Orbital Angular Momentum Waves: Generation, Detection and Emerging Applications

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

The physics of angular momentum radio

Wireless communications, radio astronomy and other radio science applications are predominantly implemented with techniques built on top of the electromagnetic linear momentum (Poynting vector) physical layer. As a supplement and/or alternative to this conventional approach, techniques rooted in the electromagnetic angular momentum physical layer have been advocated, and promising results from proof-of-concept radio communication experiments using angular momentum were recently published. This sparingly exploited physical observable describes the rotational (spinning and orbiting) physical properties of the electromagnetic fields and the rotational dynamics of the pertinent charge and current densities. In order to facilitate the exploitation of angular momentum techniques in real-world implementations, we present a systematic, comprehensive theoretical review of the fundamental physical properties of electromagnetic angular momentum observable. Starting from an overview that puts it into its physical context among the other Poincar\'e invariants of the electromagnetic field, we describe the multi-mode quantized character and other physical properties that sets electromagnetic angular momentum apart from the electromagnetic linear momentum. These properties allow, among other things, a more flexible and efficient utilization of the radio frequency spectrum. Implementation aspects are discussed and illustrated by examples based on analytic and numerical solutions.Comment: Fixed LaTeX rendering errors due to inconsistencies between arXiv's LaTeX machine and texlive in OpenSuSE 13.

ORBITAL ANGULAR MOMENTUM ORTHOGONALITY-BASED CROSSTALK REDUCTION: THEORY AND EXPERIMENT

Full duplex communication systems allow a single channel to be used for simultaneous two-way communication, increasing spectral efficiency. However, full duplex communication systems suffer from the issue of self-interference between local transmitter and receiver antennas. Analog subtraction and signal processing methods have previously been used to reduce this problem. This dissertation proposes the use of waves carrying orbital angular momentum (OAM) to mitigate the problem of self-interference by offering a means of additional isolation between local antennas. Orbital angular momentum has been widely studied both in the photonics and radio domain. The theoretically infinite orthogonal states of an OAM signal make it highly desirable in the field of communication. The application of OAM in a full duplex system, may be the answer to the problem of self-interference. This dissertation shows how the use of OAM waves may create an additional isolation between local antennas in a full duplex system. Motivated by the promise that OAM orthogonality holds, this dissertation explores the crosstalk reduction achieved through OAM. One of the main contributions of this dissertation is to provide insight into the nature of the effect. It motivates OAM orthogonality as a direction of research for use in future full duplex systems. The effect of OAM on crosstalk must be studied experimentally and theoretically. To this effect, a patch array antenna was designed using the High Frequency Simulation Software (HFSS), to generate OAM beams. The designed antennas are fabricated and characterized. This dissertation discusses the experiments carried out to determine the amount of crosstalk reduction achieved due to the OAM nature of the signal transmitted. The impact of the change in distance between the local transmitter and receiver antennas on crosstalk is also studied. The results obtained are verified through theoretical analysis using simulations in HFSS. This dissertation reports a maximum theoretical crosstalk reduction of 3.6dB, and a crosstalk reduction of 2.6 dB realized experimentally. Building on these results, a compact, more practical antenna configuration was designed. This nested design yields more than 60dB crosstalk reduction and provides for a more elegant system realization. The dissertation includes the design of a parabolic dish antenna to build a complete system, which is also studied in this dissertation. The symmetry of the nested antenna configuration allows for analytic theoretical study which is included herein. The study mathematically proves the orthogonality of OAM modes, and the isolation between two antennas with different OAM modes. A similar study is simulated in HFSS using coaxial based loop antennas, and the crosstalk in the nested design is investigated. The design offers a crosstalk isolation of more than 90dB, and further affirms the mathematical analysis. This dissertation provides a detailed analysis of the isolation offered by OAM orthogonality in local antennas which can be useful in a full duplex system. The work consists of practical, simulated, and mathematical investigation, and considers various antenna configurations and designs. Additionally, it presents and analyses a design for a full duplex system