New Way of Observing Light May Boost Info Content

md_seymour observes: "Today's Astronomy Picture of the Day from NASA has a description and image of light that can twist as well as spin, based on research from Miles Padgett and Johannes Courtial of the University of Glasgow. They and their colleagues have apparently been able to sort individual photons by their orbital angular momentum. Since this characteristic of the photon is able to take on an infinite number of values, it may be possible to pack much more information into a light beam."

we should harvest this new light to make:

[theMerovingian]

STAR FIBER!

Star Fiber Router could be called the "X-wing"

I hereby reserve angles/degrees/radians ...

[torpor]

... cross-coordinates ... any, and all, with the digits "8008" in them, in that string ...

For practical use

[Vaevictis666]

For practical use, we need to not only be able to generate photons with a desired spin. As it is, this is still useful for cryptography, but if we want to start packing each photon (on a fibre-optic line or something) with a base 64 value instead of a base 2 value (for example) we need to be able to reliably generate the photon with the correct spin out of the 64. But once that goes say hello to cheaper internet speeds :)

Re:For practical use

[Yazeran]

For practical use, we could use it's quirkyness to see earth sized planets orbiting stars without building monsterous interferometers.


Sorry nope. This would do us no good in detecting planets at interstellar distances. First of all, you still need large interferometers (or mirrors) to resolve small angular distances (read planetary orbits at interstellar distances). Secondly, ordinary light (from stars and planets etc. is randomly polarised and the orbital angular momentum would be distributed randumly

Some light humour :)

[stjobe]

Measuring the orbital angular momentum of single photons is a "brilliant" achievement, says Keith Burnett of the University of Oxford.

Not that I understand one bit of what they're talking about, though :)

Re:Some light humour :)

[torpor]

Well, for one, thats a 'pun', since 'brilliance' is of course a type of optical quality, and its use in science is derived from its context in gemology, where a 'brilliant' (gemstone) often is carved in a manner which implies orbital angular momentum, which is incidentally, or 'was' (in the days of gemology) a measure of its worth, since its supposed to be difficult to carve a diamond in such a manner that its outer edge implies such things ...

Those wacky scientists.

Re:Some light humour :)

[stjobe]

Seeing as I'm totally in the dark when it comes to gemstones, I'll take your word as enlightenment.

However, what my comment about my ignorance referred to was the subject matter of the article, that is the orbital angular momentum of photons, which is still somewhat murky to me.

But then again I might not be very bright...

Re:Some light humour :)

[MindStalker]

angular momentum = mass * (angular velocity)
angular velocity is velocity divided by radius of rotation.

I'm not possitive about orbital angular velocity, but it seems as though it refers to the fact that the center point of the rotation is moving. So basically a point with an orbital angular velocity is spiraling along.

infinite?

[Tom7]

Since this characteristic of the photon is able to take on an infinite number of values,

Not really though, right? Such values are discretized in the sense that the Planck length discretizes distance, right?

Re:infinite?

[Anonymous Coward]

There's an infinite number because any integer multiple of the base value is possible.

To use your parallel, Planck length places a bound on fractions of 1 meter, but not on multiples of 1 meter.

Re:infinite?

[rpresser]

As the other poster said, you can have L = +1, +2, +3, ..., -1, -2, -3 ... to any value. Which makes me wonder though, does a high L mean the photon carries more energy?

Re:infinite?

[Mr Foot]

Photons carry momentum which they can transfer to a solar sail, but they massless as far as we can tell.

Re:infinite?

[rpresser]

Thank you for confirming my understanding so far. (Somebody please mod that AC up as informative.) But the question remains: does the angular momentum carried by the photons affect the energy? I mean, they're talking about stuffing bits into this; anything that carries information usually requires energy. By the way, there is a lot of new work in gravitational lensing. The Hubble has discovered a couple dozen definite lenses; some of them even show some distant objects that are not conventionally visible

Re:infinite?

[omega_cubed]

Yes, actually an infinite number of values. The same way that the integers in discrete, but infinite in number.

Re:infinite?

[Anonymous Coward]

I had a problem with that claim too.
I think they should have said the number of encodable bits is reliant on the sensitivity of our measurments. otherwize one could say that a 5 foot long piece of rope has infinate encoding capacity.
Well duhh,, 5 / 3 = 1.666666666666666666666666~~

Old News

[Rubyflame]

This is just circularly-polarized light, isn't it? Shine a laser through a polarizer and a quarter-wave plate, and that's what you get.

No.

[Anonymous Coward]

No, they're different.

Take a beam of circularly-polarized light (without orbital-angular-momentum), freeze time in your imagination, and look at the E-field vectors along the beam. The E-field vectors all point in the same direction. Over time they rotate around the beam axis -- that's what circular polarization means -- but the E-field-vectors are always aligned along the entire length of the beam.

Now instead imagine a beam of light with orbital-angular-momentum, and again freeze the beam in your imagination. Now the E-field vectors make a helix along the beam.

You get circularly polarized light by passing a beam through a polarizer and quarter-wave plate. You get light with orbital angular momentum by spinning the light source around the beam axis.

A bit more information from Scientific American

[UnknowingFool]

There's a short article [sciam.com] about this property of light in this month's edition of Scientific American. Apparently this propery isn't new but rather largely ignored.

Lots of bits on ONE PHOTON!!!

[harrkev]

Wow. First, let's assume linear polarization. The polarization angle could vary between 0 and 179.999 degrees. If the "twist" of the light could be considered as an "amplitude," then we could do a variant of QAM on a single photon. Depending upon how sensitive the receiving equipment is, and how precise the transmitting equipment is, it should be possible (in theory) to then encode at least 4 bits in one single photon.

Of course, building such a transmitter/receiver would be an engineering nightmare. B

scientific american article

[mdmarkus]

Scientific American has this article [sciam.com] as well. I admit, i'm still scratching my head over it after reading it when i got the paper version last month...

Total energy and mass?

[stonewolf]

Is orbital angular momentum (OAM) a bit of energy added to the photon, or is it just a redistribution of the "normal" energy of the photon? If it is a redistribution then does a photon with OAM have a different wavelength than a photon with the same energy but no OAM?

Does generating a photon with OAM transfer angular momentum from the generator to the photon? That is does emitting an OAM beam cause the source to spin?

Many questions that boggle my mind.

Stonewolf