing two new parameters m, n into the vortex beam electric field strength equation to modulate the field strength distribution of the vortex beam generated by the programmable metasurface in the near field, we achieve the tunable focusing function of the vortex beam.

Double-split-ring structure based ultra-broadband and ultra-thin dual-polarization terahertz metasurface with half-reflection and half-transmission

In this paper, we propose a dual-polarization ultra-wideband metasurface with half-reflection and half-transmission based on a double-split-ring (DSR) structure operating in a terahertz (THz) frequency range. The designed metasurface can simultaneously control the circularly polarized (CP) wave and linearly polarized (LP) wave in reflection mode and transmission mode, covering an extensive THz frequency range. The unit-cell architecture of the metasurface consists of a periodic arrangement of the DSR structure made of metal, which is affixed to an ultra-thin dielectric substrate. By manipulating the size and rotation direction of the DSR structure, we achieve full phase coverage of 0–2π of the orthogonally polarized LP wave and CP wave across a frequency span of 0.3–1.2 THz, encompassing transmission and reflection scenarios. The relative bandwidths of the corresponding orthogonal LP wave and CP wave with an average amplitude of 0.45 reach 86% and 120%, respectively. Specifically, through numerical simulations, we demonstrate that the designed metasurface has the ability to achieve THz beam deflection and vortex beam generation while reflecting and transmitting LP wave and CP wave. The proposed dual-polarization ultra-wideband metasurface holds great promise for various applications in the terahertz frequency range. These findings pave the way for the development of flexible and versatile THz devices with expanded functionality, thereby opening up new possibilities for wavefront manipulation in metasurfaces.

Recent Advances and Perspective of Photonic Bound States in the Continuum

Recent advancements in photonic bound states in the continuum (BICs) have opened up exciting new possibilities for the design of optoelectronic devices with improved performance. In this perspective article, we provide an overview of recent progress in photonic BICs based on metamaterials and photonic crystals, focusing on both the underlying physics and their practical applications. The first part of this article introduces 2 different interpretations of BICs, based on far-field interference of multipoles and near-field analysis of topological charges. We then discuss recent research on manipulating the far-field radiation properties of BICs through engineering topological charges. The second part of the article summarizes recent developments in the applications of BICs, including chiral light and vortex beam generation, nonlinear optical frequency conversion, sensors, and nanolasers. Finally, we conclude with a discussion of the potential of photonic BICs to advance terahertz applications in areas such as generation and detection, modulation, sensing, and isolation. We believe that continued research in this area will lead to exciting new advancements in optoelectronics, particularly in the field of terahertz devices.

Influence of wind-dominated thermal blooming on orbital angular momentum and phase singularity of dual-mode vortex beams

The effects of thermal blooming on orbital angular momentum (OAM) and phase singularity of dual-mode vortex beams under different wind directions and wind speeds are studied in this paper. Owing to the different symmetries of dual-mode vortex beams superimposed by different modes, the effects of thermal blooming on them depend on not only wind speed, but also wind direction. Based on the scalar wave equation and the hydrodynamic equation, a four-dimensional (4D) computer code to simulate the time-dependent propagation of dual-mode vortex beams in the atmosphere is devised by using the multiphase screen method and finite difference method. It is found that for a certain wind direction, the value of OAM increases with the wind speed decreasing because the thermal blooming becomes more serious, i.e. the thermal blooming effect promotes the OAM of dual-mode vortex beam to grow. For example, when the angle between the wind direction and the beam is 0 < <i>θ</i> < 50°, the OAM of the dual-mode vortex beams with a topological charge difference of 2 increases with wind speed decreasing, and there is an optimal angle (<inline-formula><tex-math id="M1">\begin{document}$ \theta \approx {20^ \circ } $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="16-20230684_M1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="16-20230684_M1.png"/></alternatives></inline-formula>) to maximize OAM. Therefore, for a certain wind direction and wind speed, the OAM of dual-mode vortex beam propagating in the atmosphere can be larger than that in free space, and can be larger than the OAM of single-mode vortex beam. The dual-mode vortex beam with higher modes requires smaller wind speed to make its OAM larger than the OAM in free space. In addition, the larger the difference in topological charge between the two element beams of a dual-mode vortex beam, the more stable the OAM of the dual-mode vortex beam is. On the other hand, the evolution of linear edge dislocation singularity under atmospheric thermal blooming is also investigated in this paper. When the wind direction is perpendicular to the dislocation line, the linear edge dislocation singularity disappears. If the wind direction is parallel to the dislocation line, the linear edge dislocation singularity always exists. At other angles, the linear edge dislocation singularity will evolve into optical vortex pairs. The results obtained in this paper have a certain reference value for the propagation of lasers in the atmosphere and optical communication.

