pith. machine review for the scientific record. sign in

arxiv: 2605.13272 · v1 · submitted 2026-05-13 · ⚛️ physics.optics

Recognition: unknown

Robust High-Precision Time Transfer over 91-km Hollow-Core Fiber: Immunity to Dispersion and Nonlinearity

Bo Liu , Xinxing Guo , Jiang Chen , Huibo Hong , Qian Zhou , Xiang Zhang , Ru Yuan , Rongduo Lu
show 3 more authors
Tao Liu Ruifang Dong Shougang Zhang
Authors on Pith no claims yet

Pith reviewed 2026-05-14 18:40 UTC · model grok-4.3

classification ⚛️ physics.optics
keywords hollow-core fibertime transferchromatic dispersionnonlinear effectsoptical Kerr effecthigh-precision timingfiber opticsstability
0
0 comments X

The pith

Hollow-core fiber supports high-precision time transfer over 91 km with time deviations below 80 ps by minimizing dispersion and nonlinearity effects.

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

The paper compares hollow-core fiber to standard single-mode fiber in bidirectional time transfer experiments over links of 91 km, 68 km, and 54 km. It establishes that hollow-core fiber greatly reduces chromatic dispersion to a mean of 3.4 ps/nm/km and shows much lower sensitivity to power, wavelength, and environmental changes. This results in over 24 dB higher signal-to-noise ratio and time deviations confined to less than 80 ps on the 91 km link, compared to more than 600 ps for standard fiber. Over 24 hours, the 68 km hollow-core link exhibits only 24.5% of the time delay fluctuations seen in standard fiber, achieving 0.2 ps stability at 1000 s integration time.

Core claim

In comparative experiments using a bidirectional time transfer platform over 91 km, 68 km, and 54 km links, hollow-core fiber demonstrates significantly reduced chromatic dispersion with a mean coefficient of 3.4 ps per nm per km and lower environmental sensitivity than standard single-mode fiber. The HCF link provides over 24 dB SNR enhancement and confines time deviation to less than 80 ps, nearly an order of magnitude better than SMF's exceedance of 600 ps, while remaining nearly immune to power and wavelength fluctuations. Under 24-hour monitoring on the 68 km link, environment-induced time delay fluctuations are 776 ps for HCF versus 3166 ps for SMF, yielding TDEV of 0.2 ps at 1000 s.

What carries the argument

Hollow-core fiber transmission medium that confines light propagation to an air core, minimizing interaction with silica and thus suppressing chromatic dispersion and optical Kerr nonlinearity.

If this is right

  • HCF links can maintain high SNR and low time deviation over distances up to 91 km without dispersion compensation.
  • The approach shows nearly order-of-magnitude improvement in time deviation compared to SMF.
  • Time transfer stability reaches 0.2 ps TDEV at 1000 s, twofold better than SMF.
  • Reduced environmental sensitivity enables more robust 24-hour operation with 24.5% of SMF fluctuations.

Where Pith is reading between the lines

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

  • This could be extended to frequency distribution networks for optical clocks.
  • Integration with existing fiber infrastructure might improve global timing precision.
  • Longer distance tests would confirm if the immunity scales further.

Load-bearing premise

The bidirectional time transfer platform ensures equivalent non-reciprocal error sources and environmental exposure for both HCF and SMF without unaccounted setup biases.

What would settle it

If measurements on the 91 km HCF link under varying power and wavelength show time deviations exceeding 600 ps similar to SMF, the immunity claim would be falsified.

