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Vortex Lasers May Be a Boon for Data

85 points by headalgorithm 6y ago

pm90 6y ago
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 6y ago
  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 6y ago
    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_symbols https://en.wikipedia.org/wiki/Angular_momentum_coupling#Term...
  - raziel2701 6y ago
    Yeah you can change the magnetization direction of materials by irradiating with circularly polarized light. Synchrotrons use circularly polarized x-rays to probe magnetic materials routinely. The underlying mechanism of these effects is simply the transfer of angular momentum.
- dghughes 6y ago
  I think this property of light is fairly new I recall reading about twisting light/torque light not that long ago. Searching brings up articles only a few years old but I think it was about ten yeas ago that I read about it.
  - contravariant 6y ago
    Polarized light has been known for ages, I think this is some kind of coherent state that allows those bundles of photons to carry more angular momentum than normal. I think the classical solution also allows for these twisted EM waves, but I'm not 100% sure. Edit: To be precise I think it's something like group velocity but applied to angular momentum, but I'm not an expert.
  - raziel2701 6y ago
    No this property of light has been known for ages, it's commonly known as circularly polarized light. There is a bit of fuckery here with trying to coin the term vortex laser to make it more marketable/sexier, but researchers have been playing with circularly polarized light for decades.
    - mturmon 6y ago
      I’m doubtful of this claim. I’m not an expert but I hear about vortex optical components at lunchtime conversation, and from what I understand these effects have only become exploited in the past 20 years or so. I'm open to correction or further context about this. See also the first paragraphs of https://en.wikipedia.org/wiki/Optical_vortex https://en.wikipedia.org/wiki/Optical_vortex, which distinguish between circular polarization from spin angular momentum, vs. orbital angular momentum which is modified by these vortex components.
elwell 6y ago
> 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 6y ago
  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).
b34r 6y ago
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.
peter_d_sherman 6y ago
>"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!
aDfbrtVt 6y ago
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.
neatze 6y ago
Can such method also work with radio frequencies ?
- phkahler 6y ago
  I believe the answer is yes. I recall something a few years ago where they modified a dish antenna to create a form of spiral signal. Multiple variations could be used at the same base frequency.
- mturmon 6y ago
  Yes, see https://en.wikipedia.org/wiki/Orbital_angular_momentum_multiplexing https://en.wikipedia.org/wiki/Orbital_angular_momentum_multi...
- packet_nerd 6y ago
  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

85 points by headalgorithm 6y ago

pm90 6y ago

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 6y ago
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 6y ago
  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_symbols https://en.wikipedia.org/wiki/Angular_momentum_coupling#Term...
- raziel2701 6y ago
  Yeah you can change the magnetization direction of materials by irradiating with circularly polarized light. Synchrotrons use circularly polarized x-rays to probe magnetic materials routinely. The underlying mechanism of these effects is simply the transfer of angular momentum.
dghughes 6y ago
I think this property of light is fairly new I recall reading about twisting light/torque light not that long ago. Searching brings up articles only a few years old but I think it was about ten yeas ago that I read about it.
- contravariant 6y ago
  Polarized light has been known for ages, I think this is some kind of coherent state that allows those bundles of photons to carry more angular momentum than normal. I think the classical solution also allows for these twisted EM waves, but I'm not 100% sure. Edit: To be precise I think it's something like group velocity but applied to angular momentum, but I'm not an expert.
- raziel2701 6y ago
  No this property of light has been known for ages, it's commonly known as circularly polarized light. There is a bit of fuckery here with trying to coin the term vortex laser to make it more marketable/sexier, but researchers have been playing with circularly polarized light for decades.
  - mturmon 6y ago
    I’m doubtful of this claim. I’m not an expert but I hear about vortex optical components at lunchtime conversation, and from what I understand these effects have only become exploited in the past 20 years or so. I'm open to correction or further context about this. See also the first paragraphs of https://en.wikipedia.org/wiki/Optical_vortex https://en.wikipedia.org/wiki/Optical_vortex, which distinguish between circular polarization from spin angular momentum, vs. orbital angular momentum which is modified by these vortex components.

elwell 6y ago

> 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 6y ago
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).

b34r 6y ago

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.

peter_d_sherman 6y ago

>"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!

aDfbrtVt 6y ago

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.

neatze 6y ago

Can such method also work with radio frequencies ?

phkahler 6y ago
I believe the answer is yes. I recall something a few years ago where they modified a dish antenna to create a form of spiral signal. Multiple variations could be used at the same base frequency.
mturmon 6y ago
Yes, see https://en.wikipedia.org/wiki/Orbital_angular_momentum_multiplexing https://en.wikipedia.org/wiki/Orbital_angular_momentum_multi...
packet_nerd 6y ago
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