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Coherent injection locking of quantum cascade laser frequency combs


Quantum cascade laser (QCL) frequency combs are a promising candidate for chemical sensing and biomedical diagnostics1,2,3,4. They are electrically pumped and compact, making them an ideal platform for on-chip integration5. Until now, optical feedback is fatal for frequency comb generation in QCLs6. This property limits the potential for integration. Here, we demonstrate coherent electrical injection locking of the repetition frequency to a stabilized radio-frequency oscillator. We prove that the injection-locked QCL spectrum can be phase-locked, resulting in the generation of a frequency comb. We show that injection locking is not only a versatile tool for all-electrical frequency stabilization, but also mitigates the fatal effect of optical feedback. A prototype self-detected dual-comb set-up consisting only of an injection-locked dual-comb chip, a lens and a mirror demonstrates the enormous potential for on-chip dual-comb spectroscopy. These results pave the way to miniaturized and all-solid-state mid-infrared spectrometers.

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Fig. 1: Schematic of the device.
Fig. 2: SWIFTS analysis of the free-running comb.
Fig. 3: Coherent injection locking.
Fig. 4: Comb operation under strong optical feedback.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.


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This work was supported by the Austrian Science Fund (FWF) in the framework of ‘Building Solids for Function’ (Project W1243), the projects ‘NanoPlas’ (P28914-N27) and ‘NextLite’ (F4909-N23). H.D. acknowledges support by the ESF under project CZ.02.2.69/0.0/0.0/16_027/0008371. A.M.A was supported by projects COMTERA—FFG 849614 and AFOSR FA9550-17-1-0340.

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J.H. and B.S. built up the SWIFTS set-up. J.H. carried out the experiments and wrote the manuscript, with B.S. and A.M.A. providing editorial input. H.D., A.M.A. and G.S. were responsible for MBE growth. B.S. developed the algorithm for the SWIFTS data processing and supervised this work. All authors contributed to analysing the results and commented on the paper.

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Correspondence to Benedikt Schwarz.

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Hillbrand, J., Andrews, A.M., Detz, H. et al. Coherent injection locking of quantum cascade laser frequency combs. Nature Photon 13, 101–104 (2019).

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