
Vortex Lasers May Be a Boon for Data - headalgorithm
https://spectrum.ieee.org/tech-talk/semiconductors/optoelectronics/vortex-laser
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pm90
This was an incredible read. I had no idea that light possessed momentum,
especially angular momentum.

> A potentially extraordinarily useful property of vortex beams is that they
> do not interfere with each other if they all possess different twisting
> patterns. This means a theoretically infinite number of vortex beams can get
> overlaid on top of each other to carry an unlimited number of data streams
> at the same time.

...

> The researchers began with a microring laser consisting of a ring of indium
> gallium arsenide phosphide only 7 microns in diameter in which light could
> flow in a loop, via a channel 650 nanometers wide. By varying the light
> pumped into this circle from microscopic arms on either side of this ring,
> the researchers could alter the orbital angular momentum of the beam emitted
> from the laser. Instead of emitting a single orbital angular momentum mode,
> they showed it could emit five distinct modes.

> The scientists also developed a light detector based on tungsten
> ditelluride, which can act like a so-called Weyl semimetal, a material with
> properties lying between a conductive metal and a pure semiconductor. Their
> experiments found that different orbital angular momentum modes of light
> each generated unique patterns of electrical current within the
> photodetector, and they suggest this electronic method of detecting the
> orbital angular momentum of light could be scaled to work on microchips.

Amazing stuff.

~~~
gibolt
Absolutely agree! Wouldn't have dove into the article without your comment.
Thanks!

Does anyone know if there have been experiments confirming that light's
angular momentum can be transferred like its linear momentum? Perhaps firing a
rotating beam at a tiny sheet in space to induce spin and then reverse the
light spin and confirm that the sheet eventually reverses.

Since this technique could induce some extreme spin over long time/distance, I
could imagine using it to pull crazy maneuvers in space. For example, aim a
tiny slightly off balance disc at a distant planet. Once it started entering
the planet's atmosphere, a correct entry angle and spin could take it from
being head on to entering orbit.

~~~
thatcherc
There are experiments like this! One is where circularly polarized light is
used to spin up a small piece of glass to really high angular velocity
(billions of rotations per second!) [1].

There are also atomic transition selection rules that depend photons
transferring angular momentum into or out of an atom electronic orbitals.
Essentially, when an electron jumps between the orbitals (s, p, d, etc from
chemistry class), it can gain or lose angular momentum depending on its start
and end state. But that momentum must be conserved, so in these cases a photon
is emitted or absorbed to account for that angular momentum. The topic is kind
of addressed here [2], but I'd have to dig up my old AMO notes to find a
better reference. Lots of cool physics to dive into here if you're interested!

[1] - [https://phys.org/news/2018-07-world-fastest-
rotation.html](https://phys.org/news/2018-07-world-fastest-rotation.html) [2]
-
[https://en.wikipedia.org/wiki/Angular_momentum_coupling#Term...](https://en.wikipedia.org/wiki/Angular_momentum_coupling#Term_symbols)

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elwell
> This means a theoretically infinite number of vortex beams can get overlaid
> on top of each other to carry an unlimited number of data streams at the
> same time.

This reminds me of how a fourier tranformation can increase the throughput by
stacking frequencies and then parsing upon detection.

~~~
javajosh
Another way to think of fiber optics is to imagine the analog case, like
pumping a movie through the fibers. From there you can go in two directions,
one making the channel machine readable, and the other increasing throughput.
For machine readability you get something like a fast succession of QR codes.

Throughput is, I think, more interesting because it turns out you can overlay
2 movies on each other! You can see this in various 3D movie technologies. Two
channels are combined, and then separated by your glasses. The separation can
happen by frequency (classic red/blue, a) or by polarization (the more modern
style). NOW, apparently, there's a whole new way to distinguish the movies:
angular momentum! Each physically differentiable thing gets you, very roughly
speaking, one additional movie. So now you can pump 4 movies in one. Of
course, it turns out you can split up each channel into smaller slices than 2,
e.g. you could put up 2 distinct 3D movies if half the audience has red/blue
and the other half orange and purple (would those colors work?) Frequency
really is the big one, since light extends well outside the visible range, in
both directions - your radio tunes by putting on very finely differentiated
light filter (although really a reverse light filter in the sense that it only
lets one very narrow set of frequencies in, rather than only keeping one
narrow set of frequencies out).

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peter_d_sherman
>"A beam of light can possess two kinds of angular momentum.

The _spin angular momentum_ of a ray of light can make objects it shines on
rotate in place, whereas its _orbital angular momentum_ can make objects
rotate around the center of the ray.

A beam of light that carries orbital angular momentum resembles a vortex,
moving through space with a spiraling pattern like a corkscrew. Whereas a
conventional light beam is brightest at its center, vortex beams have ringlike
shapes that are dark in the center, due to how some of the waves making up
vortex beams can interfere with one another."

Fascinating!

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b34r
I’m curious if this is applicable to fiber optics? If so it could vastly
decrease the width of our undersea cables and allow for more redundancy in a
non-complete cable cut scenario.

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aDfbrtVt
Trying to transmit via multiple spatial modes has been tried in the past. I'd
be interested to see if OAM modes don't suffer from the same mode coupling
behavior.

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neatze
Can such method also work with radio frequencies ?

~~~
packet_nerd
Circular polarized antennas are often used in ham radio especially to
communicate with satellites[1].

I'm not expert enough to know, is this the same physics as what the article is
talking about?

[1] [https://www.qsl.net/sv1bsx/antenna-
pol/polarization.html](https://www.qsl.net/sv1bsx/antenna-
pol/polarization.html)

