Highly Sensitive Photothermal Gas Detection Enabled by a Hollow-Core Antiresonant Fiber With Fiber Bragg Gratings

Fabry-Pérot interferometry (FPI) is frequently adopted for interferometric phase signal measurements in photothermal gas sensing owing to its compact size and high signal-to-noise ratio. In this study, we proposed an FPI design that incorporated a hollow-core antiresonant fiber sandwiched between fiber Bragg gratings (FBG). In a pump-probe photothermal sensing setup, the FBG enhanced the cavity finesse and improved the phase-to-intensity conversion for the probe wave. Comparative experiments between our proposed FPI and the conventional design based on bare single-mode fibers exhibited an increase in signal amplitude by a factor of 4. Additionally, the FBG effectively eliminated the unwanted interference from the pump wave. In a methane gas detection demonstration, the noise equivalent concentration (NEC) was estimated at 0.7 ppm, corresponding to an absorbance of 1.6×10⁻⁶. The FBG FPI offers an affordable and accessible way to improve the sensitivity of PTS gas detection.