Polarized Vortex Beams Research Articles

Pulsed polarized vortex beam enabled by metafiber lasers

Pulsed polarized vortex beams, a special form of structured light, are generated by tailoring the light beam spatiotemporally and witness the growing application demands in nonlinear optics such as ultrafast laser processing and surface plasma excitation. However, existing techniques for generating polarized vortex beams suffer from either low compactness due to the use of bulky components or limited controlment of pulse performance. Here, an all-fiber technique combining plasmonic metafibers with mode conversion method is harnessed to generate high-performance pulsed polarized vortex beams. Plasmonic metafibers are utilized as saturable absorbers to produce Q-switched pulses with micro-second duration, while the offset splicing method is employed to partially convert the fundamental transverse mode (LP01\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{01}$$\\end{document}) to higher-order mode (LP11\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{11}$$\\end{document}). Eventually, a polarized vortex beams laser is achieved at the telecom band with a repetition frequency of 116.0 kHz. The impact of geometrical parameters including period of metafibers and offset of splicing on the spatiotemporal properties of pulsed polarized vortex beams is systematically investigated. Our findings could pave the way for design, control and generation of all-fiber pulsed polarized vortex beams, and also offer insights into the development of other types of structured laser sources.

Angular momentum properties of a circularly polarized vortex beam in the paraxial optical systems

The angular momentum (AM) properties of circularly polarized vortex beams (CPVBs) in two paraxial optical systems [free space and a gradient-index (GRIN) fiber] are demonstrated. The transverse light intensity, the longitudinal light intensity, the phase of the longitudinal electric field, the kinetic momentum, the total spin AM (SAM), the transverse-type SAM (t-SAM), the longitudinal-type SAM (l-SAM), and the orbital angular momentum (OAM) of CPVBs in the two paraxial optical systems are characterized. Spin-orbit coupling of CPVBs is studied during propagation in free space and in a GRIN fiber. When the OAM and the SAM of a CPVB have the same direction of rotation and when they have opposite directions of rotation, the spin-orbit coupling exhibits different characteristics in free space and in the GRIN fiber.

Flexible generation of azimuthally/radially polarized beams and hybrid polarized vortex beams using a thinned helical fiber grating.

An efficient method allowing the flexible generation of the azimuthally/radially polarized (AP/RP) beam and the hybrid polarized vortex (HPV) beam has been proposed and experimentally demonstrated by using a thinned helical fiber grating (T-HFG) with an intermediate period. This is the first time, to the best of our knowledge, that such three kinds of cylindrical vector beams can be flexibly generated by using only one fiber component. The proposed method provides the potential application of the HFG to not only the laser processing but also the optical manipulator and the optical tweezer.

Non-uniform phase distribution of a tightly focused elliptically polarized vortex beam

Abstract Tight focusing of elliptically polarized vortex beams has been previously studied for optical manipulation, optical information encoding, and so on. Still, there is a lack of research on the status of the phase distribution on the focal plane. In this study, we found that the phase distribution of a tightly focused elliptically polarized vortex beam is non-uniform, i.e., the phase distribution exhibits flatter and steeper regions due to the elliptical polarization of the input vortex beam. It is mentioned that the phase non-uniformity was related to the ellipticity of the polarization of the incident beam. Furthermore, we analyzed the intensity and phase distribution of a tightly focused elliptically polarized vortex beam. We found that the spin angular momentum was converted to the orbital angular momentum because the topological charge of the output beam was greater than that of the input beam. The non-uniform phase distribution of a tightly focused elliptically polarized vortex beam enables control over light–matter interaction, leading to advancements in optical tweezers, quantum information processing, and super-resolution microscopy.

