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arxiv: 2606.23434 · v1 · pith:ADIE4VOUnew · submitted 2026-06-22 · ⚛️ physics.optics

Free-running single-cavity dual combs with Hz-level relative linewidth

Yuan Chen , Ming Yan , Jia Xu , Yueting Hu , Jieming Zhang , Zhaoyang Wen , Zijian Wang , Xiangze Ma
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Min Li Heping Zeng
This is my paper

Pith reviewed 2026-06-26 07:04 UTC · model grok-4.3

classification ⚛️ physics.optics
keywords dual-comb spectroscopysingle-cavity laserfree-running coherencepolarization-maintaining fiberrelative linewidthgas sensingmutual coherence
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The pith

Symmetry engineering in an all-polarization-maintaining fiber single-cavity dual-comb laser yields Hz-level relative linewidths without feedback.

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

The paper demonstrates a bidirectional single-cavity dual-comb laser built with symmetry engineering in all-polarization-maintaining fiber. This architecture produces free-running mutual coherence at the Hz level for relative linewidths and achieves record-low jitter in the repetition rate difference. The performance supports resolving tens of thousands of comb lines across THz bandwidths and capturing molecular spectra in milliseconds. Readers would care because it removes the need for active stabilization, making dual-comb spectroscopy more practical for compact and robust applications in gas sensing.

Core claim

The authors show that their symmetry-engineered bidirectional single-cavity dual-comb laser in an all-polarization-maintaining fiber architecture exhibits Hz-level relative linewidths and a time-averaged absolute jitter of the repetition-rate difference of 4.7*10^-7 min^-1 without any active feedback or phase correction. This coherence level permits the resolution of approximately 49,000 comb lines over a 5.4 THz optical bandwidth and the measurement of carbon monoxide absorption spectra with faithful line shape retrieval at millisecond acquisition times.

What carries the argument

Symmetry-engineered bidirectional single-cavity dual-comb architecture in all-polarization-maintaining fiber that suppresses relative noise sources.

If this is right

  • The system enables comb-line-resolved high-resolution spectroscopy without stabilization.
  • Millisecond-scale line-shape-resolved gas sensing becomes feasible with broadband coverage.
  • The jitter performance improves by nearly two orders of magnitude compared to earlier free-running dual-comb systems.
  • Compact and robust platforms for molecular spectroscopy are now achievable in free-running operation.

Where Pith is reading between the lines

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

  • This design could simplify integration into portable dual-comb spectrometers for real-world environmental monitoring.
  • The symmetry engineering technique might be adapted to other laser cavities to enhance coherence in multi-comb setups.
  • Long-term stability tests beyond the reported measurements could reveal limits for extended operation in varying environments.

Load-bearing premise

The bidirectional single-cavity design with symmetry engineering in all-polarization-maintaining fiber is sufficient by itself to suppress relative noise sources enough to reach the claimed Hz-level coherence and jitter levels without hidden stabilization, post-processing, or unaccounted environmental controls.

What would settle it

A direct measurement of the relative linewidth exceeding several Hz or the repetition-rate difference jitter failing to reach 4.7*10^-7 min^-1 in a free-running implementation without any stabilization would falsify the central claim of exceptional coherence.

read the original abstract

Single-cavity dual-comb lasers provide a compact and efficient source for dual-comb spectroscopy in gas sensing applications; however, achieving sufficient free-running mutual coherence for comb-line-resolved, high-resolution measurements remains challenging. Here, we present a symmetry-engineered bidirectional single-cavity dual-comb laser based on an all-polarization-maintaining fiber architecture. The system exhibits exceptional free-running mutual coherence, achieving Hz-level relative linewidths without active feedback or phase correction. The time-averaged absolute jitter of the dual-comb repetition-rate difference reaches 4.7*10^-7 min-1, representing an improvement of nearly two orders of magnitude over previously reported free-running systems. As a spectroscopic demonstration, we resolve ~49,000 comb lines over a 5.4 THz optical bandwidth and measure the absorption spectrum of carbon monoxide (12CO), faithfully retrieving molecular line shapes with millisecond acquisition times. This architecture provides a compact and robust free-running platform for broadband molecular spectroscopy and millisecond-scale, line-shape-resolved gas sensing.

