[HN Gopher] Petabit-class transmission over > 1000 km using stan...
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Petabit-class transmission over > 1000 km using standard 19-core
optical fiber
Author : the_arun
Score : 69 points
Date : 2025-07-13 00:06 UTC (2 days ago)
(HTM) web link (www.nict.go.jp)
(TXT) w3m dump (www.nict.go.jp)
| eqvinox wrote:
| 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 (125um) 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.)
| bcrl wrote:
| 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 wrote:
| You're confusing multi-core in a single cladding with multiple
| strands of cladding. This is 19 cores in a single cladded 125um
| (which is quite impressive manufacturing from Sumitomo).
| bcrl wrote:
| 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 wrote:
| 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 wrote:
| For us Americans, thats about 295,680 toilet paper rolls or
| 2,956 KDC (kilo donkey kicks).
| chasd00 wrote:
| Or about 3 MAG (mega Ariana Grandes).
| https://x.com/GatorsDaily/status/1504570772873904130
| aDfbrtVt wrote:
| 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 wrote:
| 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 wrote:
| 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_D
| CI_...
| eqvinox wrote:
| 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 19x19 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.
| cycomanic wrote:
| 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.
| aDfbrtVt wrote:
| Depending on phase matching criteria of lambda's on a
| given core, I would mostly agree that various wavelengths
| are not significantly coupled. I also agree there are a
| different power budget for LH modems vs. DCI, but power
| on LH modems is not something that often gets publicly
| disclosed. I am not too concerned with the overall power,
| more the power density (and component density) that 19
| channel MIMO would require.
|
| The main point I was trying to make is the impracticality
| of MIMO SDM. The topic has been discussed to death (see
| the endless papers from Nokia) and has yet to be deployed
| because the spatial gain is never worth the real world
| implementation issues.
| quickthrowman wrote:
| 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)
| throw0101c wrote:
| 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
| exabrial wrote:
| 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?
| bradfitz wrote:
| Because your switch is mapping a 4 tuple to a certain link and
| these people aren't, is my guess.
| eqvinox wrote:
| > 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.
| cycomanic wrote:
| It's also important to note that many optical links don't use
| ethernet as a protocol either (SDH/SONET are the common
| ones), although this is changing more and more.
| wmf wrote:
| Looks like SDH/SONET topped out at 40 Gbps which means it
| died 10 years ago.
| meepmorp wrote:
| SONET is widely used in the US.
| eqvinox wrote:
| Used, maybe, but [citation needed].
|
| Built, no, definitely not voluntarily1, Ethernet is the
| only non-legacy thing surviving for new installations for
| anything more than short range (few kilometer) runs.
| InfiniBand, CPRI and SDI are dying too and getting
| replaced with various over-Ethernet things, even for low-
| layer line aggregation there's FlexE these days.
|
| 1 some installations are the exception confirming the
| rules; but as a telco sinking more money into keeping an
| old SONET installation alive is totally the choice of
| last resort. You'll have problems getting new hardware
| too.
|
| Disclaimer: I don't know what military installations do.
| wmf wrote:
| I assume this is just a PHY-level test and no real switches or
| traffic was involved.
| toast0 wrote:
| 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 wrote:
| the data out of order is the key bit.
|
| How do these guys get the data in order and we dont?
| aaronax wrote:
| 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.
| Keyframe wrote:
| 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?
| wmf wrote:
| There's been a ton of research on optical computing and it just
| isn't impressive.
| Keyframe wrote:
| yet
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