Nondiffracting Beams Research Articles

A Compound Phase-Modulated Beam Splitter to Distinguish Both Spin and Orbital Angular Momentum

Based on a phase-modulated metallic nanoslit array, an angular momentum (AM) beam splitter has been demonstrated to distinguish both spin and orbital components carried by the light beam. With such a device, the AM modes could be coupled into nondiffracting surface plasmonic beams propagating toward different directions. According to the experimental results, the extinction ratio for spin AM beam splitting is larger than 10 and the spatial interval of adjacent orbital AM modes (with a topological charge interval of 2) is more than 1.1 μm. We believe that such a device would have great potential to achieve a highly compact photonic integrated circuit with the plasmonic beam.

Self-aligning CMOS photodetector sensor for application on an NDB-based optical encoder

In this work, a complementary metal-oxide-semiconductor (CMOS) photodetector specifically designed to be used in a non-diffracting-beam (NDB) optical encoder is introduced. The sensor is aimed to address the critical alignment of the NDB-based optical encoder head and consists of a hexagonal array of photodiodes that can be interconnected among themselves. The photodiodes' interconnection is configured by means of static random access memory (SRAM) cells and transistors that operate as configurable connection switches between each photodiode and three of its neighbor photodiodes. This feature of the photodetector makes it possible to implement a search algorithm in order to find the photodiode where the NDB center impinges and then configure the appropriate detectivity pattern centered on that photodiode. It is shown that the new sensor design remarkably simplifies the alignment of the system.

Divide and conquer algorithm for nondiffracting beams.

We put forward a robust technique to encode a plethora of arbitrary images as nondiffracting beams by optimizing their respective phase components. This technique works directly under the constraint of a ring of infinitesimal width in Fourier space. The procedure reported is based on a stochastic direct search and global optimization: the differential evolution method. Unlike previous methods reported, the present approach is also able to optimize the spatial frequency of the image used. Remarkably, this technique also demonstrates that it is possible to encode even more arbitrary images on demand into nondiffracting forms by allowing a segmentation of the profile. We provide some codes to generate nondiffracting beams by using this algorithm.

Creation of an ultralong non-diffracting magnetization light beam with multiple energy oscillations using the inverse Faraday effect.

Diffraction and scatter effects are two big challenges that make the magnetization induced by a light beam endure a finite propagation distance and vulnerable to the defect of magneto-optic film. Here we propose a method to overcome both challenges by creating an ultralong non-diffracting (UND) magnetization light beam with multiple energy oscillations. By simply increasing the number of energy oscillations using the optical pen, the magnetization light beam can propagate over an ultralong distance without significant divergence. Besides, as a kind of non-diffracting light beam, this magnetization light beam possesses the property of self-healing, which makes it robust to the scatter effect. This Letter demonstrates for the first time, to the best of our knowledge, the creation of an UND magnetization beam, which may open a new avenue for high-density all-optical magnetic recording and atomic trapping, as well as confocal and magnetic resonance microscopy.

On the beam shape coefficients of fundamental nondiffracting beams

In generalized Lorenz–Mie theory (GLMT) applied to structured beams the evaluation of beam shape coefficients (BSCs) constitutes a challenge. In this paper, we propose to calculate BSCs of fundamental nondiffracting beams, cosine beams, Bessel beams, Mathieu beams and parabolic beams. The aim of our method is the use of the Whittaker integral related to a scalar nondiffracting beam, and well known angular spectrum decomposition. Also, we exploit the relationship between solutions of scalar Helmholtz equation to expand the BSCs of nondiffracting beams in terms of higher order Bessel Beams (HOBB) BSCs. Some numerical simulations and discussions are given to validate our results.

Research on the special bottle beam generated by asymmetric elliptical Gaussian beams through an axicon-lens system

A special bottle beam was obtained by shaping the elliptical Gaussian beam through an axicon optical system. When elliptical Gaussian beams have a different eccentricity (σ = 0, 0.3, 0.6, 0.9), the optical field distribution after axicon and the focusing lens was investigated. By comparison with a circular Gaussian beam, this asymmetry leads to the formation of a non-diffracting beam from a quasi-Bessel beam characteristic to a quasi-Mathieu beam characteristic after the incident axicon. At the same time, the bottle beams produced by the asymmetric light source incident on the axicon-lens system showed changes in the front and rear sides. In addition, the variation of the diffraction spot in the optical space region on the bottle beam axis was also analyzed. On this basis, a hollow light spot tweezer with “quasi-Pearcey beam handle” was obtained, which is expected to expand the application of particle trapping operation.

