Generation Of Multiple Beams Research Articles

Generation of multiple vector beams through cascaded beam displacers and a segmented digital hologram

Complex vector light modes, characterized by a non-uniform transverse polarization distribution, have pervaded a wide range of research fields. In this study, we propose an approach that enables the simultaneous generation of multiple vector beams based on a spatially segmented digital hologram and two or more cascaded beam displacers. More precisely, an input beam is separated into multiple parallel copies spatially separated, which are then sent to the center of each segmented hologram, enabling independent modulation of each beam. The modulated beams are then judiciously recombined with a beam displacer to generate multiple vector modes in a simultaneous way. We demonstrated our technique with two arbitrary vector modes but the technique can be easily extended to more by inserting additional beam displacers. To assess the quality of the generated vector modes, we employed Stokes polarimetry to reconstruct their transverse polarization distribution and to measure their degree of non-separability. We envision that this technique will find significant applications in various fields, including optical communications, optical sensing, and optical tweezers to mention a few.

Broadband multifunctional metasurfaces enabling polarization multiplexed focused vortex array generation

Metasurfaces are ultrathin artificially engineered structures exquisitely designed to tailor the wavefront, polarization, and amplitude of incident light, offering a versatile platform for implementing compact and integrated photonics devices. Metasurface-based structured light generation has gained considerable attention in the scientific community for its various exotic applications, including optical communication, particle manipulation, and high-resolution lithography. State-of-the-art design techniques include polarization multiplexing, multiple vortices beam generation, and vortex arrays. However, there needs to be more techniques for generating polarization switchable vortex arrays, despite the apparent advantages in significant application fields, necessitating a simple design technique. Here, we present a straightforward design technique utilizing computer-generated holography (CGH) and photonic spin Hall effect (PHSE) to realize a metadevice platform capable of generating broadband multiple optical vortex arrays with switchable polarization output. Our approach involves designing phase masks for the vortex arrays using CGH, which are then encoded onto the metasurface. By leveraging PSHE, the designed metasurfaces produce the desired optical response depending on the input polarization state. Using the proposed design technique as proof of concept, different all-dielectric metasurfaces capable of generating optical vortex arrays of different dimensions are demonstrated. The results verify the effectiveness of the proposed methodology. The design has potential applications in data communications, storage, quantum computation, nanoscale physical manipulation, and microscopy.

Multiplexed vortex beam-based optical tweezers generated with spiral phase mask

The design and implementation of a multiplexed spiral phase mask in an experimental optical tweezers setup are presented. This diffractive optical element allows the generation of multiple concentric vortex beams with independent topological charges and without amplitude modulation. The generalization of the phase mask for multiple concentric vortices is also shown. The design for a phase mask of two multiplexed vortices with different topological charges is developed. We experimentally show the transfer of angular momentum to the optically trapped microparticles by enabling nearly independent orbiting dynamics around the optical axis within each vortex. The angular velocity of the confined particles versus the optical power in the focal region is also discussed for different combinations of topological charges.

Wideband Multiple Bessel Beams With Desired Directions and Energy Distribution Proportion Based on Time Reversal and Genetic Algorithm in Microwave

In this paper, a simple synthesis technique for versatile and flexible generation of multiple bessel beams with desired directions and energy distribution proportion based on time reversal (TR) and genetic algorithm (GA) is provided. As example, three transmission metasurfaces (TMSs) are designed based on the proposed technique: (1) Single Bessel beam along z axis direction. (2) Dual bessel beams with equal energy distribution proportion for (θ = 30°,φ = 45°) and (θ = -30°,φ = 45°). (3) Dual Bessel Beam with desired energy distribution proportion (1:0.8) for (θ = 30°,φ = 45°) and (θ = -30°,φ = 45°). The TMSs with size 8.21λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ×8.21λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> are formed by units with three-metal layer, which can provide high transmission amplitude (>0.9) and 360° phase shift in a wide frequency band from 10GHz to 18GHz. For validating the design technique, TMS (3) is fabricated and measured, and the simulated and measured results agree well. There are three innovations in the paper: (1) Flexible design technique based on TR and GA. (2) High efficiency TMSs. The maximum Bessel beam conversion efficiency is 37%. (3) wideband 57.1%. The developed design technique can be used in designing high efficiency TMSs in the near field application scenarios such as dense channel communication, high-resolution microwave imaging, near-field detection, efficient wireless energy transmission, medical hyperthermia, etc.

