RF Orbital Angular Momentum

Virtual Von Neumann Probes using Self Amplification and Replication of Electromagnetic Signals through Natural Stellar Processes

noreply@blogger.com (Bstarn) — Thu, 11 Jun 2026 06:36:26 +0000

In their recent post on Centauri Dreams Roger Guay and Scott Guerin (https://centauri-dreams.org/?p=36802) make a compelling argument that fading electromagnetic halos may be all that’s left for us to discover of an extraterrestrial civilization. They argue that there is only a short window in the evolution of a sufficiently intelligent species in which it will broadcast its presence through inefficient electromagnetic transmission of radio, TV and radar signals.

Current SETI searches assume that an advanced civilization will use extremely powerful omnidirectional transmitters or highly directional and focused beacons targeted at our solar system. The challenge with either approach is the fact that successful one-way communication between intelligent species is dependent on the “L” term in the Drake equation. L represents the length of time for which such civilizations release detectable signals into space. If L is relatively short then the possibility of two separate intelligent civilizations being coincident in time to send and receive a signal is very small, as demonstrated by Guay-Guerin. So even though there may have been many intelligent civilizations we will probably never be aware of their existence.

On the other hand, Stephen Webb, in his book If the Universe is Teeming with Aliens .. Where Is Everybody? argues that we may be the only intelligent civilization in our galaxy, if not perhaps the known universe. This is often referred to as the Rare Earth Hypothesis. Given the large multiplier of improbabilities from the creation of simple life, through the prokaryotic-eukaryotic transition, and the many divergent evolutionary pathways in human evolution leading to technology savvy beings, Webb argues that the odds of this being replicated elsewhere in the universe are extremely low.

The bottom line from both Guay-Guerin and Stephen Webb is that regardless of whether the universe is teeming with advanced civilizations or limited to only a very few it would seem that the probability of detecting a SETI signal by conventional means is very limited.

In another line of reasoning in SETI exploration it has been suggested that we look for physical artifacts as well as electromagnetic signals. These artifacts could include devices like Von Neumann probes and physical remains of past advanced civilizations.

A Von Neumann probe is a self replicating spacecraft that would travel from stellar system to stellar system through a galaxy where it would seek out raw materials extracted from planets to create replicas of itself. These replicas would then be sent out to other stellar systems.

Searching for small physical artifacts such as Von Neumann probes would seem to be even more daunting than looking for the proverbial “needle in the haystack” electromagnetic signals. If a civilization were advanced enough to launch artifacts through space you would think at some earlier stage in its existence it would have initially deployed electromagnetic beacons or omnidirectional broadcasts. Of course this is assuming that they do want to make their presence aware to other advanced civilizations.

Von Neumann Signaling

But perhaps there is another approach to SETI that avoids many of the challenges of looking for physical artifacts and the limitation of the possibility of a small L in the Drake equation. Maybe we can look for “electromagnetic artifacts.” Electromagnetic artifacts can be thought of as “virtual” Von Neumann probes where instead of having physical devices replicate and propel themselves through the galaxy, electromagnetic signals are initially transmitted where their signaling properties are designed to be amplified and replicated using natural stellar and physical processes. Such natural processes might include gravitational lensing to refocus signals and using stellar lasers or masers to amplify a given signal.

Such self amplifying and replicating electromagnetic signals are different than normal transmissions used in beacons in that they are not intended to be point to point communications. Like Von Neumann probes they are expected to randomly propagate through a galaxy using passing stellar systems to amplify and replicate the original transmission. This capability might allow electromagnetic Von Neumann probes to propagate throughout a galaxy much faster than physical probes. The advantage of a low cost self amplifying and replicating signal is that you only need one replicant signal in a billion or trillion to multihop many hundreds of stars and be detected by another civilization.

Gravitational lensing has been used in astronomy for some time. In an interesting post (https://centauri-dreams.org/?p=10123), Claudio Maccone calculates that by using gravitational lens and with satellites at the appropriate focal points of each solar system a detectable radio signal could be sent from our solar system to Alpha Centauri that uses less than 10-4 watts, i.e. one tenth of a milliwatt!!