Characteristics of non-diffractive beam generation related to concentration and propagation distance in highly random media

Laser beam propagation in highly random media can potentially be applied to various optical studies, though the light penetration is often limited to the surface or skin regions of the targets. In free space, it is known that the use of a non-diffractive beam (Bessel beam) is useful for achieving a long-distance propagation by reducing the influence of diffraction. In our previous work [Z. Peng, and T. Shiina, Opt. Commun. 391, 94–99 (2017)], the generation and propagation of such a non-diffractive beam were studied in a scattering medium of colloidal suspension (diluted milk) up to the concentration of 1.2% using cell lengths between 10 and 30 cm. The transformation from an annular beam to a non-diffractive beam was observed using a detector with a narrow view angle of 5.5 mrad. In the present study, experimental results are reported for much higher concentrations using shorter cell lengths of 3 and 5 cm. It is found that a non-diffractive beam is generated as a central peak superposed on widely distributed intensity due to multiple scattering. The polarization property is preserved during the transformation from annular ring to central peak. At the propagation distance of 3 cm, the intensity of non-diffractive beam is maximized with a high media concentration of 22.0% which yields the scattering coefficient of 5 cm−1. Furthermore, it is found that the media concentration range that leads to the generation of the non-diffractive beam becomes wider for such shorter propagation distances.

Method to Remove Tilt-to-Length Coupling Caused by Interference of Flat-Top Beam and Gaussian Beam

We discuss the tilt-to-length (TTL) coupling noise caused by interference between a flat-top beam and a Gaussian beam. Several physical models are presented to research the effects of non-diffracted and diffracted beams on TTL noise. A special case that can remove TTL coupling noise is discovered and is verified via both theoretical analysis and numerical simulations. The proposed case could provide desirable suggestions for the construction of high-precision interferometers such as the Laser Interferometer Space Antenna (LISA), Taiji program, or other interferometry systems.

Finite-energy Airy-Lorentz-Gaussian beam and its paraxial propagation.

We theoretically propose a new form of laser beam, named the finite-energy Airy-Lorentz-Gaussian (ALG) beam, which can be decomposed into an exponentially modified Airy function in the x direction and a Lorentz-Gaussian function in the y direction. Based on the Huygens diffraction integral formula, an analytical propagation expression for the finite-energy ALG beam passing through a paraxial ABCD optical system has been derived. For special cases, the propagation properties of the finite-energy ALG beam through the free space, a thin lens, and a fractional Fourier transformation (FrFT) system are studied numerically and graphically. Our results provide an effective and alternative way to describe the finite-energy non-diffracting light beams.

Dynamical Manipulation of Surface Plasmon Polaritons

As the fundamental and promising branch of nanophotonics, surface plasmon polaritons (SPP) with the ability of manipulating the electromagnetic field on the subwavelength scale are of interest to a wide spectrum of scientists. Composed of metallic or dielectric structures whose shape and position are carefully engineered on the metal surface, traditional SPP devices are generally static and lack tunability. Dynamical manipulation of SPP is meaningful in both fundamental research and practical applications. In this article, the achievements in dynamical SPP excitation, SPP focusing, SPP vortex, and SPP nondiffracting beams are presented. The mechanisms of dynamical SPP devices are revealed and compared, and future perspectives are discussed.

Reflected acoustic wavefront manipulation by an ultrathin metasurface based on three-dimensional generalized Snell’s law

We theoretically derive three-dimensional (3D) generalized Snell’s law which is demonstrated by reflected wavefront manipulations based on ultrathin quasi-3D acoustic metasurfaces. Acoustic metasurfaces with a deep subwavelength thickness of λ/10 are constructed with 16 unit cells composed of a straight pipe and two ring-like Helmholtz resonators. Based on the 3D generalized Snell’s law, many fascinating reflected wavefront manipulations in 3D space are realized separately, including anomalous reflections, point focusing, line focusing in two perpendicular directions, non-diffracting Bessel beam and self-bending beam. Our results provide a new design methodology for 3D sound wavefront manipulations and practical applications of 3D sound devices.

Diffractive gratings with varying period’s shape

Diffractive gratings with varying period’s shape

Momentum and energy considerations of a Bessel-Bessel laser bullet

A Bessel-Bessel laser bullet is the ultra-short and tightly-focused analogue of a non-diffracting and non-dispersing laser Bessel beam. Analytic investigation of the energy, linear momentum, energy flux, and angular momentum, associated with the fields of a Bessel-Bessel bullet, propagating in an under-dense plasma, is conducted in this work. The analytic results reported here are essential for the further understanding of the bullets and to their ultimate experimental realization and utilization in practical applications.

Generation of Nondiffracting Vector Beams with Ring-Shaped Plasmonic Metasurfaces

Optical nondiffracting vector beams, with their invariant transverse profiles and longitudinal polarization states, have drawn interest in many areas, from optical tweezers to imaging and metrology, but bulky optical components still limit their utilization. The authors design ultrathin, ring-shaped plasmonic metasurfaces to produce nondiffracting Bessel, Mathieu, and Weber vector beams across a broad wavelength range. These metasurfaces present a compact, effective platform for producing complex optical beams, and thus for advancing numerous applications related to conversion of spin and orbital angular momentum, optical manipulation, and optical communication.

