{"id":"dfb0b283-b13f-40c1-8966-a212ff57d972","arxiv_id":"2607.27970","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":4.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":3,"one_line_summary":"Field measurements on a 7 km metro fiber show C-band Raman noise from O-band classical light matches lab trends, with extra local spectral anomalies, and identify quieter DWDM channels for quantum use.","lead":"Researchers measured Raman noise created in the telecom C-band by ordinary O-band classical light on a real 7 km city fiber loop. The work gives practical channel-picking guidance for putting quantum signals on existing metro fiber next to classical traffic.","discovery_kind":"extension","skeptic_critique":{"model":"grok-4.5","headline":"Raman-dominance and channel-allocation claims rest on classical-pump C-band count spectra alone, without a co-propagating quantum signal or protocol-level SNR/fidelity measurement.","rationale":"The reader correctly flagged the load-bearing gap: count spectra of Raman light from classical O-band pumps, without a quantum protocol or even a weak C-band signal under co-propagation, do not establish Raman dominance of quantum SNR or justify channel-allocation guidelines for entanglement. The empirical core (normalized metro Raman shape matches the lab spool; peaks are present with no pump and are therefore non-Raman) is credible given the stated controls (WDM cascades, 25 GHz tunable filter, SNSPD, segment losses in Table I). No stronger internal inconsistency in the Raman measurement chain is evident from the text. Novelty remains incremental vs. the authors’ lab work [5] and prior coexistence literature. CONDITIONAL stands: accept the field Raman characterization if SNR/allocation language is narrowed and data/error bars are addressed; a protocol-level check would settle the overreach.","tokens_in":8206,"tokens_out":605,"duration_ms":32054,"concrete_test":"On the same 7 km loop, launch a calibrated weak C-band probe (or SPDC pairs) into a candidate quiet DWDM channel from Fig. 3b, with and without the O-band pump at the reported powers; measure excess noise and SNR (or CAR/QBER). If Raman is not the majority of excess noise above dark/background in those channels, or if anomaly wavelengths remain worse despite low Raman, the dominance and allocation claims weaken.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The strongest claim (Abstract; §V) — that Raman noise is a dominant contribution to quantum SNR beyond background/detector noise, so the measured spectra give practical guidelines for optimal C-band quantum channel allocation beside O-band classical traffic — treats O-band-pumped C-band photon counts (SFP and CW, full 7 km loop and 3.5 km path) versus no-pump background and SNSPD dark counts (~100 cps) as a sufficient proxy for the noise that would limit entanglement distribution. No entangled pairs, weak coherent quantum channel, coincidences, fidelity, or QBER are measured on the metro loop (§II–IV). The Intro also calls this a “first experimental demonstration of quantum networking” with C-band quantum / O-band classical, while the data are Raman characterization only. Fig. 3a further shows field peaks that remain with no launched signal (non-Raman artifacts), so ranking DWDM channels by Raman shape alone may miss operationally dominant real-world noise. Lab–field spectral agreement after power/length normalization is supported; the leap to quantum-SNR dominance and allocation guidelines is not.","agreement_with_reader":"agree"},"referee_report":{"model":"grok-4.5","summary":"The manuscript reports a field characterization of spontaneous Raman scattering (SpRS) into the C-band produced by O-band classical pumps (commercial SFP at ~−0.8 dBm and a narrowband 1310 nm laser at ~−4.6 dBm) over a ~7 km metropolitan fiber loop (and a 3.5 km one-way path) of the University of Naples Federico II network. Cascaded WDMs isolate bands; a 25 GHz tunable filter steps across 1525–1565 nm; C-band photons are counted on an SNSPD (~80% SDE, ~100 cps dark counts). Loss is tabulated per segment (Table I). Raw and power/length-normalized spectra (Fig. 3) are compared to a no-launch control and to a 5 km lab spool reference from prior work. The authors report overall spectral agreement with the lab after normalization, attribute residual field peaks (present with no launched signal) to fiber imperfections or possible inter-fiber crosstalk, and conclude that Raman noise is a dominant contribution to quantum SNR beyond background/detector noise, so C-band operating frequencies must be chosen carefully and that less-affected spectral regions provide practical guidelines for quantum channel allocation beside O-band classical