Generation Of Optical Vortex Beams Research Articles

Generation of optical vortex beams with bandwidth exceeding 550 nm using a helical fiber needle exhibiting strong mode coupling.

A strong-coupling helical fiber needle (HFN) is proposed and demonstrated for the realization of bandwidth-enhanced broadband optical vortex beam (OVB) generation. The HFN is based on a single mode fiber and operates at the dispersion-turning-point (DTP) of the lowest radial order of the cladding mode (i.e., LP11) but with a remarkably high mode coupling efficiency. By utilizing this novel, to the best of our knowledge, HFN, successful generation of the first-order OVB with an impressive bandwidth up to 556 nm at -10 dB and a center wavelength of ∼1570 nm has been achieved. This represents the broadest bandwidth demonstrated among all fiber grating-based OVB generators to date. The proposed HFN-based OVB generator exhibits a relatively compact size, ultra-wide bandwidth, and customizable center wavelength, making it highly promising for applications in optical vortex-based endoscopic imaging as well as particle detection and manipulation.

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.

Tunable vortex beams generation in visible band via Pr3+:YLF laser with a spot defect

The generation of optical vortex beams with user-configurable topological charge and spatial profile is a topic of intense research due to the numerous potential applications for these types of laser beams. In this work, we demonstrate the direct generation of vortex laser beams with controllable topological charge and tunable spatial profile from a Pr3+:YLF laser cavity using a spot-defect technique. A theoretical model is established to examine the relationship between the topological charge of the generated vortex beam and how this relates to laser cavity parameters. Experimentally, the selective operation of first- and second-order vortex beams and tunable optical vortex lattices with one to four singularities at 607 nm can be achieved by adjusting the position of the defect spot. This work offers insight into methods for the generation of visible optical vortex beams with controllable topological charge and tunable singularities for a range of applications.

Broadband optical vortex beam generation using flat-surface nanostructured gradient index vortex phase masks

We developed a new kind of compact flat-surface nanostructured gradient index vortex phase mask, for the effective generation of optical vortex beams in broadband infrared wavelength range. A low-cost nanotechnological material method was employed for this work. The binary structure component consists of 17,557 nano-sized rods made of two lead–bismuth–gallium silicate glasses which were developed in-house. Those small rods are spatially arranged in such a way that, according to effective medium theory, the refractive index of this internal structure is constant in the radial direction and linearly changes following azimuthal angle. Numerical results demonstrated that a nanostructured vortex phase mask with a thickness of 19 μm can convert Gaussian beams into fundamental optical vortices over 290 nm wavelength bandwidth from 1275 to 1565 nm. This has been confirmed in experiments using three diode laser sources operating at 1310, 1550, and 1565 nm. The generation of vortex beams is verified through their uniform doughnut-like intensity distributions, clear astigmatic transformation patterns, and spiral as well as fork-like interferograms. This new flat-surface component can be directly mounted to an optical fiber tip for simplifying vortex generator systems as well as easier manipulation of the generated OVB in three-dimensional space.

Switchable optical vortex beam generator based on an all-dielectric metasurface governed by merging bound states in the continuum.

The polarization topology around the bound states in continuum (BIC) affects the optical vortex (OV) beam generation. We propose a cross-cross-shaped resonator based on a THz metasurface to realize an OV beam generator in real space by exploiting the inherent winding topology around the BIC. The BIC merging at the point Γ is achieved by tuning the width of the cross resonator, which significantly improves the Q factor and enhances the field localization. Furthermore, the switching between the high-order OV beam generator governed by the merged BIC and the low-order OV beam generator is realized. This extends the application of BIC in modulating orbital angular momentum.

Optical Vector Vortex Generation by Spherulites with Cylindrical Anisotropy.

Materials with crystalline structures of circular symmetry are rare in nature; however, they are highly desired in optical applications with structured lights, whose characteristics are of cylindrical symmetry. In this work, using a naturally existing circular anisotropy from a spherulite formed by molecular self-assembly, we obtain a cylindrical vector optical vortex beam generation transformed from the spin angular momentum in the wide visible range. The proposed strategy provides promising and broad opportunities for the applications of spherulites in the generation of structured lights and modulations of both the polarization and the angular momentum.

Tunable, high-power, high-order optical vortex beam generation in the mid-infrared.

We report the generation of tunable high-order optical vortices in the mid-infrared (mid-IR) using a picosecond optical parametric oscillator (OPO). The OPO is based on MgO:PPLN as the nonlinear gain medium and synchronously pumped by a mode-locked Yb-fiber laser at 1064 nm. Using a singly-resonant oscillator configuration for the OPO, we have achieved direct transfer of pump optical vortices to the non-resonant idler beam, with the resonant signal in the Gaussian cavity mode. We demonstrate the successful transfer of pump optical vortices of order, lp = 1 to 5, to the idler beam of the same order across the mid-IR, with an output power of 630 mW to 130 mW across 2538 nm to 4035 nm for the highest idler vortex order, li = 5. To the best of our knowledge, this is the first report of an OPO pumped by a vortex beam of order as high as lp = 5 and generating idler vortices of high order in the mid-IR.