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 describes a symmetry-engineered bidirectional single-cavity dual-comb laser in an all-polarization-maintaining fiber architecture. It reports exceptional free-running mutual coherence with Hz-level relative linewidths, a time-averaged absolute jitter of the repetition-rate difference of 4.7×10^{-7} min^{-1}, and a spectroscopic demonstration resolving ~49,000 comb lines over 5.4 THz for CO absorption spectrum measurement.

Significance. If the reported performance holds, this work would mark a notable improvement in free-running dual-comb sources, offering nearly two orders of magnitude better jitter than prior systems and enabling compact, robust platforms for high-resolution, line-shape-resolved gas sensing without active stabilization.

major comments (2)
  1. [Abstract] Abstract: The assertion of Hz-level relative linewidths relies on the time-averaged jitter metric of 4.7*10^{-7} min^{-1}, but this primarily captures slow drift and does not by itself establish the instantaneous linewidth without accompanying RF beat-note spectrum, short-term Allan deviation, or frequency noise PSD details to confirm the translation between quantities.
  2. [Spectroscopic demonstration] Spectroscopic demonstration: The claim that the system resolves ~49,000 comb lines and retrieves molecular line shapes in free-running operation requires explicit confirmation that no phase correction, filtering, or post-processing was applied to the dual-comb signal, as residual fast noise sources could still affect the effective coherence.
minor comments (2)
  1. Clarify the exact definition of 'time-averaged absolute jitter' including the integration time and measurement bandwidth used for the reported figure.
  2. Provide additional details on the bidirectional symmetry engineering in the all-PM fiber architecture to support reproducibility of the noise suppression mechanism.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their careful review and positive assessment of the significance of our work. We address each major comment below with clarifications and note where revisions will be made.

read point-by-point responses

  1. Referee: [Abstract] Abstract: The assertion of Hz-level relative linewidths relies on the time-averaged jitter metric of 4.7*10^{-7} min^{-1}, but this primarily captures slow drift and does not by itself establish the instantaneous linewidth without accompanying RF beat-note spectrum, short-term Allan deviation, or frequency noise PSD details to confirm the translation between quantities.

    Authors: We thank the referee for highlighting this important distinction. The reported Hz-level relative linewidth is based on the exceptionally low time-averaged jitter of the repetition rate difference. We agree that providing supporting data such as the RF beat-note spectrum would better substantiate the instantaneous coherence. Accordingly, we will revise the manuscript to include these details. revision: yes

  2. Referee: [Spectroscopic demonstration] Spectroscopic demonstration: The claim that the system resolves ~49,000 comb lines and retrieves molecular line shapes in free-running operation requires explicit confirmation that no phase correction, filtering, or post-processing was applied to the dual-comb signal, as residual fast noise sources could still affect the effective coherence.

    Authors: As stated in the abstract, the spectroscopic demonstration was performed without active feedback or phase correction. To make this explicit for the results section, we will add a sentence confirming that the ~49,000 comb lines were resolved directly from the raw dual-comb interferogram with no post-processing corrections applied. revision: yes

Circularity Check

0 steps flagged

No circularity: experimental measurements only

full rationale

The paper is an experimental report on a bidirectional single-cavity dual-comb laser, presenting direct measurements of relative linewidths, repetition-rate jitter (4.7*10^-7 min^-1), spectra, and spectroscopic performance. No derivations, predictions, or first-principles results are claimed that reduce by the paper's own equations or self-citations to fitted inputs. The abstract and available text contain no load-bearing steps matching any enumerated circularity pattern; all reported quantities are measured observables independent of internal fitting or renaming.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

The paper is an experimental demonstration relying on standard laser physics and fiber optics principles; no new free parameters, axioms, or invented entities are introduced in the abstract.

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discussion (0)

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Reference graph

Works this paper leans on

46 extracted references

  1. [1]

    Z. Wang, H. Ma, J. Luo, M. Yan, K. Huang, J. Fang, J. Ge, H. Zeng, Nat. Commun. 2025, 16, 6839

    2025

  2. [2]

    Millot, S

    G. Millot, S. Pitois, M. Yan, T. Hovhannisyan, A. Bendahmane, T. W. Hä nsch, N. Picqué, Nat. Photonics 2016, 10, 27–30

    2016

  3. [3]

    M. Yan, P. L. Luo, K. Iwakuni, G. Millot, T. W. Hä nsch, N. Picqué, Light Sci. Appl. 2017, 6, e17076

    2017

  4. [4]