traffic.","tokens_in":8438,"tokens_out":1659,"duration_ms":37669,"significance":"Field Raman spectra on deployed metro fiber with a commercial SFP, dual path lengths, a no-launch control, and explicit lab–field comparison after standard power/length normalization are a useful incremental contribution to quantum–classical coexistence engineering. The C-band quantum / O-band classical orientation (lowest-loss band for the quantum channel) is less common than the reverse and is practically motivated. If scoped strictly as noise characterization that informs channel planning, the data set has clear value for groups deploying entanglement or QKD over existing plant. The work does not, however, ship protocol-level metrics, machine-checked models, or a closed-form SNR derivation; its significance is empirical and infrastructure-facing rather than foundational.","major_comments":[{"comment":"Abstract and §V claim that Raman-induced noise is a dominant contribution to quantum SNR beyond background and detector noise, and that the measured spectra yield practical guidelines for optimal C-band quantum channel allocation. The data are O-band-pumped C-band photon-count spectra only (Fig. 3); no co-propagating quantum signal, entangled pairs, weak-coherent channel, coincidences, fidelity, or QBER is measured on the metro loop (§II–IV). Dominance is argued by comparing Raman counts to the no-launch background and ~100 cps dark counts, without a protocol-level SNR (or QBER) formula that folds in expected pair rate, filter bandwidth, timing window, and classical launch power. The allocation guideline therefore rests on the Raman spectral shape alone. Either add a co-propagating quantum/entanglement measurement or a quantitative SNR/QBER model using the reported counts, or substantial","section":"Abstract; §V"},{"comment":"§I states that, to the authors’ knowledge, this work is “the first experimental demonstration of quantum networking” with C-band quantum and O-band classical (contrasted with reverse configurations [13], [14]). The experiment demonstrates Raman characterization under that band assignment, not entanglement distribution, teleportation, or any quantum networking protocol. That phrasing overstates the result and should be corrected to match what was measured.","section":"§I"},{"comment":"Fig. 3a shows localized peaks that remain in the no-launch control and raise counts by up to an order of magnitude; §IV–V attribute them to deployed-fiber imperfections or possible inter-fiber crosstalk (Fig. 4), with analysis “on-going.” §V still presents Raman-shape-based channel selection as the practical guideline. If non-Raman field artifacts can dominate selected DWDM channels (e.g., near 1560 nm / channels 21–22), ranking channels by the smooth Raman profile alone is incomplete for operational allocation. Clarify how anomalies are handled in any recommended channel list, or restrict recommendations to wavelengths where the no-launch control is flat and Raman is the leading excess noise.","section":"Fig. 3a; §IV–V"},{"comment":"Normalization (Fig. 3b) rescales by launched power and effective length and compares to a 5 km lab spool attenuated at 0.35 dB/km. Table I shows strongly inhomogeneous, wavelength-dependent segment losses (SMF-28 vs SMR; Lab–PoP vs PoP–PoP), and SpRS generation is distributed along the fiber with local pump power. A single effective-length factor can distort the absolute noise level used for the “Raman-dominant SNR” claim even if the spectral shape is preserved. State the effective-length model explicitly (integral of P_pump(z) e^{-α_s z} or equivalent) and report absolute noise spectral density (e.g., cps/nm/mW or photons/s in the 25 GHz filter) before and after normalization so readers can recompute SNR for their launch powers.","section":"§III–IV; Table I; Fig. 3b"}],"minor_comments":[{"comment":"Abstract and body: repeated grammar/typos — “generated by a classical the O-band signal”; “The main contribution of this study lays in”; “The experimental results shows”; “allo iwng us to identifiy”; “theorethical modelling”; “asses whether”. A full copy-edit pass is needed.","section":"Abstract; §I; §IV–V"},{"comment":"Fig. 3 caption and §IV: “in-ab measurements” should be “in-lab”. Axis labels and units (cps vs normalized units) should be stated unambiguously in both panels.","section":"Fig. 3"},{"comment":"SFP model is given (Finisar FTLF1321P1BTL) but its optical spectrum / linewidth under the drive conditions used is not shown; a brief OSA trace would strengthen the commercial-vs-narrowband comparison.","section":"§II"},{"comment":"Heavy dependence on the authors’ own preliminary lab preprint [5] for the reference spectrum is fine if the metro data are independent, but the citation