[HN Gopher] An all-optical general-purpose CPU and optical compu...
___________________________________________________________________
An all-optical general-purpose CPU and optical computer
architecture
Author : PaulHoule
Score : 184 points
Date : 2024-03-09 14:49 UTC (1 days ago)
(HTM) web link (arxiv.org)
(TXT) w3m dump (arxiv.org)
| bevekspldnw wrote:
| Claims like this require peer review, not to mention this is a
| private company not a university lab.
|
| I'm worried over this trend of private companies putting press
| releases into LaTeX templates.
| staunton wrote:
| > I'm worried over this trend of private companies putting
| press releases into LaTeX templates.
|
| People need to realize once and for all that templates no
| longer represent quality or truthfulness, if they ever did.
| Maybe that lesson has to hurt a bit.
| bevekspldnw wrote:
| People have forgotten the whole point of "preprint" is you're
| still supposed to, ya know, print!
| moffkalast wrote:
| Most people don't have printers anymore, they'd rather read
| it online /s
| mometsi wrote:
| Peer review for commercial press releases is an interesting
| idea!
| bevekspldnw wrote:
| Now that is a job for GPT if I ever heard one. Garbage in
| garbage out.
| bee_rider wrote:
| I wonder if there's room for a section on Arxiv that is
| exclusively for papers that are on a peer-review track.
|
| Or maybe "peer or open review," or something like that.
| mistercow wrote:
| I think there are two ways to look at it, both of which are
| true: 1) scientific literature is being polluted with non-peer-
| reviewed PRs which makes it harder to figure out what is
| actually well validated, and 2) press releases are being nudged
| into being a hell of a lot more technically substantive and
| rich in relevant citations. The first one isn't great, but as
| consolation prizes go, (2) isn't bad.
| aj7 wrote:
| Are you sure? Are you expert enough to read those papers? How
| do you achieve large scale integration in waveguides
| transparent to available laser sources? How does 250nm
| compare to the integration in your cell phone's cpu?
|
| And we are decades away from modulatable miniaturized 250nm
| laser sources. It is typically 1.5um with today's devices.
| mistercow wrote:
| > Are you expert enough to read those papers?
|
| Not in this case, no. But in cases where I do have more
| knowledge, the additional detail makes it much easier to
| tell if there's anything of substance there, compared to
| traditional press releases which just make superficial
| marketing claims with minimal technical detail.
|
| And if this were something more relevant to me, but where I
| didn't have expertise necessary to look at it, I could
| reach out to someone with the expertise needed to take a
| look. The point here is that it's very difficult talk at
| great length and in great detail about BS without making it
| apparent to experts that you're talking BS, whereas with a
| more traditional PR, the best you can often say is "well,
| if this is anything, these are very big claims."
| bevekspldnw wrote:
| I disagree, people who are not expert consumers of
| information, but do think "arXiv is science stuff" are easily
| misled, and I trust citations from private companies without
| strong academic pedigree as worthless at best, harmful at
| worst.
|
| It's pretty easy to con investors if you have the same "look"
| as a real lab.
| mistercow wrote:
| > I disagree, people who are not expert consumers of
| information, but do think "arXiv is science stuff" are
| easily misled
|
| I think you are talking about an extremely small segment of
| the population, so I don't think we're talking about a very
| large social impact. I'm also unconvinced that that segment
| doesn't generally take ordinary tech press releases at face
| value anyway.
|
| > I trust citations from private companies without strong
| academic pedigree
|
| OK, but the first two authors on this have doctorates in ML
| and applied photonics respectively. They don't have peer
| review on this paper, but I don't think you can say they're
| lacking in academic pedigree.
|
| > It's pretty easy to con investors if you have the same
| "look" as a real lab.
|
| I don't know. My feeling is that the "conning investors who
| are terrible at due diligence" game is largely unavoidable
| and mostly a zero-sum competition between con artists. So
| while it's obviously bad, I'm not convinced that the
| specifics matter all that much. Fools and their money, and
| all that.
| bevekspldnw wrote:
| Fair points all, but the fact that this made it to the
| front page of HN is itself problematic vis-a-vis the
| points raised.
| rokkitmensch wrote:
| The peer review community has torched its reputation over the
| last decade, so it should surprise precisely nobody paying
| attention that profit-motivated publishers are crawling over
| what remains of that barrier.
