Generation Of Multiple Beams Research Articles

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.

Quasi-Passive Indoor Optical Wireless Communication Systems

Optical wireless communications (OWCs) have been widely studied to provide high-speed wireless services in indoor environments, and the combination of beam steering with localization has been explored to extend the coverage area and to provide user mobility. However, beam steering typically consumes continuous power, even when the user is stationary. In this paper, we propose and demonstrate a quasi-passive indoor OWC system with zero power consumption when the user is stationary or quasi-stationary. It also supports the generation of multiple signal beams for multi-user access. 10 Gb/s transmission is demonstrated and users at different locations are served simultaneously. Experimental results show that no power penalty is observed compared to traditional systems consuming continuous power. The proposed quasi-passive system provides a multi-user access and low-power consumption solution for indoor applications.

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

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

Broadband high-efficiency multiple vortex beams generated by an interleaved geometric-phase multifunctional metasurface

Vortex beams have witnessed tremendous development in the past decade by exhibiting profound implications for both fundamental physics and a multitude of novel engineering applications. In this work, broadband high-efficiency multiple vortex beams with independent topological modes and inclination angles are generated leveraging an interleaved geometric-phase multifunctional metasurface operating in a very broadband frequency range. A set of meta-atoms are elaborately engineered to offer broadband high-efficiency complete phase control covering the entire 2π range. Multiple geometric-phase sub-arrays implemented by the designed meta-atoms are synthesized into one metasurface via a shared-aperture interleaved manner, in which each sub-array can be individually manipulated and serves as an independent channel for launching a vortex beam. According to the established design methodology, two vortex beams with topological modes of −1 and +2 and distinct inclination angles are generated by one metasurface. Experimental results are provided to corroborate the proposed mechanism for multiple vortex beams generation, which exhibit broadband and high-efficiency features. The presented multifunctional metasurface paves the way for the generation of broadband high-efficiency multiple vortex beams in the microwave, millimeter-wave and terahertz regions. This work is of significance for high-capacity wireless communication applications, high-efficiency manipulation of electromagnetic waves, and novel design of radar and imaging systems.

A N260 Band 64 Channel Millimeter Wave Full-Digital Multi-Beam Array for 5G Massive MIMO Applications

In this paper, a 37-42.5GHz (N260 Band) 64 channel full-digital multi-beam array for 5G massive multiple input multiple output (MIMO) applications is developed. The multi-beam array is built on a time division duplexing (TDD) architecture in which the transmitter and receivers are independent and working separately to enable more flexible channel configuration and hardware distribution. The 64 antenna elements of the array are aligned in a way that 16 elements lie in the horizontal and 4 in the vertical direction to deliver higher beam resolution in the horizontal plane. By using cables of unequal lengths, the $16\times 4$ antenna elements are connected to a cluster of $8\times 8$ transmitters/receivers. The hardware design of the transmitters, receivers, antennas and other circuits is demonstrated, with excellent measured RF performance achieved. Furthermore, the calibration of the massive MIMO array is presented, and the influence of inequality of array feedlines on calibration accuracy in a wide bandwidth is analyzed and experimentally verified. Finally, experimental studies on single beam scanning, multiple concurrent beam generation and over-the-air (OTA) performance of the transmitting and receiving array have been done. Simulation and measurement results suggest that the array has an excellent beam-forming capability that supports beam steering and generation of multiple concurrent beams. The OTA test reveals that the array can provide high modulation and demodulation accuracy for communication.

Optimised XUV holography using spatially shaped high harmonic beams.

We present a novel method for controlling the transverse positions and relative powers of multiple high-order harmonic beams. A phase-only spatial light modulator is used to produce multiple infrared foci, the positions and intensities of which can be controlled programmably, enabling the generation and control of multiple HHG beams. To demonstrate the utility of this method we perform Fourier transform holography with separate illumination of the object and reference pinhole by a pair of HHG beams, which makes optimal use of the available photon flux. The programmable control of the spatial distribution of HHG beams demonstrated here offers new opportunities for experiments at extreme ultraviolet (XUV) wavelengths, particularly for photon intensive applications such as imaging.

Compensation of optical path difference in heterodyne Φ-OTDR systems and SNR enhancement by generating multiple beat signals.

In conventional heterodyne phase-sensitive optical time domain reflectometry (Φ-OTDR), the optical path difference (OPD) between sensing and reference arms deteriorates the signal-to-noise ratio (SNR). We counteract this effect by introducing a loop path in reference arm. This facilitates the use of laser source with low coherence length. Compared with an ordinary Φ-OTDR system, SNR increased from ~1 dB to 5 dB. Regardless of OPD compensation features, the probability to getting a better output increases by generation of multiple reference beams (and consequently multiple beat signals), as compared to conventional systems. The method is cost efficient and suitable for practical purposes.