should note status (accepted/submitted) and what is new here versus reused.","section":"References; §IV"},{"comment":"DWDM channel numbering (e.g., channels 21–22 at ~1560 nm) should be tied to a standard ITU grid table or explicit center wavelengths so readers can map recommendations without ambiguity.","section":"§V"}],"recommendation":"major_revision","confidential_remarks":"The experimental chain (loss table, dual sources, loop vs one-way vs lab, no-launch control, normalization) is coherent and publishable as a short characterization / invited systems note once claims are scoped to what was measured. The main risk is overclaim: “quantum networking demonstration” and “Raman-dominant quantum SNR / optimal allocation guidelines” without a quantum channel or protocol metric. I would not reject on novelty of the band assignment alone, but I would not accept until Abstract/Intro/§V are aligned with the data. Fit is reasonable for an applied quantum-communications or network-engineering venue; borderline for a high-impact physics letter unless the quantum-SNR claim is substantiated."},"author_rebuttal":null,"desk_editor":{"model":"grok-4.5","letter":"The real payload here is a careful field Raman map: O-band classical (commercial SFP and narrowband laser) into C-band counts on their 7 km Naples metro loop, with a no-launch control, one-way vs loop, and power/length normalization that lines up with their own 5 km lab spool. That lab–field agreement is the solid result. The dual-source comparison and the loss table are done properly. The field-only peaks that survive with no launched light are usefully flagged as non-Raman artifacts rather than forced into the Raman story.\n\nWhat is new is modest and local: this specific deployed loop, the C-band-quantum / O-band-classical ordering they emphasize, and the commercial SFP under real plant conditions. Raman coexistence itself is not new; their prior lab work and the usual literature already cover the physics. Calling this a “first experimental demonstration of quantum networking” is a stretch—there is no entangled pair, weak coherent quantum channel, coincidence, fidelity, or QBER on the loop. The Abstract and Discussion assert that Raman is a dominant term in quantum SNR and that the spectra give optimal channel-allocation guidelines. Those claims rest on classical-pump C-band counts versus dark counts and background. That is a reasonable engineering proxy, but it is not a measured quantum SNR. The stress-test note is right on that point; the central spectra still stand.\n\nSoft spots in proportion: unfinished anomaly physics (they say so), heavy self-reference to [5] as the lab baseline, no error bars or released counts in what we have, and over-claim language that a referee will cut. None of that sinks the measurement chain.\n\nWho it is for: people planning classical/quantum coexistence on existing metro plant who need a field sanity check and a reminder that deployed fiber is messier than a spool. Not a theory or protocol paper. I would send it to peer review with instructions to narrow the SNR and “quantum networking” framing to what was actually measured. Worth a look if you care about field noise budgets; skip if you only want new physics or a protocol result.","headline":"Clean metro-loop Raman spectra for O→C coexistence, but the quantum-SNR and “networking demo” language outruns the photon-count data.","tokens_in":9126,"tokens_out":530,"would_cite":false,"duration_ms":21273,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"grok-4.5","headline":"Raman noise from O-band classical light dominates C-band quantum SNR on real metro fiber, so channel frequency must be chosen carefully.","keywords":["quantum communications","Quantum Internet","entanglement distribution","Raman scattering","classical-quantum coexistence","metropolitan fiber","C-band","O-band"],"falsifier":"Repeat the same metro-loop launch while distributing entangled photon pairs (or running QKD) and show that measured fidelity or QBER does not track the reported Raman photon-count spectrum, or that the spectral spikes vanish when the classical O-band source is truly absent and all neighboring fibers are dark.","tokens_in":9029,"feed_emoji":"📡","tokens_out":907,"duration_ms":26237,"temperature":0.7,"pith_summary":"This paper shows that when quantum signals travel in the C-band on the same deployed fiber as ordinary O-band classical traffic, Raman scattering from the classical light is a leading noise source for the quantum channel—larger than background light or detector dark counts. The authors measure the resulting C-band photon counts over a 7 km metropolitan loop using both a commercial transceiver and a narrow-line laser, then compare the spectra