    X. Ren, J. Pan, M. Yan, J. Sheng, C. Yang, Q. Zhang, H. Ma, Z. Wen, K. Huang, H. Wu, H . Zeng, Nat. Commun. 2023, 14, 5037

    2023

  5. [5]

    Z. Wan, Y . Chen, X. Zhang, M. Yan, H. Zeng, Light Sci. Appl. 2025, 14, 257

    2025

  6. [6]

    X. Ren, M. Yan, Z. Wen, H. Ma, R. Li, K. Huang, H. Zeng, Photoacoustics 2022, 28, 100403

    2022

  7. [7]

    Z. Chen, M. Yan, T. W. Hä nsch, N. Picqué , Nat. Commun. 2018, 9, 3035

    2018

  8. [8]

    H. Yu, Q. Zhou, X. Li, X. Wang, K. Ni, Opt. Express 2021, 29, 6271–6281

    2021

  9. [9]

    H. Tian, L. A. Sterczewski, Opt. Express 2025, 33, 5075–5087

    2025

  10. [10]

    Fritsch, T

    K. Fritsch, T. Hofer, J. Brons, M. Iandulskii, K. F. Mak, Z. Chen, N. Picqu é, O. Pronin, Nat. Commun. 2022, 13, 2584

    2022

  11. [11]

    C. P. Bauer, Z. A. Bejm, M. K. Bollier, J. Pupeikis, B. Willenberg, U. Keller, C. R. Phillips, Nat. Commun. 2024, 15, 7211

    2024

  12. [12]

    Zhang, F

    C. Zhang, F. Qu, P. Ou, H. Sun, S. He, B. Fu, Photonics 2023, 10, 221

    2023

  13. [13]

    Pupeikis, B

    J. Pupeikis, B. Willenberg, S. L. Camenzind, A. Benayad, P. Camy, C. R. Phillips, U. Keller, Optica 2022, 9, 713–716

    2022

  14. [14]

    L. Ling, W. Lin, Z. Liang, M. Pan, C. Wei, X. Chen, Y . Yang, Z. Xiong, Y . Guo, X. Wei, Z. Yang, Light Sci. Appl. 2025, 14, 133

    2025

  15. [15]

    Zhang, Y

    X. Zhang, Y . Yan, R. Zhao, H. Ren, J. Yan, X. Han, J. Che n, Appl. Phys. Lett. 2025, 127, 111101

    2025

  16. [16]

    X. Zhao, T. Li, Y . Liu, Q. Li, Z. Zheng, Photon. Res. 2018, 6, 853–857

    2018

  17. [17]

    X. Gu, G. Wang, Y . Li, H. Gong, Y . Liang, T. Wu, J. Wang, Y . Liu, Opt. Express 2023, 31, 56– 64

    2023

  18. [18]

    Prakash, S.-W

    N. Prakash, S.-W. Huang, B. Li, Optica 2022, 9, 717–723

    2022

  19. [19]

    Galtier, C

    S. Galtier, C. Pivard, J. Morville, P. Rairoux, Opt. Express 2022, 30, 21148–21158

    2022

  20. [20]

    Ł. A. Sterczewski, A. Przewłoka, W. Kaszub, J. Sotor, APL Photonics 2019, 4, 116102

    2019

  21. [21]

    J. Chen, K. Nitta, X. Zhao, T. Mizuno, T. Minamikawa, F. Hindle, Z. Zheng, T. Yasui, Adv. Photonics 2020, 2, 036004

    2020

  22. [22]

    Y . Xia, M. Li, Z. Liu, D. Liu, S. Bai, M. He, X. Shen, K. Yang, S. Yuan, M. Yan, K. Huang, H. Zeng, Opt. Laser Technol. 2023, 162, 109314

    2023

  23. [23]

    T. Lim, S. Xu, L. Hooper, M. Davey, M. Y . Sander, Photonics 2025, 12, 361

    2025

  24. [24]

    V . J. Matsas, D. J. Richardson, T. P. Newson, D. N. Payne, Opt. Lett. 1993, 18, 358–360

    1993

  25. [25]

    G. P. Agrawal, Nonlinear Fiber Optics, 6th ed., Academic Press, Cambridge, MA, USA, 2019

    2019

  26. [26]

