pseudo-Bessel Beams Research Articles

Generation of Multiple Pseudo Bessel Beams with Accurately Controllable Propagation Directions and High Efficiency Using a Reflective Metasurface

In this paper, a generation method procedure based on a reflective metasurface is proposed to generate multiple pseudo Bessel beams with accurately controllable propagation directions and high efficiency. Firstly, by adjusting the miniaturized unit cell of the reflective metasurface to modulate the electromagnetic waves using the proposed method, some off-axis pseudo Bessel beams with different propagation directions are generated. Then, by achieving the large-angle deflection and comparing the results with previous existing methods, the superiority of the proposed method is demonstrated. Based on the generated single off-axis pseudo Bessel beam and the superposition principle of the electromagnetic wave, a reflective metasurface with 47 × 47 elements is designed and fabricated at 10 GHz to generate dual pseudo Bessel beams. Full-wave simulation and experimental measurement results validate that the dual pseudo Bessel beams were generated successfully. The propagation directions of the dual pseudo Bessel beams can be controlled accurately by the reflective metasurface, and the efficiency of the beams is 59.2% at a propagation distance of 400 mm. The energy of the beams keeps concentrating along the propagation axes, which provides a new choice for wireless power transfer and wireless communication with one source to multiple receiving targets.

THz Pseudo-Bessel Beam Generation Base on Axicon-frustum Antenna Array

An axicon-frustum antenna array was designed. Circular microstrip antenna with coaxial feeding was taken as an element to place on concentric rings at equal intervals, constructing a phased axicon-frustum antenna array, which were then simulated and optimized by Ansoft HFSS. The results showed this antenna array can not only radiate a 0-order narrow beam with stable gain, but also generate a high-order radiation pattern with orbital angular momentum, which was demonstrated as an axicon-frustum antenna array which can generate pseudo-Bessel beams.

Simultaneous Generation of Pseudo-Bessel Vortex Modes with a RLSA

This letter shows that it is possible to simultaneously generate, in the microwave frequency band, several pseudo-Bessel beams having an azimuthal field variation, characteristic of vortex modes, by making use of a single flat antenna. Specifically, a radial line slot array has been designed to prove the concept. The design benefits of a Butler matrix network to provide the correct phase progression along the azimuthal coordinate, and it makes use of a holographic approach to assure the required aperture field distribution.

Crossed fiber optic Bessel beams for curvilinear optofluidic transport of dielectric particles

Due to its unique non-diffracting and self-reconstructing nature, Bessel beams have been successfully adopted to trap multiple particles along the beam's axial direction. However, prior bulk-optic based Bessel beams have a fundamental form-factor limitation for in situ, in-vitro, and in-vivo applications. Here we present a novel implementation of Fourier optics along a single strand of hybrid optical fiber in a monolithic manner that can generate pseudo Bessel beam arrays in two-dimensional space. We successfully demonstrate unique optofluidic transport of the trapped dielectric particles along a curvilinear optical route by multiplexing the fiber optic pseudo Bessel beams. The proposed technique can form a new building block to realize reconfigurable optofluidic transportation of particulates that can break the limitations of both prior bulk-optic Bessel beam generation techniques and conventional microfluidic channels.

Generation of Bessel Beams by Two-Dimensional Antenna Arrays Using Sub-Sampled Distributions

Bessel beams are proposed as a practical way to generate well collimated and confined beams at mm-waves or THz for quasi-optical applications. To achieve that, we propose the use of two-dimensional antenna arrays as realizable launchers. Truncated Bessel beams with a main lobe width of few wavelengths $(\lambda)$ can propagate over several hundreds of $\lambda$ if the antenna aperture is electrically large. Because such a large aperture would require a large number of antenna elements, sub-sampling distributions are proposed in this work. It is found that arrays with spacings of approximately $4\lambda$ generate high quality beams with very low amplitude oscillations over distances of about $300\lambda$ in vacuum. The optimal excitation function for such arrays greatly departs from the Bessel one. It is synthesized with an analytical method based on a least mean square error minimization. The synthesis method is scalar, but the pseudo-Bessel beams obtained are vectorial and linearly polarized. Theoretical predictions are confirmed by full-wave simulations using Ansoft Designer.

Production of THz pseudo-Bessel beams with uniform axial intensity using irregular binary axicons

To produce THz pseudo-Bessel beam with uniform axial intensity distribution within a desired range, an irregular binary axicon (IBA) is proposed and designed in the authors' paper. Unlike a regular binary axicon (RBA) having the same prism angle, the IBA consists of concentric prism-like grooves with the different prism angles. It can be obtained from the RBA by an optimisation design. Comparison results demonstrate that within a specified region the on-axis intensity distributions of the pseudo-Bessel beams generated by the designed IBAs are much smoother than those produced by the RBAs.

Generation of pseudo-Bessel beams at THz frequencies by use of binary axicons

In order to miniaturize and integrate conveniently in THz quasi-optical systems, binary axicons, based on binary optical ideas, are introduced in our paper and designed for generating pseudo-Bessel beams at THz frequencies. The designed binary axicons are easier to fabricate than holographic axicons, more compact and thus less lossy in the material when compared with classical cone axicons. To calculate the electromagnetic fields diffracted by binary axicons precisely, a two-dimension finite-difference time-domain (2-D FDTD) method in conjunction with Stratton- Chu formulas are employed in this paper. Applying this method, the properties of pseudo-Bessel beams produced by binary axicons are analyzed, and a brief summary is given in the end.

Dual-Wavelength Membrane-Based Diffractive Optical Element with Extended Depth-of-Focus for Optical Pickup Head

An improved structure and optimization method for a high-numerical-aperture application for optical pickup heads that uses a low-stress silicon–nitride-membrane-based diffractive optical element to generate dual-wavelength pseudo-Bessel beams is described in this paper. The dual-wavelength membrane-type diffractive optical element with an extended focal depth for next-generation optical pickup applications has been demonstrated. The theoretical simulation and fabrication results detailing the resolution, longer depth-of-focus and diffractive efficiency are presented for the newly designed membrane diffractive optical element (DOE). This implies that the problems of disc vibration as well as the assembly and optical alignment of the many elements are solved.

The quasi-optical analysis of Bessel beams in the far infrared

We discuss the Gaussian beam mode analysis of Bessel beams, eigen-solutions of the wave-equation in cylindrical polar coordinates which neither change form nor spread out as they propagate. Approximate, limited diffraction finite aperture, pseudo-Bessel beams having intense on-axis spots with large depths of field can be produced experimentally in the far infrared by using plastic conical lenses, known as axicons. We illustrate the physical insight provided by Gaussian beam mode analysis of such systems. Such pseudo-Bessel beams can be usefully approximated by high-order Gaussian–Laguerre modes, which have similar propagation characteristics. The size of the on-axis spot produced by an axicon, and its depth of focus, can be estimated from a single best-fit high-order Gaussian–Laguerre mode, and a more detailed description of behaviour can be achieved by adding a few additional modes of neighbouring orders. The strength of Gaussian beam mode analysis is that it is straightforward to model the propagation of Bessel beams through complex systems of long wavelength optical components, such as apertures, mirrors, and lenses. We report the experimental generation and measurement of a 0.1 THz Bessel beam, and show that useful performance is possible for an axicon having a scale size just one order of magnitude greater than the wavelength. This work confirms the technical feasibility of designing and building long-wavelength optical systems based on Bessel beams.