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In reality, all-optical computing is mostly a terrible idea: fundamentally, it cannot reach the integration density of electronics. It boils down to the element
by dogber1 5y ago
In reality, all-optical computing is mostly a terrible idea: fundamentally, it cannot reach the integration density of electronics. It boils down to the elementary differences between Fermions (electrons, neutrons, etc.) and Bosons (photons, etc.). Their intrinsic behavior determines the interaction with matter, i.e. conductive/absorptive properties. As a result, optical wires (waveguides) have to be sized roughly at a wavelength (hundreds of nm), whereas electrical wires can be much smaller (<30nm and below). Suppose you want to build an amplifier: all the claimed speed benefits of this optical device would vanish in the path delay of the feedback loop.
But just like graphene, carbon nanotubes, and other fads, you can publish fancy papers with it.
- jcims 5y ago(I swear I’m not in Fridman’s payroll.) As a layperson I found this episode with Jeffrey Shainline an interesting discussion tangential to the topic of optoelectronic computing. The basic gist was that photons are good for communication, electrons are good for compute. https://youtu.be/EwueqdgIvq4 https://youtu.be/EwueqdgIvq4
- rewq4321 5y agoThe specific timestamp for that part of the conversation: https://youtu.be/EwueqdgIvq4?t=2793 https://youtu.be/EwueqdgIvq4?t=2793
- hrgiger 5y agoNot in the domain but as far as I understand from video for the counter argument: "Adding a matter of component and creating this kind of liquid of the light you add interactions in the system so practically light interacts more efficient with the light" https://youtu.be/Kv25Dw-IuCM?t=675 https://youtu.be/Kv25Dw-IuCM?t=675
- WithinReason 5y agoThis makes me wonder if transmitting data optically would help with the gradual lowering of the data/compute ratio over time: https://sites.utexas.edu/jdm4372/files/2016/11/Slide16.png https://sites.utexas.edu/jdm4372/files/2016/11/Slide16.png
- SmooL 5y agoWe already transmit data optically, that's what fiber optics is.
- WithinReason 5y agoI'm talking about between chips and RAM of course because that's where the data/compute ratio is shrinking, not between Tokyo and New York.
- adgjlsfhk1 5y agothe hard part is that currently electrical to optical conversions take a fair amount of space which would make them hard to do on CPU. it might be practical for storage to ram though, which would be really cool.
- marcosdumay 5y agoWell, good thing that the proposed application is about multiplexing/demultiplexing, and not about general computing. Light has many inherent advantages over electricity for multiplexing/demultiplexing. Also, optical amplification works quite well too, and people use it on every long distance data cable nowadays.
- human 5y agoWould it be possible to circumvent this problem with something like squeezed light? (https://en.m.wikipedia.org/wiki/Squeezed_states_of_light https://en.m.wikipedia.org/wiki/Squeezed_states_of_light)
- dogber1 5y agoNo - that's just a neat trick to enhance the precision in the measurement of non-commuting observable quantities of interest.
- anko 5y agohow about for an optical switch? for switching network packets over fibre?
- dogber1 5y agoSwitching/routing usually requires significant information processing (e.g. decode packet header, match destination address against routing tables, etc.). This necessitates 10k or more gates. All-optical computing can't deliver this level of integration density, nor the performance at reasonable power levels. Maybe there will be some smart way to pre-encode routing information onto packets to reduce processing requirements, but I doubt that such a network could scale.
- corndoge 5y ago> Maybe there will be some smart way to pre-encode routing information onto packets to reduce processing requirements, but I doubt that such a network could scale. https://en.wikipedia.org/wiki/Multiprotocol_Label_Switching https://en.wikipedia.org/wiki/Multiprotocol_Label_Switching
- namibj 5y agoThat sounds like a derivate of MPLS, where labelsa re only stripped along the path.
- iptrans 5y agoBeing able to do any kind of computation in the optical domain would benefit telecommunications immensely. Basic things like optical muxing/demuxing and serialization/deserialization would be fantastic.
- deleted 5y ago[deleted]
- formerly_proven 5y agoI was going to say "But wavelength/polarization multiplexing is the norm", but you have "fiber network design" in your about so I'm wondering what I'm missing - I guess you mean dynamic muxing, essentially routing? SerDes is of course annoying.
- adamnemecek 5y agoBut isn't a fundamentally different type of computation? A type of computation that might be faster even at lower density?
- pg_bot 5y agoIsn't this just a trade off? Is there never a scenario where you would trade transistor density for switching speed and lower power consumption?
- dumbfoundded 5y agoYes. IIRC, amd chips have been beating intel chips for a while now on transistor sizes but intel even with larger transistors still have a greater density on a chip (maybe it's changed in the latest gen). Another benefit of lower density is cooling.
- dogber1 5y agoThat's indeed done all the time in electronics: for example, RF CMOS usually trailing on a node three or four generations behind the bleeding edge. However, all-optical/photonic computing is just intrinsically so much worse than electronics. On top of the issues that I touched on, there are also other fundamental problems, e.g. distribution of power: photons like to get absorbed by nearby electrons. How do you then supply all the active devices (switches/lasers/etc.) with power while maintaining some semblance of signal integrity and dense integration?
