Encoding many channels in the same frequency through radio vorticity: first experimental test

We have shown experimentally that it is possible to propagate and use the properties of twisted non-monochromatic incoherent radio waves to simultaneously transmit to infinity more radio channels on the same frequency band by encoding them in different orbital angular momentum states. This novel radio technique allows the implementation of, at least in principle, an infinite number of channels on one and the same frequency, even without using polarization or dense coding techniques. An optimal combination of all these physical properties and techniques represents a solution for the problem of radio band congestion. Our experimental findings show that the vorticity of each twisted electromagnetic wave is preserved after the propagation, paving the way for entirely new paradigms in radio communication protocols.Comment: 17 pages, 6 figures, with a public experiment, three audio files in mp3 forma

Matrix metalloproteinases are associated with brain atrophy in cognitively unimpaired individuals

Matrix metalloproteinases (MMPs) and their tissue inhibitors (TIMPs) have been linked to age-related neurodegeneration and Alzheimer's disease (AD), but their role in normal aging is poorly understood. We used linear mixed models to determine if baseline or rate of yearly change in cerebrospinal fluid (CSF) levels of MMP-2; MMP-3; MMP-10; TIMP-123 (composite of TIMP-1, TIMP-2, and TIMP-3); or TIMP-4 predicted changes in bilateral entorhinal cortex thickness, hippocampal volume, or lateral ventricle volume in cognitively unimpaired individuals. We also assessed effects on the CSF AD biomarkers amyloid-β42 and phosphorylated tau181. Low baseline levels of MMP-3 predicted larger ventricle volumes and more entorhinal cortex thinning. Increased CSF MMP-2 levels over time predicted more entorhinal thinning, hippocampal atrophy, and ventricular expansion, while increased TIMP-123 over time predicted ventricular expansion. No MMP/TIMPs predicted changes in CSF AD biomarkers. Notably, we show for the first time that longitudinal increases in MMP-2 and TIMP-123 levels may predict age-associated brain atrophy. In conclusion, MMPs and TIMPs may play a role in brain atrophy in cognitively unimpaired aging