Normally a signal sent from earth would not benefit from gravitational lensing as the focal point would be too far out (past Pluto). The signal might be bent but otherwise it will quickly suffer dispersion like any other signal. To achieving lensing a signal must pass both sides of the sun at roughly the same time and the wavefront recombine coherently on the far side.

One solution would be to put satellites at the focal point as Moccone has suggested. But an easier earthbound solution is to use earth-bound phased array antenna. A signal generated by a phased array could be made with a wavefront that looks like it originated from the Sun’s focal point or even a more distant point. You may want to use a more distant (or closer) artificial focal point in order to use gravitational lens of a more distant star; i.e launch our signal so that it is deliberately out of focus (but collimated) by our sun but comes into focus at a distant star. These are the same principles used in multi-lens cameras or telescopes. The converging point of the signal could be at the focal point of a distant star or perhaps even a multi-hop star.

Once you have a collimated signal with a coherent wavefront and wide aperture (i.e. the Sun’s diameter) you could in theory hop many stars that are in line with our orbital plane (or will be by the time the signal gets there). You could also steer the signal up and down a little bit from the orbital plane with a phased array antenna.

Additional amplification could use natural masers/lasers in our sun or distant star. There are several suitable natural maser frequencies – the choice of appropriate frequency will depend on the types of stars we are aiming at.

Stellar masers have been known for some time. A maser emission may be created in molecular clouds, comets, planetary atmospheres, and stellar atmospheres. They are frequently used in radio astronomy as they provide important information on distant stellar objects, such as temperature, velocity, etc. The first “natural” laser in space was detected by scientists on board NASA’s Kuiper Airborne Observatory (KAO) in 1995 as they trained the aircraft’s infrared telescope on a young, very hot, luminous star in the constellation Cygnus. Since then many other examples of both planetary and stellar lasers have been found.

The problem with natural masers/lasers is their noise level. The same is true of gravitational lensing if the signal passes through, or close to the corona. To extract the signal one would need a reference clock – and this would be the tell tale signal that it is artificial. I would theorize a good reference clock would be a distant highly regular timed quasar.

In effect we have created a beacon, but rather than looking in the water hole, a receiving civilization would have to look at the known natural maser/laser frequencies and then auto-correlate the signal to see if they can extract a reference clock. This is the same technology we use in very long baseline interferometry used in deep space radio dishes.

Now the interesting thing about natural masers/lasers is that they can amplify a given signal not only in the line of propagation but in other orthogonal directions as well. If the signal maintains its coherent wavefront ( still needs to be verified) then a given signal can be replicated in many directions from a given star. If it is still collimated then it would also look like a beacon pointed in some unknown random direction. A single star could produce many beacons like a disco ball based on the original transmission.

On a small scale, real world examples of self amplifying and replicating electromagnetic signals already exist. They are called Long Delayed Echoes (LDEs). They were first discovered in 1927 by amateur radio enthusiasts who noticed echoes of their original radio transmissions delayed by up to 40 seconds.

Up to now I have only been talking about signalling from our limited knowledge. I suspect there are other stellar phonemena, like with long delay echoes, that could be used to replicate and amplify signals.

There is no clear agreement on what causes LDEs, but there are several hypotheses on some possible natural phenomena that may enable electromagnetic echoes. These include such things as reflections from distant plasma clouds originating from the sun, magnetosphere ducting, mode conversion and four wave mixing, etc. While these natural phenomena may not be suitable processes for interstellar electromagnetic transmission they do demonstrate the possibility that perhaps equivalent stellar processes could be used on a larger scale to amplify and replicate electromagnetic signals much greater distances.