    Zhang, Y

    W. Zhang, Y . Liu, C. Wang, Z. Zhu, D. Luo, C. Gu, W. Li, Opt. Express 2018, 26, 7934–7941

    2018

  27. [27]

    L. Zhou, Y . Liu, G. Xie, W. Zhang, Z. Zhu, C. Ouyang, C. Gu, W. Li, Appl. Phys. Express 2019, 12, 052017

    2019

  28. [28]

    Nakajima, Y

    Y . Nakajima, Y . Hata, K. Minoshima, Opt. Express 2019, 27, 5931–5944

    2019

  29. [29]

    P. Li, A. Wang, J. Du, B. Yao, Y . Rao, B. Li, APL Photonics 2025, 10, 030802

    2025

  30. [30]

    Saito, M

    S. Saito, M. Yamanaka, Y . Sakakibara, E. Omoda, H. Kataura, N. Nishizawa, Opt. Express 2019, 27, 17868–17875

    2019

  31. [31]

    B. Li, J. Xing, D. Kwon, Y . Xie, N. Prakash, J. Kim, S.-W. Huang, Optica 2020, 7, 961–964

    2020

  32. [32]

    Y . Liu, Q. Liu, Q. Wang, L. Xiong, Z. Wang, Y . Liu, P. Wang, Opt. Laser Technol. 2024, 177, 111178

    2024

  33. [33]

    Zhang, T

    C. Zhang, T. Wu, S. He, C. Zhang, B. Fu, Opt. Laser Technol. 2024, 168, 109865

    2024

  34. [34]

    J. Tao, Y . Shi, C. Zhang, G. Zhou, Y . Song, M. Hu, J. Lightwave Technol. 2025, 43, 3915 – 3921

    2025

  35. [35]

    Z. Ding, G. Wang, F. Xu, Laser Photonics Rev. 2026, e71133

    2026

  36. [36]

    I. E. Gordon, L. S. Rothman, R. J. Hargreaves , et al., J. Quant. Spectrosc. Radiat. Transfer 2026, 353, 109807

    2026

  37. [37]

    D. A. Long, M. J. Cich, C. Mathurin, A. T. Heiniger, G. C. Mathews, A. Frymire, G. B. Rieker, Nat. Photonics 2024, 18, 127–131

    2024

  38. [38]

    C. Lv, F. Meng, Q. Yan, T. Zhang, Y . Tian, Z. Jia, W. Dong, W. Qin, G. Qin, Opt. Express 2024, 32, 1851–1863

    2024

  39. [39]

    S. Xu, D. Luo, Z. Deng, K. Wei, X. Qin, Z. Wang, Z. Zhu, L. Zhou, C. Gu, W. Li, Opt. Laser Technol. 2026, 193, 114263

    2026

  40. [40]

    D. Yun, R. K. Cole, N. A. Malarich, S. C. Coburn, N. Hoghooghi, J. Liu, J. J. France, M. A. Hagenmaier, K. M. Rice, J. M. Donbar, G. B. Rieker, Optica 2022, 9, 1050–1059

    2022

  41. [41]

    M. Li, Y . Xia, Y . Chen, S. Tao, M. He, K. Huang, H. Li, M. Yan, H. Zeng, Adv. Photonics 2026, 8, 026015

    2026

  42. [42]

    Y . Chen, Z. Wan, Y . Xia, M. Li, K. Huang, M. Yan, H. Zeng, Adv. Photonics Nexus 2026, 5, 026013

    2026

  43. [43]

    A. S. Makowiecki, D. I. Herman, N. Hoghooghi, E. F. Strong, R. K. Cole, G. Ycas, F. R. Giorgetta, C. B. Lapointe, J. F. Glusman, J. W. Daily, P. E. Hamlington, N. R. Newbury, I. R. Coddington, G. B. Rieker, Proc. Combust. Inst. 2021, 38, 1627–1635

    2021

  44. [44]

    R. Li, X. Ren, B. Han, M. Yan, K. Huang, Y . Liang, J. Ge, H. Zeng, Opt. Lett. 2022, 47, 5309– 5312

    2022

  45. [45]

    M.-G. Suh, K. J. Vahala, Science 2018, 359, 884–887

    2018

  46. [46]

    Vicentini, Z

    E. Vicentini, Z. Wang, K. Van Gasse, T. W. Hä nsch, N. Picqué , Nat. Photonics 2021, 15, 890– 894

    2021