5G RAN architecture based on analog radio-over-fiber fronthaul over UDWDM-PON and phased array fed reflector antennas

This manuscript introduces a 5G radio access network architecture concept based on ultra-dense wavelength division multiplexing (UDWDM) and incorporating an optical fronthaul network that uses a novel wireless antenna system for radio frequency transmission and reception. A ring topology is proposed where optical signals travel within the 5G UDWDM passive optical networks and millimeter waves are generated in the optical line terminals by optical heterodyning. The wireless transmission of the millimeter waves is conducted by an innovative phased array fed reflector antenna approach for mobile communications that grants high antenna gain due to highly focused radiation characteristics, as well as multiplexing gain by multiple beam generation. Furthermore, beam steering is provided by a radio frequency analog beamformer network. Finally, implementation options synthesizing the total system are discussed.

Approach to analysis of all-dielectric free-form antenna systems.

The analytical model is proposed for simulation of the near-field and far-field characteristics of an all-dielectric free-form antenna system. The antenna system is constructed of an array of high-refractive-index dielectric resonators. The model relies on the coupled mode theory and the perturbation theory for the Maxwell's equations. The model is validated against numerical simulations performed by the ANSYS HFSS electromagnetic solver and microwave experiments. Three designs of the free-form antenna systems are proposed, studied and experimentally tested. The mechanisms of the multiple beam generation and beam steering are demonstrated.

High-efficiency Bessel beam array generation by Huygens metasurfaces

Abstract Bessel beams have attracted considerable interest because of their unique non-diffractive, self-healing characteristics. Different approaches have been proposed to generate Bessel beams, such as using axicons, diffractive optical elements, composite holograms, or spatial light modulators. However, these approaches have suffered from limited numerical aperture, low efficiency, polarization-dependent properties, etc. Here, by utilizing dielectric Huygens metasurfaces as ultrathin, compact platforms by integrating the functionalities of Dammann gratings and axicons, we successfully demonstrate multiple Bessel beam generation with polarization-independent property. The number of two-dimensional arrays can be controlled flexibly, which can enhance information capacity with a total efficiency that can reach 66.36%. This method can have various applications, such as parallel laser fabrication, efficient optical tweezers, and optical communication.

Multibeam Generation and Measurement of a DDS-Based Digital Beamforming Array Transmitter at Ka-Band

In this paper, a Ka -band digital beamforming array transmitter (DBFAT) using direct digital synthesizer (DDS) for millimeter-wave (mmW) applications is proposed. The system architecture, realization, generation, and measurement process of multiple beams are introduced. The array element consists of two kinds of tapered slot antennas with opposite fin orientations. They are placed in the side-by-side configuration such that the undesirable orthogonal electrical field is suppressed, thereby decreasing the cross-polarization level at the majority of the scanning angles. Different sets of weighting coefficients are synthesized by the DDS module, which generates various types of multibeam patterns simultaneously. Compared with the existing realized DBFAT systems, the radiation patterns of various multibeam scenarios are investigated and measured. Also, all of the mmW channels are placed on a single board, making the overall system much more compact. In addition, compared to DBFAT, which consists of identical array elements, the cross-polarization performance of the proposed DBFAT is improved within a wide range of scanning angles. As a proof-of-concept example, a 15-element linear DBFAT system prototype is fabricated and measured, confirming the validity of the presented technology, which can be utilized as a simple and low-cost alternative for evaluating the radiation performance of mmW DBFATs.

Generation of multiple beams carrying different orbital angular momentum modes based on anisotropic holographic metasurfaces in the radio-frequency domain

In this paper, an anisotropic holographic metasurface design is proposed, fabricated, and measured, to demonstrate that it can generate multiple beams with different orbital angular momentum (OAM) modes in the radio-frequency domain. The anisotropic holographic metasurface is composed of an array of quasi-periodic square particles with a rectangular slot in the upper metallic layer covered with a dielectric ground. The classic leaky-wave theory and a microwave holography method are introduced to construct the holograms that interfere with the surface waves excited by a monopole antenna and the objective waves represented by the desired multiple beams carrying different OAM modes. Moreover, the numerical simulations and experimental results are in very good agreement, which demonstrates the excellent performance of the design and provides a method of generating multiple OAM modes simultaneously. This lays a solid foundation for a channel-multiplexing method based on OAM-mode multiplexing to expand the capacity of wireless communication systems.

Simultaneous Generation of Complex Structured Curve Beam.

At present, people are using holographic technologies to shape complex optical beams for both fundamental research and practical applications. However, most of the reported works are focusing on the generation of a single beam pattern based on the computer-generated hologram (CGH). In this paper, we present a method for simultaneously shaping the multiple beam lattice where the intensity and phase of each individual beam can be prescribed along an arbitrary geometric curve. The CGH that is responsible for each individual beam is calculated by using the holographic beam shaping technique, afterwards all the CGHs are multiplexed and encoded into one phase-only hologram by adding respective linear phase grating such that different curves are appeared in different positions of the focal regions. We experimentally prove that the simultaneous generation of multiple beams can be readily achieved. The generated beams are especially useful for applications such as multitasking micro-machining and optical trapping.

Acoustic analysis of a broadband spiral source for the simultaneous generation of multiple Bessel vortices in air.

