Optical Vortex Beams Research Articles

Optical twin-vortex multi-trapping by Kolakoski lenses

In this work, we design and implement a new bifocal diffractive spiral lens within an optical tweezers system. The proposed diffractive optical element coined Kolokaski Kinoform Spiral Lens (KKSL), generates twin optical vortices along the propagation direction. The axial positions, as well as the diameters of the generated vortex beams, are correlated with the Kolakoski aperiodic sequence introduced in the design of the diffractive lens. The unique properties of KKSLs make it ideal for optical trapping applications, allowing independent multiple trapping and particle displacement within each optical vortex beam. We present both the focusing properties of KKSL and the experimental results of its integration into the optical tweezer setup.

Femtosecond optical vortex-induced flower-shaped surface relief structures in an azo-polymer film

We study the formation of surface relief structures in azo-polymers generated via two-photon induced photoisomerization using a femtosecond near-infrared optical vortex laser beam. These structures exhibit exotic flower-like shapes with petals along the azimuthal direction, and they are formed from spatial mode instability, which is associated with third-order nonlinear effects in the azo-polymer. This process is a unique and exotic interaction between light and matter, which may be applied to the development of advanced optical data storage technologies. Here, an additional degree of freedom is offered by the number of formed petals, which themselves are a function of the topological charge of the optical vortex beam.

A simulation-based analysis of optical read-out for electrochemical reactions using composite vortex beams.

We propose an optical read-out method for extracting faradaic current in electrochemical (EC) reactions and analyze its performance using opto-EC simulations. Our approach utilizes structured electrodes to generate composite optical vortex (COV) beams upon optical illumination. Through opto-EC simulations, we demonstrate that the EC reaction of 10 mM potassium ferricyanide induces a refractive index (RI) change, RI, of approximately RI units, leading to the rotation of the COV beam's intensity profile with a peak rotation of . This rotation's magnitude is proportional to RI, while the rate correlates with the faradaic current ( ) density responsible for RI. As the opto-EC information is from bulk RI, it remains unaffected by interfering non-faradaic components at the interface and is advantageous for studying intermediate species and bulk homogeneous reactions. Furthermore, as rotation depends on density rather than itself, this method proves beneficial in low scenarios, such as when employing micro-electrodes to decrease solution resistance or obtain localized EC data. Even in low density scenarios, like monitoring slow EC reactions, our method enables signal amplification by accumulating rotation over time. This interdisciplinary approach holds promise for advancing EC research and addressing critical challenges across various fields, including energy storage, corrosion protection, environmental remediation, and biomedical sciences.

Broadband Spin and Orbital Momentum Modulator Using Self-Assembled Nanostructures.

The structural symmetry of solids plays an important role in defining their linear and nonlinear optical properties. The quest for versatile, cost-effective, large-scale, and defect-free approaches and materials platforms for tailoring structural and optical properties on demand is underway since decades. A self-assembled spherulite material comprised of synthesized molecules with large dipole moments aligned azimuthally, forming a vortex polarity with spontaneously broken symmetry, is experimentally demonstrated. This unique self-assembled structure enables new linear and nonlinear light-matter interactions, including generating optical vortex beams with complex spin states and on-demand topological charges at the fundamental, doubled, and tripled frequencies. This work will likely enable numerous applications in areas such as high-dimensional quantum information processing with large capacity and high security, spatiotemporal optical vortices, and a novel optical manipulation and trapping platform.

Generation of circular symmetric Airy vortex beams based on spin-multiplexed metasurface

Given that circular symmetric Airy vortex beam (CSAVB) was found to possess a stable central cavity and an opposing transport process to circular Airy vortex beam, it has been recognized as a potentially powerful tool for particle trapping and optical communication. In order to facilitate broader application scenarios, this paper presents a novel approach to the generation of multiple CASVBs based on a single metasurface. In the proposed method, three independent CSAVBs carrying different new kinds of power-exponent-phase vortices (NPEPVs) can be obtained under two orthogonal circularly polarized or an arbitrary linear polarized incident, respectively. Each of these vortex structures is characterized by a distinct orbital angular momentum, which is jointly determined by two parameters of the NPEPVs. This indicates that the CSAVB and the device have greater freedom than the canonical optical vortex beams and the previous vortex beam generators in controlling the optical vortex. These results have the potential to advance the development of vortex beams and enhance their applications in micromanipulation, optical communication and imaging.

