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Temporal solitons in a coherently driven active resonator


Optical frequency combs are lightwaves composed of a large number of equidistant spectral lines. They are important for metrology, spectroscopy, communications and fundamental science. Frequency combs are most often generated by exciting dissipative solitons in lasers or in passive resonators, both of which suffer from important limitations. Here we show that the advantages of each platform can be combined. We introduce a novel kind of soliton (called an active cavity soliton) hosted in coherently driven lasers pumped below the lasing threshold. We use an active fibre resonator and measure high-peak-power solitons on a low-power background, in excellent agreement with simulations of a generalized Lugiato–Lefever equation. Moreover, we find that amplified spontaneous emission has negligible impact on the soliton’s stability. Our results open up novel avenues for frequency comb formation by showing that coherent driving and incoherent pumping can be efficiently combined to generate a high-power ultra-stable pulse train.

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Fig. 1: Experimental set-up and linear characterization.
Fig. 2: Soliton excitation under continuous-wave driving.
Fig. 3: Soliton formation under pulsed driving.
Fig. 4: Radiofrequency characterization of the soliton train.

Data availability

The data that support the findings of this study are available from the corresponding author on reasonable request.


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We are grateful to J. Fatome, P. Kockaert, B. Kuyken and K. Van Gasse for fruitful discussions. This work was supported by funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 757800). N.E. acknowledges the support of the Fonds pour la formation à la Recherche dans l’Industrie et dans l’Agriculture (FRIA). F.L. and P.P.-R. acknowledge the support of the Fonds de la Recherche Scientifique (FNRS).

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Authors and Affiliations



N.E. performed the experiments and simulations of the lumped-element model. N.E. and C.M.A. derived and simulated the mean-field model. C.M.A. and P.P.-R. performed the numerical parameter continuation of the steady-state solutions. S.-P.G. and F.L. supervised the work.

Corresponding author

Correspondence to Nicolas Englebert.

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Competing interests

N.E., S.-P.G. and F.L. filed a patent application on the active resonator design (European patent office, application number EP20188731.2). The remaining authors declare no competing interests.

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Supplementary Information

Supplementary Sections 1–5.

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Englebert, N., Mas Arabí, C., Parra-Rivas, P. et al. Temporal solitons in a coherently driven active resonator. Nat. Photon. 15, 536–541 (2021).

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