| llm_trw wrote:
| Outside of academia I don't think anyone realizes just how
| broken the system is.
|
| Citation extortion rings are part of every journal. I had a
| reviewer from Nature give feedback that I should cite her
| co-authors work on a topic that had nothing to do with my
| paper. It got rejected because I wouldn't. It went into
| archive and has been cited nearly a hundred times now. To
| add insult to injury Nature News asked to interview me
| about my work.
|
| Some more info on the subject, and a vast underestimation
| of how prevalent it is:
| https://www.science.org/content/blog-post/cite-my-papers-
| els...
|
| At this point if you can figure out how to make a pdf paper
| using latex I consider your work to be on par with anything
| in a journal.
| ur-whale wrote:
| I was kind of expecting the first paragraph of this paper to
| explain first and foremost how they solved the switching problem
| (i.e. a transistor) using optical only components.
|
| After wading through the paper for 10mn, I still haven't found
| the answer. If someone spotted it, please point where they talk
| about it, I would be grateful.
|
| Or I could go ask an AI to find the answer for me I guess.
| DarkmSparks wrote:
| I believe this:
|
| The almost canonical way of performing all-optical switching
| and logic is to use semiconductor optical amplifiers (SOA) and
| exploit their cross-gain modulation (XGM) or cross-phase
| modulation (XPM) capabilities[21]. With very reliable devices
| having been shown over the past 20 years[22], SOAs have proven
| useful for various types of all-optical operation, including
| decoder logic[23, 24] and signal regeneration[25, 26, 27]. The
| recovery time of the SOA limits its performance, but it has
| been shown that more than 320 Gbit/s[28]all-optical switching
| is possible, with some implementations enabling even the Tbit/s
| domain[29].
| aj7 wrote:
| And at 1.5 um. Compare that to a 3nm electron architecture.
| thfuran wrote:
| Are you talking 3 actual nanometers or a "3nm" process?
| It's difficult to compare.
| p1esk wrote:
| Also, I remember when 20 years ago people said building
| transistors smaller than 45nm will be impossible.
| BandButcher wrote:
| Don't have time to read it all but the abstract states,
|
| "With our research, however, we are focused on the phase
| thereafter. Once optical interconnects and interposers have been
| fully established and are the main mode of inter-chip and intra-
| chip communication, solving the 6x inefficiencies... "
|
| Therefore this paper is more about a computer architecture that
| will be in place AFTER general purpose hardware swaps from
| electrical to photonic communication, but we aren't there yet.
| Also seems the paper is more about tackling the next phase of
| `energy efficiency` problems that will arise after the swap.
|
| Still useful info to consider but i agree with most here that
| these click-bait titles in research are abused. But I can't
| really argue it got me to click ;)
| aj7 wrote:
| All optical computing surfaces again!
|
| Warning.
|
| There is NO opportunity for large scale integration, the MOST
| IMPORTANT ASPECT in computing. This is because the de Broglie
| wavelength of the information carriers, typically 1.5um, is so
| HUGE.
| aj7 wrote:
| Hundreds of of millions of dollars have been raised from naive
| investors by ignoring this fact. Often, board-member and
| founder physics PhD's aid in the deception by omission.
| p1esk wrote:
| Why can't we reduce the wavelength?
| naasking wrote:
| Even UV wavelengths aren't terribly small, and the shorter
| the wavelength, the more energy it has and the more likely
| it is to destroy whatever material your optical CPU is made
| of.
| p1esk wrote:
| Sounds like an engineering problem, not a fundamental
| one.
| naasking wrote:
| Not sure what gives you that idea. It seems unlikely that
| there are materials that can withstand billions of x-ray
| pulses per second and continue to function without being
| altered. They might exist, but the higher the energy to
| get to low wavelengths for fast and information dense
| computing, the increasingly implausible it gets that a
| suitable material is physically possible.
| adgjlsfhk1 wrote:
| shorter wavelength light really doesn't like existing. It
| takes more energy to produce, there are way fewer possible
| materials to make mirrors out of etc. Just look at how much
| trouble the industry had doing EUV lithography.
| crotchfire wrote:
| I am shocked, _shocked_ that quantum computing researchers
| might have figured out this trick too.
| bigbluedots wrote:
| Please elaborate?
