Extraordinary evanescent field confinement waveguide sensor for mid-infrared trace gas spectroscopy

Vlk, Marek, Datta, Anurup, Alberti, Sebastián, Yallew, Henock Demessie, Mittal, Vinita, Murugan, Ganapathy Senthil and Jagerska, Jana (2021) Extraordinary evanescent field confinement waveguide sensor for mid-infrared trace gas spectroscopy. Light: Science & Applications, 10 (1), [26]. (doi:10.1038/s41377-021-00470-4).

Abstract

Nanophotonic waveguides are at the core of a great variety of optical sensors. These structures confine light along defined paths on photonic chips and provide light–matter interaction via an evanescent field. However, waveguides still lag behind free-space optics for sensitivity-critical applications such as trace gas detection. Short optical pathlengths, low interaction strengths, and spurious etalon fringes in spectral transmission are among the main reasons why on-chip gas sensing is still in its infancy. In this work, we report on a mid-infrared integrated waveguide sensor that successfully addresses these drawbacks. This sensor operates with a 107% evanescent field confinement factor in air, which not only matches but also outperforms free-space beams in terms of the per-length optical interaction. Furthermore, negligible facet reflections result in a flat spectral background and record-low absorbance noise that can finally compete with free-space spectroscopy. The sensor performance was validated at 2.566 μm, which showed a 7 ppm detection limit for acetylene with only a 2 cm long waveguide.

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Contributors

Author: Vinita Mittal

Author: Ganapathy Senthil Murugan

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