Array Beam Research Articles

Effect of Thermal Blooming on the Higher-Order Mode Fiber Laser Array Propagation Through the Atmosphere

The influence of thermal blooming on the propagation properties of higher-order mode (HOM) fiber laser array is studied by using the algorithm for simulating the laser beam propagation in the atmosphere. Based on the multiphase screen method and finite-difference method, the four-dimensional (4D) computer code of time-dependent propagation is designed to simulate the propagation of HOM fiber laser array through the atmosphere. In this study, the laser energy focusability of the LP11 mode beam array is investigated in detail for different beamlet arrangements, transverse wind speed, and the content of LP01 mode under the conditions of thermal blooming. In free space, the focal shape of the LP11 mode beam array depends on the arrangement of the second circle of the initial beam array, whereas the influence of the central beamlets is weak. The number of side lobes can be tailored by changing the arrangement of the beamlets. In contrast, under the conditions of thermal blooming, the central beamlet has a significant effect on focal beam shape. It is demonstrated that the laser energy focusability can be improved by rotating the central beamlet or increasing the transverse wind speed. As the content of the LP01 mode increases, the energy is gradually concentrated from the side lobes to the center lobe. Furthermore, the effects of initial beam array arrangements on the energy focus and focal shape are investigated. The optimal arrangement for obtaining high energy focusability is discussed in detail. These results could provide useful references for applications of the HOM beam array.

On-Demand Phase Control of a 7-Fiber Amplifiers Array with Neural Network and Quasi-Reinforcement Learning

We report a coherent beam combining technique using a specific quasi-reinforcement learning scheme. A neural network learned by this method enables the tailoring and locking of a tiled beam array on any phase map. We present the experimental implementation of on-demand phase control by a neural network in a seven-fiber laser array. This servo loop needs only six phase corrections to converge to the desired phase set at any profile, with a bandwidth higher than 1 kHz. Moreover, we demonstrate the dynamical feature of adaptive phase control, performing sequences of controlled phase sets. It is the first time, to the best of our knowledge, that an actual array of seven-fiber amplifiers has been successfully phase-locked and controlled by machine learning.

Numerical analyses of a spectral beam combining multiple Yb-doped fiber lasers for optimal beam quality and combining efficiency

Physical parameters of a spectral beam combining (SBC) system for multiple Yb-doped fiber lasers (YDFLs) were identified and numerically analyzed to obtain the optimal beam quality and the combining efficiency. We proposed an optimal range of the parameters that can be utilized in SBC systems. For a practical SBC system composed of a multi-layer dielectric grating and a transform mirror, we systematically varied input laser parameters such as the incident angle, beam diameter, laser linewidth, spectral spacing, number of beams, and their spatial separation. Characteristics of diffracted beams by the SBC system were numerically analyzed using a Fourier modal method (FMM). The beam quality M2 and the combining efficiency, η, were optimized by varying the laser beam parameters. We found that M2 and η were most affected by the angle of incidence and the laser linewidth, respectively. We presented the optimal parameters for three, five, and seven linear beam array SBCs along with a range of allowed parameters that could be used in the laser power scaling.

Phase‐shifted circularly polarised ring microstrip antenna and application in phased array antennas

A phase-shifted circularly polarised ring microstrip antenna (PS-CP-RMSA), which can switch between three different phases, is proposed. The phase of a circularly polarised antenna can be shifted by changing the angle of rotation. Taking advantage of this property, the proposed PS-CP-RMSA comprises a circularly polarised ring microstrip antenna (CP-RMSA) with three groups of feed lines and perturbation elements; phase shift can be achieved by switching their groups. Thus, the phase of a circularly polarised antenna can be electronically shifted without phase shifters, which has been difficult in the past. Therefore, the PS-CP-RMSA array can perform beam tilt electronically. In this study, PS-CP-RMSA and its four-element array were designed, fabricated, and measured. The maximum circular polarisation gain of the prototype PS-CP-RMSA was 6.3 dBic with an axial ratio of 1.1 dB at 5.7 GHz. The maximum gain of the boresight directional beam of the four-element array was 11.3 dBic with an axial ratio of 0.4 dB at 5.67 GHz. The proposed antenna can be a candidate for a new beam-control method for array antennas.