Given that they depend on natural physical processes for amplification and replication, the originating transmission will likely not need to be that powerful or directional. It is conceivable that low power transmissions are that all is required to launch a self amplifying and replicating electromagnetic probe. Most importantly, with electromagnetic replication a single instance of the signal may be replicated thousands or millions of times as it propagates through the galaxy or the universe. Compared with physical probes replication could accelerate on an exponential scale increasing the probability of detection, particularly in a ‘rare Earth’ situation.

Issues to Be Surmounted

Although using self amplification and replication sounds like an interesting idea there are a number of theoretical and physical challenges that still must be addressed. How, for example, to account for the proper motion of our sun versus distant stars? Will any such signal just sweep by like a beam from a lighthouse and make detection near impossible (e.g., the ‘Wow’ signal?) Other issues include accuracy and phase noise in phased array antenna – how precisely can we control a given signal?

Thermal noise in stellar atmospheres that are to be used for laser/maser gain is clearly a major issue. The “gain” of a stellar laser or maser is also very limited as there is no resonant cavity. There are also a host of well known problems with current inter-stellar electromagnetic signaling such as attenuation, dispersion, group delay, etc etc. In addition, the proper motion of our solar system and that of any intermediate amplifying and replicating stellar system would seem to make detection difficult.

To address these limitations in detecting such a signal it would be useful to explore how we might deploy a self replicating electromagnetic signal given our current technology limitations. Many techniques currently being used in modern radio and optical communication systems could be deployed to launch a self replicating and amplifying electromagnetic probe.

Clearly an external reference clock or coding reference would be required to extract any signal that was amplified by a stellar laser/maser as the inherent stellar noise would mask any external signal. A quasar may provide such a reference signal. Phased array antennae and signal preconditioning could be used to take advantage of gravitational lensing without placing transmitters at the lens focal point.

Gravitational lenses also act as gradient amplifiers and with time delay from two phased array sources it might be possible to regenerate a given signal (such as timing, shaping etc) using all electromagnetic techniques – a process now largely done by electronics. By constantly steering the phased array transmitter(s) a signal could be directed like a beacon at nearby stars that are aligned with our orbital plane to take advantage of the sun’s gravitational lens. Similarly steering of the phased array might allow a given signal to converge at the gravitational focal point of a nearby star where it could be amplified and replicated by that star to be propagated to even more distant stars.

With a little imagination and speculation on the future direction of these technologies a self amplifying and replicating electromagnetic Von Neumann probe might be within our technology capability. Once we have identified a plausible approach on how we would deploy such signals, the obvious next step would be to see if we can detect such signals.

Conclusion

Up to now we have always assumed that a distant civilization would want to send a direct beam at us and so we have been exploring that part of the electromagnetic spectrum that has the least absorption and attenuation. But if a distant civilization discovered it could use natural low cost processes to amplify and replicate a signal that would be its preferred route, especially if intelligence is a rarity in our galaxy. With laser/maser replication millions or billions of signals could be traversing the galaxy, of which only one needs to be detected by another civilization. This would be a much cheaper approach from an energy perspective than building omni-directional antennas, Dyson spheres, or aiming a beacon at our Sun, etc.

The assumption here is that a distant civilization wants to make contact with us, but I suspect that self replicating and amplifying signals will be transmitted for much more mundane reasons. If a self amplifying and replicating signal can be transmitted practically forever, really cheaply, then forget about contacting other civilizations, I want knowledge of my brief presence here on earth to be preserved forever. Paradoxically, religion and belief in the hereafter may be a driving force to transmit such signals!

Using OAM to control atoms

noreply@blogger.com (Bstarn) — Mon, 09 Jun 2025 19:38:00 +0000

https://interestingengineering.com/science/how-vortex-beams-affect-ionizaton-atoms?group=test_a

Could optical knots be a method of communicating with extra terrestrials

noreply@blogger.com (Bstarn) — Thu, 22 Feb 2018 00:18:00 +0000

http://physicsworld.com/cws/article/news/2013/oct/16/physicists-tie-light-into-knots

Physicists tie light into knots

Oct 16, 2013 20 comments

Trefoil knot of light

Fantastical knot-like structures of light could soon be created in the lab thanks to calculations made by physicists in the US, Poland and Spain. They have discovered a new family of solutions to Maxwell's equations that are knots of light that do not disperse or lose their specific topological properties as they propagate. The researchers say such knots, if made for real, could be used to trap atoms or create similar knots in plasmas or quantum fluids.

