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A quantum walk comb source at telecommunication wavelengths

Nature Photonics (2026)Cite this article

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Abstract

Optical frequency combs consist of evenly spaced single frequencies that are phase-locked to one another and are highly effective in applications such as optical spectroscopy, remote sensing and telecommunications. Integrated optical frequency combs hold great promise for a broader range of consumer technologies but face challenges in terms of stability, efficiency and controllability. Here we demonstrate a quantum walk comb in synthetic frequency space formed by externally modulating a semiconductor optical amplifier operating in the telecommunication wavelength range in a unidirectional ring cavity. Although interband active regions were generally considered to exhibit slow-gain dynamics, we show that the ultra-fast intraband component of the gain saturation is responsible for the stabilization of the comb in a broad frequency-modulated state. Compared with quantum walk combs previously demonstrated using a quantum cascade laser, our device benefits from the low thresholds associated with interband emission and demonstrates a wallplug efficiency of up to 6%. Our device produces a nearly flat broadband comb with a tunable repetition frequency reaching a bandwidth of 1.8 THz at the fundamental repetition rate of 1 GHz while remaining fully locked to the radio frequency drive. Comb operation at harmonics of the repetition rate up to 14.1 GHz is also demonstrated.

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Fig. 1: Quantum walk comb laser model.
Fig. 2: External cavity quantum walk comb laser and characteristics.
Fig. 3: Complex optical spectra measured at RF power is 5 dBm and 18 dBm atop a 300 mA d.c. current.
Fig. 4: Controllability of the comb laser.
Fig. 5: Experimental setup for coherent data transmission using an optical frequency comb operated at 13 × Ω (~14 GHz), with the output spectrum shown in the inset.

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Data availability

The datasets generated and/or analysed during the current study are available from the corresponding authors upon reasonable request.

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Acknowledgements

We thank P. Täschler and B. Schneider from the Quantum Optoelectronics Group at ETH Zurich for valuable discussions and for providing initial code related to time-resolved measurements. This work was supported by the following: MIRAQLS: Staatssekretariat für Bildung, Forschung und Innovation SBFI (grant no. 22.00182) in collaboration with EU (grant agreement no. 101070700); ETH Fellowship programme (grant no. 22-1 FEL-46 to A.D.).

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Authors and Affiliations

  1. Institute of Quantum Electronics and Quantum Center, ETH Zürich, Zurich, Switzerland

    Bahareh Marzban, Lucius Miller, Alexander Dikopoltsev, Mathieu Bertrand, Giacomo Scalari & Jérôme Faist

  2. Institute of Electromagnetic Fields, ETH Zürich, Zurich, Switzerland

    Tobias Blatter, Laurenz Kulmer & Juerg Leuthold

Authors
  1. Bahareh Marzban
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  2. Lucius Miller
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  3. Alexander Dikopoltsev
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Contributions

B.M. built the setup, with assistance from M.B. B.M. and A.D. performed the modelling and simulations. B.M. and L.M. performed the characterizations. L.M. performed and analysed the time-resolved measurements with assistance from B.M. The data communication measurements were conducted in the group of J.L., where his expertise was of significant benefit. T.B., L.K. and B.M. carried out the data transmission measurements. B.M. wrote the original paper draft. B.M., A.D. and L.M. wrote Supplementary Information. J.F. conceptualized the idea. G.S. and J.F. acquired the funding and administrated and supervised the project. All authors contributed to the interpretation of the results and the review and editing of the draft.

Corresponding authors

Correspondence to Bahareh Marzban or Jérôme Faist.

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Nature Photonics thanks Minhao Pu and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary File, Figs. 1–8 and Table 1.

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Marzban, B., Miller, L., Dikopoltsev, A. et al. A quantum walk comb source at telecommunication wavelengths. Nat. Photon. (2026). https://doi.org/10.1038/s41566-026-01851-0

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