The Role of the Instrumental Response in 21 cm Epoch of Reionization Power Spectrum Gridding Analyses

Reconstruction of the sky brightness measured by radio interferometers is typically achieved through gridding techniques, or histograms in spatial Fourier space. For Epoch of Reionization (EoR) 21 cm power spectrum measurements, extreme levels of gridding resolution are required to reduce spectral contamination, as explored in other works. However, the role of the shape of the Fourier space spreading function, or kernel, also has consequences in reconstructed power spectra. We decompose the instrumental Murchison Widefield Array (MWA) beam into a series of Gaussians and simulate the effects of finite kernel extents and differing shapes in gridding/degridding for optimal map making analyses. For the MWA, we find that the kernel must extend out to 0.001–0.0001% of the maximum value in order to measure the EoR using foreground avoidance. This requirement changes depending on beam shape, with compact kernels requiring far smaller extents for similar contamination levels at the cost of less-optimal errors. However, simple calibration using pixelated degridding results, regardless of shape of the kernel, cannot recover the EoR due to catastrophic errors caused by the pixel resolution. Including an opaque horizon with widefield beams also causes significant spectral contamination via a beam–horizon interaction that creates an infinitely extended kernel in Fourier space, which cannot be represented well. Thus, our results indicate that simple calibration via degridded models and optimal map making for extreme widefield instrumentation are not feasible.

Beamforming-Based Mitigation of Hovering Inaccuracy in UAV-Aided RFET

Hovering inaccuracy of unmanned aerial vehicle (UAV) degrades the performance of UAV-aided radio frequency energy transfer (RFET). Such inaccuracy arises due to positioning error and rotational motion of UAV, which lead to localization mismatch (LM) and orientation mismatch (OM). In this paper, antenna array beam steering based UAV hovering inaccuracy mitigation strategy is presented. The antenna beam does not accurately point towards the field sensor node due to rotational motion of the UAV along with pitch, roll, and yaw, which leads to deviation in the elevation angle. An analytical framework is developed to model this deviation, and its variation is estimated using the data collected through an experimental setup. Closed-form expressions of received power at the field node are obtained for the four cases arising from LM and OM. An optimization problem to estimate the optimal system parameters (transmit power, UAV hovering altitude, and antenna steering parameter) is formulated. The problem is proven to be nonconvex. Therefore, an algorithm is proposed to solve this problem. Simulation results demonstrate that the proposed framework significantly mitigates the hovering inaccuracy; compared to reported state-of-the-art the same performance can be achieved with substantially less transmit power.

Large Scale Hydrodynamically Coupled Brownian Dynamics Simulations of Polymer Solutions Flowing through Porous Media.

Large scale simulations of polymer flow through porous media provide an important tool for solving problems in enhanced oil recovery, polymer processing and biological applications. In order to include the effects of a wide range of velocity and density fluctuations, we base our work on a coarse-grain particle-based model consisting of polymers following Brownian dynamics coupled to a background fluid flow through momentum conserving interactions. The polymers are represented as Finitely Extensible Non-Linear Elastic (FENE) dumbbells with interactions including slowly decaying transient forces to properly describe dynamic effects of the eliminated degrees of freedom. Model porous media are constructed from arrays of parallel solid beams with circular or square cross-sections, arranged periodically in the plane perpendicular to their axis. No-slip boundary conditions at the solid–fluid interfaces are imposed through interactions with artificial particles embedded within the solid part of the system. We compare the results of our simulations with those of standard Smoothed Particle Hydrodynamics simulations for Newtonian flow through the same porous media. We observe that in all cases the concentration of polymers at steady state is not uniform even though we start the simulations with a uniform polymer concentration, which is indicative of shear-induced cross-flow migration. Furthermore, we see the characteristic flattening of the velocity profile experimentally observed for shear-thinning polymer solutions flowing through channels as opposed to the parabolic Poiseuille flow profile for Newtonian fluids.

Biogeography-based optimization with adaptive migration and adaptive mutation with its application in sidelobe reduction of antenna arrays

Biogeography-based optimization (BBO) is a swarm intelligence optimization algorithm based on migration and mutation operations, which is usually used to solve the complex optimization problems. However, it is also a challenging task for conventional BBO to solve some complex and diversified optimization problems with a perfect balance between the performance of exploration and exploitation. In this paper, we propose a variant of BBO approach called BBO with improved migration and adaptive mutation (BBOIMAM) to improve the performance of conventional BBO for dealing with different optimization problems. First, BBOIMAM introduces an improved migration strategy which includes the generalized sinusoidal migration model and immigration strategy based on elite-learning mechanism for the improvement of the local search ability. Second, we propose an adaptive mutation strategy based on the spring vibration to further enhance the population diversity, so that improving the global search ability of the algorithm. By the combination of the proposed improved migration and adaptive mutation strategies, the exploration and exploitation performance of the algorithm can be balanced. We make a large number of experiments on a set of various kinds of benchmark functions, and the experimental results demonstrate that the proposed BBOIMAM approach achieves better performance than several state-of-the-art peer algorithms on CEC 2017 and CEC 2020 test function sets and three cases of the antenna array beam pattern optimization problems.