Identified by Hridesh Kedia at the University of Chicago, along with colleagues at the Polish Academy of Sciences in Warsaw and the Spanish National Research Council in Madrid, the new family of solutions to Maxwell's equations have field lines describing all "torus knots" and "links". Torus knots are those knots that can lie on the surface of a torus, whereas a link is a collection of such knots.

One solution involves magnetic-field lines that trace out a familiar "trefoil" knot around a torus that is aligned in the plane perpendicular to the direction of propagation of the light (see figure). As the light propagates, the knot is distorted but retains the topological property of being a trefoil knot. The electric-field lines have the same structure as the magnetic-field lines but are rotated about the propagation axis by an angle that depends upon the knot. Other solutions include cinquefoil knots and linked rings.

Knotty problem

Kedia and colleagues believe that these knots could be made in the lab using tightly focused Laguerre–Gaussian beams. These beams have been created and studied extensively because – unlike most other beams of light – they carry orbital angular momentum.

If these optical knots can be made in the lab, they could have a number of scientific applications. Physicists are already exploring how focussed Laguerre–Gaussian beams can be used to trap ultracold atoms and this latest theoretical development could lead to new ways of trapping them. Firing such knots into a plasma or quantum fluid could also result in knot-like entities propagating through those materials, thereby offering new ways of studying these states of matter.

Once the preserve of mathematicians, knot theory is playing an increasingly important role in how physicists describe the behaviour of physical systems, ranging from liquid crystals to superconductors. Most of these descriptions arise from numerical simulations of complex systems, rather than the exact solution of the equations describing the system of interest.

The research is described in Physical Review Letters.

About the author

Hamish Johnston is editor of physicsworld.com

Object Identification Using Correlated Orbital Angular Momentum

noreply@blogger.com (Bstarn) — Mon, 28 Jan 2013 16:54:00 +0000

Using spontaneous parametric down-conversion as a source of correlated photon pairs, correlations are measured between the orbital angular momentum (OAM) in a target beam (which contains an unknown object) and that in an empty reference beam.
Unlike previous studies, the effects of the object on off-diagonal elements of the OAM correlation matrix are examined. Because of the presence of the object, terms appear in which the signal and idler OAM do not add up to that of the pump. Using these off-diagonal correlations, the potential for high-efficiency object identification by means of correlated OAM states is experimentally demonstrated for the first time. The higher-dimensional OAM Hilbert space enhances the information capacity of this approach, while the presence of the off-diagonal correlations allows for recognition of specific spatial signatures present in the object. In particular, this allows the detection of discrete rotational symmetries and the efficient evaluation of multiple azimuthal Fourier coefficients using fewer resources than in conventional pixel-by-pixel imaging. This represents a demonstration of sparse sensing using OAM states, as well as being the first correlated OAM experiment to measure properties of a real, stand-alone object, a necessary first step toward correlated OAM-based remote sensing.

Object Identification Using Correlated Orbital Angular Momentum States
http://prl.aps.org/abstract/PRL/v110/i4/e043601

Detection of objects with remote sensing using OAM

noreply@blogger.com (Bstarn) — Wed, 26 Sep 2012 12:12:00 +0000

Object Identification Using Correlated Orbital Angular Momentum States

http://arxiv.org/abs/1209.4130

Nestor Uribe-Patarroyo, Andrew Fraine, David S. Simon, Olga Minaeva, Alexander V. Sergienko

(Submitted on 19 Sep 2012)