| dvh wrote:
| Current electron based computers are 10s of nanometers per
| transistor. Optical equivalent of transistor cannot be
| smaller than 1um. Equivalent optical CPU to your smartphone
| would be the size of several football fields.
| throwaway69123 wrote:
| While this is true doesn't ignore the difference in clock
| rate capacity ? If the photonic cpu can run 10,000x the
| clock rate without the extreme heat build up that would
| melt the smartphone
| skykooler wrote:
| Isn't part of the point that you don't need as many
| transistor equivalents because you can run them thousands
| of times faster?
| nazgul17 wrote:
| Asking from a position of total ignorance. The energy
| savings mean you can increase clock speeds, right? Assuming
| a big enough jump, won't that relieve a CPU from the need
| to have most specialised instruction sets and potentially
| also that many cores? In that case, wouldn't it be
| acceptable that transistors grow (back) in size?
| Dylan16807 wrote:
| Energy savings on what basis?
|
| If your gate gets 50x50x50 times bigger, you need some
| pretty extreme savings per area/volume of circuit if you
| want to reduce the per-gate usage. Can they save that
| much?
| simne wrote:
| > Optical equivalent of transistor cannot be smaller than
| 1um
|
| For classics optics. Exists superlens optics, which using
| metamaterials and monochromatic light source, and could
| "see" artifacts of size much less then wave length.
| Panoramix wrote:
| If I was designing one of these things my goal would not be to
| replace present day computers - which at this point is nearly
| impossible given the millions of man hours spent optimizing
| them - but to carve a niche where you outperform them in
| specific tasks. I have the vague impression that should be
| possible.
| volemo wrote:
| That's why most optical computers lean into quantum
| computing.
| enslavedrobot wrote:
| Plasmonics may solve this problem. The interaction of light
| at an interface can lead to what essentially amounts to
| photon confinement. This allows for what's called near field
| optics which overcomes the limitations of wavelength and
| unlocks nanometer scale optoelectronics. For examples, see
| the solar sail for the "starshot" project.
| throwaway14356 wrote:
| Right, Modern computers don't know what their purpose is,
| that makes it such a mind boggling challenge. Nothing is ever
| good enough. If you define the purpose it can be better and
| much cheaper.
| glitchc wrote:
| Not sure what this means. De Broglie waves are defined for
| matter (mass is required). While photons have relativistic
| mass, this isn't the same thing.
| LoganDark wrote:
| "Information carrier" means the actual medium the light is
| travelling through, doesn't it? Which has to be matter of
| some sort.
| orlp wrote:
| Last time I checked the sun transfers its light through the
| vacuum of space to us.
| LoganDark wrote:
| Sorry, I must've missed that these optical CPUs contain
| vacuums of space for the light to travel through.
| glitchc wrote:
| Indeed, as orlp mentioned, light is self-propagating and
| does not require a medium. This is broadly true for all EM
| waves.
| Dylan16807 wrote:
| We're talking about a CPU, not light traveling in a
| straight line forever.
| goatlover wrote:
| Why isn't the EM field the medium? Or even spacetime?
| aj7 wrote:
| You are confusing geometry, and the excitation traveling
| through that geometry.
| aj7 wrote:
| But it needs SPACE, on the order of a few um minimum,
| that cannot be occupied by other devices.
| aj7 wrote:
| The deBroglie wavelength of the photon IS its wavelength.
| That's why it can't squeeze into nm features and optical
| waveguides are still not used on-chip, after 35 years of
| effort.
| varjag wrote:
| One potential of optics is teraherz frequencies.
| Salgat wrote:
| There's some factors to consider here. For visible light yes,
| the smallest feature probably won't be smaller than several
| hundred nanometers, however, optical computing comes with
| several major advantages over traditional electrical circuits.
|
| The first is that light beams can cross paths without
| interfering with each other, allowing for a level of
| parallelism and density of signal paths without the concern of
| crosstalk/interference or shorting. Additionally, the
| information density of an optical signal is vastly higher than
| an electrical signal, and multiple optical signals can share
| the same pathways simultaneously. Also, energy usage is greatly
| reduced, so the constraints due to heat waste are much less.
|
| Having said all that, the idea of optical circuits in a VLSI is
| still a very foreign and exotic concept for us, so it's hard to
| say how far we can take it if we invest at the level we have
| for electrical ICs. It's naive though to say it's not feasible
| due to some oversimplification of feature size limitations.