read the original abstract

To address the fundamental limitations imposed by chromatic dispersion and environmental susceptibility in standard single-mode fiber (SMF) for long-haul high-precision time transfer, we systematically explore the application potential of hollow-core fiber (HCF) through comparative experiments. We designed a bidirectional time transfer platform enabling direct comparison between HCF and SMF links across distances of 91 km, 68 km, and 54 km. We quantitatively characterize the impact of critical non-reciprocal error sources, specifically the optical Kerr effect and chromatic dispersion, under varying laser power, wavelength drift, and environmental perturbations. Our results show that HCF exhibits significantly suppressed dispersion, with a mean coefficient of 3.4 ps per nm per km, and reduced environmental sensitivity compared with SMF. Notably, over the 91 km link, the HCF yields a signal-to-noise ratio (SNR) enhancement of more than 24 dB and confines the time deviation to less than 80 ps, which is nearly an order-of-magnitude improvement over SMF, where the time deviation exceeds 600 ps, while remaining nearly immune to power and wavelength fluctuations. Under 24 hour diurnal monitoring, the 68 km HCF link demonstrates strong robustness, with environment-induced time delay fluctuations of 776 ps, corresponding to only 24.5% of those in SMF, which reach 3166 ps. Consequently, the time transfer stability, evaluated by time deviation (TDEV), reaches 0.2 ps at an integration time of 1000 s, representing a twofold improvement over SMF. These findings validate HCF as a superior transmission medium with low latency, low nonlinearity, and high thermal stability, paving the way for next-generation ultra-stable, long-haul time-frequency distribution networks.

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 / 2 minor

Summary. The manuscript reports experimental results from a bidirectional time transfer platform comparing hollow-core fiber (HCF) and standard single-mode fiber (SMF) links at 91 km, 68 km, and 54 km. It claims HCF exhibits a mean dispersion coefficient of 3.4 ps/nm/km, >24 dB SNR enhancement, time deviation <80 ps (vs. >600 ps for SMF), near-immunity to power/wavelength fluctuations, 24-hour environmental delay fluctuations of 776 ps (24.5% of SMF's 3166 ps), and TDEV reaching 0.2 ps at 1000 s integration time.

Significance. If the results hold under rigorous controls, the work provides concrete evidence that HCF can deliver substantial gains in SNR, time stability, and environmental robustness for long-haul time-frequency transfer. This would support HCF as a practical medium for next-generation ultra-stable distribution networks, with quantified benefits in dispersion suppression and reduced nonlinearity.

major comments (2)
  1. [Abstract] Abstract: The headline quantitative claims (time deviation <80 ps vs. >600 ps, >24 dB SNR gain) are presented only as summary statistics. No full error budgets, raw time-series data, or explicit exclusion criteria for environmental perturbations are supplied, leaving the statistical significance and reproducibility of the order-of-magnitude improvement difficult to assess.
  2. [Experimental Setup] Bidirectional platform description: The direct HCF–SMF comparison rests on the assumption that the platform exposes both fiber types to identical non-reciprocal sources (Kerr effect, dispersion residuals, splice/connector losses, routing). No explicit cross-checks (fiber-swapping experiments, power-sweep residual analysis, or mode-field matching verification) are described, so setup-specific biases cannot be excluded as contributors to the observed differences.
minor comments (2)
  1. [Abstract] The dispersion value is stated as a 'mean coefficient of 3.4 ps per nm per km' without clarifying whether this is absolute for HCF or a differential value relative to SMF; consistent notation and a brief derivation or measurement method would improve clarity.
  2. A summary table listing TDEV, time deviation, and environmental fluctuation amplitudes for both fiber types across all three distances would facilitate direct comparison and strengthen the multi-distance claim.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the detailed and constructive review. The comments highlight important aspects of statistical rigor and experimental validation that we have addressed through targeted revisions and clarifications. We believe the updated manuscript now provides stronger support for the reported improvements in time transfer performance using hollow-core fiber.

read point-by-point responses

  1. Referee: [Abstract] Abstract: The headline quantitative claims (time deviation <80 ps vs. >600 ps, >24 dB SNR gain) are presented only as summary statistics. No full error budgets, raw time-series data, or explicit exclusion criteria for environmental perturbations are supplied, leaving the statistical significance and reproducibility of the order-of-magnitude improvement difficult to assess.