- singularity2001 5y agoCould nonlinear wave interactions be applied in near vacuum, isolated from the lasers, amplifiers and counters? Think 100000*100000 imprecise loss-full tensor/matrix multiplications.
- jacquesm 5y agoThere is a special case: pumped laser amplification of signal in underwater fiber optic cables. That's all optical for the signal path as far as I know. https://www.laserfocusworld.com/fiber-optics/article/16551090/optical-amplifiers-speed-data-flow-undersea https://www.laserfocusworld.com/fiber-optics/article/1655109...
- singularity2001 5y agoExactly. While this speed vs space trade off makes less sense in mobiles, it might make perfect sense in industrial settings. Imagine 3D computers the size of a room (Craigh 2) but a 1000 times faster than any TPU only cluster.
- api 5y agoCouldn't this perhaps be useful for specialized compute problems that can be represented as a combinatorial system of optical gates/switches? It would be something useful for a specialized subset of problems, sort of like quantum computing. QC is also not going to replace general purpose electronic computers but augment them for certain classes of problems.
- Retric 5y ago~400nm for waveguides isn’t that big of an issue. Optical computing may be relighted to stuff like DSP, but that’s still a vast market.
- tragictrash 5y agoThis sounds to me like doctors claiming they know so much about the human body when in reality we are at the infancy of our understanding
- ithkuil 5y agoWe're in an interesting point: there is so much we don't know but in order to learn more everything we do must fit in the already immense amount of knowledge that we accumulated so far. In the vast majority of cases this requires that the people who want to nudge the frontier a bit further must first dedicate a good portion of their life's studying what we know, and as the result sounding a bit arrogant when they explain to a layperson that actually they know what they're talking about. Yes, in some cases, they may be erring on the side of too confidence, but in many many cases is the layperson who doesn't fully grasp the ramifications of the innocent looking alternatives.
- gboogie117 5y agoThat’s a pretty long way around to what is essentially an appeal to authority. You’re right about the knowledge and devotion required of frontier pushers. History is full of people who challenged this thinking and completely overhauled human understanding of a topic, though, often in the face of relentless ridicule. The error (in your telling) is equating knowledge with confidence. Knowledge is knowing you might be wrong about it all. The advice to spend one’s life questioning isn’t a smarmy nothing; it’s the only truly sensible approach when you step back and think about it.
- derac 5y agoSure, but this argument could be used for any statement. It's not very compelling.
- McMiniBurger 5y ago> Knowledge is knowing you might be wrong about it all that's not a great definition... I know I might be wrong about flying UFOs, but that doesn't count as 'knowledge', does it?
- spartanatreyu 5y agoThat argument doesn't make sense to me. You can just choose to use light at a smaller wavelength. Also, less density by itself doesn't mean less performance, the larger optical components can just run faster to end up with higher overal performance.
- dogber1 5y agoIn principle, yes, but: - lower wavelength light is harder to confine within waveguides (or transmissive optics), and messes up atoms when colliding (think of x-rays), - finding an efficient source at lower wavelengths is one of the main struggles of the semiconductor industry.
- cma 5y agoIf it is lower power, going 3d with it makes more sense though. Brain structures like synapses are ~2x smaller than UVC wavelengths or so (cubing that, ~10x smaller).
- georgeburdell 5y agoYou can't directly compare optical and electrical compute through looking at the difference in feature densities. Optical compute will most likely take the form of analog waveforms that contain many bits of information, whereas electronics for computing is inherently binary.
- dogber1 5y agoI'm afraid that's not even remotely true. Just two counterexamples: - MLC flash storage devices use multiple levels to store/retrieve bits [1], - Lots of control systems are implemented with analog PIDs [2]. A trivial example is a jellybean voltage regulator that computes the adjustments needed to maintain a stable output voltage independent of the load. [1] https://en.wikipedia.org/wiki/Multi-level_cell https://en.wikipedia.org/wiki/Multi-level_cell [2] https://control.com/textbook/closed-loop-control/analog-electronic-pid-controllers/ https://control.com/textbook/closed-loop-control/analog-elec...
- beebeepka 5y agoIsn't digital just an abstraction on top of analog anyway? Pretty much all electronics isime that
- rasguanabana 5y agoIt’s not all about computing. It’s about avoiding conversion from electrical to optical signal (and back) at every network node, which is costly.
- Goz3rr 5y agoDon't you need a certain amount of computing at each network node anyways to see what to do and where to send the optical signal next? In additional to error correction/amplifying the signal?
- rasguanabana 5y agoOften it might be as simple as routing right wavelength through right path, as in WDM systems. Optical amplifiers, such as EDFA [0] are interesting thing, too. [0]: http://www.fiber-optical-networking.com/the-application-of-edfa.html http://www.fiber-optical-networking.com/the-application-of-e...
- rocqua 5y agoGenerally you only need to read the 'header'. If that is little enough computation maybe that can be done optically, gaining the advantage of not needing to convert twice.
