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arxiv: 1907.01459 · v1 · pith:62QJH7PDnew · submitted 2019-07-02 · 📡 eess.SP · cs.CR

Coexistence of 11.2Tb/s Carrier-Grade Classical Channels and a DV-QKD Channel over a 7-Core Multicore Fibre

Emilio Hugues-Salas , Qibing Wang , Rui Wang , Kalyani Rajkumar , George T. Kanellos , Reza Nejabati , Dimitra Simeonidou This is my paper

Pith reviewed 2026-05-25 10:45 UTC · model grok-4.3

classification 📡 eess.SP cs.CR
keywords multicore fibrequantum key distributionclassical quantum coexistencediscrete variable QKDoptical communicationC bandsecret key generationcrosstalk
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The pith

11.2 Tb/s of classical channels can share a 7-core fibre with a working discrete-variable QKD channel while maintaining continuous secret key generation.

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

The paper demonstrates that a single 7-core multicore fibre can carry both high-volume classical data traffic and a quantum key distribution channel at the same time. Record classical throughput of 56 channels at 200 Gb/s each reaches 11.2 Tb/s while the QKD link continues to produce secret keys without interruption. Classical channels remain below the SDFEC performance limit and the quantum channel maintains a 17 nm minimum spacing within the C-band. The demonstration relies on the fibre's core-to-core isolation to prevent the strong classical signals from overwhelming the weak quantum signals.

Core claim

We successfully demonstrate coexistence of record-high 11.2 Tb/s (56x200Gb/s) classical channels with a discrete-variable-QKD channel over a multicore fibre. Continuous secret key generation is confirmed together with classical channel performance below the SDFEC limit and a minimum quantum channel spacing of 17nm in the C-band.

What carries the argument

The 7-core multicore fibre and its inter-core isolation, which keeps classical-channel crosstalk from degrading the quantum channel below the threshold for continuous key generation.

If this is right

  • Classical networks can incorporate QKD without requiring separate fibres for the quantum channel.
  • Existing multicore fibre deployments can support both carrier-grade data rates and quantum-secure key distribution.
  • Minimum 17 nm spacing allows the quantum channel to sit inside the C-band alongside dense classical WDM channels.
  • Continuous key generation remains possible while classical performance stays below the SDFEC limit.

Where Pith is reading between the lines

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

  • If crosstalk scales predictably with added cores or higher launch powers, the same fibre type could support even denser classical loading or additional QKD channels.
  • Operators facing fibre scarcity in data-center interconnects or metro links could test this coexistence approach before committing to new fibre plants.
  • The 17 nm spacing result supplies a concrete design parameter for wavelength planning in mixed classical-quantum systems.

Load-bearing premise

The 7-core multicore fibre supplies enough isolation and low enough crosstalk that the intense classical channels leave the quantum channel intact enough for ongoing secret key generation.

What would settle it

An experiment in which the secret key rate falls to zero or the quantum bit error rate exceeds the QKD threshold once all 56 classical channels operate at full power inside the same fibre.

Figures

Figures reproduced from arXiv: 1907.01459 by Dimitra Simeonidou, Emilio Hugues-Salas, George T. Kanellos, Kalyani Rajkumar, Qibing Wang, Reza Nejabati, Rui Wang.

Figure 1
Figure 1. Figure 1: Experimental Testbed for Coexistence of 11.2Tb/s of Classical Channels and a DV-QKD quantum channel over a 1km-long 7-core Multicore Fibre. Inset: Launching power levels for coexistence in MCF [PITH_FULL_IMAGE:figures/full_fig_p001_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: shows the spectrum of the 8x200Gb/s classical channels coexisting with the quantum channel over the central core of the MCF. As illustrated in [PITH_FULL_IMAGE:figures/full_fig_p002_2.png] view at source ↗
read the original abstract

We successfully demonstrate coexistence of record-high 11.2 Tb/s (56x200Gb/s) classical channels with a discrete-variable-QKD channel over a multicore fibre. Continuous secret key generation is confirmed together with classical channel performance below the SDFEC limit and a minimum quantum channel spacing of 17nm in the C-band.

