REVIEW 3 major objections 4 minor 19 references
On the Feasibility of SCL-Band Transmission over G.654.E-Compliant Long-Haul Fibre Links
T0 review · 3 major / 4 minor · reviewed 2026-08-06 · deepseek-v4-flash
Pith's one-line read This paper reports the first SCL-band long-haul transmission over G.654.E-compliant fibre, reaching 100.85 Tb/s of GMI over 1552 km despite the fibre's 1520 nm cutoff, and shows the link can match a Raman-amplified G.652.D system with…
desk verdict A credible first SCL-band long-haul result on G.654.E fiber; the headline rate is GMI-based with ASE-emulated WDM neighbors, but the qualitative feasibility claim holds. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The central object is the G.654.E-compliant fibre span itself: a 86.2 km Vascade EX2500 fibre with about 0.148 dB/km attenuation at 1550 nm and about 125 square micrometres of effective area. Its low loss and low nonlinearity are what allow a DFA-only SCL-band link to match a Raman-amplified G.652.D system, while its 1520 nm cutoff does not produce a measurable MPI penalty. The experimental machinery around it is a recirculating loop with three lumped gain blocks (an S-band TDFA plus C- and L-band EDFAs), optional backward E-band Raman pumps, and spectrally-shaped ASE noise standing in for co-propagating WDM channels; a simplified ISRS-aware Gaussian-noise model sets the pump powers and per-band launch powers. These components together determine how much of the reported throughput comes from the fibre's linear advantages rather than from Raman gain.
What would settle it
Transmit a fully populated or densely sampled grid of real 112 GBd modulated channels across S, C, and L bands over the same 18-span G.654.E loop and compare per-channel SNR and total GMI; if the real full-grid S-band SNR or total throughput falls below the shaped-ASE result by more than the system margin, the reported 100.85 Tb/s is not a faithful capacity for this fibre.
Extended reading notes
Core claim
In this paper, the authors claim that G.654.E-compliant fibre can support SCL-band long-haul transmission despite a cutoff wavelength around 1520 nm. Using 18 spans of Vascade EX2500 fibre totalling 1552 km, they transmit 112 GBd channels across 15.08 THz of S+C+L spectrum and obtain 100.85 Tb/s of total GMI with E-band Raman assistance (92.8 Tb/s after decoding), and 88.8 Tb/s decoded with only lumped S-, C-, and L-band amplifiers. The decoded throughput with lumped amplification is effectively equal to the 89.9 Tb/s decoded from a Raman-amplified low-water-peak G.652.D link on the same span length, while the GMI comparison is 97.02 Tb/s versus 97.90 Tb/s. The authors conclude that the fibre's ultra-low loss and larger effective area compensate for its higher water-absorption peak and roughly halved Raman gain coefficient, making DFA-only UWB long-haul transmission viable on G.654.E.
Load-bearing premise
The 100.85 Tb/s headline assumes that spectrally-shaped ASE noise faithfully emulates the co-propagating WDM channels, so that the measured SNR and GMI reflect true multi-channel nonlinear propagation rather than a stand-in that could miss cross-phase modulation and four-wave mixing.
Editorial extensions
If this is right
- With Raman pumps, the G.654.E link achieves 100.85 Tb/s GMI (92.8 Tb/s decoded) over 1552 km across 15.08 THz of S+C+L spectrum at 112 GBd.
- Without Raman, the same G.654.E link delivers 88.8 Tb/s decoded, comparable to the 89.9 Tb/s of a Raman-amplified G.652.D link, so distributed Raman is not required to match standard fibre performance.
- Signals below the 1520 nm cutoff suffer negligible multipath-interference penalty, so the S-band remains usable on cutoff-shifted G.654.E fibre.
- E-band Raman pumping mainly helps the short-wavelength S-band, improving average GMI by 0.86 bit/4D-symbol for 1480 to 1500 nm channels, while C- and L-band performance is largely unchanged.
- These results position G.654.E fibre as suitable for DFA-only long-haul ultra-wideband transmission, reducing amplifier complexity relative to Raman-based UWB links.
