Array Beam Research Articles

Anomalous beam spreading of Airy vortex beam arrays propagating in a moderate turbulent atmosphere

The effects of transverse displacement parameter d and topological charge (TC) m on the beam spreading (BS) of Airy vortex beam array (AVBA) and Airy Gaussian vortex beam array (AGVBA) propagating in a moderate turbulent atmosphere are analysed and studied numerically. Due to the Gaussian function truncation and optical vortex modulation, the behaviours of the BSs of AVBA and AGVBA in turbulent atmosphere are anomalous. Compared with the AVBA, the BS of lower order AGVBA is less affected by atmospheric turbulence when d is small but more affected when d is large. With the increase of m, the BSs of two vortex beam arrays decrease nonlinearly and AVBA is broadened more seriously by atmospheric turbulence than that of AGVBA as d is set to be zero. Compared with AGVBA, the BS of AVBA with lower TC is less affected by atmospheric turbulence but more seriously affected with higher TC.

Controllable multi-sector array beams

A controllable multi-sector array beam is proposed in this Letter. The beam can be generated with the metalens phase. The intensity distribution of the beam at the focal plane is analyzed in detail. The influence of the parameters a and l on the focal field distribution is discussed. The theoretical and experimental results demonstrate that the parameter a affects the size of the beam, and the additional factor l can adjust the sub-region number of the multi-sector array beams. The beam shows potential for use in optical manipulation and image transmission.

Design of scalable metalens array for optical addressing

Large-scale trapped-ion quantum computers hold great promise to outperform classical computers and are crucially desirable for finance, pharmaceutical industry, fundamental chemistry and other fields. Currently, a big challenge for trapped-ion quantum computers is the poor scalability mainly brought by the optical elements that are used for optical addressing. Metasurfaces provide a promising solution due to their excellent flexibility and integration ability. Here, we propose and numerically demonstrate a scalable off-axis metalens array for optical addressing working at the wavelength of 350 nm. Metalens arrays designed for x linearly polarized and left circularly polarized light respectively can focus the collimated addressing beam array into a compact focused spot array with spot spacing of 5 μm, featuring crosstalk below 0.82%.Graphical

Spectrum Sensing of Noncooperative Beam Signals

In this paper, we investigate the issue of spectrum sensing of noncooperative beam signals that are emitted by a multiantenna transmitter. When the sampling period of the sensing node includes the whole process of beam scanning, that is, spectrum sensing is performed in an ideal situation, we use the traditional energy detection algorithm for spectrum sensing and get good results; for multiantenna beam scanning spectrum sensing in nonideal situation, the performance of traditional energy detection algorithm is seriously degraded. To deal with this problem, a sensing period selection (SPS) algorithm is proposed. The simulation results show that the proposed algorithm can effectively improve the performance of spectrum sensing in the multiantenna array beam scanning scenario.

Design and Realization of a Broadband Multi-Beam 1×2 Array Antenna Based on 2×2 Butler Matrix for 2.45 GHz RFID Reader Applications

This paper presents design and analysis of a beam switchable [Formula: see text] array patch antenna fed by a [Formula: see text] Butler matrix based hybrid coupler for 2.45[Formula: see text]GHz radio frequency identification (RFID) reader applications in the ISM band. The proposed beam switchable array antenna arrangement consists of two identical patch elements, a pleated quarter-wavelength impedance transformer (PQWIT), and a hybrid coupler. The concept of PQWIT has been utilized to reduce the overall implementation area of the patch elements. The overall area of the patch element is miniaturized by 50% due to the implementation of PQWIT. This miniaturized antenna is used as a radiating element for designing a beam switchable [Formula: see text] array antenna fed by a hybrid coupler. The proposed antenna prototype has been fabricated on a 1.56[Formula: see text]mm thick Rogers RT/duroid 5880 substrate with a physical area of [Formula: see text][Formula: see text]mm2. The simulation and measured results exhibit good agreements. The designed antenna offers a broad bandwidth of 844[Formula: see text]MHz (1.956–2.80[Formula: see text]GHz), peak gain of 8.86 dB, peak radiation efficiency of 99.52% and has two switchable beams in the directions [Formula: see text] and [Formula: see text]. The suggested switched beam array antenna is suitable for RFID reader applications at 2.45[Formula: see text]GHz for tracking of moving objects.

