Generation Of Bessel Beams Research Articles

Terahertz Bessel beam generator.

The Bessel beam has broad application prospects in wireless energy transmission and high-speed communications. The traditional Bessel beam generation method has the problems of large volume, low efficiency, and complex manufacturing. To solve the above problems, we present a terahertz Bessel beam generator based on the reflective metasurface, which is composed of a metal pattern, dielectric layer, and bottom metal plate. Under the incidence of right circularly polarized (RCP) wave, the zero-order Bessel beam and zero-order symmetric double Bessel beam are generated. It can be found that the bottom angle of the axicon of the first-order Bessel beam is inversely proportional to the propagation distance of the Bessel beam. Comparing the electric field intensity distribution, phase distribution, and mode purity of the second-order Bessel beam and the second-order vortex beam in different observation planes, it can be seen that the energy of the higher-order Bessel beam is more concentrated and the field distribution is more stable than those of the ordinary vortex beam. The reflective terahertz Bessel beam generator has potential application value in terahertz wireless communications, measurement, radar detection, and imaging.

Wavelength-Independent Excitation Bessel Beams for High-Resolution and Deep Focus Imaging.

Bessel beams are attaining keen interest in the current era considering their unique non-diffractive, self-healing nature and their diverse applications spanning over a broad spectral range of microwave to optical frequencies. However, conventional generators are not only bulky and complex but are also limited in terms of numerical aperture (NA) and efficiency. In this study, we experimentally develop a wavelength-independent Bessel beam generator through custom-designed metasurfaces to accomplish high resolution and large depth-of-focus imaging. These meta-axicons exhibit a high NA of up to 0.7 with an ability to generate Bessel beams with a full width at half maximum (FWHM) of 300 nm (~λ/2) and a depth of focus (DOF) of 153 μm (~261λ) in a broad spectral range of 500-700 nm. This excitation approach can provide a promising avenue for cutting-edge technology and applications related to Bessel beams for imaging along with a high axial resolution and an ultra-large depth of focus.

High-efficiency ultrathin metasurfaces with simultaneous control of complete phase, amplitude, and polarization.

Metasurfaces that can simultaneously manipulate both amplitude and phase have garnered interest and have promising applications owing to their strong beam-steering ability; however, achieving a high maximum transmission while covering the full phase shift remains challenging. This paper proposes a chiral-structured meta-atom composed of two external cross-polarized patches and an internal coupling structure. It enables the independent modulation of the phase, amplitude, and polarization at large incidence angles and ensures a high maximum transmission with a complete phase shift enabled by the two internal rotation structures. The transmission phase and amplitude can be independently controlled by adjusting the geometry and rotation angle of the meta-atoms. The performance and feasibility of the method were verified using an ultra-thin high-order Bessel beam generator sample with a thickness of 2 mm (about λ0/11 at 14 GHz). This design can meet arbitrary requirements for extreme beam steering and has broad application prospects in the fields of electromagnetism and photonics.

Spin-multiplexed full-space trifunctional terahertz metasurface [Invited

The widespread use of multifunctional metasurfaces has started to revolutionize conventional electromagnetic devices due to their unprecedented capabilities and exceedingly low losses. Specifically, geometric metasurfaces that utilize spatially varied single-celled elements to impart arbitrary phase modulation under circularly polarized (CP) waves have attracted more attention. However, the geometric phase has intrinsically opposite signs for two spins, resulting in locked and mirrored functionalities for the right-handed and left-handed CP beams. Additionally, the demonstrated geometric metasurfaces so far have been limited to operating in either transmission or reflection modes at a single wavelength. Here, we propose a double-layered metasurface composed of complementary elliptical and reversal ring resonator structures to achieve simultaneous and independent control of the reflection and transmission of CP waves at two independent terahertz frequencies, which integrates three functions of reflected beam deflection, reflected Bessel beam generation, and transmitted beam focusing on the whole space. The high efficiency and simple design of our metasurface will open new avenues for integrated terahertz metadevices with advanced functionalities.

