2D Airy Beams Research Articles

Tailoring the Generalized 2D Airy Beam

Tailoring the Generalized 2D Airy Beam

Generation and regulation of two-dimensional autofocusing Airy beams based on holographic metasurfaces

This paper proposes a new method to generate a two-dimensional (2D) Airy beam and Airy autofocusing beam by using the scalar holographic metasurface with amplitude-phase modulation in the microwave band. The proposed holographic metasurface comprises subwavelength patch unit cells with a period of fewer than 1/8 wavelengths, which means that it has the finer sampling for electromagnetic waves and can simultaneously achieve precise modulations for the amplitude and phase of electromagnetic waves. Firstly, the 2D-Airy beam with quasi-non-diffraction and self-bending characteristics is generated, from which the holographic metasurface is designed to realize four different 2D-Airy beams with the same focus, achieving the 2D-Airy autofocusing beam in the microwave frequency. The holographic metasurface for Airy beam generation has high efficiency and an ultra-lower profile. Meanwhile, for applying the Airy beam in wireless power transfer (WPT), the efficiency of the generated Airy beam and Airy autofocusing beam is calculated for the first time in the microwave field. The simulation results show that the efficiency of the 2D-Airy beam can reach 66% at 150 ​mm away from the metasurface, while the efficiency of the 2D-Airy autofocusing beam at the focus, which is 280 ​mm from the metasurface, can reach 35%. The theoretical, simulated, and measured results show that the proposed method and holographic metasurfaces can flexibly achieve the special characteristics of self-autofocusing and self-bending Airy beams in the microwave domain, providing an effective path for wireless power transfer (WPT) scenario with radial obstructions.

Ultra-wideband two-dimensional Airy beam generation with an amplitude-tailorable metasurface.

Airy beams, accelerating optical beams with exotic properties of self-bending, self-healing and non-diffraction, are essential for a wide range of photonics applications. Recently, metasurfaces have provided an efficient platform for generating desired Airy beams within a thin thickness, but they suffer from the narrow bandwidth, especially for two-dimensional (2D) Airy beams. Here, we propose an amplitude-tailorable polarization-converting metasurface to enable ultra-wideband 2D Airy beam generation. The amplitude and phase profiles for the 2D Airy beam can be realized by tuning only the orientation of the multi-resonant meta-atom, which can operate in the range of 6.6 GHz to 23.7 GHz, or fractional bandwidth of 113%. An exemplary prototype is measured to validate the design principle, which is in agreement with the simulation results. The proposed method holds great promise for wavefront shaping, and may facilitate the uses of Airy beam for practical applications.

Generation and Modulation of a Two-Dimensional Airy Beam Based on a Holographic Tensor Metasurface

The Airy beam has the characteristics of nondiffraction, self-bending, and self-healing, so it is of great significance to wireless power transfer (WPT) and wireless communication in the radio-frequency (rf) field. This paper proposes the generation and modulation method of the two-dimensional (2D) Airy beams based on a holographic tensor metasurface, which can generate 2D Airy beams with different trajectories. A multidimensional controllable tensor metasurface unit operating at 10 GHz is designed to concentrate the electromagnetic energy to achieve the linearly polarized Airy beam. The unit with tiny size can also precisely regulate both the amplitude and the phase of the electromagnetic wave so that the high-performance 2D Airy beams can be generated by the holographic tensor metasurface in the microwave band. Meanwhile, the Airy beams with varying deflected angles are designed based on beam-steering theory to obtain different energy transmission trajectories for WPT. The simulation and measurement results show that the deflected 2D Airy beam still maintains the characteristics of nondiffraction and self-bending.

Scattering analysis of two-dimensional Airy beams by typical non-spherical particles.

The scattering of structured light beams by various particles is an important subject of research with myriad practical applications, such as the manipulation, measurement, and diagnosis of small particles. We carry out an analysis of the scattering of two-dimensional (2D) Airy beams by typical non-spherical particles. The electric and magnetic field vectors of the incident Airy beams are derived by introducing a vector potential in the Lorenz gauge. The scattered fields of the particles are obtained by utilizing the method of moments based on surface integral equations. Some numerical simulations for the scattering of 2D Airy beams by several selected non-spherical particles are performed and analyzed. Especially, a spheroidal particle is taken as an example, and the effects of various parameters describing the 2D Airy beams on its differential scattering cross section are examined. It is expected that this work will be helpful for understanding the interactions of 2D Airy beams with non-spherical particles and their further applications.

