Dynamic Distributed Brillouin Optical Fiber Sensing Based on Dual-Modulation by Combining Single Frequency Modulation and Frequency-Agility Modulation

Dynamic Brillouin optical fiber sensors based on fast scanning of Brillouin gain spectrum (BGS) are one of the most promising techniques to measure dynamic strains, where an ~11-GHz bandwidth arbitrary waveform generator (AWG) or a vector microwave generator is essential for frequency agility. A dynamic Brillouin optical fiber sensor based on dual-modulation is proposed here, which aims to realize dynamic sensing via a low-bandwidth AWG. In this protocol, the scanning of BGS is implemented by the combination of a single-frequency modulation and a frequency-agility modulation. The frequency of the single-frequency modulation is slightly lower than the Brillouin frequency shift of the fiber under test so that the tuning range of the frequency-agility modulation is required to cover only several-hundred MHz for the scanning of the BGS, which significantly reduces the bandwidth requirement for the AWG. In experiment, an 11.8-Hz strain is measured with a 30-m fiber, where the spatial resolution and the sampling rate are 1 m and 200 Hz, respectively. Furthermore, by tracking the damping vibration of the optical fiber, its resonant frequency is measured with a sampling rate of 100 Hz.