Multi-beam optical phase array for long-range LiDAR and free-space data communication

We present a multi-beam optical fiber phased array (OPA) with simultaneous light detection and ranging (LiDAR) and free-space optical communication (FSO) data transmission functions. The OPA component can achieve a stable phase and a high turning speed. First, the 55-element OPA is phase-locked through the stochastic parallel gradient descent (SPGD) algorithm to maintain the high light intensity of the main beam in real time. The OPA with a 5 × 11 beam array achieved a wide field of view (FOV) of 58°×32°, a single beam array steering angle of0.48°, and a steering speed of 40 MHz. Subsequently, this OPA was used to detect targets within a range of approximately 2 km, and we theoretically verified that two-dimensional coherent frequency-modulated continuous wave (FMCW) LiDAR could extract the target characteristics. In addition, a free-space optical communication link of up to 3 km was also demonstrated, with a data rate of 8 Gbps. The proposed system easily increases the array-to-MHz steering speed and yields a high-power output.

Properties of the Rotation and Mergence of Twisted Gaussian Schell Model Array Beams Propagating in Turbulent Biological Tissues

In this paper, an analytical expression for describing propagation properties of twisted Gaussian Schell model array (TGSMA) beams through turbulent biological tissues is derived based on the extended Huygens Fresnel integral. With the help of the formulae, properties of the rotation and mergence for the TGSMA beams in turbulent biological tissues are researched in detail. It is found that the TGSMA beams go through the distinct mergence period in the far field besides phenomena of abruption and rotation in the near field, and turbulent biological tissues play a dominated role in mergence of the TGSMA beams. These novel results may be helpful in optical trapping.

Integrated all-fiber structures for generating doughnut beam arrays and hollow Bessel-like beams

Two all-fiber structures for generating doughnut beam arrays and hollow Bessel-like beams are demonstrated experimentally based on mode-selective couplers at the visible band. The mode-selective couplers are acted as mode converters to produce doughnut beams, which have the properties of high mode conversion efficiency (94%), low insertion loss (<0.5 dB) and wide bandwidth (∼100 nm). A compact and efficient approach is presented through integrating a tapered multicore fiber with a mode-selective coupler, and a doughnut beam array with nearly equal power distribution is obtained based on the mechanism of coupled-power theory in the tapered multicore fiber. The hollow Bessel-like beams with different cylindrical vector modes and orbital angular momentum are achieved by fabricating a polymer microtip at the facet of the few-mode fiber output port of a mode-selective coupler. The self-healing characteristics of a Bessel-like beam are investigated in detail and the application in an optical tweezer system of a hollow Bessel-like beam exhibits a longer focal depth than that of a Gaussian beam. Both methods used for generating all-fiber-based doughnut beam arrays and hollow Bessel-like beams have the advantages of compactness, flexibility, and easy integration with free-space optical systems. Generated two kinds of beams show huge potentials for the application fields of super-resolution microscopy, laser material process and optical trapping and so on.

Efficient Frequency Conversion with Geometric Phase Control in Optical Metasurfaces.

Metasurfaces have appeared as a versatile platform for miniaturized functional nonlinear optics due to their design freedom in tailoring wavefronts. The key factor that limits its application in functional devices is the low conversion efficiency. Recently, dielectric metasurfaces governed by either high‐quality factor modes (quasi‐bound states in the continuum) or Mie modes, enabling strong light–matter interaction, have become a prolific route to achieve high nonlinear efficiency. Here, an effective way of spatial nonlinear phase control by using the Pancharatnam–Berry phase principle with a high third harmonic conversion efficiency of 10−4 W−2 is demonstrated both numerically and experimentally. It is found that the magnetic Mie resonance appears to be the main contributor to the third harmonic response, while the contribution from the quasi‐bound states in the continuum is negligible. This is confirmed by a phenomenological model based on coupled anharmonic oscillators. Besides, the metasurface provides experimentally a high diffraction efficiency (80%–90%) in both polarization channels. A functional application of this approach is shown by experimentally reconstructing an encoded polarization‐multiplexed vortex beam array with different topological charges at the third harmonic frequency with high fidelity. The approach has the potential viability for future on‐chip nonlinear signal processing and wavefront control.

