paper

Mid-infrared frequency comb generation with silicon nitride nano-photonic waveguides

arXiv:1704.02478 · doi:10.1038/s41566-018-0144-1

Abstract

Mid-infrared optical frequency combs are of significant interest for molecular spectroscopy due to the large absorption of molecular vibrational modes on one hand, and the ability to implement superior comb-based spectroscopic modalities with increased speed, sensitivity and precision on the other hand. Substantial advances in mid-infrared frequency comb generation have been made in recent years based on nonlinear frequency conversion, microresonator Kerr frequency combs, quantum cascade lasers and mode locking regimes. Here we demonstrate a simple, yet effective method for the direct generation of mid-infrared optical frequency combs in the region from , i.e. covering a large fraction of the functional group region, directly from a conventional and compact erbium-fiber-based femtosecond laser in the telecommunication band (i.e. ). The wavelength conversion is based on dispersive wave generation within the supercontinuum process in large-cross-section and dispersion-engineered silicon nitride () waveguides. The long-wavelength dispersive wave, with its position lithographically determined, performs as a mid-infrared frequency comb, whose coherence is demonstrated via optical heterodyne measurements. Such a simple and versatile approach to mid-infrared frequency comb generation is suitable for spectroscopic applications in the first mid-infrared atmospheric window. Moreover, the compactness and simplicity of the approach have the potential to realize compact dual-comb spectrometers. The generated combs have a fine teeth-spacing, making them also suitable for gas phase analysis.

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