Generation of Airy beams with transmissive cross-polarization conversion metasurfaces

This paper present a 1D finite-energy Airy beam generator at 8.0 GHz using a transmissive metasurface composed of coupling-propagation-decoupling unit cells. The phase and amplitude of the cross-polarized transmitted waves can be controlled by changing the length of the stripline and the position of loaded shorting pins, respectively. Utilizing this property to reshape the field of transmitted waves in accordance with the desired phase and amplitude profile of 1D finite-energy Airy beams. The designed metasurface is fabricated to measure the quasi-nondiffraction and self-bending properties of the generated 1D Airy beams at 8.0 GHz. In addition, the presented Airy beams generator has a very thin thickness of 0.05 (≈2 mm). The measured results were found to be in good agreement with the simulated results. Thanks to the independent control of phase, amplitude and polarization, the designed unit cell can be used in structured light, beam shaping, and holography etc.

Generation of 2D Airy beams with switchable metasurfaces.

Airy beams exhibit intriguing characteristics, such as diffraction-free propagation, self-acceleration, and self-healing, which have aroused great research interest. However, the spatial light modulator that generates Airy beams has problems such as narrow operational bandwidth, high cost, poor phase discretization, and single realization function. In the visible region (λ∼532 nm), we proposed a switchable all-dielectric metasurface for generating transmissive and reflective two-dimensional (2D) Airy beams. The metasurface was mainly composed of titanium dioxide nanopillars and vanadium dioxide substrate. Based on the Pancharatnam-Berry phase principle, a high-efficient Airy beam can be generated by controlling the phase transition of vanadium dioxide and changing the polarization state of the incident light. The optimized optical intensity conversion efficiencies of the transmissive and reflective metasurfaces were as high as 97% and 70%, respectively. In the field of biomedical and applied physics, our designed switchable metasurface is expected to offer the possibility of creating compact optical and photonic platforms for efficient generation and dynamic modulation of optical beams and open up a novel path for the application of high-resolution optical imaging systems.

Terahertz Airy beam generated by Pancharatnam-Berry phases in guided wave-driven metasurfaces.

Metasurface antennas scatter traveling guided waves into spatial waves, which act as extendable subsources to overcome the size limitation on emission sources. With the use of a Pancharatnam-Berry phase metasurface stimulated by a circularly polarized wave in a waveguide, the local phase distributions of scattered spatial waves can be made consistent with those of an Airy beam, thereby allowing the generation of high-quality Airy beams. In a slab waveguide, circularly polarized waves are synthesized through superposition of in-plane transverse electric modes. Simulations demonstrate that a 20 mm × 20 mm footprint all-dielectric guided wave-driven metasurface generates a 2D Airy beam at a frequency of 0.6 THz. Furthermore, we employ a metasurface deposited on a strip waveguide to generate a 1D Airy beam under direct stimulation by the fundamental transverse electric mode. Our work not only provides a large-scale emitter, but it also suggests promising potential applications in on-chip imaging and holography.

Two-photon flow cytometry with laser scanning two-dimensional airy beams

Flow cytometry is an essential technique in biomedical discovery for cell counting, cell sorting, and biomarker detection. In vivo flow cytometers based on one-photon or two-photon excited fluorescence have been developed for over a decade. One drawback of the laser beam scanning two-photon flow cytometer is that the two-photon excitation volume is limited to the focal spot due to the short Rayleigh range of focused Gaussian beams. Hence, the sampling volume is much smaller than in one-photon flow cytometers, making it challenging to count or detect rare circulating cells in vivo. Non-diffracting light waves like Bessel beams and Airy beams have narrow intensity profiles with an effective spot size as small as several wavelengths, making them comparable to Gaussian beams. More significantly, the theoretical depth of field (propagation distance without diffraction) can be infinite, making them an ideal solution as a light source for scanning beam flow cytometry. The trade-off of using Airy beams rather than Gaussian beams is side lobes Airy beams have, which contribute to background noise. Two-photon excitation can reduce this noise, as the excitation efficiency is proportional to intensity squared. Therefore, we developed a two-photon flow cytometer using 2D Airy beams to form a light-sheet that intersects the blood vessel a microfluidic channel, which was used to model a blood vessel. The setup can successfully detect and count flowing fluorescent microspheres in a microchannel.

Generation and deflection control of a 2D Airy beam utilizing metasurfaces.

Self-accelerating optical Airy beams present attractive characteristics such as self-bending and non-diffraction, which have rendered this field a research hotspot in recent years. In this paper, the desired phase changes of the unit cell structure for the transmitted cross-polarized wave can be realized by modifying the rotation angle of the unit cell, while the amplitude can be modulated by changing the inner diameter R of the double layer split-ring resonator (SRR). As such, the amplitude and phase modulations can be performed simultaneously and independently to achieve the desired transmitted wave envelope. Furthermore, a novel, to the best of our knowledge, strategy of 2D Airy beam deflection control is also presented by simultaneously modifying the phase and amplitude of the envelope of the transmitted beam, and its feasibility is theoretically and experimentally demonstrated. Our proposed designs suggest high application potentials in the fields of optical particle manipulation, controllable wireless energy transmission, and complex terrain exploration.