    Authors: We agree that additional details on the underlying statistics would improve reproducibility. In the revised manuscript we have added a dedicated error-budget subsection (Section 3.4) that itemizes all identified contributions (Kerr effect, dispersion residuals, detection noise, and environmental terms) with their estimated magnitudes. Raw time-series segments for the 91 km link are now shown in new Supplementary Figure S1, and the exclusion criteria for transient environmental events (thresholds on delay-rate and power fluctuations) are explicitly stated in the Methods section. These additions allow readers to assess the statistical significance directly. revision: yes

  2. Referee: [Experimental Setup] Bidirectional platform description: The direct HCF–SMF comparison rests on the assumption that the platform exposes both fiber types to identical non-reciprocal sources (Kerr effect, dispersion residuals, splice/connector losses, routing). No explicit cross-checks (fiber-swapping experiments, power-sweep residual analysis, or mode-field matching verification) are described, so setup-specific biases cannot be excluded as contributors to the observed differences.

    Authors: We acknowledge that a physical fiber-swap experiment was not performed, as the distinct mechanical and optical properties of HCF and SMF make direct interchange impractical without introducing new variables. However, we have added a new subsection (Section 2.3) that presents power-sweep residual analysis for both fiber types and mode-field overlap calculations confirming matched launch conditions. These checks, together with the bidirectional architecture that cancels common-path effects, support the validity of the comparison. We have also included a brief discussion of residual setup biases and why they are expected to be negligible relative to the observed order-of-magnitude differences. revision: partial

Circularity Check

0 steps flagged

No circularity; results are direct experimental measurements

full rationale

The paper reports comparative experimental measurements of SNR, time deviation, and TDEV on HCF vs SMF links of 91 km, 68 km, and 54 km. Key performance figures (24 dB SNR gain, <80 ps vs >600 ps time deviation, 0.2 ps TDEV) are presented as observed outcomes from the bidirectional platform under varying power, wavelength, and environmental conditions. No equations, fitted parameters, or derivation steps appear that reduce these metrics to self-referential inputs or prior self-citations. The bidirectional setup is described as enabling equivalent exposure, but this is an experimental design choice, not a mathematical reduction. No self-citation load-bearing steps or ansatz smuggling are present in the text.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

The work is experimental and relies on direct comparative measurements rather than theoretical derivations; no free parameters, new axioms, or invented entities are introduced to support the central claims.

pith-pipeline@v0.9.0 · 5663 in / 1274 out tokens · 58916 ms · 2026-05-14T18:40:57.799412+00:00 · methodology

discussion (0)

Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.

Reference graph

Works this paper leans on

30 extracted references · 29 canonical work pages

  1. [1]

    State-of-the-Art Review: Electronic Warfare Against Radar Systems,

    R. Reddy, S. Sinha, “State-of-the-Art Review: Electronic Warfare Against Radar Systems,” Ieee Access, vol. 13, no. pp. 57530,2025,DOI: 10.1109/access.2025.3555493

    work page doi:10.1109/access.2025.3555493 2025

  2. [2]

    Radiometric Interferometry for Deep Space Navigation Using Geostationary Satellites,

    M. Golani, Y. Rozen, H. Rotstein, “Radiometric Interferometry for Deep Space Navigation Using Geostationary Satellites,” Aerospace, vol. 12, no. 11,2025,DOI: 10.3390/aerospace12110982

    work page doi:10.3390/aerospace12110982 2025

  3. [3]

    Simultaneous multi-spacecraft observations with VLBI radio telescopes to study the interplanetary phase scintillation,

    N. M. M. Said, G. M. Calves, P. Kummamuru et al., “Simultaneous multi-spacecraft observations with VLBI radio telescopes to study the interplanetary phase scintillation,” Experimental Astronomy, vol. 59, no. 2,2025,DOI: 10.1007/s10686-025-09989-5

    work page doi:10.1007/s10686-025-09989-5 2025

  4. [4]

    On the improvement of the sensitivity levels of VLBI solutions from a combination with GNSS,

    P. K. Nehbit, S. Glaser, P. Sakic et al., “On the improvement of the sensitivity levels of VLBI solutions from a combination with GNSS,” Advances in Space Research, vol. 72, no. 8,pp. 3037,2023,DOI: 10.1016/j.asr.2023.06.021

    work page doi:10.1016/j.asr.2023.06.021 2023

  5. [5]

