Putting the Right Spin on It

Infinite-capacity wireless vortex beams carry 2.5 terabits per second

Actually, it’s not spin. It’s the other angular momentum, pork the orbital variety.

These twisted signals use orbital angular momentum (OAM) to cram much more data into a single stream. In current state-of-the-art transmission protocols (WiFi, LTE, COFDM), we only modulate the spin angular momentum (SAM) of radio waves, not the OAM. If you picture the Earth, SAM is our planet spinning on its axis, while OAM is our movement around the Sun. Basically, the breakthrough here is that researchers have created a wireless network protocol that uses both OAM and SAM.

I couldn’t get a mental image of how you’d do this, but I think that’s because I was thinking about individual photons, and I don’t see how to get a photonic orbital angular momentum state. But this is data transmission, which can be analog, or even of it’s digital a “one” is made up of a bunch of photons, i.e. it’s classical.

So I grabbed the paper I could (an earlier one that demonstrated the effect, and to which I had access). Here’s what the antenna looks like

The light being sent will have a different phase depending on what part of the antenna is transmitting it, which gives you the vortex. 3 GHz signals have a wavelength of 10 cm, so that’s probably gives you the scale of the depth of the slice in the parabolic dish.

This technique is likely to be used in the next few years to vastly increase the throughput of both wireless and fiber-optic networks.

I think this is overly optimistic. It’s going to take time to make this robust for data transmission and then you have to deploy the technology. And fiber-optics? I don’t see how this would work in a fiber (a less forgiving environment to good polarization, which is likely to cause problems here), but I also don’t see it as being necessary. I don’t think fiber is as clogged as the RF spectrum is, and you can always add more fiber if you need to.

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