{"id":"e56ee078-9447-4236-accb-baf8123b104e","arxiv_id":"2505.05351","paper_version":2,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":2.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":3,"one_line_summary":"A quantum-aware wavelength assignment plus small QKD capacity margins lets CV-QKD and classical WDM traffic share one fiber with nearly no extra classical blocking.","lead":"This conference overview argues that adding quantum key distribution to existing fiber networks can clog classical traffic unless operators reserve capacity margins and place quantum channels carefully. It summarizes simulations showing that a quantum-aware wavelength assignment keeps classical blocking almost unchanged while coexisting with CV-QKD.","discovery_kind":"review","skeptic_critique":{"model":"deepseek-v4-flash","headline":"QAWA benefit rests on a single SpRS model; the cited alternative model [18] reverses the optimal channel placement, so the claimed 'minimal impact' is not robust to model uncertainty.","rationale":"The reader's weakest_assumption correctly identifies the SpRS model dependence as the primary concern. I agree that this is the single most load-bearing issue: the QAWA heuristic's entire advantage is to place the quantum channel where SpRS noise is minimal, and the paper itself concedes that an alternative cited model gives the opposite placement. This is an internal admission, not an external attack, so it carries extra weight. The abrupt clogging threshold is secondary; it affects the magnitude of the margin benefit, but the qualitative finding of congestion with a priority-first allocation would likely survive a smoother threshold. The paper is an invited overview with explicitly qualified claims ('in certain situations'), and the authors flag the SpRS sensitivity in their conclusion, so a CONDITIONAL verdict remains appropriate. The concern does not demand rejection; it demands that the stated contingency be prominent. A concrete re-simulation with the alternative SpRS model would settle whether the heuristic's benefit is robust or an artifact of one model choice.","tokens_in":8111,"tokens_out":3528,"duration_ms":35851,"concrete_test":"Re-run the network simulation described in Section IV using the SpRS model from [18] instead of [30], keeping all other parameters identical (topology, traffic demands, margin policy, QAWA logic). If the QAWA heuristic still yields classical blocking close to the no-coexistence baseline, the claim is robust to the identified model uncertainty; if blocking increases substantially or the optimal placement flips, the central claim is model-dependent and should be qualified accordingly. A supplementary check would compare both SpRS models against a measured spontaneous Raman spectrum for SSMF in the C band, but the simulation substitution is the minimal decisive test.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim is that quantum-aware wavelength assignment (QAWA) plus QKD margin reservation allows coexistence with minimal impact on classical capacity. The QAWA heuristic chooses the CV-QKD channel location to minimize SpRS noise from classical channels, based on the SpRS model of [30]. The authors state in Section IV-B1 that a different SpRS model [18] suggests placing the CV-QKD channel on the high-frequency side of the C band, the opposite preference. If [18] is correct, or if the true SpRS spectrum differs from [30] in shape, the QAWA placement is suboptimal, and the observed near-zero classical blocking (Fig. 1(c)) may not hold. Since the manuscript provides no code, data, or exact simulation parameters, and the key figure is attributed to [19], there is no way to assess how sensitive the result is to this model choice. The 'minimal impact' claim is therefore contingent on an unvalidated physical model, and the paper itself identifies the contradiction. This is load-bearing because the entire benefit of the heuristic is to place the quantum channel in a spectral region of low SpRS noise; if the model is wrong, the heuristic could place it in a high-noise region, potentially making coexistence worse. The abstract's general phrasing 'allows coexistence with minimal impact' overreaches given this acknowledged model dependence.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The manuscript, an invited ICTON paper, argues that integrating CV-QKD into deployed optical networks requires network-level planning tools that jointly manage quantum and classical traffic. After reviewing physical limits (attenuation, decoherence, linear and nonlinear crosstalk) and management issues, it describes simulation studies on a 7-node Spanish-based topology in which CV-QKD and classical WDM channels share the C-band. QKD traffic is allocated first, with a capacity margin; classical lightpaths are then allocated around the chosen CV-QKD channel. The findings are: (i) in the authors' SpRS model, the middle of the C-band appears to be the best CV-QKD channel placement, while the alternative model in [18] favors