Exploring the origin of stronger survival of polarized vortex beams through scattering media

Laguerre–Gaussian (LG) beams carrying orbital angular momentum (OAM) have shown promise in deep tissue imaging, medical diagnostics, and optical communication due to their robust propagation properties through scattering media. The insight on the mechanism for stronger survival of OAM carrying beam in tissue-like turbid media is expected to contribute towards a better understanding of light transport in the presence of scattering, as well as guide optimization of the intensity, phase, and polarization structure of light for use in biomedical applications like in tissue imaging. We examine the scattering properties by studying the propagation of polarized vortex beams transmitted through tissue-like turbid scattering media. We demonstrate that the intensity profile has a much more profound effect on depolarization than the phase profile for LG beams. Our results indicate that the observed stronger propagation for the higher-order LG beams is due to a higher anisotropy factor g, as seen by the incident beam. We have performed the degree of polarization measurements for the forward scattered light in the case of both LG beams and perfect vortex beams with varying topological charges. A comparison between the observed depolarization trends for the two classes of OAM-carrying beams suggests that the robust scattering properties of the LG beams originate from the intensity profile while the phase profile does not seem to play a major role in the stronger survival of OAM-carrying beam in turbid media.

Spin–momentum properties in the gradient-index fiber

The vector characteristics of the kinetic momentum, spin angular momentum (SAM), and light field of a radially polarized vortex beam (RPVB) in the radial gradient-index (GRIN) fiber are analyzed using a unified methodology based on the generalized Huygens-Fresnel principle and the spin-momentum relationship. The kinetic momentum, SAM, transverse-type spin (t-SAM), longitudinal-type spin (l-SAM) and light field contain parallel and perpendicular components to the optical axis in the GRIN fiber. Moreover, the optical spin skyrmion from the SAM, t-SAM, and l-SAM can be observed at the semi-focal plane and the focal plane of the GRIN fiber. To the best of our knowledge, this is the first confirmation of spin skyrmions in the GRIN fiber. The analysis of spin-momentum properties of an RPVB in the GRIN fiber combined with the generalized Huygens-Fresnel principle and the spin-momentum relationship can be applied in describing the vector properties of transmission in atmospheric and optical systems.

Controllable Microparticle Spinning via Light without Spin Angular Momentum.

The spin angular momentum (SAM) of an elliptically or circularly polarized light beam can be transferred to matter to drive a spinning motion. It is counterintuitive to find that a light beam without SAM can also cause the spinning of microparticles. Here, we demonstrate controllable spinning of birefringent microparticles via a tightly focused radially polarized vortex beam that has no SAM prior to focusing. Tothis end, the orbital Hall effect is proposed to control the radial separation of two spin components in the focused field, and tunable transfer of local SAM to microparticles is achieved by manipulating the twisted wavefront of the source light. Our work broadens the perspectives for controllable exertion of optical torques via the spin-orbit interactions.

Optomagnetism with a plasmonic skyrmion.

Research at the frontier between optics and magnetism is revealing a wealth of innovative phenomena and avenues of exploration. Optical waves are demonstrating the capacity to induce ultrafast magnetism, while optical analogs of magnetic states, such as magnetic skyrmions, offer the prospect of novel, to the best of our knowledge, spin-optical states. In this Letter, we strengthen the synergy between light and magnetism by exploring the ability of plasmonic Neel skyrmions to create an optomagnetic field, i.e., an opto-induced stationary magnetic field, within a thin gold film. We show that, when generated using a focused radially polarized vortex beam (RPVB), a plasmonic Neel skyrmion emerges as an optimum for inducing optomagnetism in a thin gold film. Optical skyrmions offer new degrees of freedom for enhancing and controlling optomagnetism in plasmonic nanostructures, with direct application in all-optical magnetization switching, magnetic recording, and the excitation of spin waves.

Vortex Circular Dichroism: An experimental technique to assess the scalar/vectorial regime of diffraction.