Evolutions of a ring Airy vortex beam and a ring Pearcey vortex beam in turbulent atmosphere and a comparative analysis of their channel efficiencies and OAM spectra

An optical vortex beam propagating through turbulent atmosphere encounters distortions in the wavefront that result in modal scattering. Abruptly autofocusing (AAF) beams with orbital angular momentum have gained significant attention due to their non-diffracting and self-healing nature. These warrant understanding of the behavior of these beams through turbulent atmosphere absolutely necessary. With this intuition, in the present work we investigate the behavior of two AAF beams, namely the ring Airy vortex beam (RAVB) and ring Pearcey vortex beam (RPVB) through the turbulent atmosphere in two cases—multiplexed and non-multiplexed. We propagate multiplexed as well as non-multiplexed RAVB and RPVB in different levels of turbulent atmosphere. In the non-multiplexed case, channel efficiency declines for both beams with increase in mode numbers. In the multiplexed case, increasing the gap between the mode sets results in a decrease in channel efficiency. We also report that in weak atmospheric turbulence RAVB outperforms RPVB in terms of channel efficiency. We use the optical transformation sorting (log-polar) method to demultiplex the optical beams at the output. Furthermore, we investigate and compare the orbital angular momentum (OAM) spectra of both beams in different levels of atmospheric turbulence and at different propagation distances. The comparison reveals that the spectra of RPVB are more dispersive as compared to those of RAVB.

Interference of high-order perfect optical vortex beams

We investigate the interference of high-order perfect optical vortex (POV) beams with different topological charges. Through numerical simulations, we reveal a remarkable phenomenon: keeping the beam width, and beam radius fixed while changing the topological charge, the splitting of the composite POV beam into two distinct individual perfect vortices occurs exactly at the same inter-axial separation. The observed interference pattern exhibits pronounced sensitivity to factors such as axial separation, phase shift, beam radius, and topological charges of the constituent beams. Notably, our findings are contrasted with the interference of high-order Laguerre-Gauss (LG) beams, highlighting that the splitting of composite vortices into their individual components is more rapid in the case of LG beams. We also investigate the evolution of the interference pattern for both POV, and LG beams along the propagation direction in free-space. Our research provides significant insights into the distinct interference properties of high-order POV beams, presenting potential applications in the fields of optical manipulation and communication systems.

OPTIMIZATION OF MODE PROPAGATION FOR AN EMBEDIER OF OPTICALVORTEX BEAMS BASED ON A MICRO-RING RESONATOR

Light beams with orbital angular momentum have unique properties that make them valuable for research and practical applications. From revolutionizing communication technologies to enabling advanced microscopy and quantum computing possibilities, these beams continue to drive innovation and open up new frontiers in optics and photonics. In this paper, the dependence of the radiation flux density of an optical vortex beam on the geometry of the emitting structure is investigated. A micro-ring resonator with periodic structures is used as an optical vortex beam emitter structure. In our study, optimizing the width of the ring waveguide leads to an increase in the radiation flux power up to 30% for the resonant wavelength of 1563 nm. To analyze how the whispering gallery modes are distributed in the cross section of the annular waveguide, we increased the annular waveguide width from 400 nm to 500 nm. This proposed approach can be applied to radiating micro-ring resonators in various applications.

Spatiotemporal vectorial structured light that dynamically varies on higher-order Poincaré sphere

Higher-order structured light beams, including optical vortex (OV) beams and vector beams, which can be geometrically represented as points on higher-order Poincaré spheres (HOPSs), have been widely exploited in applications such as optical trapping, optical communications, optical metrology, quantum optics, to name a few. To date, traditional approaches to producing such higher-order structured light beams deal with controllable generation of different static points on HOPS. In this paper, we propose and demonstrate the generation of spatiotemporal structured light beams that dynamically vary on HOPS. By superposing OV beams with different frequencies, spatiotemporal vectorial structured light beams that dynamically vary along latitude lines, meridians, and other trajectories on the first order Poincaré sphere are generated in simulation. Our work may give new insight into arbitrarily and ultrafast tailoring higher-order structured light beams.