A THz Integrated Circuit Based on a Pixel Array to Mode Multiplex Two 10-Gbit/s QPSK Channels Each on a Different OAM Beam

We experimentally demonstrate a THz integrated circuit with a pixel-array-based orbital-angular-momentum (OAM) mode converter for the generation and multiplexing of multiple data-carrying OAM beams. The integrated device consists of (i) two coupling spikes, which serve as inputs and can couple THz signals from hollow metallic waveguides to the device; (ii) two mode expansion structures, which expand the mode profiles from the waveguide inputs to match the OAM mode converter; and (iii) a 3.6 × 3.6 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> pixel-array-based OAM mode converter, which vertically emits and multiplexes two free-space THz data-carrying OAM beams with different mode orders. The generated OAM order depends on the corresponding input port. Two different designs of the integrated OAM emitters show the generation and multiplexing of (a) OAM +1 and –1, and (b) OAM +1 and –2 at the center frequency of ∼ 0.317 THz. Crosstalk lower than –15 dB between the OAM modes can be achieved. Specifically, the OAM +1/–1 emitter has a 3-dB power bandwidth of ∼15 GHz. Using the OAM +1/–1 emitter for a free-space link at a 0.317-THz carrier frequency, we experimentally demonstrate 20-Gbit/s quadrature-phase-shift-keying (QPSK) transmission by multiplexing OAM +1 and –1. Compared to a single-beam transmission, the multiplexed link induces a ∼1-dB signal-to-noise ratio (SNR) penalty at the bit error rate (BER) of 3.8×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> .

Generation of Multiple Nondiffracting Beams Based on Transmission Metasurface in Microwave-Frequency Region

In this letter, a method to generate multiple nondiffracting beams by a transmission metasurface is proposed. The unit cell consists of two layers of the same circular resonant patch and a medium layer in the middle. The unit cell is rotated by different angles to obtain a 360 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^\circ$</tex-math></inline-formula> transmission phase shift. The method of generating multiple nondiffracting beams on the metasurface is realized by a multibeam shared-aperture method. Multiple subarrays are used to launch nondiffracting beams that propagate in different directions in a shared-aperture manner. Each subarray is independent and complementary to control the deflection of multiple nondiffracting beams more flexibly. In accordance with the method, three nondiffracting beams are generated by the same transmission metasurface. The metasurface is fabricated and measured and the results validate the proposed design method.

Multi-band orbital angular momentum mode-division multiplexing by a compact set of microstrip ring-shaped resonator antenna.

Optical beams carrying orbital angular momentum (OAM) have received much attention due to the prospects of their use in terahertz communications, biomedical engineering, and imaging. Here we propose an antenna design for the generation of multiple beams carrying OAM with different topological states at the same frequency. The proposed OAM generator is based on a compact set of microstrip ring-shaped resonators. An analytical solution for the radiated field of a single circular ring resonator antenna is derived involving the cavity model and the magnetic current approach. To verify our theoretical description, the numerical full-wave simulation is performed for an actual size OAM generator with the use of the ANSYS HFSS electromagnetic solver, and an antenna prototype operating in the microwave band is fabricated and tested. Conditions of the antenna operation in the combined OAM and mode-division multiplexing (OAM-MDM) regimes are discussed. Obtained results prove that the proposed antenna can be used as a compact and low-cost generator of multiple beams with different OAM states.

Multiple Airy beam generation by a digital micro mirror device.

The Airy beam is the solution of Maxwell's wave equation and since this equation is linear, a superposition of Airy beams still remains the solution of the wave equation. In this paper, we propose a method for generating multiple Airy beams that includes a desirable number of up to 6 individual Airy beams with desirable acceleration properties. By introducing a decenter into the designed diffractive optical element (DOE) of an Airy beam the problem of generating dual airy beams patterns by an amplitude-based spatial light modulator is solved. By superimposing the designed DOEs of individual Airy beams and scaling them to the proper gray level range, the DOE of the multiple Airy beams is generated. Displaying this DOE on a digital micromirror device, multiple Airy beams are experimentally produced. The experimental studies of these beams show good agreement with the performed simulations.