In classical electrodynamics, light-matter interactions are modelled using Maxwell equations. The solution of Maxwell equations, which is typically given by means of the electric and magnetic field, is vectorial in nature. Yet it is well known that light-matter interactions can be approximately described in a scalar (polarization independent) way for many optical applications. While the accuracy of the scalar approximation can be theoretically computed, to the best of our knowledge, it has never been determined experimentally. Here, we introduce Vortex Circular Dichroism ( VCD), an optical measurement that has the required features to assess the vectoriality of diffraction. VCD is measured as the differential transmission (or absorption) of left and right circularly polarized vortex beams. We test the VCD measurement with two different systems: i) an experimental set of single circular nano-apertures drilled in a gold film with diameters ranging from 150 to 1950 nm; and ii) a theoretical set of golden spheres with the same diameters as the nano-apertures. We observe that in both systems, VCD > 0 for smaller diameters, VCD ≲ 0 for intermediate values and VCD ≈ 0 for larger values of the diameter. Furthermore, the simulations show that a diffraction process characterized by a VCD ≈ 0 ( VCD ≠ 0) is polarization-independent (polarization-dependent). As a result, we relate VCD ≠ 0 to a vectorial diffraction, and VCD ≈ 0 to a scalar one. Overall, our results show compelling evidence that it is possible to experimentally assess the scalar/vectorial regime of a diffraction process, and that the VCD technique possesses the required features to measure the vectoriality of diffraction processes involving plasmonic cylindrically symmetric structures.

Canonical and Poynting currents in propagation and diffraction of structured light: tutorial

The local propagation and the energy flux in structured optical fields are often associated with the Poynting vector. However, the local phase gradient (i.e., local wavevector) in monochromatic fields in free space is described by another fundamental quantity: the canonical momentum density. Distributions of the Poynting and canonical momentum densities can differ significantly from each other in structured fields. We examine the role of these quantities in the propagation and diffraction of structured optical fields, exemplified by various circularly polarized vortex beams carrying orbital angular momentum. We describe the canonical and Poynting momentum distributions in such beams, experimentally measure the local transverse momentum density by a Shack-Hartmann wavefront sensor, and investigate fine features of the diffraction of various vortex beams on a knife-edge aperture. In all cases, the measured local momentum density and local beam evolution are consistent with the canonical momentum distribution rather than the Poynting vector. Furthermore, we introduce the local angular velocity in vortex beams and determine the universal integral π angle of azimuthal rotation in an arbitrary (yet circularly symmetric) propagating and diffracting vortex beam. Finally, we discuss the “supermomentum” and “backflow” effects; both of these phenomena are examples of superoscillations and are related to the properties of the canonical momentum. Our results reveal the profound role of the canonical momentum in the evolution of light and demonstrate the importance of distinguishing between it and the Poynting vector in structured light.

Second harmonic of higher-order Poincaré sphere beam with two orthogonal 5%MgO:PPLN crystals

In this work, the second harmonic (SH) of higher-order Poincaré sphere (HOPS) beam was introduced and demonstrated with two orthogonal 5%MgO:PPLN crystals. Based on the quasi-phase-matching technique, the vectorial coupled wave equations were derived to simulate the SH of HOPS beams through the two crystals, including the cylindrical vector beams (CVBs), elliptically polarized CVBs (EPCVBs), and circularly polarized vortex beams. Then, the experimental setup was established to reveal that the SH of CVBs and EPCVBs present the four-lobed structure and still exhibit vector characteristics. Meanwhile, the circularly polarized vortex beams become the linearly polarized vortex beams with double phase topology, confirming the conservation of orbital angular momentum. Moreover, the maximum SH conversion efficiency of CVBs, EPCVBs, and circularly polarized vortex beams can reach 25.3%, 23.4%, and 29.4%, respectively, which may be instructive for promoting the SH generation of vector vortex beams with high efficiency.