Microfabrication of axicons by glass blowing at a wafer-level.

This Letter reports on the generation of glass-based axicons realized at the wafer level by means of microfabrication. The technique is based on micro glass blowing allowing parallel fabrication of numerous components at a time. Blowing is achieved due to cavities containing a gas that expands when the wafer stack is introduced in a furnace. Such cavities, generated in a silicon wafer and sealed by a bonded glass wafer, act as pistons pushing locally the other side of the glass wafer where the micro-optical component profile emerges. After cavities' removal by polishing, it is shown that such a component produces nondiffracting Bessel beams.

Design and studies on gradient index metasurfaces for broadband polarization-independent, subwavelength, and dichroic focusing.

This paper presents designs for and simulation studies on planar gradient index metasurfaces for polarization-independent and dichroic subwavelength focusing for broadband applications. Polarization-independent lenses are designed based on dielectric (Si3N4 and TiO2) gradient nanopillars. Dichroic metalenses are designed based on gradient aluminum nanohelices for helicity-dependent focusing of circularly polarized light. The helical shape is considered due to its sensitivity to circularly polarized light of a specific handedness depending upon the orientation of the helices in the lattice; this may help in 3D imaging. In the designed metalenses, the variation in the spatial dimension (fill factor) is in a gradient manner, which leads to directional bending of electromagnetic waves, and strong coupling between the bent electromagnetic waves leads to subwavelength focusing over the high numerical aperture. The designed metasurface can be materialized through multibeam interference using a combination of n plane beams and a nondiffracting Bessel beam of either zeroth or first order presented through the simulated irradiance profile and a proposed single-step experimental setup. The designed TiO2-based metalens focuses the incident arbitrary or plane polarized light to a spot sized 0.314λ, at a wavelength of 635 nm, that is based on Si3N4, enabling polarization-independent subwavelength focusing over a broad (436-810 nm) wavelength range. Realization of these lenses will enable polarization-independent high-numerical-aperture focusing and super-resolution real-time imaging of biological samples.

Wavelength and topological charge management along the axis of propagation of multichromatic non-diffracting beams

Wavelength is a fundamental property of light that dictates its linear momentum and thus remains unchanged under unguided free-space propagation. Similarly, light’s orbital angular momentum is another strictly conserved property determined by light’s quantized topological charge. Here, using a superposition of co-propagating Bessel beams with different wavenumbers, wavelengths, and topological charges, we construct a new class of non-diffracting multichromatic optical beams in which the wavelength (linear momentum) and the topological charge (orbital angular momentum) can be managed locally along the axis of propagation via controlled beating. Engineering light structures with customized longitudinal profiles of wavelength and charge can offer new degrees of freedom in materials processing, optical trapping, imaging, and dense data communications.

Generation of Non-diffraction Vortex Beam and Its Application in Digital Communication

An axicon-frustum basin-type Bessel resonator is designed for generating non-diffraction vortex beams with opposite propagation directions under different conditions. Based on the theory of geometric optics, the principle of creating vortex beams is analyzed in this axicon-frustum basin-shaped resonant cavity. It is shown that a non-diffraction vortex beam can be produced in the cavity under high-order beam stimulation. In the terahertz wavebands, the dyadic Green's function algorithm is used to numerically evaluate the electromagnetic characteristics in the cavity, and the numerical results demonstrate that the conclusion of the principle analysis is valid. Finally, the application of non-diffraction vortex beams in digital communication is explored.

Optical-trapping of a red Bessel beam controlled by co-propagating green Gaussian beam in azobenzene liquid crystal

Simultaneous co-propagation of red nondiffracting Bessel beam and green Gaussian beam at milliwatt powers in a photosensitive azobenzene liquid crystal has been studied. The fine displacement of the narrow-width Gaussian beam relative to the Bessel beam central maximum showed the Bessel beam distortion and controlled bending of its core in the direction opposite to the location of green Gaussian beam. After switching off the green beam, the dynamics of restoration of Bessel beam demonstrated the pronounced optical-trapping feature of its central core and transient soliton-like propagation with reduced diameter and increased intensity and propagation depth thus forming a waveguiding channel.

Multiple non-diffracting beams by reflective surface based on admittance superposition

A method to produce multiple nondiffracting beams by a reflective metasurface is introduced. The reflective metasurface is realized by admittance superposition modulation. Only one artificial admittance surface can generate a single nondiffracting beam. The admittance superposition of multiple surfaces will produce multiple beams, which can propagate in different directions with good nondiffracting properties. Finally, the metasurface is fabricated and experimentally tested, and the results demonstrate that the design is logical. The multiple nondiffracting beams may have potential applications in imaging, multipoint communications, and object detection and identification.