the high-frequency side; (ii) prioritizing QKD without a margin can 'clog' links to classical traffic; and (iii) combining QKD margin reservation with a quantum-aware wavelength assignment (QAWA) heuristic gives classical blocking nearly identical to a classical-only baseline. The conclusion calls for further work on more complex topologies and more accurate SpRS models.","tokens_in":8311,"tokens_out":6252,"duration_ms":60799,"significance":"If the reported results hold, they offer a practical planning rule: network operators can host CV-QKD on existing C-band WDM fiber and reserve a small amount of QKD capacity to protect classical traffic almost entirely. The paper is commendably explicit about its limitations: it acknowledges the SpRS-model dependence (Section IV-B1), the low-connectivity topology, and the need for further studies. The qualitative clogging mechanism is physically plausible, and the QAWA heuristic is a concrete contribution beyond point-to-point coexistence demonstrations. However, the paper's significance is currently conditional: the key quantitative claim is supported by simulations whose details are not in this manuscript, and the leading physical input model (SpRS from [30]) is explicitly contradicted by another model cited by the authors themselves.","major_comments":[{"comment":"The placement recommendation is load-bearing: the QAWA heuristic places the CV-QKD channel where the SpRS model from [30] predicts minimal noise, and the near-zero classical blocking in Fig. 1(c) depends on that placement being optimal or near-optimal. Yet the same paragraph states that the SpRS model in [18] suggests the opposite placement (high-frequency side of the C band). This is not a small parameter shift: the two models disagree to the extent that the heuristic could select the best location under one model and the worst under the other. The manuscript should quantify the spectral difference between [18] and [30], rerun the network simulation with both models, and state the regime in which QAWA helps versus hurts. As written, the central 'minimal impact' claim is robust only if [30] is accurate, and the paper itself supplies a reason to doubt that.","section":"IV-B1, Fig. 1(b)"},{"comment":"The simulation details needed to reproduce or evaluate the key figure are missing. The text gives the topology, the distance scaling factor Lambda between 10^-2 and 10^-1, 280 Mbit/s network-wide CV-QKD traffic with 12% margins, and per-channel classical launch powers of 0 or -10 dBm, but it does not specify the exact SKR model from [22], the SpRS gain model from [30], the WDM channel grid, the classical demand arrival model, the lightpath routing and wavelength assignment algorithm, the noise acceptance criterion, or how blocking probability is computed. Fig. 1(c) is attributed to [19], so the present paper alone does not allow the reader to verify the result. The authors should add a full parameter table, clarify whether the plotted curve is a single instance or an average, and provide error bars or a range across demand patterns.","section":"IV-A, Fig. 1(c)"},{"comment":"The 'clogging' model is an all-or-nothing threshold: once a CV-QKD link's capacity is fully allocated, the text states that adding any optical power for classical channels would push SpRS noise above acceptable limits, so the link becomes unavailable to classical traffic. This is a strong modeling assumption; in reality, CV-QKD secure key rate degrades continuously as SpRS noise grows, and a small classical power increment may cause only a small key-rate reduction. The margin strategy's benefit appears to rely on this binary clogging behavior, so the simulation may overstate both the danger and the cure. The authors should either justify the threshold (e.g., a minimal SKR below which no keys can be extracted) or implement a continuous noise-to-key-rate relationship and re-evaluate the margin and QAWA results under that model.","section":"IV-B2"},{"comment":"The statement that 'a quantum-aware wavelength assignment heuristic allows coexistence with minimal impact on both capacities' is broader than what the simulations demonstrate. The reported result is for one 7-node low-connectivity topology, a particular CV-QKD load (280 Mbit/s with 12% margins), and a particular SpRS model. The paper itself says the effect occurred 'in certain situations,' and Section V acknowledges the need for studies on more complex topologies. I recommend that the abstract and conclusion explicitly state the conditions under which minimal impact was observed, and avoid implying a general guarantee.","section":"Abstract, Section V"}],"minor_comments":[{"comment":"The word 'contraints' should be 'constraints'; also check that the LaTeX escape 'na\\\"ive' renders correctly as 'naïve' in the published version.","section":"Abstract"},{"comment":"The heuristic is written as 'QAW A' in the text of Section IV-B1; use 'QAWA' consistently throughout.","section":"IV-B1"},{"comment":"The y-axis of Fig. 1(b) is not described