    Quantum Two-Way Time Transfer Over a 103 km Urban Fiber,

    H. B. Hong, R. N. Quan, X. Xiang et al., “Quantum Two-Way Time Transfer Over a 103 km Urban Fiber,” J. Lightwave Technol, vol. 42, no. 5,pp. 1479,2024,DOI: 10.1109/jlt.2023.3323434

    work page doi:10.1109/jlt.2023.3323434 2024

  6. [6]

    Bidirectional Optical Amplification in Long-Distance Two-Way Fiber-Optic Time and Frequency Transfer Systems,

    L. Sliwczynski, J. Kolodziej, “Bidirectional Optical Amplification in Long-Distance Two-Way Fiber-Optic Time and Frequency Transfer Systems,” Ieee Transactions on Instrumentation and Measurement, vol. 62, no. 1,pp. 253,2013,DOI: 10.1109/tim.2012.2212504

    work page doi:10.1109/tim.2012.2212504 2013

  7. [7]

    Stabilized Time Transfer via a 1000-km Optical Fiber Link Using High-Precision Delay Compensation System,

    B. Liu, X. X. Guo, W. C. Kong et al., “Stabilized Time Transfer via a 1000-km Optical Fiber Link Using High-Precision Delay Compensation System,” Photonics, vol. 9, no. 8,p. 522,2022,DOI: 10.3390/photonics9080522

    work page doi:10.3390/photonics9080522 2022

  8. [8]

    Optical fibers in time and frequency transfer,

    L. Sliwczynski, P. Krehlik, M. Lipinski, “Optical fibers in time and frequency transfer,” Measurement Science and Technology, vol. 21, no. 7,2010,DOI: 10.1088/0957-0233/21/7/075302

    work page doi:10.1088/0957-0233/21/7/075302 2010

  9. [9]

    Report on 3,143.6-km Time and Frequency Transfer Fiber Link with Ps-level Stability,

    B. Liu, X. X. Guo, J. Chen et al., “Report on 3,143.6-km Time and Frequency Transfer Fiber Link with Ps-level Stability,” Chin. Phys. Lett, vol. 42, no. 1,p. 1,2025,DOI: 10.1088/0256-307x/42/1/014202

    work page doi:10.1088/0256-307x/42/1/014202 2025

  10. [10]

    Fiber-optic joint time and frequency transmission with enhanced time precision,

    F. X. Zuo, Q. Li, K. F. Xie et al., “Fiber-optic joint time and frequency transmission with enhanced time precision,” Opt. Lett, vol. 47, no. 4,pp. 1005,2022,DOI: 10.1364/ol.450696

    work page doi:10.1364/ol.450696 2022

  11. [11]

    All-Passive Cascaded Optical Frequency Transfer,

    X. Zhang, L. Hu, X. Deng et al., “All-Passive Cascaded Optical Frequency Transfer,” IEEE Photonics Technol. Lett, vol. 34, no. 8,pp. 413,2022,DOI: 10.1109/lpt.2022.3164406

    work page doi:10.1109/lpt.2022.3164406 2022

  12. [12]

    Time synchronization system based on bidirectional time-division multiplexing transmission over single fiber with same wavelength,

    F. Z. Z. Chen, L. Hu, Y. Jin, J. Chen, and G. Wu, “Time synchronization system based on bidirectional time-division multiplexing transmission over single fiber with same wavelength,” Chinese Journal of Lasers, vol. 48, no. 11,p. 0906005,2021,DOI: 10.3788/cjl/2021/48/8

    work page doi:10.3788/cjl/2021/48/8 2021

  13. [13]

    Electrical Regeneration for Long-Haul Fiber-Optic Time and Frequency Distribution Systems,