Direct generation of optical vortex beams with tunable topological charges up to 18th using an axicon

The optical vortex beam carrying an orbital angular momentum is of great significance for many applications. Many approaches to generate optical vortex beams have been demonstrated, however they still suffer from some drawbacks such as low conversion efficiency, poor beam quality and so on. Thus, how to produce the high beam quality vortex beams with high topological charges is still a challenge for us. In this work, a convenient method for generation and tunability of Laguerre-gaussian (LG) vortex beams by using an axicon has been demonstrated. The high beam quality LG0,m vortex beams with tunable topological charges up to 18th order are achieved. An axicon combined with a focused lens can transform the Bessel beam into an annular beam efficiently, which can be employed to reshape the pump beam. An effective theoretical model has been present to predict the threshold pump power of each LG0,m vortex beam in this compact LD-end-pumped Nd:YVO4 laser.

Generation of optical vortex beam by surface-processed photonic-crystal surface-emitting lasers.

An optical vortex beam possesses a phase singularity that causes a null intensity at the center of the beam, and can be explained as a superposition of a phase distribution along the azimuthal direction and a plane wave. Here, we process the surface of a photonic-crystal surface-emitting laser (PCSEL) to generate an optical vortex beam. By using an eight-segmented phase plate fabricated via three chemical etching steps, a beam having null intensity is obtained. From evaluation of the beam's polarization and interference patterns, we show that the null intensity comes from the phase singularity of the optical vortex.

Fast fabrication of optical vortex generators by femtosecond laser ablation

Fast fabrication of micro-optical elements for generation of optical vortex beams based on the q-plate design is demonstrated by femtosecond (fs) laser ablation of gold film on glass. Q-plates with diameter of ∼0.5 mm were made in ∼1 min using galvanometric scanners with writing speed of 5 mm/s. Period of gratings of 0.8μm and groove width of 250 nm were achieved using fs-laser ablation at λ=343 nm wavelength. Phase and intensity analysis of optical vortex generators was carried out at 633 nm wavelength and confirmed the designed performance. Efficiency of spin–orbital conversion of the q-plates made by ablation of 50-nm-thick film of gold was ∼3%. Such gratings can withstand thermal annealing up to 800 °C. They can be used as optical vortex generators using post-selection of polarisation.

Recent advances on optical vortex generation

Abstract This article reviews recent progress leading to the generation of optical vortex beams. After introducing the basics of optical vortex beams and their promising applications, we summarized different approaches for optical vortex generation by discrete components and laser cavities. We place particular emphasis on the recent development of vortex generation by the planar phase plates, which are able to engineer a spiral phasefront via dynamic or geometric phase in nanoscale, and highlight the independent operation of these two different phases which leads to a multifunctional optical vortex beam generation and independent spin-orbit interaction. We also introduced the recent progress on vortex lasing, including vortex beam generation from the output of bulk lasers by modification of conventional laser cavities with phase elements and from integrated on-chip microlasers. Similar approaches are also applied to generate fractional vortex beams carrying fractional topological charge. The advanced technology and approaches on design and nanofabrications enable multiple vortex beams generation from a single device via multiplexing, multicasting, and vortex array, open up opportunities for applications on data processing, information encoding/decoding, communication and parallel data processing, and micromanipulations.

Direct generation of an optical vortex beam from a diode-pumped Yb:MgWO4 laser

We report for the first time, to the best of our knowledge, the generation of a multi-watt optical vortex beam based on a novel monoclinic Yb3+-doped MgWO4 crystal. The robust first-order Laguerre–Gaussian doughnut beam (LG01) with high mode purity and good beam quality can be selectively excited without using any intra-cavity handedness-selective element. Our results demonstrate the potential of the Yb:MgWO4 crystal for generation of high-power optical vortex beams from compact solid-state lasers.

Volumetric Generation of Optical Vortices with Metasurfaces

Recent advances in metasurfaces, i.e., two-dimensional arrays of engineered nanoscale inclusions that are assembled onto a surface, have revolutionized the way to control electromagnetic waves with ultrathin, compact components. The generation of optical vortex beams, which carry orbital angular momentum, has emerged as a vital approach to applications ranging from high-capacity optical communication to parallel laser fabrication. However, the typically bulky elements used for the generation of optical vortices impose a fundamental limit toward on-chip integration with subwavelength footprints. Here, we investigate and experimentally demonstrate a three-dimensional volumetric optical vortices generation based on light–matter interaction with a high-efficiency dielectric metasurface. By employing the concepts of Dammann vortex gratings and spiral Dammann zone plates, a 3D optical vortex array with micrometer spatial separation is achieved from visible to near-infrared wavelengths. Importantly, we show that...