Dynamical power flow and trapping-force properties of two-dimensional Airy-beam superpositions

Abruptly autofocusing beams have attracted more and more attention because of their potential applications in optical manipulation. Here, we not only experimentally and theoretically investigate dynamical propagation properties of two-dimensional (2D) Airy--beam superpositions in free space and disordered media, but also study their stability, dynamical power flow, and trapping force properties from a different point. 2D Airy-beam superpositions have superior stability and can easily control their autofocusing propagations and trapping forces through a changing number of superimposing beams, truncated factor, scale factor, initial position, and the angle between two wings of 2D Airy beams. Based on the analysis of the evolution of power flow and trapping force, it is demonstrated that 2D Airy-beam superpositions repeat many autofocusing propagations, leading to a series of focuses and stable trapping positions to appear in propagation. Compared to traditional autofocusing beams, i.e., circular Airy beams and one-dimensional Airy-beam superpositions, 2D Airy-beam superpositions can show a better optical trapping performance in theory. Moreover, we used 2D Airy-beam superpositions as an optical tweezer to trap particles in the experiment and quantitatively analyzed trapping force properties such as trap stiffness via the power spectra method. The experimental results further demonstrate that 2D Airy-beam superposition can show better optical trapping ability than the circular Airy beam. Our work provides a systematic understanding of the propagation and trapping properties of 2D Airy-beam superpositions in theory and experiment. It is helpful for the further applications of autofocusing beams on the optical tweezer, especially in biomedical research.

Compact broadband silicon-integrated Airy beam emitter.

Optical Airy beams have wide-ranging applications in photonics, but conventional approaches for generating Airy beams require bulky and strictly aligned optical systems. Here, we propose on-chip compact Airy beam emitters by using a shallow-etched holography grating on a silicon platform. The holography grating, formed by the binary interferogram of the guided wave and the spatial Airy beam, can scatter the guided waves into spatial waves with the phase distributions being consistent with those of Airy beam. The simulation demonstrates that a 20µm×20µm holography grating on a strip waveguide enables the realization of 2D Airy beam within the wavelength range from 1490 to 1570 nm. Our results suggest a promising avenue towards potential applications in on-chip imaging, optical forces, optical interconnection, etc.

New control scheme for a class of two-dimensional Airy beams in free space

We find a new class of Airy beams by combining in a distichous fashion two two-dimensional (2D) Airy beams propagating as counter-accelerating beams. To explore their unique characteristics, the distichous 2D Airy beams are constructed, their rotation factor is introduced, and the spatial distribution of their intensity when the rotation factor is a right, acute or obtuse angle, is discussed. The results show that the spatial distribution of the beams can be controlled by adjusting the rotation factor flexibly, and the intensity of the main lobe at the center of the beams can be greatly enhanced. This is of considerable significance for particle cleaning, using such beams as an "optical broom".

Cubic-Phase Metasurface for Three-Dimensional Optical Manipulation.

The optical tweezer is one of the important techniques for contactless manipulation in biological research to control the motion of tiny objects. For three-dimensional (3D) optical manipulation, shaped light beams have been widely used. Typically, spatial light modulators are used for shaping light fields. However, they suffer from bulky size, narrow operational bandwidth, and limitations of incident polarization states. Here, a cubic-phase dielectric metasurface, composed of GaN circular nanopillars, is designed and fabricated to generate a polarization-independent vertically accelerated two-dimensional (2D) Airy beam in the visible region. The distinctive propagation characteristics of a vertically accelerated 2D Airy beam, including non-diffraction, self-acceleration, and self-healing, are experimentally demonstrated. An optical manipulation system equipped with a cubic-phase metasurface is designed to perform 3D manipulation of microscale particles. Due to the high-intensity gradients and the reciprocal propagation trajectory of Airy beams, particles can be laterally shifted and guided along the axial direction. In addition, the performance of optical trapping is quantitatively evaluated by experimentally measured trapping stiffness. Our metasurface has great potential to shape light for compact systems in the field of physics and biological applications.