Generation and steering of airborne acoustic vortices with broadband electro-active spiral gratings

Acoustic beam shaping technology has flourished in the last decade, motivated by its important applications. For example, in the context of contactless manipulation, the use of structured ultrasonic fields has led to significant advances, such as the development of the acoustic tweezers based on the use of ultrasonic vortex beams. In this work, we present a powerful and efficient technique to structure acoustic fields based on the use of planar electro-active diffraction gratings, which can be tailored in practically arbitrary shapes. For this purpose, a lower electrode with the desired shape is printed on a circuit board and covered with an active ferroelectret film, whose metallized top surface acts as a continuous upper electrode. Importantly, these devices can be operated within a broad spectral range of ultrasonic frequencies. Two kinds of structured fields are demonstrated: a focused acoustic vortex and the simultaneous generation of multiple acoustic Bessel beams of different topological charges, well separated among each other along the propagation axis. In both cases, the main parameters of the field can be finely and continuously tuned by setting the operation frequency, which allows an axial steering of the vortices. Experimental results exhibit very good agreement with theoretical analysis and numerical simulations.

Modeling and Simulation of Relativistic Multiple Electron Beam Generation With Different Energies From a Single-Cathode Potential for High-Power Microwave Sources

The traveling wave tube (TWT) has been a reliable conventional vacuum electron device (CVED) since the 1940s. Researchers, beginning in the late 1980s, extended the TWT to the relativistic electron beam regime to generate 100- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{s}\cdot $ </tex-math></inline-formula> MW power in the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${X}$ </tex-math></inline-formula> -band. Since the mid-1990s, there has been little advancement in the field. Recently, the linear theory of a multistream TWT was published, which showed superexponential amplification properties. This article describes a novel technique for producing multiple electron beams with an energy difference of about 6%–27% with comparable currents from a single cathode at a single potential for a multistream TWT. We present a new model of two nested cathodes where two annular electron beams are generated and propagated in a smooth cylindrical pipe that emerged into a strong magnetic field. The two nested cathodes are magnetically insulated coaxial diodes (MICDs). The simulation results are obtained using the MAGIC particle-in-cell (PIC) code for the experimental vacuum diode geometry of the SINUS-6 high-current electron beam accelerator at The University of New Mexico. Results are obtained, which are then: 1) compared with earlier experimental results for a single beam; 2) study the current–voltage ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}$ </tex-math></inline-formula> ) characteristics of two electron beams powered by a single cathode at a single potential immersed in a strong magnetic field; and 3) show 6%–27% energy differences with comparable currents between two beams. This technique is viable for pulsed power-driven, relativistic electron beams for a relativistic multistream TWT.

A BER-Conscious Synthesis of Switched-Beam Antenna to Maximize Reliable Coverage in WSN Applications

A BER-conscious synthesis of switched multi-beam multi-sector access point (AP) antenna is proposed to enhance reliable communication coverage for WSN applications. The sector-based design of multi-beam AP antenna is necessary for a densely deployed WSN to achieve high system capacity with 360° azimuth coverage. However, the neighboring sectors cause high co-channel interference resulting in a low signal to interference (SIR) ratio and hence degrades the communication link quality. This leads to frequent packet re-transmissions resulting in increased energy consumption at the power deficient sensor nodes. The proposed BER-conscious array synthesis scheme incorporates projected power and SIR limits within the antenna design process to maximize the effective coverage area with acceptable BER. The optimized coverage with reliable communication implies energy saving at the sensor nodes. Based on the proposed process of coverage optimization, a multi-sector AP antenna is analytically synthesized. A prototype is fabricated, and the analytically obtained coverage results are verified through experiments. The maximum radial range of 2 – 13 m with 360° communication coverage is achieved. Moreover, high port isolation of 45.95 dB between adjacent sectors enables the generation of multiple simultaneous beams in the communication region resulting in high system capacity. The achieved performance indicates that the synthesized switched multi-beam multi-sector antenna using the proposed scheme is a good candidate for AP in WSN applications.

