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Can someone give me an overview of how OAM states are used in communications?

Using Orbital Angular Momentum States seems like a hot topic for communications. I read a few articles about the basic principles and experiments done in Italy that use OAM states to double the capacity of a wireless link.

Also if anybody knows where to find a good tutorial on OAM states or any other good place to look for more information, experiments, data, etc. related to this topic that would help me out a lot :).

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Hi Scott, and welcome to Physics Stack Exchange! What exactly did you want to know about OAM states? Even if it's just something like "Can someone give me an overview of how OAM states are used in communications?" Good questions tend to ask for an answer directly rather than asking for a resource or tutorial that explains the thing. – David Z Oct 10 '12 at 22:01
Thank you David. Then I'll try again: Can someone give me an overview of how OAM states are used in communications? – Scott Oct 15 '12 at 18:26
I meant you should edit your question - it doesn't help much if you just post stuff in a comment without editing the question accordingly. – David Z Oct 15 '12 at 18:42
Gotcha, thanks. – Scott Oct 15 '12 at 20:45

What they are referring to is Orbital Angular Momentum multiplexing, which is a type of multiplexing which uses transverse modes of light as different channels in a multiplexing scheme. The specific technology seems to be linked very closely to developments in using Orbital Angular Momentum in quantum communication as evidenced by recent successes by Anton Zeilinger in the experiments carried out at the Canary Islands.

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Thanks! I had a look at the experiments done. I'm having trouble understanding how the measurements work. If Measuring the state of one entangled photon affects the other photon's state, how can you measure the second particle and know that it wasn't like that before you measured it. I.E. how can you ensure that they were entangled...a.k.a I'm confused. – Scott Oct 16 '12 at 14:26
@Scott Short answer is to take a look at how this is described in the thesis Quantum Interferometry with Multiports: Entangled Photons in Optical Fibers which is referenced in the linked paper above. – user11547 Oct 16 '12 at 14:48

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