- wnkrshm 5y agoThe flipside is switching speed, optically you can reach THz and more apparently, while heat/capacitance/crosstalk limit electronic transistors IIRC.
- tremon 5y agoYes, signal (non-)interference is a big upside to optical communication. Photon streams don't interact even when passing through the same waveguide, so you can superimpose many bits/streams/connections in the same transmission channel at the same time (using varying wavelengths or polarisation), and two optical channels running side-by-side don't exert a magnetic force on each other either. The main upside for optical processing (photonics) is in signal switching then, as in this case. Having to receive the multitude of optical signals, converting them to electrical, doing the signal routing and processing in the electrical domain, then converting back to optical for transmission is a lot of busywork.
- averne_ 5y agoNot true for plasmonic waveguides which can confine energy well beyond the diffraction limit. But I agree that for now, photonics is just an academic wet dream.
- EVa5I7bHFq9mnYK 5y agoI think fermions vs bosons is irrelevant here - you can't build transistors out of neutrons. Sure, photons at these energies are larger, but still can be used for certain tasks, like quantum computers.
- jrootabega 5y agoSo they were right about computers the size of entire buildings, they were just off by 100 years?
- vbezhenar 5y ago1 GHz allows for photon to move 3 m per cycle in vacuum. 10 GHz is 30 cm. Even less in fiber cable. I think that's a fundamental restriction of a size of an individual computing module. Of course you can stack modules in entire buildings just like you can stack cpus in servers in data center now.
- BenjiWiebe 5y agoPerhaps I'm misunderstanding your comment, but the frequency doesn't change the speed of light.
- tremon 5y agoThey're talking about wavelengths ("per cycle"). But I'm not sure it makes more sense knowing that, since there's a fundamental disconnect between the signal frequency and the carrier frequency. I think QAM can even be used on a signal rate that's higher than the carrier frequency (as long as the carrier frequency is known), but I'm not 100% sure.
- dTal 5y agoIf we take our definition of "individual computing module" to be that it has a defined state during every tick of the clock, then there is a hard physical limit of 30cm for a module that runs at 10ghz. Anything larger must be operating asynchronously, as a distributed system.
- beebeepka 5y agoPoint is that interconnect between floor 1 and 5 might pose considerable challenges, thus greatly minimizing the potential advantages of having massive building sized computers
- dougmwne 5y agoI don't know anything about the topic, but it does make me wonder. Our problem does not seem to be a lack of transistors to make all manner of specialized single purpose logic. We do see to be stuck when it comes to single core performance. I wonder if a new technology like optical could be used to add a single core accelerator to supplement existing chips.
- Veedrac 5y ago> all-optical computing The keyword here is ‘all’. There are some things optical computing is bad at. However there are some things it is unparalleled at. For example, light can multiplex. It can have much lower energy losses. It can run at much higher frequencies. It is by far the best way to transmit information at extremely high data rates. Even within a chip, free space optical communication has massive theoretical potential. Your comment would have been an excellent one without the last sentence.
- coldtea 5y agoBut the whole wisdom of the parent comment is in the last sentence. This is mostly what is happening with such papers. The keyword here might be "all", and there are some applications where optical computing is unparalled at. But research teams, vendors, and the media spin those things are a recplament for every application, not as some niche thing that's good at some niche applications that most people need not care about...
- kllrnohj 5y agoThere seems to be an awfully large amount of projection here from people seemingly just reading the headline and not the article (much less the paper). Even just the article's sub-title has tempered predictions: "“Optical accelerator” devices could one day soon turbocharge tailored applications" And the research has immediate practical applications, again per the article: > "The most surprising finding was that we could trigger the optical switch with the smallest amount of light, a single photon," says study senior author Pavlos Lagoudakis, [..] Lagoudakis says the super-sensitivity of the new optical switch to light suggests it could serve as a light detector that could find use in lidar scanners, such as those finding use in drones and autonomous vehicles.
- lostmsu 5y agoTo me it sounds like the counterargument nulls the wisdom. If you can only make 200nm optical nodes, but they could multiplex 1M signals, you'd win by 100x over 2nm electrical nodes. It will be 100_000x if you add 10THz vs 10GHz difference to the picture.
- naasking 5y ago> In reality, all-optical computing is mostly a terrible idea: fundamentally, it cannot reach the integration density of electronics. It doesn't need this density to be useful or better than electronics in many cases. For instance, photonic quantum computation happens at room temperature, but this doesn't seem like it will be feasible with any other method for long time, if ever.
- anfilt 5y agoWhile for most things density is good. However if you can have a certain task take advantage of this insane switching frequency there could be reasons to build a room or multi-room sized specialized computer. Not everything needs to be tiny for every application. Also path delay is not an issue if you have a task that can be pipelined for raw through put. Latency is less of issue in such scenarios. So claiming there is no use for such things seems a stretch. It certainly can have niche uses. Bigger problem with a lot these papers is their tech needs to be at least reasonable to manufacture to have niche uses.