How innovations in methodology offer new prospects for volume electron microscopy

Detailed knowledge of biological structure has been key in understanding biology at several levels of organisation, from organs to cells and proteins. Volume electron microscopy (volume EM) provides high resolution 3D structural information about tissues on the nanometre scale. However, the throughput rate of conventional electron microscopes has limited the volume size and number of samples that can be imaged. Recent improvements in methodology are currently driving a revolution in volume EM, making possible the structural imaging of whole organs and small organisms. In turn, these recent developments in image acquisition have created or stressed bottlenecks in other parts of the pipeline, like sample preparation, image analysis and data management. While the progress in image analysis is stunning due to the advent of automatic segmentation and server‐based annotation tools, several challenges remain. Here we discuss recent trends in volume EM, emerging methods for increasing throughput and implications for sample preparation, image analysis and data management.

Numerical simulation of optical propagation using sinc approximation.

This paper further develops a recently proposed method for computing the diffraction integrals of optics based on sinc series approximation by presenting a numerical implementation, parameter selection criteria based on rigorous error analysis, and example optical propagation simulations demonstrating those criteria. Unlike fast Fourier transform (FFT)-based methods that are based on Fourier series, such as the well-known angular spectrum method (ASM), the sinc method uses a basis that is naturally suited to problems on an infinite domain. As such, it has been shown that the sinc method avoids the problems of artificial periodicity inherent in the ASM. After a brief review of the method, the detailed error analysis we provide confirms its super-algebraic convergence and verifies the claim that the accuracy of the method is independent of wavelength, propagation distance, and observation plane discretization; it depends only on the accuracy of the source field approximation. Based on this analysis, we derive parameter selection criteria for achieving a prescribed error tolerance, which will be valuable to potential users. Numerical simulations of Gaussian beam and optical phased array propagation verify the high-order accuracy and computational efficiency of the proposed algorithms. To facilitate the reproduction of numerical results, we provide a Matlab code that implements our numerical approach for the Fresnel diffraction integral. For comparison, we also present numerical results obtained with the ASM as well as the band-limited angular spectrum method.

Non-paraxial transformation of finite Airy Gaussian beam array in isotropic space

Based on vector Rayleigh-Sommerfeld diffraction integration, we investigate the non-paraxial transmission behavior of the finite Airy Gaussian beam array (FAGBA) in isotropic space. The intensity distribution of the x- component and longitudinal component of the FAGBA at different cross section of the free space are described numerically, respectively. The influences of truncation factor, distribution parameter, wavelength, beam waist radius and refractive index on the FAGBA evolution at several observation planes as well as its side transmission view in isotropic space are also discussed. Through the obtained analytical formulae and conclusions, the beam array transmission locus can be controlled more precisely in non-paraxial situation by altering these parameters to meet the practical usage, especially in area of optical trapping and optical tweezers.

Statistical analysis of the causes of excess variance in the 21 cm signal power spectra obtained with the Low-Frequency Array

