RF Orbital Angular Momentum

Time-division multiplexing of the orbital angular momentum of light

noreply@blogger.com (Bill St. Arnaud) — Sun, 08 Jan 2012 14:22:00 +0000

Time-division multiplexing of the orbital angular momentum of light

Ebrahim Karimi, Lorenzo Marrucci, Corrado de Lisio, and Enrico Santamato

Optics Letters, Vol. 37, Issue 2, pp. 127-129 (2012)

http://dx.doi.org/10.1364/OL.37.000127Abstract

We present an optical setup for generating a sequence of light pulses in which the orbital angular momentum (OAM) degree of freedom is correlated with the temporal one. The setup is based on a single q plate within a ring optical resonator. By this approach, we demonstrate the generation of a train of pulses carrying increasing values of OAM, or, alternatively, of a controlled temporal sequence of pulses having prescribed OAM superposition states. Finally, we exhibit an “OAM-to-time conversion” apparatus that divides different input OAM states into different time bins. The latter application provides a simple approach to digital spiral spectroscopy of pulsed light.

http://www.opticsinfobase.org/ol/abstract.cfm?URI=ol-37-2-127

Twisting Radio Waves Could Give Us 100x More Wireless Bandwidth

noreply@blogger.com (Bill St. Arnaud) — Tue, 11 Oct 2011 17:19:00 +0000

As more people stream video to their mobile devices, wireless bandwidth is becoming an increasingly precious commodity. Data traffic increased 8,000 percent in the past four years on AT&T’s network alone
. In trying to avoid what the Federal Communications Commission calls a “looming spectrum crisis,” telecommunications companies are lobbying the government to assign them more spectrum space in the 300- to 3,000-megahertz range, the sweet spot for wireless communication. But Italian astrophysicist Fabrizio Tamburini says a solution may lie in making better use of the frequencies already in use. In a recent paper, he demonstrated a potential way to squeeze 100 times more bandwidth out of existing frequencies.

The idea is to twist radio waves like corkscrews and create multiple subfrequencies, distinguished by their degree of twistedness. Each subchannel carries discrete data sets. “You can tune the wave with a given frequency as you normally do, but there is also a fingerprint left by the twist,” Tamburini says. He and Swedish colleague Bo Thidé hit upon the approach while studying waves warped by the immense gravity of black holes. This past June, the scientists set up a custom dish in Venice and successfully broadcast video encoded in both twisted and normal radio waves across St. Mark’s Basin. (Note this type of wave-twisting is fundamentally different from the better-known circular polarization of light.)

The next step is to design small, cheap smartphone antennas that can transmit and receive the warped signals. If the industry’s appetite for bandwidth is any indication, it may not be long before twisted-radio technology shows up in your new gadgets.

http://discovermagazine.com/2011/oct/13-twisting-radio-waves-100x-more-wireless-bandwidth

DARPA Funds Optical Vortices Research

noreply@blogger.com (Bill St. Arnaud) — Tue, 24 May 2011 14:59:00 +0000

DARPA Funds Optical Vortices Research by Prof. Ramachandran and MIT Lincoln Lab

http://www.bu.edu/ece/2011/05/18/optical-vortices-research/

May 18th, 2011

Our ability to manipulate and take advantage of light’s capabilities has already allowed people to do everything from creating the World Wide Web to improving vision. But some new possibilities are on the horizon, including the chance that light may be used to efficiently sort DNA codes or create highly secure communications links impervious to threats and external attacks.

Pictured above is the spiral phase structure of an optical vortex, extracted by interfering it with a conventional light beam.

As new prospects emerge, Professor Siddharth Ramachandran (ECE) and Dr. Steve Golowich of MIT Lincoln Laboratory are watching closely and in on the latest optics research.

The Defense Advanced Research Project Agency (DARPA) recently awarded $318,784 for a one-year effort to study optical vortices to Ramachandran, the Principal Investigator (PI) on the project, and Golowich. Optical vortices are light beams that possess fundamentally different properties than what we get from lasers and LEDs today.

