Artificially engineered metasurfaces provide extraordinary wave control at the subwavelength scale. However, metasurfaces proposed so far suffer due to limited bandwidths. In this paper, extremely thin metasurfaces made of single metallic layer is experimentally presented for ultra-wideband operation from 9.3 to 32.5 GHz (with a fractional band of 112%), working at both transmission and reflection modes simultaneously. The phase control is achieved by azimuthally rotating the scatterer based on Pancharatnam-Berry phase principle. Nearly uniform efficiency (≈25%), approaching the theoretical limit of the infinitely thin metasurface, is achieved throughout the operation band. Finally, the proposed design is implemented for applications, e.g., the generation of electromagnetic waves carrying orbital angular momentums as well as anomalous reflections and refractions. The metasurfaces are characterized numerically and experimentally and the results are in good agreements.

Ultrathin Single Layer Metasurfaces with Ultra-Wideband Operation for Both Transmission and Reflection.

The orbital angular momentum (OAM) intrinsically carried by vortex light beams holds a promise for multidimensional high-capacity data multiplexing, meeting the ever-increasing demands for information. Development of a dynamically tunable OAM light source is a critical step in the realization of OAM modulation and multiplexing. By harnessing the properties of total momentum conservation, spin-orbit interaction, and optical non-Hermitian symmetry breaking, we demonstrate an OAM-tunable vortex microlaser, providing chiral light states of variable topological charges at a single telecommunication wavelength. The scheme of the non–Hermitian-controlled chiral light emission at room temperature can be further scaled up for simultaneous multivortex emissions in a flexible manner. Our work provides a route for the development of the next generation of multidimensional OAM-spin-wavelength division multiplexing technology.

/pdf/tunable-topological-charge-vortex-microlaser-4kfo8vj097.pdf

Tunable topological charge vortex microlaser

There is a continuing growth in the demand for data bandwidth, and the multiplexing of multiple independent data streams has the potential to provide the needed data capacity. One technique uses the spatial domain of an electromagnetic (EM) wave, and space division multiplexing (SDM) has become increasingly important for increased transmission capacity and spectral efficiency of a communication system. A subset of SDM is mode division multiplexing (MDM), in which multiple orthogonal beams each on a different mode can be multiplexed. A potential modal basis set to achieve MDM is to use orbital angular momentum (OAM) of EM waves. In such a system, multiple OAM beams each carrying an independent data stream are multiplexed at the transmitter, propagate through a common medium and are demultiplexed at the receiver. As a result, the total capacity and spectral efficiency of the communication system can be multiplied by a factor equal to the number of transmitted OAM modes. Over the past few years, progress has been made in understanding the advantages and limitations of using multiplexed OAM beams for communication systems. In this review paper, we highlight recent advances in the use of OAM multiplexing for high-capacity free-space optical and millimetre-wave communications. We discuss different technical challenges (e.g. atmospheric turbulence and crosstalk) as well as potential techniques to mitigate such degrading effects.This article is part of the themed issue 'Optical orbital angular momentum'.

https://royalsocietypublishing.org/doi/pdf/10.1098/rsta.2015.0439

Recent advances in high-capacity free-space optical and radio-frequency communications using orbital angular momentum multiplexing

Orbital angular momentum (OAM) has aroused a widespread interest in many fields, especially in telecommunications due to its potential for unleashing new capacity in the severely congested spectrum of commercial communication systems. Beams carrying OAM have a helical phase front and a field strength with a singularity along the axial center, which can be used for information transmission, imaging and particle manipulation. The number of orthogonal OAM modes in a single beam is theoretically infinite and each mode is an element of a complete orthogonal basis that can be employed for multiplexing different signals, thus greatly improving the spectrum efficiency. In this paper, we comprehensively summarize and compare the methods for generation and detection of optical OAM, radio OAM and acoustic OAM. Then, we represent the applications and technical challenges of OAM in communications, including free-space optical communications, optical fiber communications, radio communications and acoustic communications. To complete our survey, we also discuss the state of art of particle manipulation and target imaging with OAM beams.

Orbital Angular Momentum Waves: Generation, Detection, and Emerging Applications

Time, polarization, and wavelength multiplexing schemes have been used to satisfy the growing need of transmission capacity. Using space as a new dimension for communication systems has been recently suggested as a versatile technique to address future bandwidth issues. We review the potentials of harnessing the space as an additional degree of freedom for communication applications including free space optics, optical fiber installation, underwater wireless optical links, on-chip interconnects, data center indoor connections, radio frequency, and acoustic communications. We focus on the orbital angular momentum (OAM) modes and equally identify the challenges related to each of the applications of spatial modes and the particular OAM modes in communication. We further discuss the perspectives of this emerging technology. Finally, we provide the open research directions and discuss the practical deployment of OAM communication links for different applications.