Using spontaneous parametric down conversion as a source of entangled photon pairs, correlations are measured between the orbital angular momentum (OAM) in a target beam (which contains an unknown object) and that in an empty reference beam. Unlike previous studies, the effects of the object on off-diagonal elements of the OAM correlation matrix are examined. Due to the presence of the object, terms appear in which the signal and idler OAM do not add up to that of the pump. Using these off-diagonal correlations, the potential for high-efficiency object identification by means of correlated OAM states is experimentally demonstrated for the first time. The higher-dimensional OAM Hilbert space enhances the information capacity of this approach, while the presence of the off-diagonal correlations allows for recognition of specific spatial signatures present in the object. In particular, this allows the detection of discrete rotational symmetries and the efficient evaluation of multiple azimuthal Fourier coefficients using fewer resources than in conventional pixel-by-pixel imaging. This represents a demonstration of sparse sensing using OAM states, as well as being the first correlated OAM experiment to measure properties of a real, stand-alone object, a necessary first step toward correlated OAM-based remote sensing.

Vortex radio waves could boost wireless capacity “infinitely”

noreply@blogger.com (Bstarn) — Fri, 02 Mar 2012 15:08:00 +0000

After four years of incredulity and not-so-gentle mocking, Bo Thide of the Swedish Institute of Space Physics and a team in Italy have finally proven that it’s possible to simultaneously transmit multiple radio channels over exactly the same wireless frequency

. In theory, according to Thide, we could potentially transmit an “infinite number” of TV, radio, WiFi, and cellular channels at the same time over the same frequency, blasting apart our highly congested wireless spectrum.

Thide’s approach is rather simple. Basically, electromagnetic waves can have both spin angular and orbital angular momentum (OAM). If you picture the Earth-Sun system, spin momentum is the Earth rotating on its axis (producing the day-night cycle), and orbital momentum is the Earth rotating around the sun (producing the seasons). In standard wireless communications — radio, TV, WiFi — we only modulate the spin angular momentum of waves. For years, Thide had theorized that orbital angular momentum could also be added to wireless signals, effectively creating a spiral signal that looks like fusilli pasta; or, in the words of Thide, a “radio vortex.”

Now, in an experiment in Venice, Thide and his Italian colleagues have transmitted two signals at the same time, on the same frequency, over a distance of 442 meters (1450ft). Pictured on the right is the antenna that the team used. No, your eyes don’t deceive you: To create these radio vortices, all you have to do is make a cut in a standard parabolic reflector and twist it slightly. If you imagine a corkscrew of radio signals being continuously transmitted from the outside edge of the antenna, that’s effectively what’s occurring. On the receiving end, there are two “normal” TV antennae (Yagi-Uda) set apart by the same angle as the break in the transmitter. These antennae “decode” the vortex, and voila: Two radio signals transmitted over the same frequency.

It is hard to put into words just how significant Thide’s discovery could be. If the vortex preserves other aspects of wireless communications, such as multiplexing, then in the short term we could be looking at a wireless spectrum that can carry 10 or 20 times as much data. In the long term, as our understanding of orbital angular momentum grows, our wireless spectrum could effectively be infinite. To be honest, this is such a huge twist for wireless communications that the full repercussions are not yet known.

With radio and TV, and now cellular networks, wireless spectrum is one of humanity’s most valued resources. It is because airwaves are so clogged that companies like Verizon or Vodafone pay billions of dollars for just a few megahertz. If Thide’s discovery pans out, not only would wireless spectrum lose most of its value, but the trouble and strife surrounding LightSquared, international roaming, LTE rollout, white space wireless, and digital TV simply cease to be.

http://www.extremetech.com/extreme/120803-vortex-radio-waves-could-boost-wireless-capacity-infinitely

York researchers create ‘tornados’ inside electron microscopes

noreply@blogger.com (Bstarn) — Fri, 17 Feb 2012 15:23:00 +0000

Researchers from the University of York are pioneering the development of electron microscopes which will allow scientists to examine a greater variety of materials in new revolutionary ways.

http://nextbigfuture.com/2012/02/york-researchers-create-tornados-inside.html

The team, headed by Professor Jun Yuan and Professor Mohamed Babiker, from the University’s Department of Physics has created electron beams with orbital angular momentum – electron vortex beams – which will open the way to many novel applications including the more efficient examining of magnetic materials.