“Since these beams spin as they propagate in air, there is speculation that they may be more stable and resistant to atmospheric perturbations, similar to what happens when you spin a football while throwing it,” said Ramachandran. “This could have implications for a wide array of scientific disciplines, enabling, for instance, secure quantum communications links for the future, new sorting mechanisms for DNA molecules, or long range sensing.”

It has long been known that light beams possess linear momentum in the direction they’re moving, which is why micro- or nano-particles in their paths can be pushed forward. Scientists are also aware that light can possess angular momentum that allows micro- and nano-particles in the light beam’s path to rotate.

It was only recently, however, that researchers discovered that light could additionally possess orbital angular momentum. These beams, the optical vortices, spin but allow no energy in the center.

Professor Siddharth Ramachandran (ECE)

Previously it was thought that optical vortices, while exotic and interesting, have little use because of their inherent instability. But recent work by Ramachandran has shown that novel photonic crystal fiber and related designs can indeed be used to stably manipulate these beams.

Their early findings have led to the current DARPA-funded effort to investigate the properties of these beams in optical fibers and their applicability to creating next generation secure quantum encryption links, by encoding information in different angular momentum states.

Ramachandran’s research group already earned some recognition for their work when Nenad Bozinovic (PhD ’12) won the President’s Award for a presentation on the topic at Boston University’s Science Day on March 23. They also recently published their first results at the 2011 Conference on Lasers and Electro Optics (CLEO) in Baltim

Vorticity Transmission Could Increase Spectrum Efficiency

noreply@blogger.com (Bill St. Arnaud) — Fri, 11 Mar 2011 13:53:00 +0000

Researchers are continuing to find new ways to use RF spectrum more efficiently.
More than 10 years ago, in my articleExotic Modulation – Beyond 8-VSB, I described how new technology could modulate space (using what is now called MIMO and used in 802.11n and LTE wireless systems), and time (ultra-wideband, which is not as widely adopted).

Last week I discussed research on antenna and digital cancellation techniques that would allow the same spectrum to be used for full bandwidth simultaneous reception and transmission. This week I stumbled on another technology that, according to an article Adding a twist to radio technology – Spiraling radio waves could revolutionize telecommunicationsin Nature, which suggests that the bandwidth available to mobile phones and laptop computers could be increased by a factor of nine "almost immediately" by carefully positioning four antennas inside the devices.

The extra bandwidth is obtained by transmitting signals with different amounts of "twistedness" on the same frequency. The physics behind this is really too complex to get into here, but is based on the vorticity, or orbital angular momentum (OAM) observed in light and electromagnetic fields from sources very near the black-hole event horizon.

The Swedish Institute of Space Physics Press Release Twisted Light Can Reveal Spinning Black Holes and Plasma Clouds in Space explains, "OAM is one of many properties that are carried by all types of electromagnetic radiation, including radio and light, that exist in nature. It is a kind of twist that causes the beam of radiation to spiral around its axis in a vortex like a tornado. Just as there is light of different colors, there is light of different twists. It is only that these twists have gone mostly unnoticed by astronomers and space physicists until now."

In that press release Swedish Institute of Space Physics Professor Bo Thidé commented that this principle could be applied to radio waves.

"We have recently shown experimentally how OAM and vorticity can be readily imparted onto low-frequency radio beams and received far away and analyzed there," said Thidé. "This opens the possibility to work with photon OAM at frequencies low enough to allow the use of antennas and digital signal processing, thus enabling software-controlled experimentation and space observations in manner that is not possible with other means."

For the tests described in the Nature article, Thidé and Fabrizio Tamburini, from the University of Padua, Italy, used a an eight-stepped spiral-staircase-like structure to reflect the signal from an antenna similar to the ones used on standard wireless routers. The structure twisted the normally planar wavefront and caused it to take on the shape of the reflector. The researchers used a pair of antennas seven meters away to measure the intensity pattern as one of the antennas was moved around the beam.

