The monitoring of certain gases is crucial for obtaining Air quality indicators promoting the environmental monitoring. The detection of greenhouse gases (GHG) is especially on the forefront of heath related issues, also dictated by ambitious climate worldwide accords. Currently used spectroscopic solutions remain coslty and bulky, limiting their widespread adoption. We present a study of a MID-IR spectroscopy system developed on a silicon photonics platform, utilizing a Bragg grating mirror cavity, between an optical Bragg source and grating mirror.
This paper presents a novel design of grating couplers in the SiPh platform, as part of the development of a gas sensing system, that measures specific gas concentration through on-chip absorption based spectroscopy in the mid-infrared. The grating is based on 400 nm SOI rib waveguide platform, targeting gaussian emission profile. We investigate both uniform and non-unifοrm grating designs. We show maximum coupling efficiency optimized by 65% at the center wavelength of 4.3 μm, and broadband response. A tolerance study investigating the Si height and etch depth variations indicate very good tolerance to fabrication imperfections across the investigated spectral range of 4.25-4.35 μm. The proposed methodology can be used to engineer grating coupler emission profiles for other applications and platforms.
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