An Enhanced Distributed Acoustic Sensor With Large Temperature Tolerance Based on Ultra-Weak Fiber Bragg Grating Array

Abstract

An enhanced distributed optical fiber sensor based on broadband ultra-weak fiber Bragg grating array (UWFBG) for dynamic strain measurement with large temperature tolerance range was proposed and experimentally demonstrated. The reflectivity of UWFBG is about -50 dB, and the intensity of the reflected signal is 17 dB higher than the Rayleigh back-scattering. Using an unbalanced Michelson interferometer (MI) and 3 × 3 coupler phase demodulation technique, multiple vibration events can be detected simultaneously. We experimentally demonstrated the effectiveness of the technique by monitoring dynamic strain with a large temperature range of 20-200 °C. The minimum phase detection of the system is 1.02 × 10 - 3 rad/√Hz, and the signal-to-noise ratio (SNR) is above 59.2 dB @100 Hz at different temperatures. Meanwhile, the system has a wide frequency response from 10 Hz to 4.5 kHz.

Keywords

• Broadband ultra-weak fiber bragg grating array
• dynamic strain measurement
• phase-sensitive OTDR