The writeup on phys.org is troublesome at best. Starting with the Ming Hsieh Department of Electrical and Computer Engineering, it buries the rest of that sentence in paragraph 5: USC (University of Southern California) and the Abbe Center of Photonics, Friedrich Schiller University Jena, Germany.
This team has made a nonlinear lattice that relies on something they call "Joule-Thomson-like expansion." The Joule-Thomsen effect is the ideal gas law in beginning science. PV=nRT. Compression heats a gas, expansion cools a gas.
Why they're studying the equivalent photonics principle [1] is that it focuses an array of inputs, "causing light to condense at a single spot, regardless of the initial excitation position." Usually the problem is that light is linearly independent: two beams blissfully ignore each other. To do useful switching or compute, one of the beams has to be able to act as a control signal.
A photon gas doesn't conserve the number of particles (n) like beginning physics would suggest. This lets the temperature of the gas control the output.
The temperature, driven by certain specific inputs, produces the nonlinear response. I didn't see a specific claim what gain they achieved.
This paper is more on the theoretical end of photonics research. Practical research such as at UBC Vancouver [2] where a device does "weight update speed of 60 GHz" and for clustering it can do "112 x 112-pixel images" - the tech doesn't compete well against electronics yet.
TSMC and NVidia are attempting photonics plays too. But they're only achieving raw I/O with photons. They can attach the fiber directly to the chip to save watts and boost speeds.
Basic physics gets in the way too. A photon's wavelength at near UV is 400 nanometers, but the transistors in a smartphone are measured at 7 nanometers ish. Electrical conduction is fundamentally smaller than a waveguide for light. Where light could maybe outshine electrons is in switching speed. But this research paper doesn't claim high switching speed.
Light doesnt interact with itself directly without a third non-light partner. So yes the light of course needs to interact with lattice made of atoms to make any switching possible here. This is why we can see light from the stars though it had to travel through other light for millions of years.
It's actually quite comprehensible. Nonlinear optical medium + photon gas -> a photon gas which is no longer ideal, so that things like Joule-Thompson effect can happen in it, then they build simple computing mechanisms out of it.
The almost-wrong simplification is that a nonlinear medium changes the wavelength of the light that passes through it.
If you can control the nonlinearity, you can control the wavelength change and so change properties such as the angle of refraction to change where the light goes (like in a rainbow/a prism, where the red light refracts more).
The immediate question is: how much "resistance" is there? That is, how much light will be lost per node, and as a result how long is the longest circuit you can make without boosters?
I found this article extremely hard to understand, and the linked abstract was not much more help. My impression is that the device can take light coming into one of several input ports and through some magic of nonlinear optics, ensure that it all ends up at a single output port, something like a funnel. I was unable to determine anything about what this routing mechanism is (heating a substrate, maybe?), if the routing is dynamically changeable, or it works in reverse, eg light coming in can be routed to one of several output ports. The latter would seem like a breakthrough, but my impression is that what's described here is more proof-of-concept than prototype.
As best I can understand (which is barely, and poorly!), it seems that this new, and interesting, field of optical thermodynamics allows the behavior of non-linear optical systems to be predicted, in this case allowing them to design a "photonic lattice" - some sort of system of waveguides - so that light behaves in a predictable way and can effectively be steered without having to use any active switching components.
What is even less clear than the above is how is this being used.. Presumably it's not just about routing light to some fixed location, but rather allowing it to be switched, so perhaps(?!) the phototic lattice has multiple inputs that interact resulting in light being steered to one of many outputs? Light being used to switch light?
I dunno - it was clear as mud. I'm basically just guessing here.
Sounds great, but I often find myself wondering "where's the catch?". There's not enough info in the abstract judge for myself whether the idea has legs. I'm sure it'll get more press if there's something to it.
This would have some amazing implications but they will also need to build the routing mechanism with light-based attenuation or it will never exceed the speed of electricity in a wire.
This team has made a nonlinear lattice that relies on something they call "Joule-Thomson-like expansion." The Joule-Thomsen effect is the ideal gas law in beginning science. PV=nRT. Compression heats a gas, expansion cools a gas.
Why they're studying the equivalent photonics principle [1] is that it focuses an array of inputs, "causing light to condense at a single spot, regardless of the initial excitation position." Usually the problem is that light is linearly independent: two beams blissfully ignore each other. To do useful switching or compute, one of the beams has to be able to act as a control signal.
A photon gas doesn't conserve the number of particles (n) like beginning physics would suggest. This lets the temperature of the gas control the output.
The temperature, driven by certain specific inputs, produces the nonlinear response. I didn't see a specific claim what gain they achieved.
This paper is more on the theoretical end of photonics research. Practical research such as at UBC Vancouver [2] where a device does "weight update speed of 60 GHz" and for clustering it can do "112 x 112-pixel images" - the tech doesn't compete well against electronics yet.
TSMC and NVidia are attempting photonics plays too. But they're only achieving raw I/O with photons. They can attach the fiber directly to the chip to save watts and boost speeds.
Basic physics gets in the way too. A photon's wavelength at near UV is 400 nanometers, but the transistors in a smartphone are measured at 7 nanometers ish. Electrical conduction is fundamentally smaller than a waveguide for light. Where light could maybe outshine electrons is in switching speed. But this research paper doesn't claim high switching speed.
[1] https://en.wikipedia.org/wiki/Photon_gas
[2] https://www.nature.com/articles/s41467-024-53261-x
The details are probably fiddly though.
- what is a "photon gas"? Is this a state of matter? What is the matter if photons aren't matter?
- ideal gas law, PV=nRT not obeyed? Due to ionization or something? Photon pressure?
- Joule-Thompson Effect?
- Building computers out of light?
- Which thermodynamic properties or laws are being obeyed? Is this something like a Carnot cycle, but with photons?
If you can control the nonlinearity, you can control the wavelength change and so change properties such as the angle of refraction to change where the light goes (like in a rainbow/a prism, where the red light refracts more).
What is even less clear than the above is how is this being used.. Presumably it's not just about routing light to some fixed location, but rather allowing it to be switched, so perhaps(?!) the phototic lattice has multiple inputs that interact resulting in light being steered to one of many outputs? Light being used to switch light?
I dunno - it was clear as mud. I'm basically just guessing here.