In the Nature article, Tamburini speculates that just as different wavelengths can be propagated together without interference, and thus increasing the number of signals that can be transmitted, transmission bandwidth be increased by "simultaneously transmitting waves with the same frequency but different degrees of twistedness."

More work is needed to see how the technology will work in a real-world environment with interference from other reflectors. Visit the researchers' Vortici & frequenze Website for updates. By the way, Bo Thidé's interest in electromagnetics are not purely academic, he holds the ham radio call sign SM5DFW.

http://www.tvtechnology.com/article/114290

LDPC-Coded Orbital Angular Momentum (OAM) Modulation For Free-Space Optical Communication

noreply@blogger.com (Bill St. Arnaud) — Sun, 06 Feb 2011 18:28:00 +0000

An Orbital Angular Momentum (OAM) based LDPC-coded modulation scheme suitable for use in FSO communication is proposed. They demonstrate that the proposed scheme can operate under strong atmospheric turbulence regime and enable 100 Gb/s optical transmission while employing 10 Gb/s components.
Both binary and nonbinary LDPC-coded OAM modulations are studied. In addition to providing better BER performance, the nonbinary LDPC-coded modulation reduces overall decoder complexity and latency. The nonbinary LDPC-coded OAM modulation provides a net coding gain of 9.3 dB at the BER of 10-8. The maximum-ratio combining scheme outperforms the corresponding equal-gain combining scheme by almost 2.

http://www.techrepublic.com/whitepapers/ldpc-coded-orbital-angular-momentum-oam-modulation-for-free-space-optical-communication/2423767?promo=100202

A hot new technology to keep your eye on - RF orbital angular momentum

noreply@blogger.com (Bill St. Arnaud) — Tue, 01 Feb 2011 13:29:00 +0000

[I have been fascinated by the theory of Orbital Angular Momentum (OAM) since I first read about it in the mid 1990s in a UK science publication. I believe that OAM may have some unique applications in RF signaling especially for new multi-spectral coding techniques and medical diagnostic and imaging applications.
Here is an excellent paper that describes the theory behind RF OAM and its many potential applications. I think RF OAM will have a huge impact in terms of new wireless, imaging and diagnostic applications. For more information please see my blog on the subject http://orbitalangularmomentum.blogspot.com/ --BSA]

Radio beam vorticity and orbital angular momentum
http://goo.gl/O75Rh

The experimental veriﬁcation of vorticity and OAM in radio means that a new frequency range has become available for fundamental as well as applied OAM-based experiments in disciplines ranging from relativistic astrophysics and nanotechnology and biology, to wireless communication with high spectral efﬁciency both classically and quantum mechanically. It also opens for the development of new radio and radar probing techniques, including spiral imaging. It should also be emphasized that certain physical effects and observables associated with electromagnetic OAM, for instance electromagnetic torque, are stronger for lower frequencies than for higher
------
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Electron Vortex Beams with High Quanta of Orbital Angular Momentum

noreply@blogger.com (Bill St. Arnaud) — Thu, 13 Jan 2011 21:05:00 +0000

Electron Vortex Beams with High Quanta of Orbital Angular Momentum
http://www.sciencemag.org/content/331/6014/192.abstract

Benjamin J. McMorran1,*, Amit Agrawal1,2, Ian M. Anderson3, Andrew A. Herzing3, Henri J. Lezec1, Jabez J. McClelland1 and John Unguris1
+ Author Affiliations

E-mail: mcmorran@nist.gov
ABSTRACT

Electron beams with helical wavefronts carrying orbital angular momentum are expected to provide new capabilities for electron microscopy and other applications. We used nanofabricated diffraction holograms in an electron microscope to produce multiple electron vortex beams with well-defined topological charge. Beams carrying quantized amounts of orbital angular momentum (up to 100ℏ) per electron were observed. We describe how the electrons can exhibit such orbital motion in free space in the absence of any confining potential or external field, and discuss how these beams can be applied to improved electron microscopy of magnetic and biological specimens.

NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY USING LIGHT WITH ORBITAL ANGULAR MOMEMTUM

noreply@blogger.com (Bill St. Arnaud) — Wed, 05 Jan 2011 15:08:00 +0000

NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY USING LIGHT WITH ORBITAL ANGULAR MOMENTUM
http://www.faqs.org/patents/app/20100327866

Abstract:

The present invention relates to a device capable of producing a high resolution chemical analysis of a sample, such as fluid, based upon nuclear magnetic resonance (NMR) spectroscopy, where the nuclear magnetic polarizations of the sample are generated by sequentially illuminating the sample with a focused beam of light carrying angular orbital angular momentum (OAM) and possibly momentum (spin). Unlike in usual NMR used for magnetic nuclear resonance imaging (MRI) or spectroscopy, the invention does not make use of a strong magnet.

Read more: http://www.faqs.org/patents/app/20100327866#ixzz1AAq0YAF7

Chinese researchers move closer to deploying twisted light in optical fiber

noreply@blogger.com (Bill St. Arnaud) — Wed, 05 Jan 2011 15:04:00 +0000

Chinese researchers move closer to deploying twisted light in optical fiber - dramatic increases in bandwidth http://goo.gl/BZ08s

Orbital angular momentum (OAM) of a helical beam is of great interests in the high density optical communication due to its infinite number of eigen-states. In this paper, an experimental setup is realized to the information encoding and decoding on the OAM eigen-states. A hologram designed by the iterative method is used to generate the helical beams, and a Michelson interferometer with two Porro prisms is used for the superposition of two helical beams. The experimental results of the collinear superposition of helical beams and their OAM eigen-states detection are presented.

Blog on OAM and optical tweezers

noreply@blogger.com (Bill St. Arnaud) — Thu, 16 Dec 2010 17:23:00 +0000

Blog on OAM and optical tweezers

http://opticaltweezers.blogspot.com/2010/12/optical-orbital-angular-momentum-from.html

Production and application of electron vortex beams

noreply@blogger.com (Bill St. Arnaud) — Thu, 16 Sep 2010 14:20:00 +0000

Production and application of electron vortex beams
http://www.nature.com/nature/journal/v467/n7313/full/nature09366.html

J. Verbeeck1, H. Tian1 & P. Schattschneider2

Electron Microscopy for Materials Science (EMAT), University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium
Institute for Solid State Physics and University Service Centre for Electron Microscopy, Vienna University of Technology, A-1040 Vienna, Austria
Correspondence to: J. Verbeeck1 Email: jo.verbeeck@ua.ac.be

Top of pageAbstract
Vortex beams (also known as beams with a phase singularity) consist of spiralling wavefronts that give rise to angular momentum around the propagation direction. Vortex photon beams are widely used in applications such as optical tweezers to manipulate micrometre-sized particles and in micro-motors to provide angular momentum1, 2, improving channel capacity in optical3 and radio-wave4 information transfer, astrophysics5 and so on6. Very recently, an experimental realization of vortex beams formed of electrons was demonstrated7. Here we describe the creation of vortex electron beams, making use of a versatile holographic reconstruction technique in a transmission electron microscope. This technique is a reproducible method of creating vortex electron beams in a conventional electron microscope. We demonstrate how they may be used in electron energy-loss spectroscopy to detect the magnetic state of materials and describe their properties. Our results show that electron vortex beams hold promise for new applications, in particular for analysing and manipulating nanomaterials, and can be easily produced.

To read this story in full you will need to login or make a payment (see right).

