Optical Vortex Research Articles

Tunable Liquid Crystal Twisted‐Planar Fresnel Lens for Vortex Topology Determination

AbstractThe development of straightforward and effective methods to determine the topological charge of phase singular beams is crucial for broadening the applications of optical vortices. Here, a straightforward and elegant method for determining the topological charge of an optical vortex using an innovative switchable achromatic nematic liquid crystal Fresnel lens is proposed. The approach allows for the unambiguous determination of both the absolute value and the sign of the topological charge of a singular beam across a wide range of the visible spectrum, as demonstrated both experimentally and theoretically. The research outcomes are promising for applications in optical information transmission systems, cryptography, and quantum computing.

A liquid crystal device-based apparatus for observing optical vortex and manipulating micro-particles

Abstract In this paper, we disclose a self-developed liquid crystal device-based optical apparatus for the teaching experiment of college students. Three relevant experiments have been presented. Through the teaching experiment class, the students have learnt the knowledge on the light-matter interaction, the photo-patterning of a liquid crystal q-plate and the generation of optical vortex, and the manipulation of micro-particle via angular momentum. Most students held positive remarks on the optical apparatus, and were satisfied with the assigned tasks in the experiment. Indeed, our proposed optical apparatus is not only applicable to the explorative research work, but also suitable for the college students’ teaching laboratories.

Multi-function vortex array radar

In the realm of automation systems, multi-function radars serve as essential sensory components for self-driving vehicles and airbornes. Effective resource allocation management is crucial, requiring a high level of versatility to accomplish multiple tasks, especially, for increasingly miniaturized hardware. Here, we advance a balanced protocol for detecting, positioning, and tracking moving targets in real-time. Our protocol integrates efficient data processing methods with robust hardware. Specifically, detection signals are modulated by optical vortices for imaging, and real time processing of the image field facilitates target positioning and tracking. Moreover, the protocol extends its utility to serve as a topographic laser profiling system for natural landscapes, highlighting its adaptability. This adaptability and versatility well position the proposed protocol to support a wide range of applications, spanning self-driving vehicles and aerial systems, underscoring its potential significance across multiple platforms.

Spatial momentum separation for optical vortex via phase-assembled metasurfaces

Expanding the spatial degrees of freedom is regarded to be the most innovative and effective solution for optical vortex encoding/decoding technology. A phase-assembled metasurface is proposed here to separate the momentum of the optical vortex into different spatial locations, and the incident high-order optical vortex is encoded in 18 channels. By combining both the propagation phase and the Pancharatnam-Berry (PB) phase, the fundamental Gaussian mode (solid spot) positions and other higher-order orbital angular momentum modes (hollow mode spots) positions at different channels are used to achieve the encryption of all-optical information. The scheme of grouping the mode spots on different channels into solid and hollow points greatly reduces the difficulty of encoding/decoding a high-order optical vortex. In this way, the combination of 2 incident high-order optical vortexes can represent 256 hexadecimal numbers from 00 to FF. We envision this work will open avenues for information encryption, multidimensional data storage, wavefront manipulation, and advanced orbital angular momentum detection technologies.

Nonlinear geometric phase coded ferroelectric nematic fluids for nonlinear soft-matter photonics

Simultaneous manipulation of multiple degrees of freedom of light lies at the heart of photonics. Nonlinear wavefront shaping offers an exceptional way to achieve this goal by converting incident light into beams of new frequencies with spatially varied phase, amplitude, and angular momenta. Nevertheless, the reconfigurable control over structured light fields for advanced multimode nonlinear photonics remains a grand challenge. Here, we propose the concept of nonlinear geometric phase in an emerging ferroelectric nematic fluid, of which the second-order nonlinear susceptibility carries spin-dependent nonlinearity phase. A case study with photopatterned q-plates demonstrates the generation of second-harmonic optical vortices with spin-locked topological charges by using cascaded linear and nonlinear optical spin-orbit interactions. Furthermore, we present the dynamic tunability of second-harmonic structured light through temperature, electric field, and twisted elastic force. The proposed strategy opens new avenues for reconfigurable nonlinear photonics, with potential applications in optical communications, quantum computing, high-resolution imaging, etc.

Single- and dual-tube He-Ne lasers for high-power excitation of LG01-mode vortex beam

Abstract In this study, aiming to extend the power of LG01-mode vortex light at 632.8nm, the commercial He-Ne laser was upgraded to dual-tube gain geometry with the assistance of an intracavity spot defect for spatial filtering. We investigated the impact of using single and double He-Ne gas gain tubes on the powers of vortex laser output , and achieved a maximum 4.7-mW power of LG01-mode vortex light, correspionding to an optical-optical conversion efficiency of 39.2% and making it the highest power of vortex light obtained in He-Ne laser.

