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Phase-locking of a 2.7-THz quantum cascade laser to a mode-locked erbium-doped fibre laser


Mode-locked femtosecond lasers have revolutionized the field of optical metrology by allowing the realization of ultra-stable phase-coherent links between the optical-frequency domain and the radiofrequency range1,2,3,4. In this work we have used the electro-optic effect in ZnTe (ref. 5) to demonstrate that the frequency and the phase of a 2.7 THz quantum cascade laser6 can be actively stabilized to the nth harmonic of the 90 MHz repetition rate (frep) of a commercial, mode-locked erbium-doped fibre laser7. The beating between the stabilized quantum cascade laser frequency and the harmonic of frep yield a signal-to-noise ratio of 80 dB in a bandwidth of 1 Hz. The technique is inherently broadband, that is, it is applicable to any quantum cascade laser source provided that its frequency falls within the spectral bandwidth of the femtosecond laser (5 THz)8,9. Furthermore, it is an ideal tool with which to control the phase of different quantum cascade lasers using light and compact fibre technology rather than superconducting bolometer mixers10,11.

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Figure 1: Schematic of the electro-optic detection set-up.
Figure 2: Principle of the detection technique.
Figure 3: QCL electrical and optical characteristics.
Figure 4: Experimental set-up.
Figure 5: RF spectra.


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The authors thank M. Amato for technical assistance and acknowledge partial financial support from the Délégation Générale pour l'Armement (contract no. 06.34.020) and the initiative C-Nano Ile-de-France (contract TeraCascade). Device fabrication was carried out at the CTU-IEF-Minerve, which was partially funded by the Conseil Général de l'Essonne.

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Authors and Affiliations



S.B. conceived and performed the experiment, analysed the data and wrote the paper. P.G. performed the experiment and fabricated the QCL. G.S. conceived and performed the experiment, analysed the data and contributed to the manuscript preparation. L.D. and W.M. contributed to the experimental set-up. C.S. gave conceptual advice, and contributed to data analysis and to the manuscript preparation. R.C. contributed to fabrication of the QCL and to manuscript preparation. H.E.B. and D.A.R. carried out growth of the QCL.

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Correspondence to Stefano Barbieri.

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Barbieri, S., Gellie, P., Santarelli, G. et al. Phase-locking of a 2.7-THz quantum cascade laser to a mode-locked erbium-doped fibre laser. Nature Photon 4, 636–640 (2010).

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