We present a fully integrated photonic chip spectrometer for near-infrared tunable diode laser absorption spectroscopy of methane (CH<sub>4</sub>). 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-<sup>1/2</sup> 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 2ν<sub>3</sub> R(4) CH<sub>4</sub> transition at 6057.1 cm<sup>-1</sup> (1651 nm) to avoid cross-talk with common interfering atmospheric constituents. Sensitivity analysis indicates a normalized precision of 2.0 ppmv·Hz-<sup>1/2</sup>, corresponding to a noise-equivalent absorbance (NEA) of 4.4×10<sup>-6</sup> Hz<sup>-1/2</sup> and minimum detectible absorption (MDA) coefficient of αmin = 8.8×10<sup>-7</sup> cm<sup>-1</sup>·Hz<sup>-1/2</sup>. 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 CH<sub>4</sub> 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.
Silicon photonics is rapidly becoming the key enabler for meeting the future data speed and volume required by the Internet of Things. A stable manufacturing process is needed to deliver cost and yield expectations to the technology marketplace. We present the key challenges and technical results from both 200mm and 300mm facilities for a silicon photonics fabrication process which includes monolithic integration with CMOS. This includes waveguide patterning, optical proximity correction for photonic devices, silicon thickness uniformity and thick material patterning for passive fiber to waveguide alignment. The device and process metrics show that the transfer of the silicon photonics process from 200mm to 300mm will provide a stable high volume manufacturing platform for silicon photonics designs.
Tight confinement of light in photonic cavities helps realize high optical intensity with strong field gradients. We designed a nanoscale resonator device based on a one-dimensional photonic crystal slot cavity. Our design allows for highly localized optical modes with theoretically predicted quality factors (Q factors) in excess of 10 6 . The design was implemented experimentally both in a high-contrast refractive index system (silicon), as well as in medium refractive-index-contrast devices made from aluminum nitride. We achieved an extinction ratio of 21 dB in critically coupled resonators using an on-chip readout platform with loaded Q as high as 33,000. Our approach holds promise for ultrasmall optomechanical resonators for high-frequency operation and sensing applications.