Generation of singular optical beams from fundamental Gaussian beam using Sagnac interferometer

We propose a simple free-space optics recipe for the controlled generation of optical vortex beams with a vortex dipole or a single charge vortex, using an inherently stable Sagnac interferometer. We investigate the role played by the amplitude and phase differences in generating higher-order Gaussian beams from the fundamental Gaussian mode. Our simulation results reveal how important the control of both the amplitude and the phase difference between superposing beams is to achieving optical vortex beams. The creation of a vortex dipole from null interference is unveiled through the introduction of a lateral shear and a radial phase difference between two out-of-phase Gaussian beams. A stable and high quality optical vortex beam, equivalent to the first-order Laguerre–Gaussian beam, is synthesized by coupling lateral shear with linear phase difference, introduced orthogonal to the shear between two out-of-phase Gaussian beams.

Subwavelength grating based metal-oxide nano-hair structures for optical vortex generation.

An all-dielectric, subwavelength grated based metal-oxide nano-hair structure for optical vortex beam generation has been presented in the paper. The nano-hair structure fabricated with alternating layers of alumina/hafnia on a fused silica substrate has a high diffraction efficiency of ~90% around the design wavelength, λ(o) = 1.55 μm and is insensitive to the polarization of the incident optical beam. The phase in transmission of these devices are controlled by azimuthally varying the fill fraction of the subwavelength grating. Realization of phase optical elements in an all-dielectric platform, based on subwavelength gratings offering full 0-2π phase modulation, is important for miniaturization and integration of conventional refractive optical elements.

Dielectric Meta-Reflectarray for Broadband Linear Polarization Conversion and Optical Vortex Generation

Plasmonic metasurfaces have recently attracted much attention due to their ability to abruptly change the phase of light, allowing subwavelength optical elements for polarization and wavefront control. However, most previously demonstrated metasurface designs suffer from low coupling efficiency and are based on metallic resonators, leading to ohmic loss. Here, we present an alternative approach to plasmonic metasurfaces by replacing the metallic resonators with high-refractive-index silicon cut-wires in combination with a silver ground plane. We experimentally demonstrate that this meta-reflectarray can be used to realize linear polarization conversion with more than 98% conversion efficiency over a 200 nm bandwidth in the short-wavelength infrared band. We also demonstrate optical vortex beam generation using a meta-reflectarray with an azimuthally varied phase profile. The vortex beam generation is shown to have high efficiency over a wavelength range from 1500 to 1600 nm. The use of dielectric resonators in place of their plasmonic counterparts could pave the way for ultraefficient metasurface-based devices at high frequencies.

Generation and interferometric analysis of high charge optical vortices

We report on the generation of optical vortex beams using spatial phase modulation with spiral phase mirrors. The spiral phase mirrors are manufactured by direct machining with an ultra-precision single point diamond turning lathe. The imperfection of the machined phase mirrors and its impact on the generated vortex beams are analyzed with interferometric measurements. Our phase mirror has a surface roughness of 3 nm and a maximum peak–valley deviation of λ/30. The vortex charges of our light beams are directly verified by counting the fringes of their corresponding interferograms. We directly observed the successful generation of an optical vortex beam with a charge as high as 5050. We study the Fourier images of the vortex beams to characterize the quality of the beams. We obtained a conversion efficiency of 92.8% from a TEM00 beam to a vortex beam with charge 1020. This technique of generating optical singularities can potentially be used to produce more complex optical wavefronts, such as optical knots.

Effects of misalignments in the optical vortex transformation performed by holograms with embedded phase singularity

Spatial characteristics of diffracted beams produced by a “fork” hologram from an incident circular Laguerre–Gaussian beam whose axis differs from the hologram optical axis are studied theoretically. General analytical representations for the complex amplitude distribution of a diffracted beam are derived in terms of superposition of Kummer beams or hypergeometric–Gaussian beams. The diffracted beam structure is determined by combination of the “proper” topological charge m of the incident vortex beam and the topological charge l of the singularity “imparted” by the hologram. Evolution of the diffracted beam structure is studied in detail for several combinations of m and l and for various incident beam displacements with respect to the optical axis of the hologram. Variations of the intensity and phase distribution due to the incident beam misalignment are investigated and possible applications for the purposeful optical vortex beam generation and optical measurements are discussed.

Generation of Optical Vortex Beams by NonlinearWave Mixing

It is shown that optical vortex beams can be generated from a non-vortex fundamental beam by an optical frequency conversion process taking place within a twisted nonlinear photonic crystal. This is done without any first-order (linear) refractive optics. Through such a proposed structure, all-optical switching of vortices with different helicities is made possible, as well as the simultaneous application of counter-rotating vortex beams of different frequencies.

Wavelength-scalable micro-fabricated wedge for generation of optical vortex beam in optical manipulation

An optical wedge phase plate is fabricated for the study of vortex beam generation in optical manipulation. It is demonstrated that the wedge phase element provides scalability for generating the vortex beam at different wavelengths as long as the incident beam size is adjusted accordingly. The presence of singularity for different wavelengths and the associated orbital angular momentum are confirmed experimentally in optical manipulation.