High-Order Bessel Beam Generator with High Laser-Induced Damage Threshold Fabricated by Femtosecond Laser

High-Order Bessel Beam Generator with High Laser-Induced Damage Threshold Fabricated by Femtosecond Laser

Moiré meta-device for flexibly controlled Bessel beam generation

High-order Bessel beams are of great interest for most stable long-range optical quantum communications due to their unique nondiffraction, self-healing, and orbital angular-momentum-carrying capabilities. Until now, metasurfaces based on Bessel beam generators are mostly static and focused on generating zero-order Bessel beams. A moiré meta-device made of two cascaded metasurfaces is a simple, effective strategy to dynamically manipulate the wavefront of electromagnetic (EM) waves by mutual rotation between the two metasurfaces. Here, an all-dielectric moiré meta-device integrated with the functions of an axicon and a spiral phase plate to generate terahertz Bessel beams is designed. Not only the order, but also the nondiffraction length of the generated Bessel beam can be continuously tuned. As a proof of concept of the feasibility of the platform, the case of tuning order is experimentally demonstrated. The experimental results are in good agreement with the theoretical expectations. In addition, we also numerically proved that the nondiffraction length of the Bessel beam can be adjusted with the same approach. The moiré meta-device platform is powerful in dynamically manipulating the wavefront of EM waves and provides an effective strategy for continuously controlling the properties of the Bessel beam, which may find applications in optical communications, particle manipulation, and super-resolution imaging.

Nondestructive evaluation (NDE) of multilayered attenuative structures using ultrasonic Bessel beams

In this article Nondestructive Evaluation (NDE) of structures with attenuative coating or a layer of thermal protection system is presented utilizing various designs of acoustic axicons. Generation of ultrasonic Bessel beam in single-layered and multi-layered structures to overcome the ultrasonic attenuation is discussed. The possible modulation and the effective increase of the acoustic energy inside the attenuative layer are investigated using axicons, which are proposed to be an ad-hoc element to the existing ultrasonic transducers. Upon confirming the existence and generation of the ultrasonic Bessel beam in an arbitrary host media the spatial intensity distribution of the zeroth-order Bessel beam is studied. Further, we show how the generated Bessels beams propagate and penetrate deep inside the multi-layered structures comprising of different material properties. It is shown that the intensity of the Bessel beams and their possible deep penetration capabilities are altered when the geometrical properties of the axicon and material properties of the media are changed. We also report the numerical characterization of the different degrees of Bessel beams with a unique multi-annular shaped axicon. Modulating the axicon angles and the geometry, the long-distance propagation of the Bessel beam is ensured. Such beam can correspond to the field of Nondestructive Evaluation (NDE) for investigating materials with attenuative layers.

Two-dimensional differential null interferometry of transmission wavefront of axicon lens

Axicon lenses are critical in the beam transforming, such as the Bessel beam and hollow beam generation, and its manufacturing accuracy directly affects the quality of the output beam. Aiming at the versatility and high accuracy, we propose a two-dimensional differential null interferometry for measuring transmission wavefront of axicon lens. The method uses a pair of axicon lens to construct a null interferometric setup, with one as the compensator. The two-dimensional difference separates the wavefront information introduced by the compensator and achieves the orthogonal difference of the measured wavefront. Finally, the measured wavefront is reconstructed from the differential wavefront based on the Hudgin slope method. The experiments proved that this method achieves a measurement accuracy of ±0.125 µm with a repeatability of 0.759 nm.

Generation of arbitrary vector Bessel beams on higher-order Poincaré spheres with an all-dielectric metasurface

Vector Bessel beams may have a spatially varying polarization state combined with a Bessel-type transversal intensity profile. Such beams can carry both spin angular momentum and orbital angular momentum (OAM) and be characterized by points on higher-order Poincar\'e (HOP) spheres. We report a method to produce vector Bessel beams on any point of a HOP sphere of any topological charge by utilizing only a single all-dielectric planar metasurface. Specifically, by a proper choice of the input polarization and distance from the metasurface, the entire HOP sphere surface can be covered. The proposed method is simple and efficient and applies to any $n\mathrm{th}$-order HOP sphere. Furthermore, it yields an extremely high OAM mode purity. Our paper demonstrates a robust approach for generating arbitrary high-quality vector Bessel beams and will likely inspire future applications ranging from optical manipulation to laser beam engineering.