Reading between the lines
- Editorial extension: since co-propagating neighbours were shaped ASE rather than live modulated channels, the 100.85 Tb/s GMI is a projected capacity; a fully populated WDM comb could shift SNR through cross-phase modulation and four-wave mixing that broadband noise does not reproduce.
- Editorial extension: the same fibre's weaker Raman response means designs that retain distributed Raman should re-optimise pump wavelengths around the E-band water peak rather than simply scaling G.652.D pump plans.
- Editorial extension: if production G.654.E fibres replicate this span loss and effective area, ultra-wideband long-haul repeater sites could drop Raman hardware altogether, replacing a roughly 1.5 W pump stage with lumped DFA-only gain blocks.
- Editorial extension: the simplified ISRS GN-model optimisation could be validated against per-channel SNR in a fully populated system; agreement would make the model a practical design tool for G.654.E UWB links.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper reports an experimental S+C+L-band (SCL-band) transmission over 1552 km of G.654.E-compliant Vascade EX2500 fibre, using 112 GBd channels with one real modulated channel under test per run and all co-propagating WDM channels emulated by spectrally shaped ASE. The authors report 100.85 Tb/s total throughput estimated from GMI with Raman amplification, 97.02 Tb/s without Raman, and decoded net rates of 92.8 Tb/s and 88.8 Tb/s, respectively. These results are compared with a G.652.D low-water-peak fibre link with Raman amplification, which gave 89.9 Tb/s decoded rate. The central claim is that G.654.E-compliant fibre, despite its ~1520 nm cutoff, supports long-haul SCL-band transmission with performance comparable to G.652.D with distributed Raman amplification, but without requiring Raman pumps.
Significance. If the result holds, it is a significant experimental demonstration: it would show that ultra-low-loss, large-effective-area G.654.E fibre can extend three-band WDM transmission to long-haul distances with only lumped amplification, potentially simplifying UWB system architectures. The paper has clear strengths: it directly compares G.654.E and G.652.D fibres in the same recirculating-loop setup, reports Raman on-off gain measurements, distinguishes GMI estimates from decoded net rates, and includes both Raman-amplified and DFA-only scenarios. The main caveat is that the headline throughput is a GMI sum over single-channel measurements with ASE-emulated neighbours, so the fully populated WDM performance is not directly measured; this is the load-bearing assumption that needs explicit validation or qualification.
major comments (3)
- [Experimental setup (Fig. 2) and Results (Fig. 6)] The reported totals of 100.85 Tb/s and 97.02 Tb/s are computed by summing per-channel GMI values measured with only one real 112 GBd channel per run, while all co-propagating WDM channels are emulated by spectrally shaped ASE. The paper does not demonstrate that ASE loading reproduces the inter-channel nonlinear effects of real modulated neighbours, specifically cross-phase modulation, four-wave mixing, ISRS, and, in the below-cutoff S-band, MPI. Since the central claim concerns the feasibility and throughput of a fully populated SCL-band WDM system, this assumption is load-bearing. A validation experiment with two or more real modulated neighbours, or a measurement of nonlinear-interference scaling with channel count for ASE versus modulated loading, is needed before the headline throughput can be taken at face value.
- [Results (Fig. 6)] No repeated measurements, error bars, or uncertainty estimates are reported. The claims of negligible MPI penalty, the 0.86 bit/4D-symbol S-band improvement with Raman, and the 0.67 bit/4D-symbol C-band advantage of G.654.E over G.652.D rest on single measurements per scenario. Given the small differences involved, the absence of any repeatability or statistical confidence statement makes it difficult to assess whether these comparisons are significant.
- [Results, decoded net rate] The definition of 'decoded net data rate' is incomplete. The text states only that pilot overhead was deducted; it does not specify the FEC code rate, FEC overhead, or any other overheads included in the adaptive rate decoding. Since the abstract and conclusion emphasize throughput, the relation between the GMI-based estimate (100.85 Tb/s) and the decoded rate (92.8 Tb/s) should be stated precisely.
minor comments (4)
- [Fig. 2 inset] The inset shows '116 GHz' while the text states a baud rate of 112 GBaud; please clarify whether 116 GHz is the WDM grid spacing and, if so, state the number of WDM channels and the total bandwidth accordingly.