Fast-speed algorithm to compute tight focusing of laser beams: Effectiveness of circularly polarized vortex beam series as a mathematical basis

Fast-speed algorithm to compute tight focusing of laser beams: Effectiveness of circularly polarized vortex beam series as a mathematical basis

Full higher-order Poincaré sphere beam mode-locked fiber laser

In this paper, the controlled generation of full higher-order Poincaré sphere (HOPS) beams from a mode-locked fiber laser was introduced and demonstrated. In the cavity, two mirror-placed spatial mode converters, consisted of the vortex waveplate, quarter waveplate and half waveplate, were applied to achieve the mutual conversion of the LP01 mode and HOPS beams. Then, the full HOPS beams mode-locked fiber laser was established to obtain the circularly polarized vortex beams, cylindrical vector beams (CVBs), and elliptically polarized CVBs, with pulse width of 390 ps, repetition frequency of 14.7 MHz, central wavelength of 1043.35 nm and 3 dB bandwidth of 0.53 nm. The results may be potentially important for the generation of full HOPS beam from a mode-locked fiber laser.

Manipulation of optical orbit-induced localized spin angular momentum using the periodic edge dislocation.

Orbit-induced localized spin angular momentum (OILS) has recently garnered significant attention. This paper introduces periodic edge dislocation (PED) into the tight focusing system. The study delves into the tight focusing characteristics of the radially polarized vortex plane beam with PED, demonstrating that PED serves as a straightforward and effective means of manipulating OILS, especially when both the orbital angular momentum and the polarization of the incident beam are fixed. Our findings indicate that the longitudinal OILS reaches its maximum when the difference between the period of PED and the vortex topological charge is equal to 1. Conversely, when the difference is 0, the transverse OILS reaches its maximum, while the longitudinal OILS reaches its minimum. Similar patterns are also observed in linearly polarized vortex beams. This research proposes a simple and practical way to control OILS, contributing to our understanding of optical orbit-spin coupling.

The Propagation Characteristics of Circular Airy Beams with Propagational Fractional-Order Optical Vortices

We investigate the propagation properties of circular Airy beams (CABs) with propagational fractional-order optical vortices (OVs). The superposition of the phase singularity and polarization singularity from a vortex vector beam (VVB) plays a significant role in creating a propagational fractional vortex beam. Propagational fractional vortex beams can be considered as a superposition of left and right circularly polarized vortex beams with different integer topological charges (TCs). We study the propagation characteristics of two kinds of propagational fractional vortex CABs, and the results show that both of the two kinds of beams can stably propagate in free space, and they exhibit an “abruptly auto-focusing” property and “self-healing” property during the propagation. The intensity distribution of the first kind of propagational fractional vortex CAB has an odd number of petals (2m + 1), while the second kind of beam has a crescent-shaped intensity distribution. The influence of turbulence on the beam propagation through atmosphere under different turbulence strengths is also numerically studied in this paper. A fractional vortex CAB with an initial radius r0 = 10 mm can retain its shape after propagating 20 m when the atmospheric refractive-index structure constant CN2=0.2×10−12m−2/3. Our results are expected to broaden the application of CABs.

Observation of Magnetic Quadrupole Endowed Helical Dichroism in Artificial Propeller Meta‐Molecules

AbstractThis study demonstrates that the magnetic quadrupole (MQ) can make an indispensable contribution to helical dichroism (HD), which is distinct from HD caused by electric quadrupole (EQ). Specifically, the established multipole expansion theory of the light–matter interaction reveals that EQ‐induced HD belongs to the pure electric dipole–quadrupole (E1‐E2) excitation, while newly discovered MQ‐induced HD belongs to the pure magnetic dipole‐quadrupole (M1‐M2) excitation. Metallic propeller meta‐molecules are used to elaborate on this novel physical mechanism and demonstrate that HD can be significantly enhanced and flexibly tuned by increasing stereo twist of propeller meta‐molecules or slightly focusing the linearly polarized vortex beam to improve the orbital angular momentum number. Importantly, the aforementioned intriguing phenomena are validated by fabricating stereo twisted propeller meta‐molecules via nano‐kirigami method. The findings reveal a paradigm‐shift approach to manipulate the chiroptical response of a single metallic nanostructure via photonic orbital angular moment, opening prospects for optical encryption, communication, next‐generation chiroptical spectroscopy, and chiral vortex optical devices.