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 / 1 minor

Summary. The manuscript reports an experimental demonstration of coexistence between record-high 11.2 Tb/s classical channels (56 × 200 Gb/s) and a discrete-variable QKD (DV-QKD) channel over a 7-core multicore fibre, claiming continuous secret key generation, classical performance below the SDFEC limit, and a minimum quantum-classical channel spacing of 17 nm in the C-band.

Significance. If the measurements hold, the result would be significant for practical quantum-classical integration in space-division multiplexed systems, showing that MCF can support ultra-high classical capacity alongside DV-QKD without prohibitive crosstalk. The explicit use of a 7-core fibre and the reported 17 nm spacing provide a concrete test case for coexistence limits.

major comments (2)
  1. [Abstract] Abstract: The central claim of continuous secret key generation and successful coexistence is asserted without any reported quantitative metrics (secret key rate, QBER, error rates, or power levels), rendering independent verification of the result impossible from the given text.
  2. [Results] The load-bearing assumption that 7-core MCF inter-core isolation keeps classical-channel crosstalk below the threshold for positive secret-key rate is not supported by any measured crosstalk values (dB/km or total), QBER vs. classical-power curves, or explicit confirmation that the observed key rate is fibre-limited rather than dominated by other noise. This directly affects the validity of the coexistence result.
minor comments (1)
  1. The title writes '11.2Tb/s' without a space; standard notation is '11.2 Tb/s'.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their detailed review and constructive comments. We address each major point below and will revise the manuscript to improve clarity and explicit presentation of supporting data while maintaining the integrity of the reported results.

read point-by-point responses

  1. Referee: [Abstract] Abstract: The central claim of continuous secret key generation and successful coexistence is asserted without any reported quantitative metrics (secret key rate, QBER, error rates, or power levels), rendering independent verification of the result impossible from the given text.

    Authors: We agree that the abstract would be strengthened by the inclusion of key quantitative metrics. In the revised manuscript we will update the abstract to report the achieved secret key rate, measured QBER, classical channel power levels, and error rates to enable independent verification from the abstract alone. revision: yes

  2. Referee: [Results] The load-bearing assumption that 7-core MCF inter-core isolation keeps classical-channel crosstalk below the threshold for positive secret-key rate is not supported by any measured crosstalk values (dB/km or total), QBER vs. classical-power curves, or explicit confirmation that the observed key rate is fibre-limited rather than dominated by other noise. This directly affects the validity of the coexistence result.

    Authors: The manuscript already contains measured inter-core crosstalk values for the 7-core fibre and QBER data taken as a function of classical launch power. We will revise the results section to explicitly quote the crosstalk figures (in dB), reference the relevant figure showing QBER versus classical power, and add a short paragraph confirming that the observed key-rate dependence on classical power indicates fibre-crosstalk limitation rather than other noise sources. revision: partial

Circularity Check

0 steps flagged

Purely experimental report with no derivation chain or fitted parameters

full rationale

This is an experimental demonstration paper reporting measured coexistence of 11.2 Tb/s classical channels with a DV-QKD channel over 7-core MCF. It contains no equations, no derivations, no fitted parameters, and no self-citations invoked to justify a mathematical result. The central claim rests on direct experimental outcomes (secret-key generation rate, BER below SDFEC limit, observed spacing) that are independently verifiable by replication rather than by construction from prior inputs. No load-bearing step reduces to a self-definition, fitted prediction, or self-citation chain.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Experimental demonstration paper; abstract contains no free parameters, axioms, or invented entities.

pith-pipeline@v0.9.0 · 5608 in / 956 out tokens · 37129 ms · 2026-05-25T10:45:41.008713+00:00 · methodology

discussion (0)

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Reference graph

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