- [Fig. 1] The band labels 'SCL', 'CLU', 'SCLU', and 'SCLUX' in the figure legend are not defined in the caption; please define them for readers unfamiliar with the notation.
- [Abstract and Conclusion] The abstract correctly qualifies the headline as '100.8 Tb/s (GMI)', but the conclusion repeats 'more than 100 Tb/s throughput' without the GMI qualifier; recommend consistently noting that this figure is a GMI-based estimate, not a decoded rate.
- [References [16] and modulation formats] The geometric shaping parameters for GS-16-QAM and GS-64-QAM (e.g., number of constellation points, shaping block length) are not given; adding these details would improve reproducibility.
Circularity Check
No significant circularity: the 100.8 Tb/s headline is a measured GMI sum, not a model output; the ISRS-GN model is used only to set operating powers, and self-citations are not load-bearing.
full rationale
The central claim is an experimental measurement: the abstract's '100.8 Tb/s (GMI) over 1552 km' is obtained by summing the per-channel GMI values measured after 18 recirculations and shown in Fig. 6(a). No equation in the paper derives this throughput from the model; the only model usage is operational, namely 'pump powers and signal launch power per band were optimised for both fibre types using a simplified ISRS GN model [19] to maximise throughput'. That optimisation sets the operating point but does not generate the reported rates, which would be falsified by a different measured SNR/GMI. The self-cited refs [19] (same-group GN model) and [11] (MPI-penalty-free S-band transmission over G.654.E) are supporting or corroborating, not the source of the headline quantity. The spectrally-shaped ASE used to emulate co-propagating WDM channels is an experimental fidelity assumption about inter-channel nonlinear effects, not a circular reduction: the paper never defines the measured GMI in terms of the ASE loading, and the claim remains externally testable against a fully populated WDM experiment. Thus the derivation chain is self-contained as an experimental demonstration, with only minor self-citation that is not load-bearing.
Assumptions & free parameters
free parameters (2)
- Per-band signal launch power =
S 19.7 dBm, C 19.4 dBm, L 18.5 dBm (G.654.E); S 19.7, C 16.6, L 18.5 dBm (G.652.D)
- Raman pump powers =
G.654.E: 3 pumps at ~500 mW each (max); G.652.D: 447, 501, 331, 224 mW
assumptions (3)
- domain assumption Shaped ASE noise faithfully emulates co-propagating WDM channels
- domain assumption Simplified ISRS GN model with per-band averaged gains/losses provides near-optimal power settings
- domain assumption Recirculating loop measurements represent straight-line transmission
Cite this review
Pith. "Pith review of On the Feasibility of SCL-Band Transmission over G.654.E-Compliant Long-Haul Fibre Links." pith.science (2026). https://pith.science/paper/5GUMLXT5
@misc{pith2026250721865,
author = {Pith},
title = {Pith review of: On the Feasibility of SCL-Band Transmission over G.654.E-Compliant Long-Haul Fibre Links},
year = {2026},
howpublished = {\url{https://pith.science/paper/5GUMLXT5}},
note = {Machine review of arXiv:2507.21865}
}
read the original abstract
We demonstrate the first SCL-band long-haul transmission using G.654.E-compliant fibre, achieving 100.8 Tb/s (GMI) over 1552 km, despite its 1520 nm cutoff wavelength. Due to the fibre's ultra-low loss and low nonlinearity, the achievable-information-rate with lumped amplification is comparable to that of G.652.D-compliant fibre links with distributed-Raman-amplification.