3-Bit coded metasurface for linear and circular polarized vortex beam broadband modulation based on dual-frequency multistage resonance

A metasurface design scheme is proposed based on reflective double vertical U-shaped resonators. Compared to planar resonators with the same parameters, vertical meta-atom can excite magnetic dipole resonance and quaternary resonance respectively at low and high frequency to achieve stable wideband phase shift and unique free regulation. Vertical meta-atoms can be applied as 3-bit coding elements in linearly polarized (LP) and circularly polarized (CP) states with bandwidths of 0.7–1.1 THZ and 0.55–1.5 THZ, respectively. At the same time, as a half-wave plate, the deflection conversion rate is 95%, the relative bandwidth is 69%, and the operating Angle is 80°. In order to verify the application capability of the designed meta-atom, the excitation and separation of multi-stage vortex beams are performed in the wide frequency range of LP and CP using the coded convolutional addition method. The designed meta-atom only needs to regulate a single structural parameter to fully satisfy the requirements of 3-Bit broadband coding under LP and CP incidence, so it has multi-type polarization wave universality and ultra-wide working bandwidth. Meanwhile, the method can be effectively applied to optical band and microwave band.

Ultracompact Metasurface for Simultaneous Detection of Polarization State and Orbital Angular Momentum

AbstractIn the field of optical communications and quantum informatics, polarization and orbital angular momentum (OAM) offer a promising way to expand the dimension of information. However, detecting the polarization state and topological charge of the OAM beam on‐chip way can be challenging. To address this, an ultracompact metasurface is proposed and demonstrated. The metasurface is composed of six polarization‐sensitive metalenses that occupy 60°annular sectors each and are capable of simultaneous polarization state and orbital angular momentum detection. The metasurface focuses the coaxial polarized vortex beam into six locations, and the foci displacement is related to the value of the topological charge. The corresponding polarization state can be obtained through the reconstructed Stokes parameter using the six focus light intensities. For proof‐of‐concept, an ultracompact metasurface operating at a wavelength of 1064 nm is fabricated, which exhibits exceptional polarization and orbital angular momentum recognition ability. The proposed metasurface possesses the merits of ultra‐compact size and simultaneously entire polarization state and orbital angular momentum identification capability, which may encourage the development of on‐chip optical communication systems.

Evolution of coherence singularities in polarization singular beams.

The evolution of correlation singularities in partially coherent polarization singular beams (PC-PSBs) is investigated. Since PSBs are the superposition of two orthogonally polarized vortex beams, the occurrence of coherence singularities in PC-PSBs is strongly governed by the topological charge of the component vortex beams and the spatial coherence length. Coherence singularities appear in the form of ring dislocations in the modulus of the spectral degree of coherence (SDoC) profile, and the number of ring dislocations is equal to the higher value of the topological charge of the superposing vortex beam. Furthermore, the SDoC phase profile can be used to determine the polarity of a PC-PSB. The findings of the study could be valuable in various applications that rely on the spatial coherence of beams, such as free-space communication and imaging.

Ultracompact Single-Photon Sources of Linearly Polarized Vortex Beams.

Ultracompact chip-integrated single-photon sources of collimated beams with polarization-encoded states are crucial for integrated quantum technologies. However, most of currently available single-photon sources rely on external bulky optical components to shape the polarization and phase front of emitted photon beams. Efficient integration of quantum emitters with beam shaping and polarization encoding functionalities remains so far elusive. Here, ultracompact single-photon sources of linearly polarized vortex beams based on chip-integrated quantum emitter-coupled metasurfaces are presented, which are meticulously designed by fully exploiting the potential of nanobrick-arrayed metasurfaces. The authors first demonstrate on-chip single-photon generation of high-purity linearly polarized vortex beams with prescribed topological charges of 0, - 1, and +1. The multiplexing of single-photon emission channels with orthogonal linear polarizations carrying different topological charges are further realized and their entanglement is demonstarated. The work illustrates the potential and feasibility of ultracompact quantum emitter-coupled metasurfaces as a new quantum optics platform for realizing chip-integrated high-dimensional single-photon sources.