with laboratory spools. The overall Raman shape matches the lab, yet the live fiber also produces sharp spectral spikes that appear even with no classical launch and are tied to real-world fiber imperfections. From the clean parts of the spectrum they mark C-band windows that stay quieter, giving concrete guidance on where to park a quantum channel so entanglement distribution can share existing city fiber without being swamped.","feed_headline":"Raman noise rules C-band quantum links on live metro fiber","feed_subtitle":"7 km city-loop spectra show which wavelengths stay quiet enough for entanglement beside O-band traffic","key_machinery":"Wavelength-resolved photon-count spectra of C-band light generated by O-band pumps (commercial SFP or CW laser), obtained by cascading WDMs, scanning a 25 GHz tunable filter across the C-band, and detecting with an SNSPD on the live metro loop versus a lab spool; normalization by launch power and effective length isolates the Raman shape and the extra live-fiber peaks.","core_discovery":"In a real 7 km metropolitan single-mode fiber loop, spontaneous Raman scattering generated by co-propagating O-band classical sources produces a C-band noise floor that is the dominant contribution to quantum signal-to-noise ratio, beyond ambient and detector noise; laboratory Raman profiles remain predictive once the live-fiber spectral anomalies are excluded, and quieter C-band DWDM windows can therefore be identified for quantum allocation.","pith_inferences":["If the unexplained spikes are confirmed as inter-fiber crosstalk inside the shared cable jacket, multi-fiber ducts may need spatial or spectral isolation rules that single-fiber lab models never captured.","The same measurement recipe could be turned into a routine pre-deployment audit that maps every new metro span before quantum equipment is installed.","Because the C-band is preferred for low loss, the reverse band assignment (quantum in O, classical in C) may remain systematically noisier; the data here already hint that the quieter windows are not uniform across the C-band."],"forward_implications":["Quantum channels sharing fiber with O-band classical traffic should be parked in the quieter C-band windows identified by the scan rather than chosen only by ITU grid convenience.","Network planners can treat laboratory Raman models as a first-order predictor for metro deployments once live-fiber anomaly maps are subtracted.","An operational quantum SNR metric must explicitly fold in Raman counts from co-propagating classical power, not only dark counts and ambient light.","Commercial SFP sources and narrow-line lasers produce comparable Raman envelopes after power and length normalization, so either can be used for planning."],"fun_headline_variants":["Metro fiber loop shows Raman noise dominates C-band quantum SNR","O-band traffic sets C-band Raman floor on 7 km city fiber","Live 7 km spectra flag quiet C-band windows beside O-band","Lab Raman profiles hold on metro fiber once anomalies drop","Raman from O-band classical outweighs detector noise in C-band"],"cache_read_input_tokens":128,"weakest_assumption_plain":"That raw C-band photon-count spectra measured without actually sending entangled photons or running a quantum protocol are enough to declare Raman the dominant term in quantum SNR and to prescribe which channels are safe.","fun_headline_variants_meta":{"raw":{"variants":["Metro fiber loop shows Raman noise dominates C-band quantum SNR","O-band traffic sets C-band Raman floor on 7 km city fiber","Live 7 km spectra flag quiet C-band windows beside O-band","Lab Raman profiles hold on metro fiber once anomalies drop","Raman from O-band classical outweighs detector noise in C-band"]},"model":"grok-4.5","effort":"low","cost_usd":0.00341,"raw_usage":{"total_tokens":1160,"prompt_tokens":833,"num_sources_used":0,"completion_tokens":78,"cost_in_usd_ticks":34104000,"prompt_tokens_details":{"text_tokens":833,"audio_tokens":0,"image_tokens":0,"cached_tokens":128},"completion_tokens_details":{"audio_tokens":0,"reasoning_tokens":249,"accepted_prediction_tokens":0,"rejected_prediction_tokens":0}},"tokens_in":833,"tokens_out":78,"duration_ms":6636,"temperature":1.0,"reasoning_tokens":249,"cache_read_input_tokens":128,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-07-31T21:47:46.816021+00:00","model_set":{"reader":"grok-4.5"},"falsifier":"Repeat the same metro-loop launch while distributing entangled photon pairs (or running QKD) and show that measured fidelity or QBER does not track the reported Raman photon-count spectrum, or that the spectral spikes vanish when the classical O-band source is truly absent and all neighboring fibers are dark.","supporting_citations":[],"review_version":1}