Figures
Figures from the paper (3 more)
Reference graph
Works this paper leans on
-
[1]
Investigation of long-haul S-, C- + L-band transmission
B. J. Puttnam, R. S. Luís, G. Rademacher, Y . Awaji, and H. Furukawa, “Investigation of long-haul S-, C- + L-band transmission”, in Optical Fiber Communication Conference (OFC) 2022, San Diego, CA, USA: Optica Publishing Group, 2022, W3C.5. DOI: 10 . 1364 / OFC . 2022.W3C.5
work page 2022
-
[2]
F . Hamaoka, M. Nakamura, T. Sasai,et al., “110.7-Tb/s single-mode-fiber transmission over 1040 km with high- symbol-rate 144-GBaud PDM-PCS-QAM signals”, in Optical Fiber Communication Conference (OFC) 2024, San Diego, CA, USA, 2024, Tu3E.6. DOI: 10.1364/OFC. 2024.Tu3E.6
doi:10.1364/ofc 2024
-
[3]
J. Y ang, H. Buglia, E. Sillekens, et al., “Experimental validation of the closed-form GN model accounting for distributed Raman amplification in an S+C+L-band hy- brid amplified long-haul transmission system”, in ECOC 2024; 50th European Conference on Optical Communi- cation, Frankfurt, Germany, 2024, pp. 67–70
work page 2024
-
[4]
F . Hamaoka, K. Kimura, M. Nakamura,et al., “Net 107.7- Tb/s triple-band WDM transmission over 1200-km single- mode fiber with forward- and backward-pumped dis- tributed Raman amplifiers”, in Optical Fiber Communica- tion Conference (OFC) 2025, San Francisco, CA, USA, 2025, Th3C.2
work page 2025
-
[5]
Trans- mission over field-deployed standard single-mode fibre using >100 nm S+C+L-band
J. Y ang, E. Sillekens, M. Jarmoloviˇcius, et al., “Trans- mission over field-deployed standard single-mode fibre using >100 nm S+C+L-band”, Journal of Lightwave Technology, pp. 1–9, 2025. DOI: 10.1109/JLT.2025. 3546075
doi:10.1109/jlt.2025 2025
-
[6]
T. Kobayashi, S. Shimizu, A. Kawai,et al., “C+L+U-band 14.85-THz WDM transmission over 80-km-span G.654.E fiber with hybrid PPLN-OPA/EDFA U-band lumped re- peater using 144-Gbaud PCS-QAM signals”, in 2024 Optical Fiber Communications Conference and Exhibi- tion (OFC), San Diego, CA, USA, 2024, Th4A.1
work page 2024
-
[7]
S. Shimizu, T. Kobayashi, M. Abe,et al., “133-Tbps 1040- km (13× 80 km) lumped-amplified transmission over 22 THz in S-to-U-band using hybrid multiband repeater with PPLN-based optical parametric amplifiers and EDFAs”, in ECOC 2024; 50th European Conference on Optical Communication, Frankfurt, Germany, 2024, Th3B.2
work page 2024
-
[8]
27-THz ISRS- supported transmission over 1040 km in S+C+L+U and extreme longer-wavelength band
S. Shimizu, K. Kimura, A. Kawai, et al., “27-THz ISRS- supported transmission over 1040 km in S+C+L+U and extreme longer-wavelength band”, in Optical Fiber Com- munication Conference (OFC) 2025, San Francisco, CA, USA, 2025, Th4A.2
work page 2025
Show all 19 references
-
[9]
G. 654. E optical fibers for high-data-rate terrestrial transmission systems with long reach
J. D. Downie, S. Makovejs, J. Hurley, M. Mlejnek, and H. de Pedro, “G. 654. E optical fibers for high-data-rate terrestrial transmission systems with long reach”, in Next-Generation Optical Communication: Components, Sub-Systems, and Systems VII, SPIE, vol. 10561, 2018, pp. 12...