Generating first-order optical vortex beams by photonic crystal slabs

Optical vortices, which are beams with helical wavefronts and spiral phase mismatches, have garnered considerable attention in various fields. In this study, we theoretically proposed and experimentally implemented a simple method for generating first-order optical vortices. To generate first-order vortex beams using the polarization field in the momentum space of photonic crystal slabs, topological half charges are required. We propose a method to divide the polarization vortex in the momentum space by breaking symmetry, which results in Dirac points or circularly polarized points. This approach enables the transformation of topological integer charges into topological half-integer charges, thereby facilitating the generation of first-order vortex beams. This approach extends the application of bound states in continuum and topological photonics.

On the orbit-induced spin density of tightly focused optical vortex beams: ellipticity and helicity

It has recently been established that a linearly-polarized optical vortex possesses spin angular momentum density in the direction of propagation (longitudinal spin) under tight-focusing. The helicity of light has long been associated with longitudinal spin angular momentum. Here we show that the longitudinal spin density of linearly-polarized vortices is anomalous because it has no associated helicity. It was also recently determined that the polarization-independent helicity of tightly-focused optical vortices is associated with their transverse spin momentum density. The key finding of this work is the fact that, in general, longitudinal spin can not necessarily be associated with helicity, and transverse spin is in general not associated with a zero helicity, and such extraordinary behaviour manifests most clearly for optical vortices under non-paraxial conditions.

Orbital Hall diffraction and its application for vortex measurement.

We observe significant orbital angular momentum (OAM)-helicity-dependent centroid shifts in the Fraunhofer patterns for the far-field diffraction of optical vortex beams passing through a thin single wire, thus suggesting the orbital Hall effect (OHE) of light in diffraction. Based on the OHE with a thin cross wire, we further experimentally develop a compact and robust alignment-free method to measure the OAM states of light. These findings indicate that not only does the OHE of light offer insights into vortex diffraction with broken rotational symmetry, it may also provide a reliable and efficient way to simplify the vortex measurement for waves of different natures.

Wigner distribution and entropy of partially coherent light generated by perfect optical vortices.

We developed analytical expressions for the Wigner distribution function of partially coherent fields generated by the scattering of beams with a particular phase structure, namely perfect optical vortex beams. In addition, we provide the modal decomposition of the field correlations and evaluate the evolution of Shannon entropy associated with the partially coherent field.

Electro-active superposed optical ring vortex beams based on PEDOT: SULF composite metasurface

Electro-active metasurfaces with high efficiency and ultra-small scale active control of integrated components are crucial for developing complex optical devices. Recent attention has focused on vortex beams with ring intensity distribution independent of topological charge, enhancing particle manipulation and fiber optic transmission efficiency. This paper presents a composite metasurface utilizing the conductive polymer PEDOT: SULF, capable of generating and dynamically switching between two types of superposed ring vortex beams. We investigate their characteristics and polarization detection capabilities. Accurate detection of major axis, ellipticity, and handedness of incident polarized light is achieved based on the two superposed ring vortex beams. The metasurface exhibits excellent switching performance, enabling flexible tuning of the ring vortex beams on demand. Additionally, we demonstrate the metasurface's good polarization detection performance for incident polarized light as an application example. The PEDOT: SULF composite metasurface holds great potential in polarization detection, quantum science, and compact photonics-integrated devices.

Characterizing the fractional coherence vortices through the area of the intensity cross-correlation function

We have generated the fractional coherence vortices using the speckle patterns obtained from the scattering of the fractional vortex beams. In this study, we found the topological charge of the fractional vortex beam with a resolution of 0.01 using the area of the coherence function of scattered fractional optical vortex beams. We have also provided accuracy for the measurement of topological charges of fractional vortex beams using the studies of the area of the coherence function. Our experimental results are well matched with the theoretical results. These fractional coherence functions can be used to generate a security key for data authentication and data encryption. In addition, fractional vortex beams have multiple OAM modes and can be used to address the explosive growth in free-space optical communication.