in the caption or text; please add a clear label with units (e.g., SpRS noise power in dBm) and state whether higher or lower is better.","section":"Fig. 1(b)"},{"comment":"Because Fig. 1(c) is explicitly 'Previously published in [19],' the paper should clarify which results, if any, are new to this manuscript and which are reproduced from the earlier ECOC paper.","section":"Reference [19]"},{"comment":"The subsection on decoherence and latency is only loosely connected to the network planning results; either integrate it with the simulation discussion or shorten it.","section":"II-B"}],"recommendation":"major_revision","confidential_remarks":"This is a short invited conference-style paper that appears to summarize results already published in [19], with the key figure explicitly taken from that prior work. For a journal editor, the central question is whether the paper is intended as a self-contained archival contribution or as a summary of ongoing work. As a standalone manuscript, the missing simulation details and the unresolved SpRS-model contradiction make the main quantitative claim difficult to evaluate. The paper would be suitable if the authors add the requested sensitivity analysis and parameter disclosure; otherwise, the contribution is more a position/vision statement than a validated result. I have no concerns about author conduct or citation ethics beyond the need to clarify the overlap with [19]."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Colleague,\n\nIf you are looking for new results, this is not the paper. It is an invited ICTON overview of the authors' earlier simulation work, and it says so plainly: the congestion finding is from [15], the QAWA heuristic and Fig. 1 are from [19]. What the paper does well is frame the planning problem clearly for network operators and lay out the physical constraints—attenuation, decoherence, SpRS—that make coexistence hard. The \"clogging\" idea is worth taking seriously: if you allocate QKD capacity first without margin, links can become unusable for classical traffic, and reserving a few percent of QKD capacity restores classical throughput in their seven-node simulation. That is a practical insight, and the paper deserves credit for making it accessible.\n\nThe honest part matters. Section IV-B1 states outright that their placement recommendation (middle of the C band) depends on the SpRS model of [30], and that a different published model [18] gives the opposite answer. That is a significant caveat, and they do not bury it. The abstract's \"minimal impact\" wording is a bit more bullish than the body supports, but it is qualified with \"in certain situations,\" so I would not call it misleading. The citation pattern is clean: they attribute the simulations to the original publications, and the only self-citations are the ones that actually contain the results.\n\nThe soft spots are the usual ones for an overview. The simulation is not self-contained: no code, no exact parameters, no error bars; the key figure is credited to [19]. The clogging threshold is abrupt—once QKD capacity is fully allocated, any additional classical power is treated as intolerable, with no gradual tradeoff. That may be a fine modeling choice, but it is not defended, and the near-zero blocking result could be sensitive to it. The SpRS model sensitivity is the load-bearing issue, and the authors themselves flag it. If the true SpRS spectrum differs from [30], the QAWA heuristic could place the quantum channel in a worse spot, and the \"virtually no effect\" result could evaporate. So treat the quantitative claim as conditional, as the paper partly does.\n\nWho gets value: network planners, QKD system integrators, and researchers wanting a quick entry point to the coexistence literature. Nobody should cite this for new numbers; the ECOC and IEEE PTL papers are the sources.\n\nFor peer review: as an invited overview, this is acceptable. If it were submitted as a regular research paper, I would desk reject for lack of new material, but I would also note that the authors are upfront about provenance and limitations. My recommendation: accept it in the invited-overview context, and ask them to soften the abstract so it matches the body's caveats.","headline":"Honest invited overview of prior CV-QKD planning simulations; the value is the planning insight, not new results, and the authors openly flag the SpRS model dependence that limits the main claim.","tokens_in":8902,"tokens_out":3866,"would_cite":false,"duration_ms":39395,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"Quantum-aware wavelength assignment allows CV-QKD to coexist with classical WDM traffic on deployed fiber with minimal impact on either capacity, provided a few-percent QKD capacity margin is reserved.","keywords":["quantum key distribution","CV-QKD","quantum-classical coexistence","wavelength assignment","spontaneous Raman scattering","network planning","classical network capacity","blocking probability"],"falsifier":"Rerun the same