Petabit-class transmission over > 1000 km using standard 19-core optical fiber
30 comments
·July 13, 2025eqvinox
Contrary to the "highlights" section (which seems to be the only place calling it a "standard" 19-core optical fiber), this is not in fact a 'standard' fiber, rather the origin seems to be the standard (125µm) diameter ("Sumitomo Electric was responsible for the design and manufacture of a coupled 19-core optical fiber with a standard cladding diameter (see Figure 1)"). Looks like the "diameter" simply got lost for the highlights section.
(Nonetheless impressive, and multi-core fiber seems to be maturing as technology.)
exabrial
Alright, I have a dumb question...
How come with a LAG group on ethernet, I can get "more total bandwidth", but any single TCP flow is limited to the max speed of one of the LAG Components (gigabit lets say), but then these guys are somehow combining multiple fibers into an overall faster stream? What gives? Even round robin mode on LAG groups doesn't do that.
What are they doing differently and why can't we do that?
toast0
You don't really want to, but if you configure all of the LAG participants on the path to do round-robin or similar balancing rather than hashing based on addresses, you can have data in one flow that exceeds an individual connection. You'll also be pretty likely to get out of order data, and tcp receivers will exercise their reassembly buffer, which will kill performance and you'll rapidly wish you hadn't done all that configuration work. If you do need more than one link's worth of throughput, you'll almost always do better by running multiple flows, but you may need still need to configure your network so it hashes in a way that you can get diverse paths between two hosts, defaults might not give you diversity even on different flows.
exabrial
the data out of order is the key bit.
How do these guys get the data in order and we dont?
aaronax
Consider that a QSFP28 module uses four 25gbps lanes to support sending one single 100gbps flow. So electronics do exist that can easily do what you are asking. I think it is just the economics of doing it for the various ports on a switch, lack of a standard, etc.
eqvinox
> What are they doing differently and why can't we do that?
You're (incorrectly) assuming they're doing Ethernet/IP in that test setup. They aren't (this is implied by the results section discussing various FEC, which is below even Ethernet framing), so it's just a petabit of raw layer 1 bandwidth.
bradfitz
Because your switch is mapping a 4 tuple to a certain link and these people aren't, is my guess.
wmf
I assume this is just a PHY-level test and no real switches or traffic was involved.
aDfbrtVt
As others have mentioned, this is mostly a proof of concept for a high core count weakly-coupled fibre from Sumitomo. I also want to highlight the use of a 19 channels MIMO receiver structure which is completely impractical. The linked article also fails to mention a figure for MIMO gain.
eqvinox
Worse, it's offline MIMO processing! ;D
I would guesstimate that if you try to run it live, the receiver [or rather its DSPs] would consume >100W of power, maybe even >1000W. (These things evolve & improve though.)
(Also, a kilowatt for the receiver is entirely acceptable for a submarine cable.)
aDfbrtVt
To get a ballpark power usage, we can look at comparable (for some definition thereof) commercial offerings. Take a public datasheet from Arista[1], they quote 16W typical for a 400Gbps module for 120km of reach. You would need 2500 modems at 16W (38kW) jointly decoding (i.e. very close together) to process this data rate. GPU compute has really pushed the boundaries on thermal management, but this would be far more thermally dense.
[1] https://www.arista.com/assets/data/pdf/Datasheets/400ZR_DCI_...
cycomanic
It's important to note that wavelength channels are not coupled, so modems with different wavelengths don't need to be terribly close together (in fact one could theoretically do wavelength switching so they could be 100s of km apart). So the scaling we need to consider is the scaling of the MIMO which in current modems is 2x2. The difficulty is not necessarily just power consumption (also the power envelope of long haul modems is higher than the DCI modem you link, up to 70W IIRC), but also resourcing on the ASIC, your MIMO part (which needs to be highly parallel) will take up significant floorspace and you need to balance the delays.
The 38kW is not a very high number btw, the switches at the end points of submarine links are quite a bit more power hungry already.
eqvinox
I think the scaling parameters are a bit different here since the primary concern is the DSP power processing and correlating for MIMO 19 signals simultaneously. But the 16W figure for a 120km 400Gbps module includes a high-powered¹ transmitter amplifier & laser, as well as receive amplifiers on top of the DSP. My estimate is based on O(n²) scaling for 19×19 MIMO (=361) and then assuming 2≈3W of DSP power per unit factor.
[but now that I think about it… I think my estimate is indeed too low; I was assuming commonplace transceivers for the unit factor, i.e. ≤1Tb; but a petabit on 19 cores is still 53Tb per core…]
¹ note the setup in this paper has separate amplifiers in 86.1km steps, so the transmitter doesn't need to be particularly high powered.
quickthrowman
38kW ~= 50 HP ~= 45A at 480V three-phase, which is a relatively light load handled by 3#6 AWG conductors and a #10 equipment ground.
I mean, it’s a shitload more power than a simple media converter that takes in fiber and outputs to a RJ-45 but not all that much compared to other commercial electrical loads. This Eaton/Tripplite unit draws ~40W at 120V - https://tripplite.eaton.com/gigabit-multimode-fiber-to-ether...
A smallish commercial heat pump/CRAC unit (~12kW) can handle the cooling requirements (assuming a COP of 3)
Keyframe
while fascinating I'm still waiting for that transformative move from electrical. Whichever optical route you're taking, at the beginning and at the end of it has to be an electrical conversion which hinders speed, consumes power and produces (sometimes tons of) heat. Wen optical switching?
bcrl
Interesting work, but 19 cores is very much not standard. Multiples of 12 cores are the gold standard in the telecommunications industry. Ribbon fibre is typically 12, sometimes 24 fibres per ribbon, and high count cables these days are 864 cores or more using a more flexible ribbon structure that improves density while still using standard tooling.
eqvinox
You're confusing multi-core in a single cladding with multiple strands of cladding. This is 19 cores in a single cladded 125µm (which is quite impressive manufacturing from Sumitomo).
bcrl
I wasn't confusing anything. To interoperate with industry standard fibre optic cables it should have a multiple of 12 or 24 cores, not the complete oddball number of 19. Yes it's cool that it's that small, but that is not the limiting factor in the deployment of long haul fibre optic telecommunications networks.
Sumitomo sells a lot of fusion splicers at very high margins. It is in their best interest to introduce new types of fibre that requires customers to buy new and more expensive fusion splicers. Any fibre built in this way will need rotational alignment that the existing fusion splicers used in telecom do not do (they only align the cores horizontally, vertically and by the gap between the ends). Maybe they can build ribbon fibres that have the required alignment provided by the structure of the ribbon, but I think that is unlikely.
Given that it does not interoperate with any existing cables or splicers, the only place this kind of cable is likely to see deployment in the near term is in undersea cables where the cost of the glass is completely insignificant compared to everything that goes around it and the increased capacity is useful. Terrestrial telecom networks just aren't under the kind of pressure needed to justify the incompatibility with existing fibre optic cables. Data centers are another possibility when they can figure out how to produce the optics at a reasonable cost.
ksec
The actual figures are 1,808 km. For reference US is 2,800 miles (4,500 km) wide from east to west, and 1,650 miles (2,660 km) from north to south.
exabrial
For us Americans, thats about 295,680 toilet paper rolls or 2,956 KDC (kilo donkey kicks).
chasd00
Or about 3 MAG (mega Ariana Grandes). https://x.com/GatorsDaily/status/1504570772873904130
The NANOG has had a regular presentation by Richard Steenbergen called "Everything You Always Wanted to Know About Optical Networking – But Were Afraid to Ask"; last year's:
* https://www.youtube.com/watch?v=Y-MfLsnqluM