Mid-infrared ChG-on-MgF2 waveguide gas sensor based on wavelength modulation spectroscopy

At the end of 2021 researchers from the College of Electronic Science and Engineering, Jilin University, China, Changchun Institute of Optics Fine Mechanics and Physics, Chinese Academy of Sciences, and Rice University, Texas, USA published in Optics Letters an article where they describe a system for carbon dioxide (CO2) detection in which one of the main roles is played by the VIGO Photonics detection module.

In the presented waveguide gas sensor scientists used wavelength modulation spectroscopy (WMS) and they obtained >8 times lower the limit of detection than the same sensor using direct absorption spectroscopy (DAS). As a light source, they used an interband cascade laser (ICL) working in the wavelength range 4317.28 - 4321.40 nm to cover the CO2 absorption line. ICL mainly emitted polarized light in the vertical direction so the quasi-TM mode of the waveguide was sufficient. The used sensing waveguide length was 1 cm, and the width of the coupling waveguide was 16 µm (to improve the mode confinement effect of the core layer and to reduce the absorption loss of polydimethylsiloxane). The output light from the waveguide was directly detected by a cooled, immersed Mercury Cadmium Telluride (MCT) photodiode characterized by a specific wavelength of 5 µm (PVI-4TE-5) produced by VIGO Photonics.

The combination of WMS with the waveguide gas sensor, MgF2 lower cladding layer, and MCT VIGO Photonics detector provides an interesting measurement scheme for the performance improvement of on-chip gas detection. Works such as this are of great significance to the miniaturization of the waveguide sensor chip, which is desirable nowadays.

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