seven-node simulation replacing the Raman-spectrum model used here with the competing published model that favors the high-frequency side of the C band. If the quantum-aware wavelength assignment no longer brings classical blocking back to the no-QKD baseline, the claimed benefit is an artifact of the chosen spectrum rather than a general property of the heuristic. A direct measurement of the Raman gain spectrum on deployed standard single-mode fiber across the C band would settle which placement is correct.","tokens_in":7825,"feed_emoji":"🔑","tokens_out":6562,"duration_ms":61986,"temperature":0.7,"pith_summary":"This paper argues that adding continuous-variable quantum key distribution (CV-QKD) to already-deployed optical fiber does not have to cost classical network capacity, as long as planning is quantum-aware. In simulations on a small seven-node network, allocating QKD traffic first and then adding classical lightpaths can clog links once QKD capacity is exhausted, because any extra classical power raises spontaneous Raman scattering above the QKD noise limit. The proposed fix has two parts: a quantum-aware wavelength assignment heuristic that places classical channels to minimize Raman noise at the QKD channel, and a small few-percent margin of unallocated QKD capacity that leaves each link some noise tolerance. With both, the simulated classical blocking probability returns essentially to the level of a network carrying no QKD at all. The authors frame this as evidence that coexistence is a network-planning problem, not only a device problem.","feed_headline":"Wavelength choice lets QKD and classical traffic share fiber","feed_subtitle":"Adding a few-percent QKD margin removes nearly all classical traffic blocking in simulations.","key_machinery":"The central object is the SpRS noise floor: spontaneous Raman scattering spreads photons from each classical channel over a broad spectrum of roughly 15 THz in silica fiber, so it cannot be removed by filtering and becomes the dominant crosstalk term at high power. The QAWA heuristic treats this spectrum as a cost landscape, choosing a QKD wavelength where the summed SpRS from neighboring classical channels is minimal, then packing classical channels around it. The second mechanism is the QKD capacity margin: by leaving a few percent of each link's QKD capacity unallocated, the noise budget is not fully consumed, so a link can accept classical power without pushing QKD beyond its noise limit. Together these convert a hard coexistence limit into a soft planning tradeoff.","core_discovery":"On its own terms, the paper's central claim is that spontaneous Raman scattering (SpRS) is the dominant obstacle to quantum-classical coexistence in the C band, and that this obstacle can be planned around. Using a model of secure key rate versus attenuation and SpRS, the authors simulate a scaled seven-node mesh network in which CV-QKD traffic is allocated first and classical lightpaths afterward. They find that a naive QKD-first allocation can saturate a link's noise budget and thereby block all classical traffic on that link, isolating parts of a low-connectivity network. A quantum-aware wavelength assignment (QAWA), which places classical channels around the QKD channel to minimize SpRS, combined with reserving a few percent of QKD capacity as margin, makes the classical blocking probability nearly identical to the no-QKD baseline. The paper is explicit that this result depends on the SpRS spectral model; a competing published model would place the QKD channel on the opposite side of the C band.","pith_inferences":["A testable engineering rule follows that the authors do not state explicitly: operators should provision QKD demand forecasts with deliberate headroom of a few percent, treating the margin as a noise-budget buffer rather than unused capacity.","Because SpRS is broadband, the size of the QAWA benefit will depend on how finely classical channels can be spaced around the QKD channel; repeating the simulation on a coarse fixed ITU grid would quantify how much of the gain survives in practice.","The same methodology could be turned into a field-deployment test: measure the Raman spectrum of a specific fiber span, run the heuristic with that measured spectrum, and compare classical blocking against the mid-band rule, decoupling the heuristic's value from the disputed model.","The clogging result suggests a broader principle: when a fragile service has a hard noise budget in a shared medium, reserving headroom on the fragile service is cheaper than reserving capacity on the robust one."],"forward_implications":["Network operators can host CV-QKD on deployed fiber without dedicating dark fibers, as long as planning tools include the quantum channel in the wavelength assignment problem.","QKD-first allocation without margins is risky in low-connectivity topologies: exhausting one link's noise budget can isolate nodes and cut classical capacity disproportionately.","Reserving a few percent of QKD capacity as