Fabio Spinello

Near-Field Experimental Verification of Separation of OAM Channels

The experimental proof that near-field radio communication channels based on orbital angular momentum (OAM) are naturally isolated is presented. In near-field zone, we show that two antennas, built for producing a beam with the same value of OAM, have a good throughput. On the other hand, antennas of different types, i.e., built for generating beams with different OAM values, including a standard l = 0 antenna, exhibit a good modal isolation .

Space-Division Demultiplexing in Orbital-Angular-Momentum-Based MIMO Radio Systems

Radio beams that carry nonzero orbital angular momentum (OAM) are analyzed from the viewpoint of a multiple-input-multiple-output (MIMO) communication system. Often, the natural OAM-beam orthogonality cannot be fully exploited because of spatial constraints on the receiving antenna size. Therefore, we investigate how far OAM-induced phase variations can be exploited in spatial demultiplexing based on conventional (linear momentum) receivers. Performances are investigated versus position and size of the transmitting and receiving devices. The use of OAM-mode coherent superpositions is also considered, in view of recent work by Edfors et al. Our final goal is to assess the merits of an OAM-based MIMO system, in comparison with a conventional one.

Tripling the capacity of a point‐to‐point radio link by using electromagnetic vortices

In this paper we report the results from outdoor experiments showing that it is possible to increase the data transmission capacity using at least three coherent, orthogonal beams on the same frequency, 17.128 GHz, each in a unique orbital angular momentum state. Each beam was encoded with the digital modulations used in present-day telecommunications. We achieved an error-free throughput of 3 × 11 Mbit/s with four-Quadrature Amplitude Modulation over a 7 MHz bandwidth over 100 m and 150 m long links.

High-Order Vortex Beams Generation in the Radio-Frequency Domain

A novel technique for generating high-order vortex beams in the radio-frequency domain is reported. Vortex beams with non-null radial index are generated by means of a dielectric mask, mounted upon either a twisted parabolic reflector or a conventional one. The far-field intensity pattern is compared to analytical models and numerical simulations, thus illustrating how diffraction and illumination can affect the generated fields.

Angular Momentum Radio

Wireless communication amounts to encoding information onto physical observables carried by electromagnetic (EM) fields, radiating them into surrounding space, and detecting them remotely by an appropriate sensor connected to an informationdecoding receiver. Each observable is second order in the fields and fulfills a conservation law. In present-day radio only the EM linear momentum observable is fully exploited. A fundamental physical limitation of this observable, which represents the translational degrees of freedom of the charges (typically an oscillating current along a linear antenna) and the fields, is that it is single-mode. This means that a linear-momentum radio communication link comprising one transmitting and one receiving antenna, known as a single-input-single-output (SISO) link, can provide only one transmission channel per frequency (and polarization). In contrast, angular momentum, which represents the rotational degrees of freedom, is multi-mode, allowing an angular-momentum SISO link to accommodate an arbitrary number of independent transmission channels on one and the same frequency (and polarization). We describe the physical properties of EM angular momentum and how they can be exploited, discuss real-world experiments, and outline how the capacity of angular momentum links may be further enhanced by employing multi-port techniques, i.e., the angular momentum counterpart of linear-momentum multiple-input-multiple-output (MIMO).

General theorem on the divergence of vortex beams

The propagation and divergence properties of beams carrying orbital angular momentum (OAM) play a crucial role in many applications. Here we present a general study on the divergence of optical beams with OAM. We show that the mean absolute value of the OAM imposes a lower bound on the value of the beam divergence. We discuss our results for two different definitions of the divergence, the so-called rms or encircled energy. The bound on the rms divergence can be expressed as a generalized uncertainty principle, with applications in long-range communication, microscopy, and two-dimensional quantum systems.