Mid-infrared frequency comb via coherent dispersive wave generation in silicon nitride nanophotonic waveguides


Mid-infrared optical frequency combs are of significant interest for molecular spectroscopy due to the large absorption of molecular vibrational modes on the one hand, and the ability to implement superior comb-based spectroscopic modalities with increased speed, sensitivity and precision on the other hand. Here, we demonstrate a simple, yet effective, method for the direct generation of mid-infrared optical frequency combs in the region from 2.5 to 4.0 μm (that is, 2,500–4,000 cm−1), covering a large fraction of the functional group region, from a conventional and compact erbium-fibre-based femtosecond laser in the telecommunication band (that is, 1.55 μm). The wavelength conversion is based on dispersive wave generation within the supercontinuum process in an unprecedented large-cross-section silicon nitride (Si3N4) waveguide with the dispersion lithographically engineered. The long-wavelength dispersive wave can perform as a mid-infrared frequency comb, whose coherence is demonstrated via optical heterodyne measurements. Such an approach can be considered as an alternative option to mid-infrared frequency comb generation. Moreover, it has the potential to realize compact dual-comb spectrometers. The generated combs also have a fine teeth-spacing, making them suitable for gas-phase analysis.

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Fig. 1: Principle of mid-IR frequency comb in dispersion-engineered Si3N4 waveguides.
Fig. 2: Comparison between SCG experiment and numerical simulation.
Fig. 3: Lithographical tuning of the mid-IR frequency comb.
Fig. 4: Coherence measurements of the mid-IR frequency comb.


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The authors acknowledge E. Lucas, M. Anderson, J. Jost and A. Feofanov for fruitful discussions and suggestions regarding the manuscript, and assistance with device configuration. This publication was supported by contract W31P4Q-16-1-0002 (SCOUT) from the Defense Advanced Research Projects Agency (DARPA), Defense Sciences Office (DSO). This material is based on work supported by the Air Force Office of Scientific Research, Air Force Material Command, United States Air Force (USAF) under award no. FA9550-15-1-0099. H.G. and W.W. acknowledge support by funding from the European Union's Horizon 2020 research and innovation programme under Marie Sklodowska-Curie IF grant agreement no. 709249 and no. 753749, respectively. A.B., D.G. and C.-S.B. acknowledge support from the European Research Council under grant agreement ERC-2012-StG 306630-MATISSE. All samples were fabricated and grown in the Center of MicroNanoTechnology (CMi) at Swiss Federal Institute of Technology Lausanne (EPFL).

Author information

H.G. and C.H. conceived the design of large-cross-section Si3N4 waveguides. C.H fabricated the large-cross-section waveguides, and performed supercontinuum experiments with A.B. A.B. and D.G. performed supercontinuum experiments in conventional Si3N4 waveguides, under the supervision of C.-S.B. M.H.P.P. fabricated conventional waveguides. H.G. and C.Z. designed and performed coherence experiments, under the supervision of T.J.K. H.G. and W.W. performed noise analysis. All authors discussed the data. H.G. and T.J.K. wrote the manuscript with input from others. T.J.K. supervised the project.

Correspondence to Camille-Sophie Brès or Tobias J. Kippenberg.

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This file contains information on large-size Si3N4 waveguides beyond cracking limitation, mid-infrared efficiency and spectral coverage, and intensity and phase noise measurements.

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Guo, H., Herkommer, C., Billat, A. et al. Mid-infrared frequency comb via coherent dispersive wave generation in silicon nitride nanophotonic waveguides. Nature Photon 12, 330–335 (2018). https://doi.org/10.1038/s41566-018-0144-1

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