Electron microscopes use a beam of electrons to illuminate a specimen and produce a magnified image, allowing scientists to investigate atomic arrangements. Compared to conventional electron beams, electron vortex beams improve the resolution and sensitivity of imaging, which is key when determining the structure of biological specimens such as proteins. They also have applications in the manipulation of nano-scale objects such as atoms and molecules.

As the electron vortex consists of moving charged particles, there is a magnetic field associated with the vortex. This magnetic field will be invaluable in examining magnetic materials, enabling the nanoscale magnetic structure to be imaged.

The York team has created a design for a holographic mask to generate an electron vortex beam and now plans to use this to improve the imaging capabilities of the electron microscope in its York-JEOL nanocentre.

Arxiv - Quantised orbital angular momentum transfer and magnetic dichroism in the interaction of electron vortices with matter

Following the very recent experimental realisation of electron vortices, we consider their interaction with matter, in particular the transfer of orbital angular momentum in the context of electron energy loss spectroscopy, and the recently observed dichroism in thin lm magnetised iron samples. We show here that orbital angular momentum exchange does indeed occur between electron vortices and the internal electronic-type motion, as well as center of mass motion of atoms in the electric dipole approximation. This contrasts with the case of optical vortices where such transfer only occurs in transitions involving multipoles higher than the dipole. The physical basis of the observed dichroism is explained.

In conclusion, we have shown by direct analysis that it
is possible to transfer OAM between an electron vortex
beam and the internal electron states of an atom in the
dipole transition and we have checked by direct analysis that (orbital angular
momentum) OAM transfer occurs for quadupole transitions and in principle in the case of all higher multipoles. This is in direct contrast to the case of optical OAM transfer in the interaction with similar systems. It has been demonstrated both theoretically and experimentally that optical vortices are not speci c in their interaction with chiral matter. Here we have shown that although orbital angular momentum transfer can occur between electron vortices and matter in electric dipole transitions for a given topological charge, there is no intrinsic di fference in absorption for the two opposite helicities. We have concluded that the OAM dichroic electron energy loss spectroscopy of the type performed by Verbeeck et al. shows a dichroism due to the magnetic nature of the material, in which magnetic sublevels would be unequally populated.

Details of York’s latest work - part of the research by second year PhD student Sophia Lloyd - showing that orbital angular momentum of electron beams with vortex structure are more efficient than light for probing atomic magnetism, are published in the February edition of the Physical Review Letters.

Professor Yuan said: “The introduction of vortex beams into electron microscopy, with its screw-like revolving wave front – much like tornados, will revolutionise the study of magnetic nanostructures, as well as creating new applications in terms of nanoparticle manipulation and trapping, and edge contrast detection.”

Professor Babiker, an expert in light vortex research, added: “Optical vortex beams, created using beams of light photons, have been studied for the past 20 years. They have found a great many applications, most notably in fine scale manipulation of single molecules and nano-objects in so-called optical tweezers and optical spanners.

“Research being carried out at York is intended to further current understanding of electron vortices so that a similarly broad range of applications can be realised.”

Time-division multiplexing of the orbital angular momentum of light

noreply@blogger.com (Bstarn) — 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 (Bstarn) — 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 (Bstarn) — 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 (Bstarn) — 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 (Bstarn) — 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 (Bstarn) — 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 (Bstarn) — 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 (Bstarn) — 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 (Bstarn) — 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 (Bstarn) — 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 (Bstarn) — 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.

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Quantum tornado in the electron beam

noreply@blogger.com (Bstarn) — 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 (Bstarn) — 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 (Bstarn) — 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 (Bstarn) — 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 (Bstarn) — 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 (Bstarn) — 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 (Bstarn) — 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.

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