| aj7 wrote:
| Unless computation can be accomplished on differing
| overlapping frequencies, wdm devices, which resemble train
| switchyards, are huge, on the order of mm. So optical
| computing would have to take place at multi THz switching
| rates using very short pulses.
| musicale wrote:
| As I understand it, microring resonators can be very small,
| um rather than mm.
| nextaccountic wrote:
| Do optical computing need to use visible light?
| musicale wrote:
| Since you can carry 100+ frequencies around 1500 nm, the
| feature-size per data stream is more like 15 nm/stream, which
| is closer to electronics, and the heat dissipation of optical
| waveguides may be much lower than with equivalent electronics.
| Photonics also have the advantage of better signal propagation
| over longer distances, for efficient interconnection of
| multiple devices.
|
| So there is a likely opportunity for large-scale integrated
| photonics, as long as you have enough parallelism.
| aj7 wrote:
| Referring to computing, not data transmission. Perhaps some
| day, using quantum computing, all those differing 'portly'
| photons, superimposed, could yield advances in density. To
| mix different wavelength streams on chip involves wdm
| devices, which are huge.
| musicale wrote:
| Optics/photonics can potentially perform analog as well as
| digital computation. One trendy thing at the moment is
| accelerators for neural networks.
|
| Some potential benefits of optics include high data rate,
| parallel processing of multiple streams, transmission over
| longer distances, and lower heat dissipation.
| nwiswell wrote:
| > There is NO opportunity for large scale integration
|
| What about vertically?
|
| CMOS logic is still "mostly planar". With sufficiently low heat
| dissipation, you could make a cube and easily overcome the
| planar density problem.
|
| The main challenge seems like it would be lithography cost for
| each of the many layers, but if the minimum feature size is
| 1.5um, there might be a clever way to make this work cheaply
| (DLP projection + gradual extrusion?)
| morphle wrote:
| The arguments from the abstract of this paper have been refuted
| by Attojoule Optoelectronics for Low-Energy Information
| Processing and Communications: a Tutorial Review [1] and several
| other papers.
|
| [1] https://arxiv.org/abs/1609.05510
| hilbert42 wrote:
| I'm still digesting this interesting paper but the Figure 3 chart
| is particularly informative as it puts the whole aspect of
| electronic and optical computing into perspective.
|
| I cannot recall ever having seen Power Dissipation versus Compute
| Performance together with Total global power generation, Total
| global data center electricity consumption, Electronic thermal
| noise limit and the Landauer Limit all graphed together before.
| Presenting the data in this fashion provides a stark and very
| clear overview of what's actually possible together with the
| theoretical limits. Graphing the Landauer Limit is a masterstroke
| because we can instantly see computation vs power efficiency for
| any given tech.
|
| I think the visual impact of this chart is important enough to
| see it expanded further and the authors and/or others should
| think about doing so. It would make an excellent poster-sized lab
| wall chart if the graticule lines were subdivided from 103 to 10
| (leaving 103 lines bold) to provide finer granularly and allow
| more detail of the tech together with the dates of their
| introduction and phase out, etc.
| wiz21c wrote:
| Figure 3 is intriguing to me: I thought GPU's where order of
| magnitude faster than CPU (because of parallelism) and although
| the chart is log-scale, I don't see that. I wonder why...
| projectileboy wrote:
| The optical equivalent of transistors have useful applications,
| but there are many shipwrecks on the shore of general-purpose
| optical computing, going back decades. I need more than a paper
| to get excited.
| p1esk wrote:
| At least they built a PoC. Many others just do simulations.
| peter_d_sherman wrote:
| This is the best paper I've read in a long time -- this has to go
| in my "Top 10" favorite posts of all time on HN...
|
| (To PaulHoule: Another truly excellent post of yours to HN,
| _thank you very much_ , the HN community and myself appreciate it
| greatly!)
|
| Anyway, let's delve into it -- here's the key quote, IMHO:
|
| >"As the previous discussion showed, SUBLEQ is, of course, not
| the target realization for optical computing. Its purpose is to
| showcase the simplest form a general-purpose optical computer
| could take and an intermediary step we take.
|
| _It can be implemented with less than 100 logic gates and, given
| enough memory, able to emulate a full x86_
|
| with a graphics card running Windows and Doom(tm) loaded, while
| crunching AI models as a background task (admittedly all
| extremely slowly)."