Generation and regulation of coaxial composite vortex beams based on liquid crystal devices

Generation and regulation of coaxial composite vortex beams based on liquid crystal devices

Generation of THz Vortex Beams and Interferometric Determination of Their Topological Charge

In this article, we developed and demonstrated the efficacy of 3-D printed spiral phase plates (SPPs) for the generation of vortex terahertz (THz) beams with angular momenta <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\ell = \pm 1$</tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\ell = \pm 2$</tex-math></inline-formula> . The vortex beam generation was confirmed by means of frequency-domain transmission spectroscopy. The topological charge <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\ell$</tex-math></inline-formula> of the vortex beams was determined via phase-sensitive Mach–Zehnder interferometry, which enabled the superposition of a vortex beam with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\ell$</tex-math></inline-formula> and its conjugate beam with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-\ell$</tex-math></inline-formula> . The resulting interference patterns were found to be consistent with the expected intensity distributions for a given <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\ell$</tex-math></inline-formula> , which provides strong confirmation of the spatial phase structure of the generated vortex beams in the THz regime.

Dual-mode orbital angular momentum generated based on dual-polarization coding metasurface

In this paper, a dual-polarization 4-bit coding metasurface is proposed to achieve the flexible manipulation of different polarization electromagnetic wave reflection angles and the generation of dual-mode vortex beams by independent manipulation of orthogonal linearly polarized waves. The proposed metasurface is composed of an H-type metal patch, dielectric substrate, and metal grounding layer from top to bottom. To prove the proposed concept, we design and fabricate four coding metasurfaces based on the superposition theorem and holographic theory. One of the coding metasurfaces is designed to verify the ability to manipulate the beam angle, and each of the other three coding metasurfaces is designed to carry a vortex beam with different topological charges under orthogonal linearly polarized waves with a central frequency of 24 GHz. The experimental results show that the theoretical design is highly consistent with the simulation results. Therefore, it is verified that our proposed 4-bit dual-polarization coding metasurface has a strong and flexible ability to manipulate the beam reflection angle and generate a high-performance dual-mode vortex beam antenna. Because of the wide application prospect of vortex beams in the communication field, we have reason to believe that the proposed ultra-thin dual-mode vortex generator will have potential applications in wireless communication systems in the fields of images and microwaves.

Generation of high-order and fractional vortex beams using gratings simulated by spatial light modulators

Generation of high-order and fractional vortex beams using gratings simulated by spatial light modulators

Generation and switching of arbitrary vector vortex beams on two hybrid-order Poincaré spheres with different orders based on liquid crystal device

Generation and switching of arbitrary vector vortex beams on two hybrid-order Poincaré spheres with different orders based on liquid crystal device

High-Purity Multi-Mode Vortex Beam Generation With Full Complex-Amplitude-Controllable Metasurface

Vortex beam with inherent orbital angular momentum (OAM) is promising in high-capacity communication. On multimode vortex beam generation, metasurface has shown exceptional advantages of integration and miniaturization. For the current widely used phase-only methods on multimode vortex beam generation by metasurface, the purity of the OAM-mode spectrum is severely affected. A new method for generation of multimode vortex beam with high mode purity is proposed in this article by reconstructing the complete complex amplitude information on the meta-device aperture. A 20 dB suppression of the crosstalk modes is experimentally observed for the co-directional multimode vortex beam generation, which is much improved compared to the traditional phase-only scheme. In addition, the proposed scheme also provides the capability of generating high-purity multimode vortex beams with arbitrary preset propagation directions and power allocations. This study provides a platform for high-performance vortex beam communication by increasing the signal-to-noise ratio and enabling the multicasting scenarios with customized capacity requirements.