Quantum tornado in the electron beam

noreply@blogger.com (Bill St. Arnaud) — Thu, 16 Sep 2010 14:16:00 +0000

Quantum tornado in the electron beam
http://www.nanowerk.com/news/newsid=18071.php

(Nanowerk News) Manipulating materials with rotating quantum particles: a team from the University of Antwerp and TU Vienna (Professor Peter Schattschneider, Institute of Solid State Physics) has succeeded in producing what are known as vortex beams: rotating electron beams, which make it possible to investigate the magnetic properties of materials. In the future, it may even be possible to manipulate the tiniest components in a targeted manner and set them in rotation. The physicists report on this breakthrough in electron physics and its application in the current edition of Nature ("Production and application of electron vortex beams").
Rotating current: the quantum tornado
Electron beams have been used to analyse materials for some time now – for example in electron microscopes. For the most part, the beams' rotation does not affect this analysis. In classical physics, an electron current in a vacuum does not have any orbital angular momentum. In quantum mechanics, however, the electrons must be envisaged as a wavelike current – which can rotate as a whole about its propagation direction, similar to the air flow in a tornado.

A flat wave (left) meets the specially shaped grid screen, which converts the electron beam into right-rotating and left-rotating vortex beams (top and bottom), and a middle beam that does not rotate. Similar to in a tornado, the rotation of the electron current is low internally

Vortex light beams have been used in optics for some time (for example, as optical tweezers for manipulating small particles). Vortex beams made from electrons also offer many new possibilities for managing nanoparticles or measuring angular momentum-related parameters. However, there were previously no really efficient methods of producing them. "When I was working on an idea of how these beams could be technically produced, it emerged that colleagues from Antwerp had had the same idea", explains Prof Schattschneider. "We therefore decided to pursue the project together: Antwerp had progressed further with the production and Vienna came up with a suggestion for the first application."

The trick with the screen

The production of vortex electron beams was made possible with the help of a grid-like screen cut from platinum foil. When it passes through the platinum screen, the electron beam is diffracted in a similar way to light beams when they pass through a fine grid. The shape of this screen, which measures only a few millionths of a metre, was specifically calculated so that a flat incident electron wave is converted into vortex beams. Right-rotating and left-rotating vortex beams are thus formed behind the grid and in the middle there is a conventional electron beam that does not rotate.

If the electrons are used to irradiate a material which for its part also influences the angular momentum of the electrons, and if the electrons are subsequently directed through the made-to-measure platinum screen, then, after this, either the right-rotating or the left-rotating vortex beam will be more intense. "This enables us to investigate processes affected by angular momentum in nanomaterials much more precisely than was previously possible", explains Prof Schattschneider.
Better than science fiction
The physicist, who also occasionally writes science fiction, does not find it hard to imagine more exotic applications for the vortex beams: "These electron beams could be used in a targeted way to set tiny wheels in motion on a microscopic motor. Also, the magnetic field of the rotating electrons could be used in the tiniest length scales", Schattschneider speculates. Even applications in data transfer (quantum cryptography) and quantum computers are feasible.
Source: Vienna University of Technology

Orbital angular momentum in radio: Measurement methods

noreply@blogger.com (Bill St. Arnaud) — Mon, 02 Aug 2010 19:09:00 +0000

Orbital angular momentum in radio: Measurement methods
Authors:
Mohammadi, Siavoush M.; Daldorff, Lars K. S.; Forozesh, Kamyar; Thidé, Bo; Bergman, Jan E. S.; Isham, Brett; Karlsson, Roger; Carozzi, T. D.
Affiliation:
AA(Department of Electrical and Computer Engineering, Interamerican University of Puerto Rico, Bayamón, Puerto Rico); AB(Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden); AC(Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden); AD(Swedish Institute of Space Physics, Uppsala, Sweden); AE(Swedish Institute of Space Physics, Uppsala, Sweden); AF(Department of Electrical and Computer Engineering, Interamerican University of Puerto Rico, Bayamón, Puerto Rico); AG(Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden); AH(Department of Physics and Astronomy, University of Glasgow, Glasgow, UK)
Publication:
Radio Science, Volume 45, Issue 4, CiteID RS4007 (RaSc. Homepage)
Publication Date:
07/2010
Origin:
AGU
AGU Keywords:
Radio Science: Radio wave propagation, Radio Science: Instruments and techniques (1241), Radio Science: Radio astronomy
Abstract Copyright:
(c) 2010: American Geophysical Union
DOI:
10.1029/2009RS004299
Bibliographic Code:
2010RaSc...45S4007M