Multiple electron beam generation with different energies and comparable currents from a single cathode potential for high power traveling wave tubes (TWTs)

We present a technique for generating multiple electron beams with different energies and comparable currents from a single cathode stalk at a single potential using nested magnetically insulated coaxial diodes (MICDs). The application is for a multi-stream traveling wave tube. Particle-in-cell simulations are performed for an experimental parameter-based geometry where two thin-walled intense relativistic electron beams immersed in a strong uniform magnetic field propagate through a cylindrical vacuum channel. The analytically derived results are obtained by extending Fedosov’s solution for generating a hollow electron beam from an MICD on a cathode stalk in an infinite magnetic field. Two electron beams are generated and accelerated downstream assuming zero initial kinetic energy of the electrons from the cathodes. Results show both electron beam currents ranging from 66 to 2.8 kA with an energy difference ranging from 6% to 27% depending on voltages applied from 100 to 600 kV and the geometry of the two MICDs. An optimal geometry is a crucial factor in achieving the maximum energy difference between the electron beams for comparable currents. The analytical and numerical simulation results show good agreement. We are currently in the process of planning experiments using the electron beam accelerator (SINUS-6 at UNM) to validate the analytical and simulation results.

Multiple electron beam generation from InGaN photocathode

In this study, we generated 25 multielectron beam (MEB) using an InGaN photocathode with a negative electron affinity state irradiating with 25 multilaser beam. The uniformity of the MEB and the total electron beam current were evaluated. A laser beam was split into 25 laser beams using a spatial light modulator. The coefficient of variation (CV) of laser power was 20%. The CV of quantum efficiency was 1.1%. The CV of electron beam current was 12%, and the total current was about 1.2 μA. These results will enhance the development of the MEB-defect inspection using the InGaN photocathode.

Dual-frequency multiple compact vortex beams generation based on single-layer Bi-spectral metasurface

Vortex beams carrying orbital angular momentum (OAM) have attracted considerable attention owing to the potential to expand channel capacity of microwave and optical communication. However, the OAM generations usually suffer from divergence along propagation. In this work, we proposed a strategy to generate multiple vortex beams with compact energy distributions based on a single-layer reflective metasurface. First, the mechanism is developed for the generation of multiple compact vortex beams. Then, an advanced single-cell bi-spectral meta-atom, which is composed of a double C-shaped slot resonator and a modified double C-shaped resonator, is proposed to actualize independent geometric phase controls at two frequencies. As an illustrative example, a dual-frequency metasurface that can achieve four compact vortex beams (two beams at each frequency) with different OAM modes at 9 and 13 GHz is designed, and each OAM beam features a much more compact energy distribution compared to the conventional OAM beam. The measured results agree very well with the simulated results, which validate the proposed design methodology.

Generation of Multiple Vector Optical Bottle Beams

We propose binary diffractive optical elements, combining several axicons of different types (axis-symmetrical and spiral), for the generation of a 3D intensity distribution in the form of multiple vector optical ‘bottle’ beams, which can be tailored by a change in the polarization state of the illumination radiation. The spatial dynamics of the obtained intensity distribution with different polarization states (circular and cylindrical of various orders) were investigated in paraxial mode numerically and experimentally. The designed binary axicons were manufactured using the e-beam lithography technique. The proposed combinations of optical elements can be used for the generation of vector optical traps in the field of laser trapping and manipulation, as well as for performing the spatial transformation of the polarization state of laser radiation, which is crucial in the field of laser-matter interaction for the generation of special morphologies of laser-induced periodic surface structures.

Development of terahertz two-dimensional phase gratings for multiple beam generation based on a high-accuracy phase retrieval algorithm.

High efficiency and accuracy phase gratings are of crucial importance for large format heterodyne array receivers at terahertz frequencies. Here, by developing a design approach that can create gratings with arbitrary two-dimensional diffraction distributions, we have realized a reflective metallic phase grating that generates 2×2 diffraction beams at 0.85 THz. The measured total power efficiency of the diffraction beam pattern is 81.9%, which demonstrates at least 17% improvement in efficiency compared with the standard pseudo-2D Fourier phase grating. In addition, we report the realization of up to 10×10 diffraction beam two-dimensional phase grating designs at terahertz wavelengths, using an adaptation of the Gerchberg-Saxton (GS) scheme known as the Mixed-Region-Amplitude-Freedom algorithm. Rigorous full wave simulation proves the efficiency and accuracy of the design, which overcomes the inaccurate intensity of the beam distribution drawbacks originated from the standard GS algorithm. The results pave the way for the development of large-pixel terahertz multi-beam heterodyne receivers.

