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arxiv: 2604.05208 · v1 · submitted 2026-04-06 · ⚛️ physics.optics

Sparsely repeated 21.7 Tb/s Net-Rate Transoceanic Transmission with 266 km Ultra-Long Spans Enabled by Low IMI and Low loss Hollow Core Fiber

Rajiv Boddeda , Carina Castineiras Carrero , Ha\"ik Mardoyan , Amirhossein Ghazisaeidi , Peng Li , Shuhai Li , Lei Zhang , Jie Luo
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J\'er\'emie Renaudier
This is my paper

Pith reviewed 2026-05-10 18:42 UTC · model grok-4.3

classification ⚛️ physics.optics
keywords hollow core fibertransoceanic transmissionultra-long spanslow inter-modal interferenceWDM21.7 Tb/ssparse repeatersGTA-ST-HCF
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The pith

A new hollow-core fiber design enables 21.7 Tb/s net-rate transmission over 6660 km using only 266 km spans and fewer than 30 repeaters.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper shows that a specially engineered hollow-core fiber can support very long amplifier spans in wavelength-division multiplexed optical links. This reduces the total number of repeaters needed for transoceanic distances while still delivering a net data rate of 21.7 terabits per second. The approach combines the fiber's low inter-modal interference and low loss with high-power boosters and adaptive per-channel rates. A sympathetic reader would see this as a route to simpler, lower-cost submarine cable systems that still meet modern capacity demands.

Core claim

We demonstrate 21.7-Tb/s net-rate transmission across 6660-km with 266-km ultra-long spans of HCF. By exploiting a newly designed GTA-ST-HCF, high-power booster, and adaptive channel rates, we realize WDM transoceanic transmission with fewer than 30 repeaters.

What carries the argument

GTA-ST-HCF, a hollow-core fiber engineered for low inter-modal interference (IMI) and low loss, which supports 266 km spans without excessive signal degradation.

If this is right

  • Transoceanic WDM systems can operate with spans of 266 km instead of the usual 80-100 km, cutting repeater count below 30 for 6660 km links.
  • High-power boosters combined with adaptive channel rates maintain performance despite the longer spans.
  • Net data rates of 21.7 Tb/s remain achievable when the fiber properties hold.
  • Sparse repeater placement becomes practical for high-capacity submarine transmission.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • If the fiber properties scale to real cables, total system power and maintenance costs could drop because fewer amplifiers are needed.
  • The same low-IMI, low-loss fiber approach might extend to other long-haul routes or enable even longer spans in future designs.
  • Integration with existing WDM transceivers would require only the fiber change and booster adjustments rather than a full system redesign.

Load-bearing premise

The GTA-ST-HCF fiber keeps its low inter-modal interference and low loss performance unchanged over the entire 6660 km length under real deployment conditions.

What would settle it

A direct measurement after 6660 km transmission showing loss or inter-modal interference rising enough to drop the achievable net rate below 21.7 Tb/s.

read the original abstract

We demonstrate 21.7-Tb/s net-rate transmission across 6660-km with 266-km ultra-long spans of HCF. By exploiting a newly designed GTA-ST-HCF, high-power booster, and adaptive channel rates, we realize WDM transoceanic transmission with fewer than 30 repeaters.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 0 minor

Summary. The manuscript reports an experimental demonstration of 21.7 Tb/s net-rate WDM transmission over 6660 km using 25 concatenated 266 km spans of a newly designed GTA-ST hollow-core fiber (HCF). The result is achieved with fewer than 30 repeaters by exploiting the fiber's low inter-modal interference (IMI) and low loss, in combination with high-power boosters and adaptive channel rates.

Significance. If validated with complete data, the work would be significant for long-haul optical communications, as it demonstrates the practicality of ultra-long fiber spans in transoceanic links. This could substantially reduce repeater count, system cost, and power consumption while highlighting the potential of low-IMI HCF technology for high-capacity transmission.

major comments (2)
  1. [Abstract] Abstract: The headline claim of 21.7 Tb/s net-rate transmission with 266 km spans and fewer than 30 repeaters rests on the GTA-ST-HCF preserving its low-loss and low-IMI performance across all 25 spliced spans. No quantitative measurements of end-to-end span loss, splice loss, or accumulated IMI after the full 6660 km distance are provided, directly weakening support for the ultra-long-span and sparse-repeater assertions.
  2. [Results] Results/Methods: Detailed bit-error-rate (BER) data, power-budget calculations, and explicit measurement methodologies for the complete link are not reported. This leaves the exact performance numbers with only moderate evidential support, as noted in the absence of full experimental characterization.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the constructive review and for recognizing the potential significance of ultra-long-span HCF transmission for reducing repeater count in transoceanic systems. We address each major comment below.

read point-by-point responses

  1. Referee: [Abstract] Abstract: The headline claim of 21.7 Tb/s net-rate transmission with 266 km spans and fewer than 30 repeaters rests on the GTA-ST-HCF preserving its low-loss and low-IMI performance across all 25 spliced spans. No quantitative measurements of end-to-end span loss, splice loss, or accumulated IMI after the full 6660 km distance are provided, directly weakening support for the ultra-long-span and sparse-repeater assertions.