Orbital Angular Momentum – Bo Thide and Jan Bergman (SETI Talks)

noreply@blogger.com (Bill St. Arnaud) — Wed, 28 Jul 2010 13:52:00 +0000

Link to SETI Archive: seti.org On the extraction of all information embedded in radio siganls: Implications for SETI: A new idea for utilizing all of the information in photons for communication involves a little-know electromagnetic property: the photon’s orbital angular momentum (POAM). The communication and computer industries are actively looking at the possibilities. We will discuss current research and the implications for SETI.

http://ufo-tv.com/orbital-angular-momentum-bo-thide-and-jan-bergman-seti-talks

Generation of electron beams carrying orbital angular momentum

noreply@blogger.com (Bill St. Arnaud) — Thu, 01 Apr 2010 12:21:00 +0000

Generation of electron beams carrying orbital angular momentum

Nature 464, 737 (2010). doi:10.1038/nature08904

Authors: Masaya Uchida & Akira Tonomura
All forms of waves can contain phase singularities. In the case of optical waves, a light beam with a phase singularity carries orbital angular momentum, and such beams have found a range of applications in optical manipulation, quantum information and astronomy. Here we report the generation of an electron beam with a phase singularity propagating in free space, which we achieve by passing a plane electron wave through a spiral phase plate constructed naturally from a stack of graphite thin films. The interference pattern between the final beam and a plane electron wave in a transmission electron microscope shows the ‘Y’-like defect pattern characteristic of a beam carrying a phase singularity with a topological charge equal to one. This fundamentally new electron degree of freedom could find application in a number of research areas, as is the case for polarized electron beams.

Link: http://feeds.nature.com/~r/nature/rss/current/~3/fny431UlOME/nature08904
Author: Masaya Uchida

NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY USING LIGHT WITH ORBITAL ANGULAR MOMENTUM

noreply@blogger.com (Bill St. Arnaud) — Sun, 27 Dec 2009 14:57:00 +0000

http://www.wipo.int/pctdb/ja/ia.jsp?ia=IB2009%2F050145&IA=IB2009050145&DISPLAY=DESC

NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY USING LIGHT WITH ORBITAL ANGULAR MOMENTUM

FIELD OF THE INVENTION The present invention relates to a sample analysis method based on nuclear magnetic resonance (NMR) spectroscopy. The invention also relates to a corresponding computer program product and device for carrying out the method.
....

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a method of analyzing a sample consisting of molecules, the analysis being based upon nuclear magnetic resonance spectroscopy, the method comprising the following steps:

- turning on a light source;

- introducing orbital angular momentum into the light;

- obtaining a focused light beam carrying orbital angular momentum; sequentially illuminating the sample with the focused light beam carrying orbital angular momentum for obtaining nuclear magnetic polarizability of the sample; and

- obtaining a free induction decay signal resulting from the illumination, the free induction decay signal carrying characteristics of the sample.

This provides clear advantages, namely for instance the obtained free induction decay (FID) signal is much stronger than the corresponding signal obtained by using traditional NMR spectroscopy methods. Thus, the sensitivity of the measurement technique is greatly improved. The obtained FID signal is also less noisy and better resolution can be achieved. As a consequence smaller samples can be analyzed.

According to a second aspect of the invention there is provided a computer program product comprising instructions for implementing the method according the first aspect of the invention when loaded and run on computer means of an analysis device.