Achieving a macroscopic Nondiffracting length from a microscopic All-fiber Bessel beam generator

The objectivesWe carried out a thorough parametric analysis by varying the dimension of the fiber optic Bessel-beam generator (BBG) to obtain the maximum a macroscopic nondiffracting length (NDL). BBG consisted of a single mode fiber (SMF) and serially concatenated coreless silica fiber (CSF), where multimode interference took place to shape the incoming fundamental LP01 mode to the Bessel-like mode propagating in water. Methodology usedFocusing on three wavelengths λ = 635 nm, 980 nm, and 1550 nm, we used the beam propagation method package for commercially available SMFs for each wavelength to find optimal CSF geometry. We also optimized the SMF parameters to increase the NDL further. Results obtainedUtilizing a simple all-fiber structure, we theoretically predicted that NDL in water reaching ~4 mm could be obtained from a microscopic fiber optic BBG. Their significanceThis result can be readily applied to optical manipulation of biological substances in aqueous solutions and laser material processing and imaging.

Creation of rotating spiral structures using interfering Bessel beams for optical manipulation

A simple and effective optical tweezer setup which uses the interference of two counter propagating Bessel beams is proposed and investigated. The potential energy of a Rayleigh particle in the generated interference patterns is numerically evaluated by writing a MATLAB code. A rigorous analytical treatment is also performed for verification of the numerical results. The results show that the generated patterns have a spiral structure. It is also found that these spiral patterns and consequently the trapped particles can be rotated about the axis of the patterns by introducing a phase difference between the two beams. The suggested setup is hoped to provide an effective way for guiding particles along the spiral trajectories, making a laser-driven micro- and nanomotor, measuring the torsional properties of biological molecules, and separating particles from a liquid mixture according to their mass, size, or refractive index.

Spatial Bessel-like beams along arbitrary convex trajectories based on a 3D-printed metasurface.

A 3D-printed all-dielectric metasurface is presented in this Letter which can generate an accelerating beam with a circularly symmetric non-spreading transverse profile that can propagate along arbitrary convex trajectories. The curved trajectory is mapped to the corresponding direct-space spatial phases by the basic cube units with different geometrical heights. The required phase distribution is derived in detail based on the enveloping theory of differential geometry and the Bessel beam generation method. A metasurface with a preset trajectory is simulated and measured to demonstrate the validity of the phase distribution calculated by the proposed theory. The full-wave simulation and measurement results verify that the Bessel-like beam whose intensity follows a curved (off-axis) trajectory can be produced by the proposed metasurface. The generated hybrid beam merges the advantages of non-accelerating and accelerating diffractive-free beams. Therefore, the proposed metasurface has great potential in ultrahigh-speed communication, secure communication, near-field imaging, wireless energy transmission applications, and so on. The all-dielectric characteristic provides the proposed metasurface with the competitive advantages of low cost and easy large-scale processing.

3D-printed fiber-based zeroth- and high-order Bessel beam generator

Bessel beams (BBs) have gained prominence thanks to their diffraction-free propagation and self-healing properties. These beams are conventionally generated using different approaches, namely by transforming a narrow circular beam with a lens, using axicons or holographic beam-shaping techniques. These methods involve space-consuming optics. To overcome this limitation, in the past, efforts have been made to create BBs directly from optical fibers. However, these solutions have limited capability to generate BBs with on-demand optical parameters and only focused on creating zeroth-order BBs. Here, we propose a photonic structure that uses stacked miniaturized optical elements 3D printed in a single step on the fiber facet. Our design allows for the generation of both zeroth- and high-order BBs and fully controllable tailoring of the beams’ parameters, such as their diffraction-free propagation distance or the width of their central peak or node. Remarkably, we report for the first time, to the best of our knowledge, the generation of high-order BBs from optical fibers. We expect our approach to be useful in applications such as optical and quantum communications, fiber-based sensors, microscopy, spectroscopy, and optical trapping.