Optical vortex diffractive optics for terrestrial and space applications

Optical vortices are topological dislocations due to phase singularities in light beams carrying orbital angular momentum (OAM). The wavefront of the electromagnetic wave that carries OAM is twisted around its axis of propagation, with a helicoidal shape. Along the axis of the helicoid the phase is undefined, so the waves cancel each other out. Hence, the intensity distribution of a vortex presents a dark core due to the destructive interference, that is surrounded by a ’ring of light’. The vortex is characterized by a number, called the topological charge that indicates how many 2π-twists the wave does around the axis within one wavelength. In the past decade, the OAM of a beam was paid great attention in many applications in physics. Among these, the most promising are those in optical communications, nanotechnolo- gies, biology and astronomy. Optical vortices may be created by a variety of different methods, one of which is by the use of a diffractive vortex mask, the spiral phase plate. The spiral phase plate is a helicoidal device that looks like a spiral staircase with a certain number of steps, that imposes an azimuthally dependent phase retard on an incident optical wavefront. The object of the research presented in this dissertation is the study of the properties of these particular optical devices and some of their possible applications. Firstly, we have studied the spiral phase plate in the visible domain. We have found, through numerical simulations and experimental test on optical bench, a relationship between the number of steps, which build the phase gap, and the topological charge imposed to incident light beam. This result allowed us to optimize the design parameters of the spiral phase plates manufac- tured on PMMA for astronomical purpose. We have assembled our first prototype of the optical vortex coronagraph inserting in the optical path the spiral phase plate. Coronagraphs are instru- ments designed to block the light from a bright source so that nearby much fainter sources can be directly imaged without glare. The optical vortex coronagraph exploits the dark area in the intensity distribution of the even-topologically charged optical vortices produces by spiral phase plate, attenuating the light of the bright source keeping intact that of secondary sources. In this framework of our project we performed coronagraphic tests at Asiago 122 cm tele- scope extinguishing the light of one component of a stellar double system of almost one order of magnitude. The astronomical use of the spiral phase plate has suggested to us to investigate the efficiency of this device with respect to the angular distance at which the secondary source crosses the central singularity. Through numerical simulations we found that the optical vortex coronagraph works also above the limit posed by the Rayleigh criterion. The research has led to the proposition of a new method to determine the angular separation between two sources above sub-Rayleigh condition, exploiting the asymmetric intensity distribution of the OVs produced by a double system that crosses spiral phase plate. As Maxwell’s equations are equally valid for all the bandwidths, optical vortices can be pro- duced also in radio frequencies. Based on this fundamental principle, we have studied diffractive optics also for radio domain, presenting the first experimental evidence of a radio vortex. We built a reflective spiral phase plate made on styrofoam and aluminum, with a design based on the re- sults obtained in the visible domain. The experimental verification that OAM-carrying beams can be generated and exploited by using radio techniques has opened the way to the experiment that we carried out in radio communication. We have showed, in a real-world setting, that is possible to simultaneously transmit two radio channels on the same frequency encoded in two different orbital angular momentum states. This novel radio technique allows, in principle, the implementation of an infinite number of channels in a band centered on one and the same frequency. Our experimental findings that electromagnetic OAM can be used for radio and TV transmission are likely to open new perspectives on wireless communications and radio-based science.I vortici ottici, sono caratteristiche topologiche dell’onda, legate alle singolaritá di fase nei campi elettromagnetici che trasportano momento angolare orbitale (OAM). Il fronte d’onda ha forma elicoidale, si attorciglia spiraleggiando attorno all’asse di propagazione in cui la fase é indefinita. Lungo l’asse dell’elica le onde fanno interferenza distruttiva le une con le altre, con il risultato di una distribuzione d’intensitá caratterizzato da una regione buia nel centro, circondata da luce a forma di ciambella. I vortici ottici sono caratterizzati da un valore, detto carica topologica che indica quante volte la fase compie una completa variazione di 360 gradi attorno all’asse ottico in una lunghezza d’onda. I vortici ottici possono essere prodotti con l’utilizzo di strumenti ottici. In particolare in questa tesi sono state studiate delle particolare ottiche diffrattive dette spirali di fase. Le spirali di fase sono ottiche il cui spessore cresce gradualmente intorno ad un asse; somigliano a scale a chioc- ciola, costruite con un certo numero di scalini ed impongono al fascio incidente un ritardo di fase che dipende dall’angolo azimutale. L’oggetto di questa ricerca é lo studio delle proprietá delle spirali di fase, la caratterizzazione e alcune possibili applicazioni. Lo studio si é inizialmente concentrato sulle spirali da fase nel range del visibile. Attraverso simulazioni numeriche ed esperimenti al banco ottico, siamo riusciti a ricavare una relazione tra il numero degli scalini che costruiscono il salto di fase nella spirale e la carica topologica che viene imposta al fascio incidente. Questo risultato ci ha permesso di ottimizzare i parametri di costruzione della spirale realiz- zata in PMMA per applicazioni astronomiche. Abbiamo infatti assemblato il primo prototipo di un coronografo a vortici ottici, nel cui cammino ottico é stata inserita la spirale di fase realizzata in base ai parametri da noi definiti. I coronografi, in generale, sono strumenti progettati per bloccare la luce proveniente da una sorgente brillante in modo tale da poter osservare direttamente delle sorgenti piú deboli nelle vicinanze. Il coronografo a vortici ottici sfrutta la regione buia nella di- stribuzione d’intensitá di un vortice ottico per attenuare la luce di una sorgente luminosa, senza diminuire l’intensitá della sorgente secondaria. Abbiamo testato il nostro prototipo al telescopio ’Galileo’ 122cm di Asiago, attenuando l’in- tensitá di una componente del sistema stellare doppio Epsilon2 Lyrae di quasi un ordine di magnitudine. L’applicazione astronomica della spirale di fase ci ha spinto allo studio delle sua efficienza, ovvero del contrasto che si ottiene nella zona buia del vortice ottico, a diverse distanze angolari della sorgente secondaria rispetto alla singolaritá centrale della spirale. Simulazioni numeriche hanno mostrato che il coronografo a vortici ottici funziona anche al di sotto del limite di risoluzione di Rayleigh. La ricerca si é sviluppata fino alla formulazione di un nuovo metodo per determinare la distanza angolare tra due sorgenti distanti meno del criterio di Rayleigh. Il nuovo metodo sfrutta la distribuzione d’intensitá asimmetrica dei vortici ottici prodotti dalla sorgente secondaria che passa attraverso la spirale di fase, ma non in corrispondenza della singolaritá centrale. Poiché le equazioni di Maxwell sono valide su tutto lo spettro elettromagnetico, i vortici posso- no essere prodotti anche in diverse bande rispetto al visibile. Basandoci su questo fondamentale principio abbiamo studiato delle ottiche diffrattive per la produzione di vortici nel range del radio. Abbiamo costruito con polistirolo e alluminio una spirale di fase basandoci sui risultati trovati nel visibile ed abbiamo ottenuto la prima evidenza sperimentale di un vortice radio. La verifica speri- mentale della possibilitá di generare e sfruttare vortici radio ha spianato la strada all’esperimento successivo che é stato condotto nel campo della comunicazione radio. Abbiamo compiuto la prima trasmissione OAM in cui due segnali sono stati trasmessi con- temporaneamente e sulla stessa frequenza, su due canali radio codificati in due diversi stati di momento angolare orbitale. Questa nuova tecnica radio permette, in teoria, di codificare un infinito numero di canali in una singola banda centrata su una frequenza. I risultati dei nostri esperimenti nel dominio del radio aprono nuove prospettive nel mondo della comunicazione