Superposition of helical beams by using a Michelson interferometer

noreply@blogger.com (Bill St. Arnaud) — Tue, 22 Dec 2009 21:15:00 +0000

Superposition of helical beams by using a Michelson interferometer

Chunqing Gao, Xiaoqing Qi, Yidong Liu, and Horst Weber

http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-18-1-72

Orbital Angular Momentum in Radio - A System Study

noreply@blogger.com (Bill St. Arnaud) — Mon, 21 Dec 2009 14:38:00 +0000

Orbital Angular Momentum in Radio - A System Study

Mohammadi, S. M. Daldorff, L. K. S. Bergman, J. E. S. Karlsson, R. L. Thide, B. Forozesh, K. Carozzi, T. D. Isham, B.

This paper appears in: Antennas and Propagation, IEEE Transactions on
Accepted for future publication
ISSN: 0018-926X
Abstract
Recent discoveries concerning rotating (helical) phase fronts and orbital angular momentum (OAM) of laser beams are applied to radio frequencies and comprehensive simulations of a radio OAM system are performed. We find that with the use of vector field-sensing electric and magnetic triaxial antennas, it is possible to unambiguously estimate the OAM in radio beams by local measurements at a single point, assuming ideal (noiseless) conditions and that the beam axis is known. Furthermore, we show that conventional antenna pattern optimization methods can be applied to OAM-generating circular arrays to enhance their directivity.

Index Terms
Available to subscribers and IEEE members.

Quantum Multiplexing with the Orbital Angular Momentum of light

noreply@blogger.com (Bill St. Arnaud) — Wed, 11 Mar 2009 16:35:00 +0000

Quantum Multiplexing with the Orbital Angular Momentum of light
Authors: Juan Carlos Garcia-Escartin, Pedro Chamorro-Posada
(Submitted on 29 Jan 2009)

http://arxiv.org/abs/0901.4740

Abstract: The orbital angular momentum, OAM, of photons offers a suitable support to carry the quantum data of multiple users. We present two novel optical setups that send the information of n quantum communication parties through the same free-space optical link. Those qubits can be sent simultaneously and share path, wavelength and polarization without interference, increasing the communication capacity of the system. The first solution, a qubit combiner, merges n channels into the same link, which transmits n independent photons. The second solution, the OAM multiplexer, uses CNOT gates to transfer the information of n optical channels to a single photon. Additional applications of the multiplexer circuits, such as quantum arithmetic, as well as connections to OAM sorting are discussed.

Twisted radio beams could untangle the airwaves

noreply@blogger.com (Bill St. Arnaud) — Fri, 13 Feb 2009 18:10:00 +0000

http://www.newscientist.com/article/dn16591-twisted-radio-beams-could-untangle-the-airwaves.html

The human race is not only exhausting tangible resources such as oil. The radiofrequency spectrum available for wireless communication is becoming the increasingly crowded, with virgin "veins" of frequency running short.

However, Swedish physicists say that twisting radio beams into a helical shape as they are transmitted could help ease the congestion.

Radio frequency encompasses electromagnetic waves between 3 kilohertz and 300 gigahertz, and as wireless communications technology advances much of that range is being used.

Satellite TV, wireless computer networks and cellphones are among the growing technologies vying for space up to 30 gigahertz, with some technology even beginning to extend beyond 100 gigahertz leaving a dwindling supply of virgin terrain to exploit.

Physicist Thomas Leyser at the Swedish Institute of Space Physics in Uppsala, Sweden, thinks he has a novel solution. Along with an international team of physicists, he has demonstrated that it is possible to put a spin on radio beams during their transmission to produce a twisted beam.

"Twisted laser beams have been researched since the 1990s, but it has only now become possible to create twisted beams at the much lower radio frequencies," he says.