Context.The detection of the 21 cm signal of neutral hydrogen from the Epoch of Reionization (EoR) is challenging due to bright foreground sources, radio frequency interference (RFI), and the ionosphere as well as instrumental effects. Even after correcting for these effects in the calibration step and applying foreground removal techniques, the remaining residuals in the observed 21 cm power spectra are still above the thermal noise, which is referred to as the “excess variance.”Aims.We study a number of potential causes of this excess variance based on 13 nights of data obtained with the Low-Frequency Array (LOFAR).Methods.We focused on the impact of gain errors, the sky model, and ionospheric effects on the excess variance by correlating the relevant parameters such as the gain variance over time or frequency, local sidereal time (LST), diffractive scale, and phase structure–function slope with the level of excess variance.Results.Our analysis shows that the excess variance, at the current level, is neither strongly correlated with gain variance nor the ionospheric parameters. Rather, excess variance has an LST dependence, which is related to the power from the sky. Furthermore, the simulated StokesIpower spectra from bright sources and the excess variance show a similar progression over LST with the minimum power appearing at LST bin 6h to 9h. This LST dependence is also present in sky images of the residual StokesIof the observations. In very-wide sky images based on one night of observation after direction-dependent calibration, we demonstrate that the extra power comes exactly from the direction of bright and distant sources Cassiopeia A and Cygnus A with the array beam patterns.Conclusions.These results suggest that the level of excess variance in the 21 cm signal power spectra is related to sky effects and, hence, it depends on LST. In particular, very bright and distant sources such as Cassiopeia A and Cygnus A can dominate the effect. This is in line with earlier studies and offers a path forward toward a solution, since the correlation between the sky-related effects and the excess variance is non-negligible.

The deception effect of FDA counteracting amplitude-comparison monopulse reconnaissance

Conventional phased array radar can direct the high-gain beam, resulting in high visibility under the reconnaissance system and even direct exposure to the enemy. As an amplitude-based direction-finding system, the amplitude monopulse system can recognize the traditional radar signals. However, there are still some issues with the countermeasures of the monopulse system, so it is necessary to find better styles of jamming. Since the beam of the frequency diverse array (FDA) signal at a certain angle varies with the range, we studied the deception effect of the FDA against the amplitude-comparison monopulse direction-finding system. By analyzing the established FDA-based direction-of-arrival location deception model against the amplitude-comparison monopulse system, we found that the introduction of the frequency increment might cause the FDA signals to deceit the monopulse system in principle. Then, to indicate the superiority of our deception method, we obtain the instantaneous signal-to-noise ratio, Cramér–Rao lower bound, root-means-square error, and variation. Numerical simulation results demonstrate that the FDA can generate deceptive signals to counteract the amplitude-comparison monopulse direction-finding system.

Creation of cylindrical vector beams through highly anisotropic scattering media with a single scalar transmission matrix calibration

Cylindrical vector (CV) beams have attracted increasing interest due to their particular properties and their applications in optical imaging, optical manipulation, and light–matter interactions. However, it is challenging to construct CV beams through highly anisotropic scattering media (HASM), such as thick biological tissue, posing a barrier to the applications of CV beams that involve HASM. Here, we present a scheme to construct CV beams beyond high scattering that only requires a single scalar transmission matrix (TM) calibration and manipulation of the spatial degrees of freedom of the scalar input field. Assisted by a radial polarization converter (S-waveplate) and a polarizer, the scheme enables one to obtain the correct incident wavefront for the creation of CV beams through HASM with only one single scalar TM calibration. Compared to the existing method, this user-friendly approach is fast and simple in terms of the optical implements and computations. Both radially and azimuthally polarized beams are experimentally constructed through a ZnO scattering layer to demonstrate the viability of the method. Arbitrarily generalized CV beams and arrays of CV beams are also created through the HASM to further prove the flexibility of the method. We believe this work may pave the way for applications of CV beams that involve a highly anisotropic scattering environment.

Beam steering at the nanosecond time scale with an atomically thin reflector

Techniques to mold the flow of light on subwavelength scales enable fundamentally new optical systems and device applications. The realization of programmable, active optical systems with fast, tunable components is among the outstanding challenges in the field. Here, we experimentally demonstrate a few-pixel beam steering device based on electrostatic gate control of excitons in an atomically thin semiconductor with strong light-matter interactions. By combining the high reflectivity of a MoSe2 monolayer with a graphene split-gate geometry, we shape the wavefront phase profile to achieve continuously tunable beam deflection with a range of 10°, two-dimensional beam steering, and switching times down to 1.6 nanoseconds. Our approach opens the door for a new class of atomically thin optical systems, such as rapidly switchable beam arrays and quantum metasurfaces operating at their fundamental thickness limit.