Experimental verification of photon angular momentum and vorticity with radio techniques

The experimental evidence that radio techniques can be used for synthesizing and analyzing non-integer electromagnetic (EM) orbital angular momentum (OAM) of radiation is presented. The technique used amounts to sample, in space and time, the EM field vectors and digitally processing the data to calculate the vortex structure, the spatial phase distribution, and the OAM spectrum of the radiation. The experimental verification that OAM-carrying beams can be readily generated and exploited by using radio techniques paves the way to an entirely new paradigm of radar and radio communication protocols. (C) 2011 American Institute of Physics. [doi:10.1063/1.3659466

Manipulating intensity and phase distribution of composite Laguerre-Gaussian beams

We propose a method to manipulate the intensity and phase distributions of a beam with non-zero orbital angular momentum (OAM). We investigate the superposition of coherent consecutive OAM modes, with concordant topological charges values, showing that it is possible to predict and control the phase and the radial and angular dimension of the resulting beam by acting on the number of superposed modes (N) and on their minimum value of the OAM (m(min)). A general analysis from the Wigner function formalism is adopted for the geometric characterization of the beam

Angular momentum properties of electromagnetic field transmitted through holey plasmonic vortex lenses

We performed three-dimensional finite elements simulations of the optical response of holey plasmonic vortex lenses, i.e., spiral grooves milled on a thin gold film with a hole at the center. We focus in particular on the properties of the wave transmitted in the underlying half-space, which is shown to be a relevant part of the transmitted field. We find out that the angular momentum selection rule for this part of the field is different from the one for the transmitted plasmonic vortex, although closely related to the plasmonic interaction of the impinging wave with the chiral geometry

Focusing dynamics on circular distributed tapered metallic waveguides by means of plasmonic vortex lenses

none6We investigate the focusing effect on circularly distributed planar tapered plasmonic waveguides by means of three-dimensional (3D) finite elements simulations. The proposed configuration allows nanofocusing on four faced planar nanotips, showing efficient condensation of surface plasmons polaritons (SPPs) at the silver/air interface toward the endpoint of the tips. By means of a plasmonic vortex lens it is possible to illuminate the tips with SPP waves carrying orbital angular momentum (OAM), namely plasmonic vortices. Our 3D simulations show that by acting on the topological charge of the plasmonic vortex the electric field charge distribution at the tips apex can be controlled accordingly to the input electric field phase distribution. The results for three particular OAM values are shown, along with a generalization for arbitrary plasmonic vortex angular momentum values.noneOngarello, Tommaso; Parisi, Giuseppe; Garoli, Denis; Mari, Elettra; Zilio, Pierfrancesco; Romanato, FilippoOngarello, Tommaso; Parisi, Giuseppe; Garoli, Denis; Mari, Elettra; Zilio, Pierfrancesco; Romanato, Filipp