Non-Targeted Effects of Synchrotron Radiation: Lessons from Experiments at the Australian and European Synchrotrons

Studies have been conducted at synchrotron facilities in Europe and Australia to explore a variety of applications of synchrotron X-rays in medicine and biology. We discuss the major technical aspects of the synchrotron irradiation setups, paying specific attention to the Australian Synchrotron (AS) and the European Synchrotron Radiation Facility (ESRF) as those best configured for a wide range of biomedical research involving animals and future cancer patients. Due to ultra-high dose rates, treatment doses can be delivered within milliseconds, abiding by FLASH radiotherapy principles. In addition, a homogeneous radiation field can be spatially fractionated into a geometric pattern called microbeam radiotherapy (MRT); a coplanar array of thin beams of microscopic dimensions. Both are clinically promising radiotherapy modalities because they trigger a cascade of biological effects that improve tumor control, while increasing normal tissue tolerance compared to conventional radiation. Synchrotrons can deliver high doses to a very small volume with low beam divergence, thus facilitating the study of non-targeted effects of these novel radiation modalities in both in-vitro and in-vivo models. Non-targeted radiation effects studied at the AS and ESRF include monitoring cell–cell communication after partial irradiation of a cell population (radiation-induced bystander effect, RIBE), the response of tissues outside the irradiated field (radiation-induced abscopal effect, RIAE), and the influence of irradiated animals on non-irradiated ones in close proximity (inter-animal RIBE). Here we provide a summary of these experiments and perspectives on their implications for non-targeted effects in biomedical fields.

Design and characterization of an orthotropic accordion cellular honeycomb as one-dimensional morphing structures with enhanced properties

This study develops the governing equations and characterizes the mechanical properties of a new orthotropic accordion morphing honeycomb structure containing periodic arrays of U-type beams reinforced with glass fibers. Castigliano’s second theorem is modified to develop the analytical equations to predict the deformation behavior of a single orthotropic ply under a combined axial, bending, and shear loadings. Accordingly, the elastic properties of the orthotropic structure including elastic stiffness, shear stiffness, and in-plane Poisson’s ratios are calculated by the developed equations. The honeycomb structure is manufactured by 3D printing, and the samples are subjected to tensile tests to experimentally validate the analytical solutions. Multiple finite element simulations are also used to validate the results. A good agreement is observed between the analytical solution, the experiments, and simulations, confirming the robustness of the analytical solution to predict the full elastic properties of the composite cellular. The results show that the periodic arrays of U-type and vertical beams can generate low in-plane stiffness in the morphing direction and high in-plane stiffness in the transverse direction, respectively. A zero Poisson’s ratio feature is achieved by employing straight beams which result in a high stiffness in the perpendicular direction. The proposed accordion cellular honeycomb structure exhibits the flexible response along the accordion shape direction, with a significant stiffness in its transverse direction. Moreover, the new orthotropic structure has considerably greater strain to failure in the morphing direction compared with a conventional isotropic configuration. These features prove that this type of structure can be applied for the aerospace morphing structures such as wings.

Circular Polarization-Agile and Continuous Beam-Steerable Array Antenna Using a Hybrid Design Approach

A circular polarization (CP)-agile and continuous beam-steerable array antenna is presented using a hybrid design approach. It is accomplished by combining digital reconfigurable antenna elements with analog continuously tunable phase shifters. To realize both polarization reconfiguration and initial phase generation for beam-scanning simultaneously, the designed antenna element enables eight states that corresponds to two CP modes with four quantized phases. The phase shifters further provide additional variable phases of -90° to 0° for antenna element excitation. Superposition of the initial and additional phases helps to satisfy a full and continuous 360° phase coverage for a beam-steerable array. Meanwhile, the phase decomposition also facilitates the design of phase shifters without complex or cascaded structures. By altering the bias states of the electronic components loaded in the array antenna, CP switching and beam scanning can be independently controlled. For verification, prototypes of the antenna element, phase shifter, and a four-element array are all fabricated and tested. Reasonable agreement is obtained between simulation and measurement. The resultant array could scan up to nearly ±40° off the boresight, along with stable radiation patterns and good CP performance.

