Sensitive Fiber-Optic Fabry–Perot Photothermal Gas Sensing System With White-Light Interferometry Demodulation

A sensitive fiber-optic photothermal (PT) gas sensor with white-light interference demodulation is proposed. It is simply a Fabry-Perot interferometer structure that is formed by a fiber, an optical fiber sleeve, and a high-reflective mirror. The volume of the gas chamber is only 3.9 μL. The white-light interference demodulation module based on the phase demodulation method is used to obtain the PT signal generated by gas absorption, which has the advantages of high sensitivity and large dynamic range. When the cavity length of the PT gas sensor is 800 μm, the signal-to-noise ratio is the highest. The PT gas sensor demonstrates the minimum detection limit (MDL) of 8 ppm for methane detection, and the response time of only 2.4 s. The normalized noise equivalent absorption coefficient is calculated as 3.23 × 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−6</sup> cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup>·W/Hz<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup>.