Evanescent Wave Lab-on-Fiber for High Sensitivity Gas Spectroscopy with Wide Dynamic Range and Long-Term Stability

Micro/nano waveguide has been widely exploited for gas sensing due to its strong confinement of evanescent field, compact size, and fast response. However, the state-or-the-art evanescent-wave gas sensors still struggle to satisfy the requirements of high sensitivity, high selectivity, large dynamic range, and long-term stability. In this work, microfiber-based evanescent-wave mode-phase-difference photothermal spectroscopy for trace gas detection is reported. With a microfiber of 5.6 cm in length and 2.36 µm in diameter, noise-equivalent-concentration of 160 ppb methane in nitrogen is achieved with a dynamic range over 6 orders of magnitude, response time of less than 6 s, and <3% instability over 7 days. The technique utilizes commercial fiber-optic components to make cost-effective lab-on-fiber probes with real-time and remote detection capability for industrial, medical, and environmental monitoring.