    Authors: We agree that explicit end-to-end characterization after splicing would strengthen the support for the headline claims. The manuscript reports the low-loss and low-IMI properties measured on individual spans and the successful transmission performance over the full concatenated link. We will add a new subsection (or supplementary figure) in the revised manuscript that tabulates the measured loss per span, estimated splice losses, and the accumulated IMI inferred from the end-to-end performance and individual-span data. revision: yes

  2. Referee: [Results] Results/Methods: Detailed bit-error-rate (BER) data, power-budget calculations, and explicit measurement methodologies for the complete link are not reported. This leaves the exact performance numbers with only moderate evidential support, as noted in the absence of full experimental characterization.

    Authors: We acknowledge that additional detail on BER statistics, power budgets, and methodologies would improve transparency. In the revised manuscript we will (i) include BER versus OSNR or distance curves for representative channels across the full 6660 km, (ii) add a comprehensive power-budget table that accounts for booster output, span loss, and receiver sensitivity, and (iii) expand the Methods section with explicit descriptions of the measurement setup, DSP parameters, and error-counting procedures used for the complete link. revision: yes

Circularity Check

0 steps flagged

No circularity: pure experimental demonstration with no derivation chain

full rationale

This is an experimental transmission paper reporting measured 21.7 Tb/s net-rate performance over 6660 km using 266 km HCF spans. No mathematical derivation, model fitting, or predictive equations are present in the abstract or described claims. The result is a direct empirical outcome from lab measurements of fiber loss, IMI, and WDM transmission, with no self-definitional loops, fitted inputs renamed as predictions, or load-bearing self-citations that reduce the central claim to its own inputs. The fiber performance assumptions are testable externally via the reported spans and do not rely on internal redefinition.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 1 invented entities

The claim rests on the unverified performance of the new fiber design and standard assumptions about optical transmission in HCF.

axioms (1)
  • domain assumption Standard principles of WDM transmission and fiber loss apply to the new HCF design
    Invoked implicitly in the experimental setup described in the abstract.
invented entities (1)
  • GTA-ST-HCF no independent evidence
    purpose: Hollow core fiber variant engineered for low inter-modal interference and low loss to enable ultra-long spans
    Introduced as a newly designed component central to achieving the reported performance.

pith-pipeline@v0.9.0 · 5403 in / 1150 out tokens · 37440 ms · 2026-05-10T18:42:03.025945+00:00 · methodology

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Reference graph

Works this paper leans on

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    Introduction The standard single-mode fibers (SMFs) have revolutionized how the information is transferred across the world and brought in an unprecedented change on how humans communicate [1]. Significant efforts are being made to boost the capacity of optical fiber communication systems ranging from digital signal processing (DSP) techniques to the desi...

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    Experimental setup Fig. 1 depicts the experimental set-up used for reproducing ultra-long-haul transmissions. The transmitted signal is made of a fully loaded wavelength division multiplexed (WDM) comb composed of carved amplified spontaneous emission (ASE) noise over 4.8 THz plus one channel under test (CUT). The CUT is made of a C-band tunable laser sou...

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    Transmission results First, we assessed the performance of one channel located at 192. 220 THz, outside the GLA peaks regions. We measured the performance of this channel modulated at 135 GBaud, packed in a 137.5 GHz grid. In Fig. 2b, we show the achievable information rate ( AIR) and the net -rate measured as a function of the distance . We estimate an A...

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    We achieved the transmission of total throughput of 21.7 Tb/s over 66 60 km, corresponding to only 25 repeaters for a transatlantic distance

    Conclusion To the best of our knowledge, this is the first demonstration of transoceanic WDM transmission using spans as long as 266 km. We achieved the transmission of total throughput of 21.7 Tb/s over 66 60 km, corresponding to only 25 repeaters for a transatlantic distance. We also showed the net rate throughputs at other distances, reporting 23.5 Tbp...

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