Vortex Lasers May Be a Boon for Data
spectrum.ieee.org
spectrum.ieee.org
> 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.
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> 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.
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.
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 [2] - https://en.wikipedia.org/wiki/Angular_momentum_coupling#Term...
Edit: To be precise I think it's something like group velocity but applied to angular momentum, but I'm not an expert.
See also the first paragraphs of 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.
This reminds me of how a fourier tranformation can increase the throughput by stacking frequencies and then parsing upon detection.
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).
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!
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