    P. Krehlik, L. Sliwczynski, L. Buczek, “Electrical Regeneration for Long-Haul Fiber-Optic Time and Frequency Distribution Systems,” Ieee T Ultrason Ferr, vol. 68, no. 3,pp. 899,2021,DOI: 10.1109/tuffc.2020.3016610

    work page doi:10.1109/tuffc.2020.3016610 2021

  14. [14]

    Picoseconds-Accurate Fiber-Optic Time Transfer With Relative Stabilization of Lasers Wavelengths,

    L. Sliwczynski, P. Krehlik, L. Buczek et al., “Picoseconds-Accurate Fiber-Optic Time Transfer With Relative Stabilization of Lasers Wavelengths,” J. Lightwave Technol, vol. 38, no. 18,pp. 5056,2020,DOI: 10.1109/jlt.2020.2999158

    work page doi:10.1109/jlt.2020.2999158 2020

  15. [15]

    Stable Optical Frequency Comb Distribution Enabled by Hollow-Core Fibers,

    Z. T. Feng, G. Marra, X. Zhang et al., “Stable Optical Frequency Comb Distribution Enabled by Hollow-Core Fibers,” Laser Photonics Rev, vol. 16, no. 11,p. 2200167,2022,DOI: 10.1002/lpor.202200167

    work page doi:10.1002/lpor.202200167 2022

  16. [16]

    Z. Feng, E. N. Fokoua, F. Poletti et al. Simultaneous Distribution of Stable Frequency and Data Signals Over Hollow-Core Optical Fibers. In 2023 Joint Conference of the European Frequency and Time Forum and IEEE International Frequency Control Symposium (EFTF/IFCS), 15-19 May 2023, 2023; pp 1. DOI: 10.1109/EFTF/IFCS57587.2023.10272078

    work page doi:10.1109/eftf/ifcs57587.2023.10272078 2023

  17. [17]

    Hollow-core fiber made of ultralow expansion glass: Toward the ultimate stability for room-temperature fiber optics,

    M. Ding, I. A. Davidson, G. Jasion et al., “Hollow-core fiber made of ultralow expansion glass: Toward the ultimate stability for room-temperature fiber optics,” Sci. Adv., vol. 11, no. 23,2025,DOI: 10.1126/sciadv.ads7529

    work page doi:10.1126/sciadv.ads7529 2025

  18. [18]

    Analytic resolution of wa veguide dispersion in single mode fiber,

    J. Ren, C. Yu, K. Wang, “Analytic resolution of wa veguide dispersion in single mode fiber,” Acta Opt Sin, vol. 24, no. p. 1301,2001,DOI

    2001

  19. [19]

    Coexistence of entanglement-based quantum channels with DWDM classical channels over hollow core fibre in a four node quantum communication network,

    M. J. Clark, O. Alia, S. Bahrani et al., “Coexistence of entanglement-based quantum channels with DWDM classical channels over hollow core fibre in a four node quantum communication network,” npj Quantum Inf, vol. 11, no. 1,p. 181,2025,DOI: ARTN 181 10.1038/s41534-025-01125-7

    work page doi:10.1038/s41534-025-01125-7 2025

  20. [20]

    Higher-Order Mode Suppression in Antiresonant Nodeless Hollow-Core Fibers,

    A. C. Ge, F. C. Meng, Y. F. Li et al., “Higher-Order Mode Suppression in Antiresonant Nodeless Hollow-Core Fibers,” Micromachines, vol. 10, no. 2,2019,DOI: 10.3390/mi10020128

    work page doi:10.3390/mi10020128 2019

  21. [21]

    Low loss and high performance interconnection between standard single-mode fiber and antiresonant hollow-core fiber,

    D. Suslov, M. Komanec, E. N. R. Fokoua et al., “Low loss and high performance interconnection between standard single-mode fiber and antiresonant hollow-core fiber,” Sci. Rep, vol. 11, no. 1,p. 8799,2021,DOI: 10.1038/s41598-021-88065-2

    work page doi:10.1038/s41598-021-88065-2 2021

  22. [22]

    All-fiber highly efficient delivery of 2 kW laser over 2.45 km hollow-core fiber,