Multibeam steered pattern synthesis in time‐modulated antenna array with controlled harmonic radiation

This article deals with the synthesis of multibeam steerable patterns in time-modulated arrays (TMAs) for electronic scanning. The simultaneous generation of multiple beams in TMAs can be achieved through the exploitation of undesired harmonic radiations emitted at the multiples of modulating frequency due to the periodic switching. The direction-dependent harmonic beams are capable of producing independent information channels with different spatial distributions beneficial for electronic beam steering. Multibeam patterns associated with harmonic frequencies along with the fundamental pattern can be synthesized with suitably designed switching schemes. The potentialities of linear TMAs are explored in this article to generate a simultaneous sum and difference pattern useful for monopulse tracking systems. Further assessment of multipattern operations with linear TMAs are proposed with beam steering at lower-order harmonics. Steered double sum pattern with controlled harmonic radiations are also generated to achieve a steered multibeam with simplified beamforming network. Towards this aim, both the analytical and the optimized solutions of periodic switching sequences for different multibeam patterns are developed. Modified differential evolution with a wavelet-based mutation strategy (DEWM) is employed for the optimal solution. Representative results are assessed and compared with other published literature results to show the effectiveness of the proposed methods.

Generating arbitrary arrays of circular Airy Gaussian vortex beams with a single digital hologram

Circular Airy Gaussian vortex (CAGV) beams have gained great popularity in areas of research such as optical tweezers and optical communications due to their fascinating properties, such as auto-focusing and self-healing. The propagation dynamics of these beams is dictated by their topological charge and launch angle. For example, larger topological charges and positive launch angles enhance the maximum intensity in the focal plane while simultaneously shortening the focal length of autofocusing. Crucially, while the generation of single CAGV beams has been widely reported, the simultaneous generation of multiple CAGV beams, has remained challenging. Here, we put forward a novel technique that enables the simultaneous generation of multiple CAGV beams with independent topological charges or initial launch angles from a single digital hologram encoded on a spatial light modulator (SLM). Our technique enables the independent manipulation of each CAGV beam, their topological charge and launch angle, at refresh rates limited only by the SLM (60 Hz). This technique paves the way for the simultaneous manipulation of microparticles in three dimensions and provides with an alternative way to realize optical communications with multiple spatial modes of light.

Review on Ultra-Wideband Phased Array Antennas

Ultra-wideband (UWB) phased array antennas are essential for radar, communication, and Electronic Warfare (EW) applications. Systems can operate over wide-band coverage. The high gain systems require wide-band, wide-angle scanning, good radiation pattern, and return loss over a multi-octave bandwidth. This review discusses the problems present in the UWB phased array system, which include mutual coupling, grating lobe rejection, active return loss, gain fluctuation with scanning, and multiple beam generation. In this, the aperture size of the array is limited by the overall gain requirement of the system. On the other hand, low gain systems require a wide-band with a good radiation pattern and axial ratio. Here the matching over wide-band is simpler as it depends on broadband balun configuration. This system has limited bandwidth over scan angles. These antennas are more preferred as wearable antennas in communication applications. This paper mainly discusses the existing UWB phased array antennas such as Vivaldi Arrays, All-metal Arrays, Spiral Arrays, Sinuous Arrays, and Coupled Arrays. This review paper presents a correct direction for selecting the type of antenna in terms of impedance bandwidth, gain, and materials influencing antenna performance, suited for different applications.

A Time Modulated Array With Polarization Diversity Capability

The Time Modulated Array (TMA) provides multiple radiation beams at different frequencies, by turning the radiating elements on and off. In this paper, we propose to add polarization diversity to a wireless communication link by leveraging the capabilities of the TMA. The proposed architecture switches between two orthogonal polarizations, instead of turning the antenna off, providing polarization diversity for the receivers. We show that the beams of each polarization at the sidebands are exactly the same. However, the switching sequence should be optimized for the fundamental frequency to provide the same radiation level at each sideband. Two different switching sequences are proposed, which are optimized for different conditions. To evaluate the switching sequences and the diversity order of the system, an 8-element array with dual polarization antennas is fabricated. The radiating antenna element is a dual feed ring slot antenna, designed for 5.8 GHz with 10% fractional bandwidth. Both the single antenna and the array are measured in an anechoic chamber. The measurements indicate that the prototype provides full diversity gain along with multiple beam generation and beam steering, while it is very low cost and has low complexity.