A hybrid trans-modal liquid crystal optical vortex generator

This work experimentally validates a large-aperture optical vortex generator using a novel hybrid structure, combining transmission electrode and modal techniques, in what we term the trans-modal technique. The continuous transmission electrode is designed to generate a linear voltage distribution between the contact electrodes, while the electrode stubs distribute the voltage across the active area. A high-resistivity layer of the conducting polymer PEDOT fills the gap between the electrodes, resulting in a completely continuous voltage distribution. A 1-cm aperture device is experimentally demonstrated, but the structure is completely scalable. Theoretical results validate the design, and experimental results demonstrate precise control over the topological charge for both positive and negative values of orbital angular momentum. Remarkably, the conversion efficiency for the first topological charges is almost 100%. The reduction in efficiency of the higher-order modes has been explained theoretically, and it is not caused by design but by the PEDOT characteristics. The fabrication process is straightforward, as the high-resistivity layer may also be inhomogeneous. This work contributes significantly to the field by introducing a novel method for optical vortex generation. The simplicity of the fabrication process, high conversion efficiency, and ability to control the topological charge make this technique a promising avenue for future research and applications.

Generation of sub-100 fs vortices from a Kerr-lens mode-locked Hermite-Gaussian Yb:CALGO oscillator.

Mode-locked oscillators with high-order transverse modes are excellent platforms for generating femtosecond optical vortices with high average power and good propagation stability. These have important applications in diverse fields such as optical communication, strong-field physics, and laser processing. So far, generating vortex pulses with ultrashort pulse duration remains a challenge. In this Letter, we report a Kerr-lens mode-locked Yb:CALGO laser oscillator delivering Hermite-Gaussian (HG) pulses with a pulse duration of 86 fs using a non-collinear pumping technique. 91 fs optical vortex pulses were generated by using a cylindrical-lens mode converter. To the best of our knowledge, this is the shortest pulse duration ever obtained from a diode pumped solid-state mode-locked oscillator with a pure high-order Hermite-Gaussian mode. The phase structures of the generated femtosecond vortices are characterized.

Particle delivery in generalized optical vortex conveyor belts with uniform orbital flow

Particle delivery in generalized optical vortex conveyor belts with uniform orbital flow

Topological-charge-tunable and wavelength- switchable vortex laser enabled by a helically twisted high-absorption few-mode erbium-doped fiber.

Vortex beams carrying orbital angular momentum (OAM) offer a solution for enhancing spatial degrees of freedom, particularly in conjunction with wavelength division multiplexing, which can significantly boost data capacity for optical communication. Addressing the increasing demand for high information-carrying capacity, we present a dynamically tunable OAM laser source in this study. We demonstrate a ring-cavity vortex fiber laser employing intra-cavity mode conversion through a helically twisted high-absorption few-mode erbium-doped fiber (HA-FM-EDF). The constructed vortex fiber laser exhibits wavelength switchability via an integrated Sagnac loop, facilitated by a homemade ring-core fiber. Furthermore, topological-charge tunability is achieved through the utilization of twisted HA-FM-EDF with varying helical pitches. To our knowledge, this marks the first successful implementation of two-dimensional multiplexing of wavelength and OAM in a vortex fiber laser. The OAM laser serves as a versatile vortex source with high tunability and flexibility, holding significant potential for deployment in ultrahigh-speed/ultrahigh-capacity communications, ultrahigh-resolution imaging, and ultrahigh-sensitivity sensing applications.

Topological charge of a Gaussian beam with an off-axis optical vortex

We show that when an optical vortex with a topological charge n shifts from the optical axis of a Gaussian beam, the orbital angular momentum decreases, whereas the topological charge remains unchanged. We experimentally confirmed this phenomenon with the aid of a q-plate array generated in a liquid crystal cell filled with a frustrated chiral nematic. We also theoretically proved that the topological charge of an optical vortex is conserved when the optical vortex is displaced from the axis.

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.

Generating optical vortex beams using cylindrical waveguides

As an initial step toward exciting optical vortices using high-power millimeter waves, this study developed a method for inducing vortex modes within a cylindrical waveguide using Gaussian beams. By examining the coupling between tilted and offset Gaussian beams and specific waveguide modes, appropriate tilt angles and offsets were obtained. Numerical simulations demonstrated that the vortex modes could be efficiently excited using four Gaussian beams. Furthermore, the results revealed that increasing the number of Gaussian beams improves the excitation efficiency of vortex modes.

