Fiber-Tip Fabry-Perot Interferometric Photothermal Flexible Gas Sensor with Capillary Microcavity.

Area of Science:

• Optical sensing
• Gas detection technologies
• Microfabrication

Background:

• Fiber-optic sensors offer high sensitivity and miniaturization for trace gas detection.
• Existing methods using long optical paths or functional coatings hinder applications in confined spaces and fast response scenarios.

Purpose of the Study:

• To develop a fiber-tip Fabry-Perot (F-P) interferometric photothermal (PT) flexible gas sensor for rapid gas detection.
• To overcome limitations of existing fiber-optic gas sensors in confined spaces and for fast response applications.

Main Methods:

• Fabrication of a fiber-tip F-P cavity using a capillary microcavity (130 μm inner diameter) with a gold reflective film.
• Optimization of the capillary microcavity structure (cavity length 392-935 μm) through simulation and experimentation.
• Implementation of a truncated spectral white-light interference demodulation method for excitation light interference suppression and high-speed PT phase demodulation.

Main Results:

• The proposed sensor utilizes a micro-gas chamber with a volume of only 10 nL.
• The photothermal (PT) signal intensity correlates positively with the cavity length within the optimized range.
• Achieved a minimum detection limit of 0.8 ppm for acetylene (C₂H₂).
• Demonstrated an exceptionally fast response time of 1 second.

Conclusions:

• The fiber-tip F-P interferometric photothermal flexible gas sensor based on a capillary microcavity is effective for fast trace gas detection.
• The sensor design overcomes limitations of conventional methods, enabling applications in confined spaces.
• The optimized microcavity and demodulation technique provide high sensitivity and rapid response for gas sensing.