High-sensitivity simultaneously distributed acoustic and temperature sensing by an air-ring microstructured optical fiber.

The sensing fiber plays a critical role in distributed acoustic sensing (DAS) as it functions as a transducer, converting external acoustic signals into optical signals that can be detected and measured. However, temperature variations significantly impact the accuracy and reliability of acoustic measurements, posing a notable challenge to DAS performance. Previous solutions have employed additional spectral-domain demodulation using ultra-weak fiber Bragg gratings or a Raman-based system, which considerably hinder real-time distributed demodulation and increase system complexity. Here, we have proposed an air-ring microstructured optical fiber (AR-MOF) to replace standard single-mode fiber in DAS system, by leveraging the air-hole microstructure to enhance elastic-optic, strain-optic, thermo-optic, and thermal expansion properties. Simultaneously distributed acoustic and temperature sensing has been achieved with an acoustic sensitivity of -126.38 dB re rad/μPa at 3 kHz and a temperature sensitivity of 263.02 rad/°C within 32.0°C-42.0°C. The results highlight its potential for advanced applications, such as early-stage acoustic and thermal anomalies in oil and gas pipelines leakage.