Scheme for generation of spatiotemporal optical vortex attosecond pulse trains

The realization of spatiotemporal vortex structure of various physical fields with transverse orbital angular momentum (OAM) has attracted much attention and is expected to expand the research scope and open new opportunities in their respective fields. Here we present theoretically the first, to the best of our knowledge, study on the generation of attosecond pulse trains featuring a spatiotemporal optical vortex (STOV) structure by a two-color femtosecond light field, with each color carrying transverse OAM. Through careful optimization of relative phase and intensity ratio, we validate the efficient upconversion of the infrared pulse into its tens of order harmonics, showing that each harmonic preserves a corresponding intact topological charge. This unique characteristic enables the synthesis of an extreme ultraviolet attosecond pulse train with transverse OAM. In addition, we reveal that ionization depletion plays an outsize role therein. Our studies pave the way for the generation and utilization of light fields with STOV in the attosecond regime.

Fourier-transform spectroscopy based on the rotational Doppler effect

We propose a new Fourier-transform spectroscopy technique based on the rotational Doppler effect. The technique offers an application for optical vortex frequency combs, where each frequency component carries a unique amount of orbital angular momentum (OAM). Here, we emulate a vortex comb using a tunable single frequency laser and a collection of spiral phase plates, generating up to 11 distinct OAM modes. Unlike in traditional Fourier-transform spectroscopy based on the Michelson interferometer (linear Doppler effect), the spectral resolution of vortex-comb spectroscopy is not limited by the mechanical scan distance of the instrument, but the instrument can be operated continuously without interruptions, leading to fast mode-resolved measurements.

Selective and Tunable Absorption of Twisted Light in Achiral and Chiral Plasmonic Metasurfaces.

The symmetry of achiral metasurfaces suggests selective absorption is nonexistent when irradiated either by circularly polarized Gaussian or twisted light beams carrying orbital angular momentum (OAM). In chiral metasurfaces, the lack of symmetry leads to differential absorption when probed with chiral light either in the form of circular polarization (circular dichroism) or helical phase fronts (helical dichroism). Here, we demonstrate differential absorption of asymmetric twisted light beams, known as helical dichroism, which exist in an array and a single achiral structure and can be controlled. When extended to chiral structures, these asymmetrical chiral light modes enable to enhance and tune chiroptical sensitivity. Our technique offers more control parameters than just changing the OAM value, as presented in previous studies. Selective response to asymmetric helical light beams is qualitatively explained in terms of induced multipole moments. The presence of dichroism in achiral nanostructures offers a significant fabrication advantage over complex chiral structures and enables the development of next-generation plasmonic-based chiroptical spectroscopy and molecular sensing.

Formation and Controlling of Optical Hopfions in High Harmonic Generation.

Toroidal vortex is a kind of novel and exotic structured light with potential applications in photonic topology and quantum information. Here, we present the study on high harmonic generation from the interaction of the intense toroidal vortices with atoms. We show that the spatial distribution of harmonic spectra reveal unique structures, which are kinds of high-order topological toroidal vortex because of the rotating of the driving fields with transverse orbital angular momentum. Then we show that, by synthesizing the toroidal vortices and optical vortices with longitudinal orbital angular momentum, it is able to generate the optical hopfions in the extreme ultraviolet range, which exhibit a completely different topological property compared with both the driving fields. Harnessing the spin angular momentum selection rules, we further show that one can control the topological texture and channel each harmonic into a single mode of controllable Hopf invariant.

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

AbstractThe 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.

Tight focusing of terahertz vortex beams formed by laser dielectric resonator

Wave characteristics of vortex laser beams during their tight focusing have been theoretically studied. The Rayleigh–Sommerfeld theory was used to describe propagation in free space of laser beams excited by the modes of a waveguide dielectric resonator. It is shown that at the topological charge of the spiral phase plate n = 0, the studied EH11 mode has a maximum of radiation intensity on the axis. Introduction of a topological charge leads to the appearance of a minimum of radiation intensity on the axis as well as to the increase in the size of the focal spot. However, for the TE01 mode with the topological charges n = 0 and n = 2, the intensity distribution retains a ring shape, while at n = 1 the beam profile turns into the Gaussian-like one. The wave front in the focal region of the lens for the components of the EH11 and TE01 modes transforms from spherical to spiral one with increasing the topological charge.