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.
We present a chip-scale spectroscopic methane sensor, incorporating a tunable laser, sensor waveguides, and methane reference cell, assembled as a compact silicon photonic integrated circuit. The sensor incorporates an InP-based semiconductor optical amplifier/photodetector array, flip-chip soldered onto a silicon photonic substrate using highprecision waveguide-to-waveguide interfaces. The InP chip provides gain for a hybrid external cavity laser operating at 1650 nm. The sensor features a 20-cm-long TM-mode evanescent-field waveguide as the sensing element and is compatible with high-volume wafer-scale silicon photonics manufacturing and assembly processes. This sensor can be an enabling platform for economical methane and more general distributed environmental trace-gas monitoring.
We present a portable optical spectrometer for fugitive emissions monitoring of methane (CH4). The sensor operation is based on tunable diode laser absorption spectroscopy (TDLAS), using a 5 cm open path design, and targets the 2ν3 R(4) CH4 transition at 6057.1 cm-1 (1651 nm) to avoid cross-talk with common interfering atmospheric constituents. Sensitivity analysis indicates a normalized precision of 2.0 ppmv·Hz-1/2, corresponding to a noise-equivalent absorbance (NEA) of 4.4×10-6 Hz-1/2 and minimum detectible absorption (MDA) coefficient of αmin = 8.8×10-7 cm-1·Hz-1/2. Our TDLAS sensor is deployed at the Methane Emissions Technology Evaluation Center (METEC) at Colorado State University (CSU) for initial demonstration of single-sensor based source localization and quantification of CH4 fugitive emissions. The TDLAS sensor is concurrently deployed with a customized chemi-resistive metal-oxide (MOX) sensor for accuracy benchmarking, demonstrating good visual correlation of the concentration time-series. Initial angle-ofarrival (AOA) results will be shown, and development towards source magnitude estimation will be described.