2018 doi
-
[10]
On the feasibility of S-band transmission over G.654.E fiber
J. D. Downie, P . Sterlingov, V. Ivanov, H. D. Pedro, S. Mishra, and D. Seddon, “On the feasibility of S-band transmission over G.654.E fiber”, in 49th European Con- ference on Optical Communications (ECOC 2023), Glas- gow, UK, 2023, pp. 499–502. DOI: 10.1049/icp.2023. 2222
2023 doi
-
[11]
Experimental demonstration of MPI-penalty-free S-band transmission over G.654.E fibres
R. Aparecido, J. Y ang, J. D. Downie,et al., “Experimental demonstration of MPI-penalty-free S-band transmission over G.654.E fibres”, in Optical Fiber Communication Conference (OFC) 2025, San Francisco, CA, USA, 2025, W4E.4
2025
-
[12]
Examina- tion of potential terrestrial system effects from Raman pumps below cable cutoff in G.654.E fibers
M. Mlejnek, J. D. Downie, and M. O’Sullivan, “Examina- tion of potential terrestrial system effects from Raman pumps below cable cutoff in G.654.E fibers”, Journal of Lightwave Technology, vol. 37, no. 17, pp. 4282–4294, 2019
2019
-
[13]
Performance analysis of lower Raman gain coefficient G.654.E fiber with distributed Raman amplifiers
V. V. Ivanov, L. Galdino, and J. D. Downie, “Performance analysis of lower Raman gain coefficient G.654.E fiber with distributed Raman amplifiers”, inOptical Fiber Com- munication Conference (OFC) 2025, San Francisco, CA, USA, 2025, Th2A.14
2025
-
[14]
201.6 Tbit/s S+ C+ L-Band transmission over 2× 75 km SSMF with doped fiber amplification
X. Zhang, M. Luo, Q. He, et al., “201.6 Tbit/s S+ C+ L-Band transmission over 2× 75 km SSMF with doped fiber amplification”, in ECOC 2024; 50th European Con- ference on Optical Communication, VDE, Frankfurt, Ger- many, 2024, pp. 946–949
2024
-
[15]
214-Tb/s transmission over 2×75-km in the S+C+L band with >1-Tb/s/λ sig- nals using only doped fiber amplifiers
Y . Zhang, M. Zuo, Q. Qiu,et al., “214-Tb/s transmission over 2×75-km in the S+C+L band with >1-Tb/s/λ sig- nals using only doped fiber amplifiers”, in Optical Fiber Communication Conference (OFC) 2025, San Francisco, CA, USA, 2025, Th3C.3
2025
-
[16]
High-cardinality geometrical constellation shaping for the nonlinear fibre channel
E. Sillekens, G. Liga, D. Lavery, P . Bayvel, and R. I. Kil- ley, “High-cardinality geometrical constellation shaping for the nonlinear fibre channel”, Journal of Lightwave Technology, vol. 40, no. 19, pp. 6374–6387, 2022. DOI: 10.1109/JLT.2022.3197366
2022
-
[17]
2048-QAM transmission at 15 GBd over 100 km using geometric constellation shaping
Y . Wakayama, T. Gerard, E. Sillekens,et al., “2048-QAM transmission at 15 GBd over 100 km using geometric constellation shaping”, Optics Express, vol. 29, no. 12, pp. 18 743–18 759, 2021.DOI: 10.1364/OE.423361
2021 doi
-
[18]
On the performance limits of high- speed transmission using a single wideband coher- ent receiver
B. Geiger, E. Sillekens, F . Ferreira, R. Killey, L. Galdino, and P . Bayvel, “On the performance limits of high- speed transmission using a single wideband coher- ent receiver”, Journal of Lightwave Technology, vol. 41, no. 12, pp. 3816–3824, 2023. DOI: 10.1109/JLT.2023. 3277624
2023 doi
-
[19]
A closed-form expression for the Gaussian noise model in the presence of Raman amplification
H. Buglia, M. Jarmoloviˇcius, L. Galdino, R. I. Killey, and P . Bayvel, “A closed-form expression for the Gaussian noise model in the presence of Raman amplification”, Journal of Lightwave Technology, vol. 42, no. 2, pp. 636– 648, 2024. DOI: 10.1109/JLT.2023.3315127
2024
Reviewed August 6, 2026 · model on record in the stance chip above.
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