[cycomanic]

The problem with both leds and imaging fibres is that modal dispersion is massive and completely destroys your signal after only a few meters of propagation. So unless you do MMSE (which I assume would be cost prohibitive), you really can only go a few meters. IMDD doesn't really make a difference here.

[adgjlsfhk1]

I think this is intended for short distances (e.g. a few cm). cpu to GPU and network card to network card still will be lasers, the question is whether you can do core to core or CPU to ram with optics

[cycomanic]

But why are they talking about multicore fibres then? I would have expected ribbons. You might be right though.

[topspin]

> I would have expected ribbons.

The cable is just 2D parallel optical bus. With a bundle like this, you can wrap it with a nice, thick PVC (or whatever) jacket and employ a small, square connector that matches the physical scheme of the 2D planar microled array.

It's a brute force, simple minded approach enabled by high speed, low cost microled arrays. Pretty cool I think.

The ribbon concept could be applicable to PCBs though.

[cycomanic]

You might be right and they are talking about fibre bundles, but that that's something different to a multicore fibre (and much larger as well, which could pose significant problems especially if we are talking cm links). What isn't addressed is that leds are quite spatially incoherent and beam divergence is strong, so the fibres they must use are pretty large, coupling via just a connector might not be easy especially if we want to avoid crosstalk.

What I'm getting at is, that I don't see any advantage over vcsel arrays. I'm not convinced that the price point is that different.

[topspin]

> You might be right and they are talking about fibre bundles

The caption of the image of the cable and connector reads: "CMOS ASIC with microLEDs sending data with blue light into a fiberbundle." So yes, fibre bundles.

> I don't see any advantage over vcsel arrays

They claim the following advantages:

    1. Low energy use
    2. Low "computational overhead"
    3. Scalability

All of these at least pass the smell test. LEDs are indeed quite efficient relative to lasers. They cite about an order of magnitude "pJ/bit" advantage for the system over laser based optics, and I presume they're privy to vcsels. When you're trying to wheedle nuclear reactor restarts to run your enormous AI clusters, saving power is nice. The system has a parallel "conductor" design that likely employs high speed parallel CMOS latches, so the "computational overhead" claim could make sense: all you're doing is latching bits to/from PCB traces or IC pins so all the SerDes and multiplexing cost is gone. They claim that it can easily be scaled to more pixels/lines. Sure, I guess: low power makes that easier.

There you are. All pretty simple.

I think there is use case for this outside data centers. We're at the point where copper transmission lines are a real problem for consumers. Fiber can solve the signal integrity problem for such use cases, however--despite several famous runs at it (Thunderbolt, Firewire)--the cost has always precluded widespread adoption outside niche, professional, or high-end applications. Maybe LED based optics can make fiber cost competitive with copper for such applications: one imagines a very small, very low power microLED based transceiver costing only slightly more than a USB connector on each end of such a cable with maybe 4-8 parallel fibers. Just spit-balling here

[nsteel]

Aren't they also claiming this is more reliable? I'm told laser reliability is a hurdle for CPO.

And given the talk about this as a CPO alternative, I was assuming this was for back plane and connections of a few metres, not components on the same PCB.

[BardiaPezeshki]

The fiber cables we use are basically 2D arrays of 50um thick fibers that match the LED and detector arrays. We've made connectors and demonstrated very low crosstalk between the fibers. Advantage over VCSELs is much lower power consumption overall, much lower cost (LEDs are dirt cheap and extremely high yield), because we are blue light, the detector arrays are much easier and can be modified camera technology, and most importantly, much better reliability. VCSELs are notorious for bad rel.

[morphle]

This might be the breakthrough we also have been working on [1] for over 20 years. It would be even better if Avicena wouldn't drive the led array and detector array with high power 10 Gbps SerDes. Even better if you align a blue led array with lenses to a detector array on a second chip: free space optics [2].

I would love to join you at Avicena and work on your breakthrough instead of just acquiring the IP from you in a few years.

[1] https://youtu.be/wDhnjEQyuDk?t=1569

[2] see schematic on page 373 of https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=780...

[cycomanic]

Just wanted to clarify that I don't necessarily doubt that you have a use case (BTW partnering up with someone like intel or so on for optical thunderbold or similar like someone else mentioned would be very interesting as well), you definitely have people who know what they are doing. I thought the ieee article however does give the wrong impressions as it mainly compares with the wrong thing, somebody here (maybe you?) was also saying 50 mu m fibres are much easier to couple into than SMF, which is correct, but also not relevant because VCSEL links typically use OM fibre with 50-60 mu m core diameters as well.