Terahertz tight-focused Bessel beam generation and point-to-point focusing based on nonlocal diffraction engineering.

Metasurfaces transform the wavefront by spatially varying the amplitude or phase of the incoming beam. Instead of encoding such variation by subwavelength unit cells, it is achievable over diffraction engineering of supercell structures, which outperforms the unit-cell method when the spatial gradient is large. In addition to tight focusing, here we apply this method to achieve plane wave-to-Bessel beam transformation and point-to-point focusing at terahertz frequencies. The Bessel beam has a small beam waist (0.57λ) and long depth of focus (9.1λ) for subwavelength-resolution imaging over a long distance. The point-to-point focusing changes the divergence angle from 16° to 70°. Both devices are validated by numerical simulations and experimental results with good agreement.

High-Compactness Bessel Beam Emitters Based on Vertical-Cavity Surface-Emitting Lasers

The existing Bessel beam generators generally require bulk optics counterparts and additional spatial laser sources, which adds complexity and bulkiness to the system. In this work, we propose Bessel beam devices with high compactness based on vertical-cavity surface-emitting lasers (VCSELs) and microdielectric axicons made by Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> . The transparent microaxicons are fabricated by one-step direct writing of focused ion beam (FIB) on the surface of meticulously designed top-emitting VCSELs. Zero- and first-order Bessel beams are obtained by engineering the lasing modes of the VCSELs through simply adjusting the oxide aperture diameter. Even if the VCSEL device works at multimode, Bessel beams can still be realized. This method provides great compatibility with different VCSEL configurations and emitting wavelengths. Such high-compactness devices may enable advanced research and applications relevant to Bessel beams.

Characterization of white-light non-diffracting beams generated using a deformable mirror

White-light non-diffraction beams such as Airy beam and Bessel beam have potential applications in multispectral imaging and micromanipulation. Generation of white-light Airy beam and Bessel beam with high quality and high efficiency still remains challenging for conventional diffractive or refractive optics which suffers from significant chromatic dispersion. In this paper, both high-quality white-light Airy beam and Bessel beam are generated using a deformable mirror by modulating the incident LED beam with tunable cubic and conical wavefronts. The main lobe of the generated white-light non-diffraction beams does not suffer from chromatic dispersion along the propagation. The results also show that the generation of the white-light Bessel beam has higher requirements for spatial coherence than white-light Airy beams. Our work expands the understanding of the white-light non-diffraction beams and paves the way for the applications.

Generation and steering of airborne acoustic vortices with broadband electro-active spiral gratings

Acoustic beam shaping technology has flourished in the last decade, motivated by its important applications. For example, in the context of contactless manipulation, the use of structured ultrasonic fields has led to significant advances, such as the development of the acoustic tweezers based on the use of ultrasonic vortex beams. In this work, we present a powerful and efficient technique to structure acoustic fields based on the use of planar electro-active diffraction gratings, which can be tailored in practically arbitrary shapes. For this purpose, a lower electrode with the desired shape is printed on a circuit board and covered with an active ferroelectret film, whose metallized top surface acts as a continuous upper electrode. Importantly, these devices can be operated within a broad spectral range of ultrasonic frequencies. Two kinds of structured fields are demonstrated: a focused acoustic vortex and the simultaneous generation of multiple acoustic Bessel beams of different topological charges, well separated among each other along the propagation axis. In both cases, the main parameters of the field can be finely and continuously tuned by setting the operation frequency, which allows an axial steering of the vortices. Experimental results exhibit very good agreement with theoretical analysis and numerical simulations.