Corrections to “Propagation Properties of Gaussian Schell-Model Beam Array in the Jet Engine Exhaust Induced Turbulence” [Dec 20 Art no. 6501113

We correct a few typographical errors in the original manuscript.

An ultra‐wideband 3 × 3 Butler matrix with unique Vivaldi array structure for high‐range resolution radars

Steerable antenna beam capability is an outstanding expectation for the development of automatic tracking systems and target detection. A switched beam array antenna, which can generate multiple fixed beams with enhanced sensitivity, emerges as a solution for beamforming tracking. On the other hand, it is known that the target can be detected with high-range resolution thanks to ultra-wideband (UWB) systems. In this work, a compact switched beam Vivaldi array antenna based on a Butler matrix for a UWB application capable of target detection with accurate target tracking is presented to meet the high gain and low side lobe level requirements. Based on a three-element antenna array, two methods have been applied to obtain small grating lobes and it has been shown that significant improvements can be achieved. Designed with a 3 × 3 UWB Butler matrix, the UWB array antenna can direct its beams in three directions in a direction range from −42 to 42°. The measured result showed that the group delay was less than about 4.5 ns with variation of less than ±0.7 ns over the entire operating frequency band.

High-Flexibility Control of Structured Light with Combined Adaptive Optical Systems

Combining the specific advantages of high-resolution liquid-crystal-on-silicon spatial light modulators (LCoS-SLMs) and reflective or refractive micro-electro-mechanical systems (MEMS) presents new prospects for the generation of structured light fields. In particular, adaptive self-apodization schemes can significantly reduce diffraction by low-loss spatial filtering. The concept enables one to realize low-dispersion shaping of nondiffracting femtosecond wavepackets and to temporally switch, modulate or deflect spatially structured beams. Adaptive diffraction management by structured illumination is demonstrated for piezo-based and thermally actuated axicons, spiral phase plates (SPPs) and Fresnel bi-mirrors. Improved non-collinear autocorrelation with angular-tunable Fresnel-bi-mirrors via self-apodized illumination and phase contrast of an SLM is proposed. An extension of the recently introduced nondiffractive Talbot effect to a tunable configuration by combining an SLM and a fluid lens is reported. Experimental results for hexagonal as well as orthogonal array beams are presented.

Generation of high-uniformity and high-resolution Bessel beam arrays through all-dielectric metasurfaces

Abstract Bessel beam arrays are progressively attracting attention in recent years due to their remarkable non-diffracting nature and parallel manipulation capabilities in diverse applications. However, the poor phase discretization of conventional approaches such as spatial light modulators leads to low numerical aperture (NA) beam arrays due to the limitation imposed by the Nyquist sampling theorem and poor uniformity of the beam intensity. The key contribution of this study is to experimentally demonstrate the generation of high-uniformity and high-resolution Bessel beam arrays by utilizing all-dielectric metasurfaces. This is attained by optimizing the design of the supercell of a Dammann grating, particularly decreasing each supercell of the grating to a proper size. We demonstrate a 4 × 4 array of Bessel beams with a subwavelength transverse dimension (570 nm, ∼0.9λ) and a large NA of 0.4 for each beam in the array, while maintaining a relatively high uniformity intensity (52.40%) for the array. Additionally, the Bessel beam arrays are generated in a broadband range through the proposed all-dielectric metasurfaces. Our results are of great significance and particularly useful for applications of metasurface-based Bessel beam arrays in multidisciplinary fields such as laser fabrication, biomedical imaging, data storage, and multi-particle trapping.

Direct construction of an optical linear transform and its application on optical complex data generation.

Optical computing technique has emerged as a promising platform for highly parallel data processing. In most optical computing architectures, optical linear transform is the basic composition, which is commonly designed by the established deep learning-based methods or general-purpose optimizers. There still lacks in-depth study to construct a solver targeted at optical linear transform applications. In this work, we propose a new algorithm that solves the transformation matrix of a linear optical system consisting of cascaded phase masks directly and show that its efficiency is significantly higher than those common solvers. As a direct application of this method, we can create target array of optical beams even with a single layer of phase mask in the experiment. The amplitude and phase of each beam in the array can be controlled independently without affecting each other. The optical system requires only one light source and one programmable phase mask. This setup can be readily incorporated into most current optical computing configurations. Our method may find broad applications in classic and quantum optical information processing.