A detailed characterization and analysis of the acoustic field radiated by an active diffraction grating is presented. This is a spiral-shaped source of constant width of the spiral paths and spacing among them, built with flexible ferroelectrets, which is suitable to operate within a broad range of ultrasonic frequencies. The simultaneous airborne generation of multiple Bessel vortex beams with different topological charges along the propagation axis is thoroughly discussed in terms of the structure of the spiral source and the driving frequency, along with some technical details of the prototype. Finally, the quality of the experimentally generated Bessel vortices is discussed, including the phase structure and the amplitude of the acoustic pressure.

Observation of the generation of multiple electron beams during a single sheath expansion phase in capacitive RF plasmas

The fundamental investigation of different electron heating modes is important in order to fully understand the generation of plasmas, as well as to optimize their technological applications. In this study, a capacitively coupled radio-frequency discharge is operated at its limit of comparably low plasma density. Phase resolved optical emission spectroscopy provides insights into the electron dynamics on a nanosecond time scale under these conditions. At low applied voltage amplitudes, it is observed that more than one electron beam is generated within a single phase of sheath expansion at a given electrode. When the voltage amplitude is increased these beams merge in time to a single electron beam. This effect has been predicted by particle in cell/Monte-Carlo collision simulations before and contradicts existing models that assume the generation of a single beam per sheath expansion phase by stochastic heating (Wilczek et al 2015 Plasma Sources Sci. Technol. 24 024002; Wilczek et al 2016 Phys. Plasmas 23 063514). In this study, results from a systematic experimental study of the effect are presented, which support the theoretically predicted phenomenon.

Space‐Frequency‐Domain Gradient Metamaterials

AbstractIn recent years, an intense research effort has focused on the flexible manipulation of electromagnetic (EM) waves using metamaterials. As an important category, gradient metamaterials (metamaterials with gradient phases) can impart subwavelength‐scale space‐variant phase changes during the electromagnetic wave propagations to shape EM radiations in which arrays of elements with certain phase gradients can form EM beam propagations as desired. Here, the concept of space‐frequency‐domain gradient metamaterial is proposed, in which new degrees of freedom are attained by introducing frequency‐domain phase gradients to the metamaterial. The frequency gradients of the metamaterial are obtained by the derivative of phase gradients with respect to frequency, which can be used to shape the uniformly distributed phase gradients to vary as demand in the working frequency band without any active devices. The combinations of space and frequency gradients in metamaterials in 1D/2D open new possibilities for more powerful controls of EM waves, thereby yielding more complicated functions such as 2D flexible beam scanning, continuous transformations of vortex modes, and generation of multiple beams with desired transmission directions and transmission modes.

Multi‐100‐Watt Femtosecond Laser Perspectives

AbstractFemtosecond lasers are today delivering output powers of several hundred watts. The challenge is to translate the available power into high throughput micromachining by combining the laser with fast scanning systems or multiple beam generation. Free triggering of the laser output pulses with good precision (also known as “pulse on demand”) is particularly useful for exploiting advanced functionalities of processing tools.

High-efficiency multi-wavelength metasurface with complete independent phase control

As a consequence of Kramers–Kronig relations, the wavelength-dependent behavior of the metasurface is one of the critical limitations in existing metasurface structures, which reduces the design freedom among different wavelengths. Here, we present an approach to construct a high-efficiency multi-wavelength metasurface with independent phase control by coding different wavelengths into orthogonal polarizations. As proof of the concept, two dual-band metasurfaces have been proposed and numerically demonstrated by multiple vortex beam generation in near-field and polarization multiplexing achromatic beam deflection. Furthermore, simulated results show that the proposed metasurface exhibits high transmission efficiency at both wavelengths, which may find widespread applications in subwavelength electromagnetics.

Generation of vector Bessel beams with diffractive phase elements based on the Jacobi-Anger expansion.

We report the design and optimization of a diffractive phase element whose phase modulation is derived from the Jacobi-Anger relation, which allows the simultaneous generation of multiple scalar Bessel beams of different integer orders. In addition, by the appropriate treatment of a couple of such Bessel beams, we generate a vector Bessel beam of arbitrary order m. This beam is constructed by the collinear superposition of the scalar Bessel beam modes of orders m-1 and m+1, with circular orthogonal polarizations. We demonstrate experimentally both the simultaneous generation of the multiple scalar Bessel beams and the generation of vector Bessel beams of orders m=0 and m=1. These tasks are performed in an optical setup based on a pixelated liquid-crystal spatial light modulator.

Simultaneous generation of multiple vector beams on a single SLM.

Complex vector light fields, classically entangled in polarization and phase, have become ubiquitous in a wide variety of research fields. This has triggered the demonstration of a wide variety of generation techniques. Of particular relevance are those based on computer-controlled devices due to their great flexibility. In particular, spatial light modulators have demonstrated their high capabilities to generate any vector beam, with various spatial profiles and polarization distributions. Here, we put forward a novel technique that exploits the superposition principle in optics to enable the simultaneous generation of many vector beams using a single digital hologram. As proof-of-principle, we demonstrated the simultaneous generation of sixteen vector vortex beams with various polarization distributions and spatial shapes on a single SLM, each with their own spatial shape and polarization distribution.