OT: Distinguishable angular momentum in radio photons?

[Jussi Eloranta]

On 05/04/2012 10:03 PM, Erik Basilier wrote:
> * The claim was not just that you can have two independent communications
> (as possible by means of circular polarization), but more than two.
> * The claim of multiple levels of angular momentum tells us that it is about
> OAM and not SAM. The abstract of the debunking research (thanks Sverre for
> posting) explicitly refers to OAM.
Indeed photons can posses orbital angular momentum which can only
interact with materials that have fairly special anisotropic properties
(which is the reason I was not even bringing it up earlier). In order to
talk to the oam component, one should subject RF photons to propagate in
such medium as well. While possible in theory (and shown in optics using
an "obscure" version of a halve wave plate), it would be a real
challenge to observe this for RF where such materials are not available
(someone correct me if I am wrong, I mostly work with optics).

However, an interesting topic and well worth looking into! I wonder if
photon orbital angular momentum would be conserved in a non-linear
process where the difference and sum generation occurs (usually just the
sum is used, for example in second harmonic generation; similar to RF
heterodyning) and the difference component would lie in RF (OK, perhaps
in GHz range in practice...; near baseband anyway ;-)? So the idea would
be to start with optical photons (prepared with oam information) at
close wavelengths and then convert to RF (RF wavelength = difference
between the two optical photons; angular momentum must be conserved).
Unfortunately, this would not work for detection that well because high
intensities are needed for the non-linear process. I would expect that
the first place where this would show up (if possible at all) for RF
would be nuclear magnetic resonance (NMR) experiments where I could see
that the extra source of angular momentum could find applications there.

I suspect that most people are getting bored already - so I will sign
off...

Best,

Jussi Eloranta
AA6KJ

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[Cookie]

Lost or confused perhaps Jussi, but not bored!  Keep it up, maybe we will learn something, maybe not!
 
Willis 'Cookie' Cooke
K5EWJ & Trustee N5BPS, USS Cavalla, USS Stewart


________________________________
 From: Jussi Eloranta <[hidden email]>
To: [hidden email]
Sent: Saturday, May 5, 2012 1:52 PM
Subject: Re: [Elecraft] OT: Distinguishable angular momentum in radio photons?
 
I suspect that most people are getting bored already - so I will sign
off...

Best,

Jussi Eloranta
AA6KJ

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[Fabio Lodrini]

Somewhere in internet there is (where ?) a video showing the experiment,
done in Venice during what it seems a Carnival event.
To me, it has a slight taste of a joke, included the strange parabolic dish.

I2LQF, Fabio

On 04/05/2012 8.25, Erik Basilier wrote:

> Oh, and the first thing I looked at was whether it was in the April issue.
> It was not. Maybe the IEEE got it from another publication's April issue?
>
> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of Erik Basilier
> Sent: Thursday, May 03, 2012 10:10 PM
> To: [hidden email]
> Subject: [Elecraft] OT: Distinguishable angular momentum in radio photons?
>
> The May 2012 issue of the IEEE Spectrum magazine reports that researchers in
> Italy and Sweden were able to conduct two separate instances of radio
> communication on the exact same frequency, without increasing bandwidth, and
> without time-division multiplexing, be making the transmissions differ in
> angular momentum. One transmission used linear polarization, and the other
> was given angular momentum by means of a dish with a radial cut, where the
> metal  was bent backwards/forwards on the two sides of the cut. Apparently
> this is not just a case of linear vs circular polarization, as circular
> polarization can be readily picked up by a linearly polarized antenna, and
> apparently the two channels did not interfere with each other. The
> researchers claim that this demonstration points to the possibility that the
> radio photons can be given multiple, quanized levels of angular momentum,
> making possible several more communication channels without increased
> bandwidth. Other researchers say that this is just a form of MIMO. Wikipedia
> describes MIMO as the technique of using multiple antennas as in diversity
> reception or in gain increases obtained by phasing the antennas.
>
>
>
> My apologies if this is too far OT.
>
>
>
> 73,
>
> Erik K7TV
>
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>

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