Ultra-miniature and sensitive optical fiber-tip optomechanical resonant photoacoustic spectroscopy gas sensors.

Optomechanical resonator (OMR)-based photoacoustic spectroscopy (PAS) sensors have garnered significant attention for ultra-sensitive and selective trace-gas detection. However, it remains challenging for optomechanical resonant PAS (OMR-PAS) sensors to achieve both high sensitivity and miniature size for trace-gas detection with minimal consumption in space-constrained environments. Here, we present a monolithically designed optical fiber-tip OMR-PAS sensor, in which a micrometer-scale planar-spiral-spring OMR (PSS-OMR) is 3D micro-printed on the end face of optical fiber, enabling ultrasensitive gas sensing with nanoliter-level consumption. Compared to off-resonance operation, this fiber-tip OMR-PAS sensor operating in resonance mode produces a significantly stronger photoacoustic signal, improving the signal-to-noise ratio by more than five times. The sensor can detect acetylene gas at 55 ppb without the need for an additional photoacoustic cell. Its response time can be as fast as 0.2 s. This ultra-miniature and highly sensitive fiber-tip OMR-PAS sensor may become a powerful tool for various trace-gas monitoring applications.