1D Self-Healing Beams in Integrated Silicon Photonics

Since the first experimental observation of optical Airy beams, various applications ranging from particle and cell micromanipulation to laser micromachining have exploited their non-diffracting and accelerating properties. The later discovery that Airy beams can self-heal after being blocked by an obstacle further proved their robustness to propagate under scattering and disordered environment. Here, we report the generation of Airy beams on an integrated silicon photonic chip and demonstrate that the on-chip 1D Airy beams preserve the same properties as the 2D beams. The 1D meta-optics used to create the Airy beam has the size of only 3 by 16 microns, at least three orders of magnitude smaller than the conventional optic. The on-chip self-healing beams demonstrated here could potentially enable diffraction-free light routing for on-chip optical networks and high-precision micromanipulation of bio-molecules on an integrated photonic chip.

An active energy compensation method of 2D Airy beam

An active amplitude-phase compensation method for energy flow convergence is derived. Here, we can actively interfere with the energy flow distribution of Airy beams (AiBs), without affecting their other excellent features, such as non-diffraction. Compared with the traditional method, distortion from phase term can be compensated by amplitude array, effectively converting the main lobes energy. In the process of light propagation, the rest intense lobes after modulating can still propagate without diffraction. Moreover, we demonstrate a variety of side lobes intensity patterns, providing diversity for optical tweeters technology.

Generation of a variety of Airy beams using a dynamic diffractive optical phase element

We demonstrate theoretically the generation of a variety of dynamic 2D Airy beams. We generate single, 2D dual-, and quad-Airy-like beams using a dynamic optical phase, obtained by the propagation of two crossed standing ultrasonic waves (UWs) in a liquid medium (water). These UWs create sinusoidal variation of the liquid medium refractive index in two dimensions. Using the asymptotic behavior of the sine function near zero, the 2D sinusoidal phase created by the piezoelectric transducer is reduced to a 2D periodic cubic phase. As it is known, the latter converts an input plane wave (Gaussian beam) into an Airy (Airy-like) beam in the far field. By acting on the dynamic optical phase parameters, one can change the characteristics of the obtained Airy beam (trajectory and acceleration). Using combined Gaussian beams, we clearly demonstrate the existence of a variety of combined dynamic Airy beams, such as Airy, dual-Airy, symmetric-Airy, anti-symmetric-Airy, and quad-Airy beams. We believe that the present work is of significant interest in the fields of dynamic focusing, curved manipulation, and transportation of microparticles.

Dual-Band Accelerating Beams Enabled Full Duplex Free-Space Optical Interconnection

High speed free-space optical interconnection (FSOI) is an effective strategy to overcome the bottleneck of short-reach electronic interconnection from chip scale to board level, due to its wide bandwidth, high energy efficiency, low latency and high interconnect density. Here, we propose an accelerating beam enabled reconfigurable FSOI scheme by harnessing its characteristics of diffraction-free, self-healing, and specifically designed trajectory. Then we experimentally demonstrate a proof-of-concept 100 Gbps full duplex FSOI enabled by dual-band 2D Airy beams over 40 cm free-space optical link with a receiver sensitivity of -17.3 dBm at bit error ratio (BER) of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> . Both O-band and C-band 2D Airy beams can be successfully generated and detected with the help of two C-band spatial light modulators (SLMs). In addition, we experimentally investigate the impact of an obstacle occurring at the free-space optical link on the BER performance. Our experimental results indicate that, the performance of accelerating beam based FSOI is superior to the conventional Gaussian beam enabled FSOI under the same free-space optical link condition.

Three-Airy autofocusing beams**Project supported by the National Natural Science Foundation of China (Grant No. 11604058), the Natural Science Foundation of Ningbo City, China (Grant No. ZX2015000617), the K C Wong Magna Fund in Ningbo University, China, and the Natural Science Foundation of Guangxi Zhuang Autonomous Region, China (Grant Nos. 2016GXNSFBA380244 and 2015GXNSFBA139011).

We numerically and experimentally demonstrate that a three-Airy autofocusing beam can be generated by superposing three deformed two-dimensional (2D) Airy beams with a triangle symmetry. When the initial angle between two wings of the deformed 2D Airy beams increases, such a three-Airy autofocusing beam exhibits that the focusing length decreases and the intensity contrast at the focal point changes. Moreover, after introducing an optical vortex phase, this three-Airy autofocusing beam displays a transverse rotation in propagation. The rotation angle is determined by the topological charge of the vortex and the initial wing angle. Our results may have some potential applications in optical manipulation.

All-optical control of pattern dynamics generated by Airy beams

We study a pattern-forming system driven by two counterpropagating 2D Airy beams in a nonlinear single feedback configuration. When increasing the Airy beam intensity, modulation instability takes place but with several successive instability thresholds that correspond to destabilization of the different Airy beam satellite lobes. Most importantly, the self-organization is accompanied by a natural drifting dynamics related to the intrinsic acceleration of the Airy beam. The drifting dynamics is controlled by the parameters of the Airy beam itself, once generated. Numerical simulations reproduce the experimental findings.