Propagation of double zero-order Bessel beam and its scattering properties to uniaxial anisotropic spheres

Based on the generalized Lorenz Mie theory, the propagation and scattering properties of a uniaxial anisotropic spherical particle illuminated separately by double zero-order Bessel beam with arbitrary propagation direction and polarization direction are studied. The propagation and scattering characteristics are compared with those of a uniaxial anisotropic spherical particle illuminated by a single zero-order Bessel beam. Using the orthogonal relation of the spherical vector wave function and coordinate rotation theorem, the expanded forms of double zero-order Bessel beams with arbitrary propagation direction and polarization direction are derived. The analytical expressions of the expansion coefficients are derived by the integral method. The expansion coefficients of total incident field are obtained through the vector superposition principle. Based on the Fourier transform and tangentially continuous boundary conditions, the internal electromagnetic field of the uniaxial anisotropic sphere is expanded in terms of the spherical vector wave function and the scattering coefficients are derived. By comparing the angular distribution of the radar cross section of the particle illuminated by single and double zero-order Bessel beam when degenerating into plane waves with those results given by the literature, the correctness of the theory and the program in this paper are both verified. The effects of the incidence angle, conic angle and polarization angle on angle distribution of the radar cross section are numerically analyzed. The theoretical and numerical results in this paper are expected to be used to study the scattering properties, particle size analysis and optical trapping for anisotropic particles, biological cells and other particles illuminated by multi-beams.

Substrate Integrated Waveguide Slot Array Antenna to Generate Bessel Beam With High Transverse Linear Polarization Purity

The transverse linearly polarized beam can maintain its polarization when reflected, which is important for a detection system. Most of the existing planar Bessel beam generators are implemented in a central feeding radial topology and hard to generate the Bessel beam with the transverse linear polarization. In this communication, a substrate integrated waveguide (SIW) slot array antenna is proposed to generate the transverse linearly polarized Bessel beam. The desired phase and amplitude distribution of the Bessel beam can be easily realized by such an array. With the inherent 0°/180° output phase of the comb-like divider considered, the desired 0°/180° phase distribution is implemented by placing adjacent slots on the opposite (0°) or the same side (180°) within a linear array and by employing adjacent linear arrays with the inverse (180°) or the same (0°) slot offset direction accordingly. The offset of the slot, as well as the tuning metalized vias within the comb-like divider, is modulated to generate the desired amplitude distribution. After reducing the influence of the rectangularly truncated aperture by adding a Gauss-tapered amplitude distribution, a transverse linearly polarized Bessel beam SIW slot array antenna is designed with more than 100 mm depth-of-field (DoF) and less than −25 dB cross polarization. To the best of our knowledge, it is the first design to generate the transverse linearly polarized Bessel beam by a planar array antenna.

Generation of Multiple High-Order Bessel Beams Carrying Different Orbital-Angular-Momentum Modes through an Anisotropic Holographic Impedance Metasurface

Conventional multiple vortex beams carrying different orbital-angular-momentum (OAM) modes propagating in different directions suffer from beam divergences along with the increasing transmission distance, which greatly limits their practical applications. This article presents a diffraction-resisting dual high-order Bessel-beam (DHOBB) generator based on an anisotropic holographic impedance metasurface (AHIM) operating at 30 and 30.5 GHz. By virtue of leaky-wave theory and the optical holographic principle, surface waves excited by a monopole antenna welded on the back of the metasurface can be modulated into nondiffractive DHOBBs. Different geometric parameters of the subwavelength meta-atoms can be mapped by the interference patterns between the reference surface waves and the desired beams. Furthermore, this designed single-layer anisotropic metasurface can be equivalent to the functionalities of spiral-phase-plate, refractive-hyperbolic, and axicon lenses synthetically utilized in the popular air-fed metasurface to generate HOBBs. Compared with the most popular air-fed metasurface, this design results in predominant performances of ultralow profile, easy fabrication, and integration with other electronic components and avoids alignment errors. Both simulated and measured results demonstrate that nondiffractive DHOBBs carrying different OAM modes can be generated by this designed AHIM. Nondiffractive DHOBBs with different Bessel orders with distinctive properties may open a window for wireless communications with multiarea coverage and multitarget radar detection.