Miniaturizing infrared laser gas sensors: from waveguides to MEMS transducers

Miniaturized, high-performance trace gas sensors are critical for environmental, industrial, and medical applications. This paper provides a comprehensive overview of recent achievements in miniaturizing infrared laser spectroscopy gas sensors employing the silicon-based platform and critically compares two converging paths: on-chip waveguide sensing and MEMS-enhanced sensing. We consider device physics, fabrication approaches, and performance metrics to enable comparison across systems. The detection limits of on-chip waveguides, based on evanescent field absorption or refractive index change, have advanced from roughly 102 parts per million (ppm) in early demonstrations to below 1 ppm in sub-cm2 layouts. In comparison, MEMS-enhanced micro-transducers achieve parts per billion (ppb) to parts per trillion (ppt) in millimetre-scale cells. Based on this, we propose future goals that emphasize stability-focused materials, nanoscale lasers, and system-level integration to balance sensitivity, robustness, and manufacturability in next-generation miniaturized gas sensors.