margin is a nearly free insurance policy: it costs little QKD throughput and removes most of the classical blocking penalty.","The accuracy of the SpRS model becomes a first-order planning input; the same heuristic can give opposite channel placements depending on which model is trusted.","The joint-optimization approach is expected to extend to entanglement distribution networks, though the authors note that more complex topologies and variable connectivity need further study."],"supporting_citations":[{"why":"Supplies the spontaneous Raman scattering spectrum used to model noise from classical channels onto the QKD channel.","marker":"[30]"},{"why":"Supplies the secure-key-rate versus attenuation model used to set QKD link capacity in the simulations.","marker":"[22]"},{"why":"Prior version of these simulation results, including the QAWA heuristic and the blocking-probability curves reproduced in Figure 1(c).","marker":"[19]"},{"why":"Alternative SDN-based coexistence study whose SpRS model favors the opposite channel placement; used as the counter-model that exposes model dependence.","marker":"[18]"},{"why":"Prior work identifying the link-clogging effect when QKD traffic is allocated before classical traffic.","marker":"[15]"},{"why":"Supplies the seven-node mesh network topology that is scaled down to CV-QKD range for the simulations.","marker":"[33]"}],"fun_headline_variants":["Quantum-aware wavelength assignment keeps classical traffic flowing","QKD planning heuristic avoids classical traffic blocking","Raman-aware wavelength plan lets QKD and classical coexist","Quantum-aware fiber planning cuts classical blocking","Heuristic minimizes QKD impact on classical fiber traffic"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The whole benefit of the heuristic depends on the exact shape of the Raman noise spectrum across the C band; the paper itself notes that a different published model would place the optimal quantum channel at the opposite end of the band.","fun_headline_variants_meta":{"raw":{"variants":["Quantum-aware wavelength assignment keeps classical traffic flowing","QKD planning heuristic avoids classical traffic blocking","Raman-aware wavelength plan lets QKD and classical coexist","Quantum-aware fiber planning cuts classical blocking","Heuristic minimizes QKD impact on classical fiber traffic"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000505,"raw_usage":{"total_tokens":2419,"prompt_tokens":855,"completion_tokens":1564,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":471,"completion_tokens_details":{"reasoning_tokens":1494}},"tokens_in":471,"tokens_out":1564,"duration_ms":11217,"temperature":1.0,"reasoning_tokens":1494,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-15T23:06:20.613991+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Rerun the same seven-node simulation replacing the Raman-spectrum model used here with the competing published model that favors the high-frequency side of the C band. If the quantum-aware wavelength assignment no longer brings classical blocking back to the no-QKD baseline, the claimed benefit is an artifact of the chosen spectrum rather than a general property of the heuristic. A direct measurement of the Raman gain spectrum on deployed standard single-mode fiber across the C band would settle which placement is correct.","supporting_citations":[{"cited_title":"Raman amplification for fiber communications systems,","cited_arxiv_id":null,"evidence_quote":"Supplies the spontaneous Raman scattering spectrum used to model noise from classical channels onto the QKD channel."},{"cited_title":"Continuous-Variable Quantum Key Distribution with Gaussian Modulation -- The Theory of Practical Implementations","cited_arxiv_id":"1703.09278","evidence_quote":"Supplies the secure-key-rate versus attenuation model used to set QKD link capacity in the simulations."},{"cited_title":"Minimal impact network-wide heuristics for the coexistence of classical and CV-QKD signals in the C-band,","cited_arxiv_id":null,"evidence_quote":"Prior version of these simulation results, including the QAWA heuristic and the blocking-probability curves reproduced in Figure 1(c)."},{"cited_title":"SDN-enabled CV-QKD and classical channels coexistence: key insights for dense wavelength division multiplexing,","cited_arxiv_id":null,"evidence_quote":"Alternative SDN-based coexistence study whose SpRS model favors the opposite channel placement; used as the counter-model that exposes model dependence."},{"cited_title":"Potential impact of CV-QKD integration on classical WDM network capacity,","cited_arxiv_id":null,"evidence_quote":"Prior work identifying the link-clogging effect when QKD traffic is allocated before classical traffic."},{"cited_title":"Net2plan: an open source network planning tool for bridging the gap between academia and industry,","cited_arxiv_id":null,"evidence_quote":"Supplies the seven-node mesh network topology that is scaled down to CV-QKD range for the simulations."}],"review_version":1}