We present a fully integrated photonic chip spectrometer for near-infrared tunable diode laser absorption spectroscopy ofmethane (CH4). The integrated photonic sensor incorporates a heterogeneously integrated III-V laser/detector chipcoupled to a silicon external cavity for broadband tuning, and a long waveguide element (> 20 cm) for ambient methanesensing. An on-chip sealed CH4 reference cell is utilized for in-situ wavelength calibration of the external cavity, and areal-time wavelength compensation method for laser calibration is described and demonstrated. The resulting signal isguided back to the III-V photodiodes for spectral signal readout using a custom-designed acquisition board, remotelycontrolled and operated by a Raspberry Pi unit. Component-level testing of the waveguide sensitivity, external cavitylaser, and reference cell is demonstrated. Full-stack testing of the integrated sensor chip yields sub-100 ppmv?Hz-1/2sensitivity, and spectral density analysis demonstrates our integrated chip sensor to have a fundamental performancewithin an order of magnitude of commercially available fiber-pigtailed DFB laser units. We envision our integratedphotonic 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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