Effects of beam deviation on the mode purity of a vortex beam

The vortex beam has extensively demonstrated impressive significance in many applications. As a key parameter, the mode purity (MP) of a vortex beam is easily influenced by beam deviation. In this paper, the deviation models of the vortex beam — a beam wander model (BWM) and a phase singularity wander model (PSWM) are proposed. The MP expressions of these models are derived, and the influence of beam parameters on MP are studied through numerical methods. It is found that MP remains constant with the variation of azimuth of phase singularity, the maximally relative radial distance varies with the topological charge inversely and the influence of PSWM on MP is greater than BWM. Furthermore, the MP of a radially symmetrical vortex beam array is equal to that of each beamlet, and will increase with the decline of relative radial distance of each beamlet. The results can provide theoretical basis for further researches on orbital angular momentum (OAM) communication and vortex beam synthesis.

A Tb/s Indoor MIMO Optical Wireless Backhaul System Using VCSEL Arrays

In this paper, the design of a multiple-input multiple-output (MIMO) optical wireless communication (OWC) link based on vertical cavity surface emitting laser (VCSEL) arrays is systematically carried out with the aim to support data rates in excess of 1 Tb/s for the backhaul of sixth generation (6G) indoor wireless networks. The proposed design combines direct current optical orthogonal frequency division multiplexing (DCO-OFDM) and a spatial multiplexing MIMO architecture. For such an ultra-high-speed line-of-sight (LOS) OWC link with low divergence laser beams, maintaining alignment is of high importance. In this paper, two types of misalignment error between the transmitter and receiver are distinguished, namely, radial displacement error and orientation angle error, and they are thoroughly modeled in a unified analytical framework assuming Gaussian laser beams, resulting in a generalized misalignment model (GMM). The derived GMM is then extended to MIMO arrays and the performance of the MIMO-OFDM OWC system is analyzed in terms of the aggregate data rate. Novel insights are provided into the system performance based on computer simulations by studying various influential factors such as beam waist, array configuration and different misalignment errors, which can be used as guidelines for designing short range Tb/s MIMO OWC systems.

Folded Resonator for Glucose Solution Density Detection Based on Airy Beam Arrays

We presented an investigation on the evolution properties of the finite Airy beam array (FAiBA) in metamaterial’s slab system constituting of right-handed materials and double negative materials combining the generalized Huygens–Fresnel integral equation and the light transfer matrix. The beam intensity distribution on the receiver plane and its side transmission view on the (z, x) plane are demonstrated numerically with several array numbers. Moreover, we put forward a kind of folded resonator to detect glucose solution density based on the derived principle and conclusion; the influence of curvature radius on the emerging beam’s evolution characteristics is discussed, and the empirical formula between FAiBA’s received power and glucose solution density is derived by using the fit linear analysis. We hope that the present concept and the derived conclusions can be employed for monitoring in the environmental field, as well as the biomedical and food safety detection.

Frequency Response of Thermo-Optic Phase Modulators Based on Fluorinated Polyimide Polymer Waveguide.

Polymer waveguide phase modulators exhibit stable low-power phase modulation owing to their exceptional thermal confinement and high thermo-optic effect, and thus, have the merit of thermal isolation between channels, which is crucial for an optical phased array (OPA) beam scanner device. In this work, a waveguide phase modulator was designed and fabricated based on a high-refractive-index fluorinated polyimide. The propagation loss of the polyimide waveguide and the temporal response of the phase modulator were characterized. Moreover, the transfer function of the phase modulator including multiple poles and zeros was obtained from the measured frequency response. The polyimide waveguide modulator device demonstrated a fast response time of 117 μs for 1 kHz input signal, however, for 1 mHz step-function input, it exhibited an additional 5% phase change in 5 s.

