From Event: SPIE Defense + Commercial Sensing, 2019
We present a fully integrated photonic chip spectrometer for near-infrared tunable diode laser absorption spectroscopy of methane (CH4). The integrated photonic sensor incorporates a heterogeneously integrated III-V laser/detector chip coupled to a silicon external cavity for broadband tuning, and a long waveguide element (>20 cm) for ambient methane sensing. An on-chip sealed CH4 reference cell is utilized for in-situ wavelength calibration of the external cavity, and a real-time wavelength compensation method for laser calibration is described and demonstrated. The resulting signal is guided back to the III-V photodiodes for spectral signal readout using a custom-designed acquisition board, remotely controlled and operated by a Raspberry Pi unit. Component-level testing of the waveguide sensitivity, external cavity laser, and reference cell is demonstrated. Full-stack testing of the integrated sensor chip yields sub-100 ppmv∙Hz-1/2 sensitivity, and spectral density analysis demonstrates our integrated chip sensor to have a fundamental performance within an order of magnitude of commercially available fiber-pigtailed DFB laser units. We envision our integrated photonic chip sensors to provide disruptive capability in SWaP-C (size, weight, power, and cost) limited applications, and we describe an achievable short-term pathway towards sensitivity enhancement to near-10 ppmv levels.
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Eric J. Zhang, Yves Martin, Jason S. Orcutt, Chi Xiong, Martin Glodde, Nathan Marchack, Elizabeth A. Duch, Tymon Barwicz, Laurent Schares, and William M. J. Green, "Monolithically integrated silicon photonic chip sensor for near-infrared trace-gas spectroscopy," Proc. SPIE 11010, Chemical, Biological, Radiological, Nuclear, and Explosives (CBRNE) Sensing XX, 110100B (Presented at SPIE Defense + Commercial Sensing: April 15, 2019; Published: 17 May 2019); https://doi.org/10.1117/12.2519206.