
The physics of angular momentum radio - leephillips
http://arxiv.org/abs/1410.4268?utm_source=twitterfeed&utm_medium=twitter
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nabla9
Photons have both spin angular momentum (SAM) and orbital angular momentum
(OAM). OAM was found theoretically by L. Allen et al. in 1992.

What if the the space is full of efficient OAM encoded radio transmissions
from alien civilizations and we are just getting close to discovery?

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spott
>What if the the space is full of efficient OAM encoded radio transmissions

Unlikely. OAM is very localized: only those along the transmission path can
determine the OAM component of the light. You can't "broadcast" an OAM signal
across a large area.

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al2o3cr
Haven't parsed the whole paper, but my first thought was "did they just re-
invent circular polarization?"

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ChuckMcM
No, they have proposed that something like polarization modulated signals
would make it possible to send data just as well as frequency modulated or
amplitude modulated signals.

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GFK_of_xmaspast
Naive question, what does multipath do to polarization?

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madengr
Circular polarized waves invert (i.e. RHCP switches to LHCP) upon reflection.
For example, precision GPS antennas need good cross-pol rejection to keep the
LHCP from multipath (reflections from buildings and ground) from interfering
with direct RHCP from the satellite.

In general, linear polarized waves retain their polarization, but I believe
there are special cases (such as Brewster angle on dielectrics) where you can
get some depolarization.

From what I read a while back, on an IEEE article on this orbital
polarization, the number of orthogonal modes you can achieve is limited by
antenna construction, and it definitely can't handle multi-path; strictly
point-to-point microwave link. I'll bet rain will really mess it up, more so
than your typical rain fade.

Still very cool though, and I still don't have my head wrapped around it,
despite 20 years of RF/Microwave engineering.

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darkmighty
From what I understood, this requires varying the complex-valued field
spatially near the receiver. Isn't that equivalent somehow to having multiple
antennas and creating streams with those (i.e. varying the field near the
receiver and detecting it, aka MIMO)?

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blueintegral
You are not alone in drawing that conclusion:
[http://lup.lub.lu.se/luur/download?func=downloadFile&recordO...](http://lup.lub.lu.se/luur/download?func=downloadFile&recordOId=2062936&fileOId=2339120)