Research progress of all-solid-state intra-cavity vortex beam generation in visible laser (invited)

Research progress of all-solid-state intra-cavity vortex beam generation in visible laser (invited)

Vanadium dioxide based terahertz dual-frequency multi-function coding metasurface

Terahertz (THz) wave has the advantages of low photon energy, high resolution, large communication bandwidth, etc. It has broad application prospects in security detection, high-resolution imaging, high-speed communication, and other fields. In recent years, as a new way to control THz wave, THz metasurface functional devices have attracted extensive attention of researchers. In this work, vanadium dioxide (VO&lt;sub&gt;2&lt;/sub&gt;), a phase change material, is introduced into the coding metasurface. By regulating a circularly polarized wave and the orthogonal linearly polarized waves independently, a multi-function coding metasurface that can work at dual frequency points is obtained. It is composed of three layers. The top layer is a metal-VO&lt;sub&gt;2&lt;/sub&gt; composite structure. The middle is a polyimide dielectric layer. The bottom is a metal ground. Under certain conditions, the double split ring resonator (DSRR) and the cross structure in the top layer are relatively independent. Designing the coding sequences for them enable the coding metasurface to have multiple functions. The electromagnetic simulation software CST is used to establish model and conduct simulation, and the obtained results are as follows. When the VO&lt;sub&gt;2&lt;/sub&gt; is in an insulating state and a circularly polarized wave at 0.34 THz is incident vertically, the characteristics of coding metasurface elements are mainly affected by the DSRR. The DSRR is rotated to meet the requirements of 3-bit Pancharatnam-Berry phase coding. The coding sequence is designed to generate vortex beams with the topological charge &lt;i&gt;l&lt;/i&gt; = ±1 at a specific angle. The VO&lt;sub&gt;2&lt;/sub&gt; state is changed into a metallic state, and the DSRR can be equivalent to a metal ring. When the orthogonal linearly polarized wave at 0.74 THz is incident vertically, the characteristics of coding metasurface elements are mainly affected by the cross structure. Because of its anisotropy, four different 2-bit coding metasurface elements can be obtained respectively by changing the length of the horizontal arm and the vertical arm. The design of appropriate coding sequences can reduce the radar cross section of the &lt;i&gt;x&lt;/i&gt;-polarized wave and the beam splitting of the &lt;i&gt;y&lt;/i&gt;-polarized wave, and the results have broadband characteristics. Multiple coding sequences can be designed by special characteristics of the coding metasurface, then various expected functions can be realized on the same metasurface. It solves the problem of single function of ordinary metasurface devices to a certain extent, and paves a novel way to the development of THz multi-function systems.

Terahertz generations of transmissive deflection, focusing, and orbital angular momentum with polarization conversion

By coding meta-atom with discrete phase, electromagnetic wavefront can be flexibly manipulated with the pre-designed coding sequence. In this work, transmissive metasurfaces are proposed to achieve wavefront reconfiguration with polarization conversion for terahertz wave. Based on composite structures of metallic resonators and polyimides, the designed meta-atoms are capable of polarization conversion and 360° phase modulation by changing notch angle and rotation angle of resonators at 2.0 THz. Then, three types of metasurfaces are designed.Firstly, transmissive wavefront of gradient metasurface is reconstructed through periodic alignment of eight meta-atoms along x axis. This metasurface realizes anomalous transmission and transforms x-polarized incidence to y-polarized wave.Secondly, two focusing lenses are implemented, and they realize single-focusing and dual-focusing under x-polarized incidence. Finally, two vortex beam generators are proposed with orbital angular momentum modes of l = 1 and l = 2 in channel of cross polarization. Our designs may be applied in the fields of terahertz communication, focusing, and encryption.

Focused vortex beam generator suitable for optical fiber spanners in a complex liquid environment.

We experimentally demonstrated an all-fiber focused vortex beam (FVB) generator which was prepared by milling a spiral zone plate (SZP) on the Au-coated end face of a hybrid fiber by focused ion beam (FIB). In this generator, the fundamental modes propagating in the hybrid fiber are focused while being modulated into high-order orbital angular momentum (OAM) mode by the SZP at the end face. The focus length and topological charge were designed and then were both theoretically and experimentally verified. The results show that, the obtained characteristics of the FVB agree with the designed ones. The measured diameters of the focal spots are 2.2 µm, 4.4 µm, and 5.2 µm for the FVB with the topological charge of 0, 1, and 2, respectively. The simulated results show that the proposed FVB generators can maintain good focusing characteristics in different liquids, so it is a good candidate for optical fiber spanner use in a complex liquid environment. Moreover, the processing efficiency of the proposed FVB generators is nearly ten times higher than that of the previously reported ones due to the Au-coated film.