    J. Shi, B. Y. Rao, Z. L. Chen et al., “All-fiber highly efficient delivery of 2 kW laser over 2.45 km hollow-core fiber,” Nat. Commun, vol. 16, no. 1,p. 8965,2025,DOI: 10.1038/s41467-025-64073-y

    work page doi:10.1038/s41467-025-64073-y 2025

  23. [23]

    Fourfold truncated double-nested antiresonant hollow-core fiber with ultralow loss and ultrahigh mode purity,

    S. F. Gao, H. Chen, Y. Z. Sun et al., “Fourfold truncated double-nested antiresonant hollow-core fiber with ultralow loss and ultrahigh mode purity,” Optica, vol. 12, no. 1,pp. 56,2025,DOI: 10.1364/optica.542911

    work page doi:10.1364/optica.542911 2025

  24. [24]

    Fundamental vector soliton dynamics governed by Kerr and Raman nonlinearities in optical fiber,

    H. E. Ibarra-Villalon, O. Pottiez, A. Gómez-Vieyra et al., “Fundamental vector soliton dynamics governed by Kerr and Raman nonlinearities in optical fiber,” Phys. Scr, vol. 100, no. 2,2025,DOI: 10.1088/1402-4896/ad9d95

    work page doi:10.1088/1402-4896/ad9d95 2025

  25. [25]

    Exploiting optical nonlinearities for group delay dispersion compensation in femtosecond optical parametric oscillators,

    I. Stasevicius, M. Vengris, “Exploiting optical nonlinearities for group delay dispersion compensation in femtosecond optical parametric oscillators,” Optics Express, vol. 28, no. 18,pp. 26122,2020,DOI: 10.1364/oe.399083

    work page doi:10.1364/oe.399083 2020

  26. [26]

    Dispersion and loss limitations on the performance of optical delay lines based on coupled resonant structures,

    J. B. Khurgin, “Dispersion and loss limitations on the performance of optical delay lines based on coupled resonant structures,” Opt. Lett, vol. 32, no. 2,pp. 133,2007,DOI: 10.1364/ol.32.000133

    work page doi:10.1364/ol.32.000133 2007

  27. [27]

    A tutorial on fiber Kerr nonlinearity effect and its compensation in optical communication systems,

    S. K. O. Soman, “A tutorial on fiber Kerr nonlinearity effect and its compensation in optical communication systems,” Journal of Optics, vol. 23, no. 12,2021,DOI: 10.1088/2040-8986/ac362a

    work page doi:10.1088/2040-8986/ac362a 2021

  28. [28]

    Modeling of a light pulse in bi-isotropic optical fiber with Kerr effect: case of Tellegen media,

    Z. Mezache, S. Aib, F. Benabdelaziz et al., “Modeling of a light pulse in bi-isotropic optical fiber with Kerr effect: case of Tellegen media,” Nonlinear Dynamics, vol. 86, no. 2,pp. 789,2016,DOI: 10.1007/s11071-016-2923-x

    work page doi:10.1007/s11071-016-2923-x 2016

  29. [29]

    Design and Study of Low Loss, High Birefringence Quasi-Symmetric Hollow-Core Anti-Resonant Fiber,

    B. H. Gao, F. Tan, D. X. Chen et al., “Design and Study of Low Loss, High Birefringence Quasi-Symmetric Hollow-Core Anti-Resonant Fiber,” Photonics, vol. 11, no. 7,2024,DOI: 10.3390/photonics11070675

    work page doi:10.3390/photonics11070675 2024

  30. [30]

    A highly birefringent and compact nonlinear photonic crystal fiber for next-generation optical fiber applications: design and investigation,

    C. Priyadharshini, S. Selvendran, A. S. Raja et al., “A highly birefringent and compact nonlinear photonic crystal fiber for next-generation optical fiber applications: design and investigation,” Optical and Quantum Electronics, vol. 55, no. 10,2023,DOI: 10.1007/s11082-023-05051-w

    work page doi:10.1007/s11082-023-05051-w 2023