|
| Now that is truly awesome!
|
| Also, it should be pointed out that if SUBLEQ could be
| implemented optically, it could also be implemented digitally,
| say, on the smallest of small gate count FPGA's...
|
| While such a FPGA Soft CPU would not be fast -- it would
| definitely be interesting, and probably very simple
| (comparatively!) to implement!
|
| (Also, it might be implementable on a tiny IC, for example, Sam
| Zeloof's "Z2" 1,000 gate IC:
| https://www.youtube.com/watch?v=IS5ycm7VfXg)
|
| Anyway, 5+ Stars for this excellent paper!
|
| Upvoted and favorited!
| luyu_wu wrote:
| A lot of people seem to be mentioning the 'size' of electrical
| transistors, but this seems to fail to include complexity scaling
| (which is non-linear)? The lower complexity of optical chips (due
| to large switch sizes) can be made up by the faster switching
| speeds, which boast a linear increase in performance if I'm not
| mistaken?
|
| Really interesting paper!
|
| Edit: Advantages of multiplexing are very real too!
| cycomanic wrote:
| It's ironic that they cite Millers work, but don't address the
| main conclusions from that work, i.e. that optical computing is
| horribly inefficient. Photons are bosons and therefore are very
| reluctant to interact, essentially requiring nonlinearities. The
| issue with nonlinearities is that they fundamentally require
| comparatively high optical intensities.
|
| The authors mainly address the issue of integration density
| (which is also an issue), but not in sufficient detail the
| problem of efficiency. They handwavy this away by referring to 2d
| materials, but 2d are not a pancea. It's true that they exhibit
| very strong nonlinear coefficients (although I'm unsure if even
| that would be sufficient to overcome the efficiency challenges),
| however the overlap between the optical field and the 2d material
| is fundamentally very small (a single sheet of 2d material in the
| plane of propagation), so the observed enhancements have been
| very modest.
| jkafjanvnfaf wrote:
| First of all, you are correct that nonlinear optics usually
| requires high field strengths. But...
|
| >Photons are bosons and therefore are very reluctant to
| interact, essentially requiring nonlinearities.
|
| Please don't throw out random sciency terms. First of all,
| interaction is pretty much by definition nonlinear. Second,
| photons are not reluctant to interact. Photon-photon scattering
| is negligible (which has nothing to do with them being bosons,
| as gluons and mesons readily demonstrate), but nonlinear optics
| doesn't rely on photon-photon scattering.
| Animats wrote:
| _" we will be implementing a 2-bit variant of SUBLEQ for
| demonstration purposes"_
|
| What they actually built was a 2-bit wide machine with one
| instruction. No, they can't run Doom, which they mention a lot.
|
| There's a lot of hand-waving about memory, around page 10. They
| seem to have used a delay line, which is very slow; you have to
| wait for the bits you want to come around. That's been a classic
| problem with photonics. You can build gates, which is nice for
| switching packets, but how do you store data?
|
| Much of the architectural discussion is about what you can do if
| memory is mostly ROM. They talk about fast-read, really slow
| write memory. Here's an article about building something like
| that.[2] It's a clunky technology. Writing involves on-chip
| heaters and switching memory cells back and forth from amorphous
| to crystalline. There's a long history of forgotten devices like
| that - photochromic memory, UV-erasable EEPROMS, rewritable DVDs,
| Ovonics, etc. All were superseded by something with better read-
| write properties.
|
| The underlying device technology is not theirs. It's from the
| Cornerstone project.[1]
|
| [1] https://www.mdpi.com/2076-3417/10/22/8201
|
| [2] https://www.nature.com/articles/s41377-023-01213-3
| throwaway69123 wrote:
| What about things like ai surely if gates are possible that
| means you could encode and entire model in photonic gates,
| surely that's worth it
| datameta wrote:
| Photonic in-memory AI inference would be a holy grail imo.
| bilsbie wrote:
| Ok I'm sure this is stupid but could memory be a glow in the
| dark chemical?
| was_a_dev wrote:
| There's photoswitchable molecules and fluorophores.
|
| https://en.m.wikipedia.org/wiki/Photoswitch
| mjevans wrote:
| Imagine this in a hypothetical setting such as Science Fiction.
| Where instead of an optical delay loop it's a fold in space or
| some other mechanism. Photonics and some sort of 'subspace' or
| toggled shift in reality? Maybe.