Vanadium dioxide-based terahertz metasurfaces for manipulating wavefronts with switchable polarization

As a unique phase transition material, vanadium dioxide (VO2) has been widely applied in switchable and modulating metasurfaces. In this work, VO2-based reflective meta-atoms are designed to achieve wavefront reconfiguration in terahertz frequency. When VO2 is metal, four optimized meta-atoms with 90o phase difference provide a full phase coverage, and they achieve high polarization conversion efficiency. After phase transition of VO2, the capability in the metallic state is lost. Thus, the corresponding phase coverage is switched from 360° to 0°, and the phenomenon of polarization conversion almost vanishes. Assembled by these meta-atoms, three metasurfaces are numerically presented. When VO2 is in the state of metal, they are anomalous reflector, metalens, and vortex beam generator. The presented metasurfaces own the abilities of wavefront manipulation and polarization conversion. When VO2 is in the insulating state, three metasurfaces are switched to specular reflector. Simulations are conducted to verify their abilities of wavefront modulation and polarization control. The proposed metasurfaces may have potential applications in the fields of terahertz switching, communication, and focusing.

Generation of vector vortex beams by axially symmetric sheared polymer network liquid crystals.

Liquid crystals have been widely used in optoelectronic devices because of their fast response and excellent electro-optic properties. Featuring a unique ability to manipulate light, they are also proposed as a good candidate in topological photonics for further applications. In this study, an axially symmetric sheared polymer network liquid crystal (ASPNLC) is fabricated to demonstrate vector vortex beams. Linearly and circularly polarized light is used to illuminate the sample, and the output vector vortex beams generated from the ASPNLC indicate that the polarization states of the output beams are dependent on the polarization of the incident light. The measured phenomena are modeled on the bases of phase retardation and Jones calculus to eventually calculate the polarization-resolved intensity profiles accordingly. Hence, our experimental study provides a holistic understanding of the method for generating vector vortex beams by an ASPNLC, which is expected to enhance the knowledge of optical mechanisms for liquid crystal applications.

Bidirectional Terahertz Vortex Beam Regulator

Most of the reported vortex beam generators with orbital angular momentum (OAM) in the terahertz region only operate in either the reflection mode or the transmission mode, which greatly limits the integration and application in terahertz technology systems. Herein, we propose a full-space vortex beam regulator at two different frequencies. By changing the VO2 phase transition state, the transmission and reflection mode OAM beams can be flexibly controlled by a single metasurface. For the transmission mode, the proposed structure realizes an OAM beam at the topological charges of l = 1 and 2 at 0.6 THz and 1.4 THz. For the reflection mode, our structure generates an OAM beam at the topological charges of l = 1 and 2 at 0.9 THz and 1.5 THz. Based on the superposition theorem and convolution operation principle, the regulation of an OAM vortex beam with a specific deflection angle and a symmetrical deflection OAM vortex beam are realized. The designed metasurface integrates multiple transmitted and reflected vortex beam functions in full space and has potential application in different terahertz systems.

Transmission of an optical vortex beam in antiresonant fibers generated in an all-fiber system.

We report an experimental study on transmission of orbital angular momentum mode in antiresonant fibers generated with a dedicated all-fiber optical vortex phase mask. The vortex generator can convert Gaussian beam into vortex beams with topological charge l = 1. Generated vortex beam is directly butt-coupled into the antiresonant fiber and propagates over distance of 150 cm. The stability and sensitivity of the transmitted vortex beam on the external perturbations including bending, axial stress, and twisting is investigated. We demonstrate distortion-free vortex propagation for the axial stress force below 0.677 N, a bend radius greater than 10 cm.

Vortex chaoticons in thermal nonlocal nonlinear media.

This paper numerically investigates the propagation of Laguerre-Gaussian vortex beams launched in nonlocal nonlinear media, such as lead glass. Our results show that the propagation properties depend on the selection of beam parameters m and p, which represent the azimuthal and radial mode numbers. When p=0, these profiles can be stable solitons for m≤2, or break up and then form a set of single-hump profiles for m≥3, which are unbounded states with scattered remnants of the energy. However, for p≥1, the broken beams can evolve into vortex chaoticons, which exhibit both chaotic and solitonlike properties. The chaotic properties are determined by the positive Lyapunov exponents and spatial decoherence, while the solitonlike properties are demonstrated by the invariance of beam width and the interaction of beams in the form of quasielastic collisions. In addition, the power and orbital angular momentum of unbounded beam states both decay in propagation, while those of the chaoticons maintain their values well.