[HN Gopher] First device based on 'optical thermodynamics' can r...
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First device based on 'optical thermodynamics' can route light
without switches
Author : rbanffy
Score : 83 points
Date : 2025-10-09 00:54 UTC (4 days ago)
(HTM) web link (phys.org)
(TXT) w3m dump (phys.org)
| anigbrowl wrote:
| 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.
| HarHarVeryFunny wrote:
| 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.
| dawnofdusk wrote:
| >what this routing mechanism is (heating a substrate, maybe?)
|
| You can engineer a waveguide if you understand the nonlinear
| theory they propose. There's no heat exchange involved, which
| is easy to get confused on because the writing in the article
| does not really understand "optical thermodynamics".
|
| >if the routing is dynamically changeable
|
| At this point probably not, it requires a finely engineered
| waveguide which has a well-defined "ground state"
|
| >it works in reverse, eg light coming in can be routed to one
| of several output ports
|
| In theory it works in reverse, as everything in this system is
| time-reversible (i.e., the "optical thermodynamics" is just an
| analogy and not _real_ thermodynamics, which would break time
| reversibility). This is demonstrated via a simulation in the
| SI, but experimentally they did not achieve this (it may be
| difficult, I am not an experimentalist so cannot comment).
| DarkSucker wrote:
| 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.
| alexfromapex wrote:
| 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.
| robotresearcher wrote:
| I don't think the author of this piece has a clue how this works.
| I certainly don't, even after reading it slowly.
| impossiblefork wrote:
| 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 details are probably fiddly though.
| echelon wrote:
| - my understanding of nonlinear optical mediums is
| negligible. Something like the crystals that cause quantum
| entanglement and emitting photon pairs?
|
| - 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?
| hangsi wrote:
| 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).
| o11c wrote:
| 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?
| lschueller wrote:
| I agree. The article is written quite superficial and when it
| gets intersting it just repeats the stuff from before. Imo the
| subject and news are really hot shit, but the author did his
| best to hide it in banality
| sounds wrote:
| 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.
|
| [1] https://en.wikipedia.org/wiki/Photon_gas
|
| [2] https://www.nature.com/articles/s41467-024-53261-x
| petermcneeley wrote:
| 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.
| yalogin wrote:
| May be somewhat tangential to the topic, there are some companies
| pushing for use of light as the data bus for AI training path. Is
| the data throughput need that high for training? Do these
| companies really have a point?
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