/pdf/communicating-using-spatial-mode-multiplexing-potentials-3l7esc1h6e.pdf

Communicating Using Spatial Mode Multiplexing: Potentials, Challenges, and Perspectives

Plane spiral orbital angular momentum (OAM) wave is a new form of OAM-carrying electromagnetic wave that propagates along the transverse direction. A traveling-wave circular slot antenna that can generate plane spiral OAM waves is developed and experimentally demonstrated in this letter. The antenna is excited by a 90 $^\circ$ hybrid coupler. In order to ensure that the OAM waves are propagating along the transverse plane, a ring horn is added outside the antenna. A prototype with OAM states l = $\pm$ 3 for 10-GHz operation is fabricated and measured. The near-field phase distributions clearly indicate the azimuth phase shifting, and the radiation patterns show the characteristic of transverse propagation, respectively. The proposed antenna provides a novel approach to implement an OAM wireless communication link that has no phase singularity or divergence problem.

Generation of Plane Spiral OAM Waves Using Traveling-Wave Circular Slot Antenna

Wireless communication using electromagnetic wave carrying orbital angular momentum (OAM) has attracted increasing interest in recent years, and its potential to increase channel capacity has been explored widely. In this paper, we compare the technique of using uniform linear array consist of circular traveling-wave OAM antennas for multiplexing with the conventional multiple-in-multiple-out (MIMO) communication method, and numerical results show that the OAM based MIMO system can increase channel capacity while communication distance is long enough. An equivalent model is proposed to illustrate that the OAM multiplexing system is equivalent to a conventional MIMO system with a larger element spacing, which means OAM waves could decrease the spatial correlation of MIMO channel. In addition, the effects of some system parameters, such as OAM state interval and element spacing, on the capacity advantage of OAM based MIMO are also investigated. Our results reveal that OAM waves are complementary with MIMO method. OAM waves multiplexing is suitable for long-distance line-of-sight (LoS) communications or communications in open area where the multi-path effect is weak and can be used in massive MIMO systems as well.

/pdf/the-capacity-gain-of-orbital-angular-momentum-based-multiple-cyrbsg2ew6.pdf

The Capacity Gain of Orbital Angular Momentum Based Multiple-Input-Multiple-Output System.

A new form of plane spiral orbital angular momentum (PS-OAM) carrying wave with the spiral harmonics of exp(− $jl\varphi$ ) as a complete set of eigenmodes is proposed to realize beam steering. Such a wave possesses the fundamental characteristics of an OAM-carrying wave, i.e., a spiral phase distribution, yet propagates along transverse directions. Hence, it owes unique advantages for use in realizing desired radiation beams, while avoids the puzzles encountered by traditional OAM-carrying beams. Various OAM mode grouping using the superposition of PS-OAM waves are demonstrated here via theoretical calculations as well as experimental verifications. The generation methods for PS-OAM waves are also proposed and experimentally validated to authenticate the feasibility. Both the calculated and experimental results show that the PS-OAM grouping is capable of providing a practical realization of eigenmode beamforming.

Realization of Beam Steering Based on Plane Spiral Orbital Angular Momentum Wave

Synergistic effect of rhenium and ruthenium in nickel-based single-crystal superalloys

In-situ tensile experiments of Ni-Al, Ni-Al-Re and Ni-Al-Re-Ru model single-crystal superalloys were performed in scanning electron microscope (SEM) at room temperature. The plastic deformation mechanisms of all the three model superalloys were double-oriented slipping of dislocations. Micro-cracks were often formed at the intersection of two sets of slip lines. The fracture surfaces of Ni-Al and Ni-Al-Re-Ru alloys were nearly parallel to (010) planes and that of the Ni-Al-Re alloys was nearly parallel to (1−11) plane. The dislocation configuration was analyzed by transmission electron microscopy (TEM). The a/2 dislocation pairs coupled with antiphase boundary (APB) cut into γʹ phase in the Ni-Al and Ni-Al-Re-Ru model superalloys. In addition to these dislocations, stacking faults also cut into γʹ phase in Ni-Al-Re model superalloys. The different fracture surfaces of different model single-crystal superalloys were attributed to the influence of elements Re and Ru on the dislocation configuration.

Effect of rhenium and ruthenium on the deformation and fracture mechanism in nickel-based model single crystal superalloys during the in-situ tensile at room temperature

Zhuofan Zhang

Papers

Generation of Plane Spiral OAM Waves Using Traveling-Wave Circular Slot Antenna

The Capacity Gain of Orbital Angular Momentum Based Multiple-Input-Multiple-Output System.

Realization of Beam Steering Based on Plane Spiral Orbital Angular Momentum Wave

Synergistic effect of rhenium and ruthenium in nickel-based single-crystal superalloys

Effect of rhenium and ruthenium on the deformation and fracture mechanism in nickel-based model single crystal superalloys during the in-situ tensile at room temperature