Rotation of liquid crystal microdroplets in the intensity minima of an optical vortex beam

An optical vortex is characterized by its donut-shaped intensity distribution and helical phase structure. In this study, we demonstrate that an optical vortex beam, generated by a spatial light modulator, can trap, circulate, and rotate liquid crystal microdroplets of various sizes at different positions within the beam. Our findings indicate that larger microdroplets are trapped at intensity minima without altering their internal liquid crystal orientation, which is fluid by nature, and the rotation of microdroplets were observed. This rotation, a rare phenomenon, occurs without damaging or altering the inner liquid crystal molecules, offering an advantage over traditional circularly polarized optical trapping, which can generally alter inner molecular arrangements of liquid crystal. This report details the relationship between trapped particle size, trapping position, and rotation angle of liquid crystal microdroplets within an optical vortex beam.

Printed Liquid Crystal Optical Vortex Beam Generators

AbstractThis study presents an innovative application of inkjet printing technology in the construction of a switchable optical vortex beam generator. The fabrication process involves drop‐on‐demand printing of liquid crystal (LC) droplets that can generate an optical vortex beam in the far‐field with the application of a voltage. Notably, this vortex beam can be activated and deactivated by manipulating the amplitude of the electric field. Both simulations and experiments are used to determine the optical characteristics of the printed LC devices and the resulting far‐field patterns for different polarizations of light. The study showcases the versatility of the generator in that it can produce both vortex and vector beams, the choice of which is simply determined by the polarization of the input light. This highlight the potential of this printed LC technology for integration into a multitude of optical systems.

Generating Optical Vortex Array Laser Beams of Superimposing Hermite–Gaussian Beams with a Dual–Phase Modulation Digital Laser System

This study presents an efficient and practical intra-cavity approach for selectively generating vortex array laser beams employing a dual-phase modulation digital laser system, which has not yet been completed in single-phase modulation digital laser. The stable optical vortex array laser beams were formed by superimposing cavity Hermite–Gaussian (HG) eigenmodes. In particular, when the selected cavity HG modes shared the same Gouy phase, the resulting optical vortex beam could preserve its light field pattern, thereby maintaining the optical vortex properties in the near and far fields. Numerical results demonstrated that employing dual-phase modulation could establish optimal boundary conditions for the selection of HG modes within the cavity, successfully generating various vortex array laser beams. The experimental validation of the proposed method confirmed the ability to select optical vortex array lasers solely by controlling the loaded phase of the dual-phase modulation digital laser. These results demonstrate the ability of digital lasers to generate and dynamically control optical vortex array lasers.

Transmission characteristics of partially coherent pin-like optical vortex beams in oceanic turbulence

Based on the Rytov approximation theory, the analytical formulae for the mode detection probability and channel capacity of the partially coherent pin-like optical (PCPO) vortex beams propagating in oceanic turbulence are obtained. The effects of light source parameters and oceanic turbulence parameters on the transmission characteristics of the PCPO vortex beams are analyzed in detail by numerical simulations. According to numerical results, a larger spatial coherence length of the partially coherent source endows the beams with a superior channel capacity performance while accompanied by a decrease in transmission robustness. Meanwhile, PCPO vortex beam with greater phase modulation power parameter and longer wavelength is conducive to enhancing the transmission quality through oceanic turbulence. In addition, the channel capacity of the system can be effectively augmented with the increase of the dissipation rate of kinetic energy per unit mass of fluid, the anisotropy factor, the inner scale radius and the decrease of the mean square temperature dissipation rate, the temperature-salinity contribution ratio. The results also indicate that PCPO vortex beam is a better candidate than Gaussian vortex beam for long-distance transmission. This paper provides a theoretical reference for studying an underwater communication link using PCPO vortex beams as the transmission carrier.

Asymmetric multi-image encoding and hiding scheme with structured fingerprint phase masks using gyrator transform and phase-shifting digital holography

We propose a novel technique for multi-image encryption and hiding schemes under an optical asymmetric framework using structured fingerprint phase masks (SFPMs) in the gyrator transform (GT) domain and three-step phase-shifting digital holography (PSDH). A SFPM contains unique features of fingerprint and structured phases of the optical vortex beam, which provides enhanced security in the cryptosystem. To encrypt multiple images, GT-based phase truncation and phase reservation techniques have been used in the first level of security, whereas three-step PSDH has been used to obtain the final cipher text. The cipher text is embedded in the host image to perform the watermarking process. In this process, the host is further decomposed into three parts in which anyone from the last two parts can be used for watermark embedding, and the first part is stored as the key. The use of polar decomposition in the watermarking process provides an additional layer of security. Numerical simulations and experimental results are presented to support the proposed scheme.