Detecting orbital angular momentum in radio signals

noreply@blogger.com (Bill St. Arnaud) — Thu, 29 May 2008 16:46:00 +0000

A good overview of some of the technical challenges of detecting RD signals with OAM

http://www.slac.stanford.edu/spires/find/hep/www?irn=7762801

Electromagnetic waves with an azimuthal phase shift are known to have a well defined orbital angular momentum. Different methods that allow for the detection of the angular momentum are proposed. For some, we discuss the required experimental setup and explore the range of applicability.

Good overview of diagnostic opportunities of OAM

noreply@blogger.com (Bill St. Arnaud) — Tue, 06 May 2008 16:45:00 +0000

http://www.aip.org/pnu/2005/split/721-3.html

Optical Vortices" Might Extract Abundant Information From Matter

"Optical vortices" might extract abundant information from matter, providing a new and potentially wide-ranging optical tool, a Spain-US team has proposed theoretically. An ordinary light beam, when viewed head-on, looks like a bright circle. But a special light beam called an "optical vortex," when viewed head-on, looks like a bright ring surrounding a dark central core (see www.aip.org/png/2001/133.htm). Optical vortices are the simplest kind of beam carrying a property called "orbital angular momentum" (see Update 639).

Extensively studied since the early 1990s, such light beams, when viewed from the side, trace out a three-dimensional corkscrew pattern (see figure at www.aip.org/png/2005/229.htm); the pattern represents regions of constant phase (for example, regions of maximum electric field). This spiraling of light represents an extra "degree of freedom" that researchers can use as a new handle to optically encode information and subsequently to retrieve information from objects the beam strikes. In conventional laser beams, the energy flows parallel to the beam axis, like water in a jet.

However, for light with orbital angular momentum (OAM), the energy spirals around the beam axis. Ordinary beams carry only "spin angular momentum," encoded in the polarization of light. All possible spin states can be constructed with just two polarization states (vertical and horizontal, or clockwise and counterclockwise). For light with nonzero OAM, however, many states are possible, with higher states denoting tighter corkscrews (and consequently, a faster spiraling of energy; see figure at www.aip.org/png/2005/229.htm). For this reason, one can encode a huge amount of information in an OAM beam by creating light made of a superposition of many OAM states.

The researchers call the different OAM components "spiral spectra." In the "digital spiral imaging" concept now put forward by Lluis Torner at the new Institute for Photonic Sciences (ICFO) in Barcelona and his colleagues, a light beam of a convenient shape illuminates a sample to be probed. The sample scatters the beam and alters its spiral components. Breaking down the altered beam into its individual orbital-angular momentum components (and thereby analyzing the “spiral spectrum” of the scattered beam) can yield a wealth of information from the object.

The spiral spectra would, for example, be sensitive to nonuniformities in geometrical and structural properties of objects, and could be potentially useful for detecting biological and chemical agents, for probing biological specimens sensitive to OAM light, and might even aide recent proposals to increase the amount of data that can be imprinted on a compact disk using OAM. (Torner, Torres, Carrasco, Optics Express, Feb. 7, 2005; contact Lluis Torner, http://www.icfo.es ; for more background on OAM light, see Physics Today, May 2004, and New Scientist, 12 June 2004).

OAM in RF applications & measuring properties of objects

noreply@blogger.com (Bill St. Arnaud) — Tue, 05 Feb 2008 19:45:00 +0000

For the longest time OAM was associated with optical photonic applications. I have suspected for some time it could be used in RF frequency bands as well. A recent paper discusses this:

"Utilization of Photon OAM in Low Frequency Radio Domain", B. Thide

Even more exciting is the use of RF OAM to probe properties of objects:

Recent digital spiral imaging experiments (Torner et al., Opt.
Express, 13, 873–881, 2005; Molina-Terriza et al., J. Eur. Opt.
Soc., Rapid Publ., 2, 07014, 2007) have demonstrated that
probing with OAM gives a wealth of new information about the
object under study.