|
| I agree though, I've never seen anything explain how to make
| this work well as a general computer with contemporary tech.
| drpixie wrote:
| > You can build gates, which is nice for switching packets, but
| how do you store data?
|
| Logic gates can be the fundamental building block. So if you
| can build logic gates, then you can use those to build flip
| flops (the basis of static RAM) which store data. Might not be
| the most efficient way (depending on your requirements) but it
| can be done.
|
| https://en.wikipedia.org/wiki/Flip-flop_(electronics)#D_flip...
| atq2119 wrote:
| Nit pick: SRAM is not built out of flip flops. It's carefully
| sized inverters and a whole lot of analog magic (writing a
| bit involves overpowering the inverters of the bit with
| larger drivers). You may be thinking of latch arrays.
| TheDudeMan wrote:
| The main point is that that you CAN build storage out of
| gates.
| adrian_b wrote:
| The overpowering of the inverters is just an area efficient
| trick to make gates (the so-called wired-OR or wired-AND).
|
| The SRAM memory cells are simpler than flip flops, they are
| just S-R latches (i.e. equivalent with a half of an M-S
| flip-flop) made from two gates (either NAND or NOR).
|
| In any technology where static gates are possible SRAM
| memories are also possible.
|
| However there are technologies where only dynamic gates are
| possible, i.e. gates that provide an output that is valid
| only during a clock pulse and which cannot remain valid
| indefinitely. Only in such technologies you cannot make
| SRAMs, but you can still make dynamic memories, which must
| consume energy all the time, for refreshing their content.
|
| All the "analog magic" that you mention has only the
| purpose of making an SRAM array much denser than when
| implemented with the standard gates of a technology, but an
| implementation with standard gates is always possible and
| it may be chosen for certain register files, where high
| speed may be more important than the occupied area.
| naasking wrote:
| > They seem to have used a delay line, which is very slow; you
| have to wait for the bits you want to come around.
|
| Macroscopic delay lines sure, but microscopic ones presumably
| can be on the order of a wavelength, if that's all that's
| needed. Not much time needed to come around in that case.
| londons_explore wrote:
| A 68k CPU has 68,000 transistors. If they have managed to
| produce all the building blocks of a CPU on a common optical
| process, why not build that?
|
| Obviously this is only an easy option if the production is
| automated via lithography or something similar. If the process
| involves tweezering parts into place by hand, then a 2 bit
| SUBLEQ CPU is what you're gonna get...
| frozenport wrote:
| This article teaches optics people about compute arch.
|
| Which is maybe fine, but its not still not clear how to implement
| these components.
| simne wrote:
| I like idea of optical delay line for registers. For other parts,
| great amount of work need to be done to achieve something
| working, so unfortunately, extremely risky project for now, need
| some time (years?) to implement all parts alone.
| anthk wrote:
| awk can simulate subleq in few lines.
|
| https://gopherproxy.meulie.net/hoi.st/9/files/subleq.awk
| crotchfire wrote:
| Electrons interact with each other, photons don't.
|
| What magical device do they use to take TWO separate 1-hot
| encoded optical signals and produce a single 1-hot output? Figure
| 6 just shows a black box labeled "decoder" which is never
| explained, anywhere.
|
| I think this word salad^H^H^H^H^H paper might have been produced
| by an LLM.
| jlokier wrote:
| Photons do interact with each other:
|
| * Gravitationally.
|
| * Conversion to matter-antimatter pairs.
|
| * In non-linear optical media, which is technically all
| substances, but effect strength varies.
|
| Of course electrons are involved in the last of those, but not
| in the way you mean. Non-linear optical media electrons remain
| bound to their atoms, and act by orbital resonance effects.
|
| The last of those is a realistic path to a general-purpose
| photonic computer. I worked on a design for one, and I was
| surprised to find our design would run not much faster than a
| good electronic computer, while being larger, due to optical
| wavelengths. But it may have been more energy efficient if we'd
| built it. Or rather, the calculation part may have been more
| efficient, with memory being less efficient than transistors.
| Also we didn't spend much time optimising it.
|
| Small photonic machines are good for particular calculations
| such as energy-efficient FFTs, but that is smaller scale than a
| general purpose processor.
|
| (If anyone is interested in photonic computer design, feel free
| to get in touch!)
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