Deceptive signal generating optimization based on frequency diverse array

The direction and position of the radar signals are essential information in the radar countermeasure, and with the development of the reconnaissance system, the radar is facing more severe threats. However, the high-gain beam and even-distribute phase of the phased-array radar restrict the further development of radar protection measures. Therefore, considering the angle-range-time-coupled beam and phase of the frequency diverse array (FDA), we proposed a deceptive signal generating method based on the FDA. Firstly, the amplitude- and phase-based reconnaissance countermeasures were established, respectively. Moreover, the regulation ability of the frequency increment sequence was studied. Therefore, by finding the appreciated frequency increment sequence that can regulate the FDA signals, the proposed FDA can generate deceptive signals that counter both the amplitude- and phase-based reconnaissance system. The instantaneous signal-to-noise ratio and Cramér–Rao lower bound were considered to verify the method. Numerical examples and simulations showed that the proposed countermeasure could generate deceptive signals with good error tolerance, whether in a noisy or non-noise environment.

Spreading evolution of a linear phase-locked hollow beam array in atmospheric turbulence.

Based on the generalized Huygens-Fresnel principle, propagation characteristics of a linear phase-locked hollow beam (PLHB) array propagating through atmospheric turbulence are investigated. Analytical expressions of the average intensity and mean-squared beam width of the PLHB array are derived. It is shown that propagation properties of a PLHB array are related to the initial beam parameters (i.e., number of beamlets, size of beam waist, range of wavelength) of the PLHB array and the strength of turbulence. These findings may provide potential applications in free-space optical communications, lidar, remote sensing, and related fields.

Control of the wetting properties of stainless steel by ultrashort laser texturing using multi-parallel beam processing

The laser surface microtexturing is increasingly used for the production of surfaces with desired wetting characteristics (i.e., superhydrophobicity). For this not only precise but also fast laser processing is needed. Microtextures not based entirely on laser induced material self-organization require relatively tight focusing of the laser beam which can not be achieved using fast beam scanning systems. Therefore, in this work, the possibility to use parallel laser processing by multi-beam array for control of the EN 1.4301 (AISI 304) stainless steel surface was investigated. High-energy picosecond laser pulses were used to pattern the polished steel surface using 8 × 8 beam array with two different patterning strategies: mesh and dot. The multi-beam patterning inevitably brings some irregularities due to variation of properties of the beams in the array. However, after the investigation of the influence of laser patterning parameters on the wetting properties of the steel surface, it was determined that multi-beam mesh patterning allows obtaining superhydrophobic surface properties through the right combination of texture depth, surface chemical properties and laser induced surface ripples. The dot patterning was even more promising and was found suitable for obtaining a broad spectrum of wetting states ranging from superhydrophobic to superhydrophilic, when appropriate patterning parameters were used, mostly by controlling self-organized surface structure shape by changing texture period (laser spot overlap).

The Combined Effect of Jet and Atmospheric Turbulence on the Propagation of Airborne Partially Coherent Array Beams

AbstractThe exhaust from engines close to the fuselage can cause extreme turbulence and have a significant impact on the performance of airborne laser systems. In this paper, the combined effect of the jet engine and atmospheric turbulence on propagation of a Gaussian Schell‐model (GSM) array beam over long distances is studied in detail. Based on the two‐step propagation method, the analytical expressions of the cross‐spectral density (CSD) function, mean‐squared beam width and spectral degree of spatial coherence (DOC) of GSM array beams are derived. It is shown that the jet engine turbulence has a significant effect on the beam broadening even at a very short distance. As the propagation distance in the jet engine turbulence increases, the beam width is less effected by the spatial coherence. Meanwhile, the resistance of lower spatially coherent beam to the turbulence increases as the distance of the jet engine turbulence or the strength of the atmospheric turbulence increases. It is demonstrated that the effect of jet engine turbulence on the beam spreading can be equivalent to moderate or even severe atmospheric turbulence. Moreover, the DOC is a function with oscillatory phenomenon when the propagation distance is short or the strength of turbulence is low.