Distributed Brillouin optical fiber sensing for dynamic strain with frequency-agility based on dual-modulation

A dynamic distributed Brillouin optical fiber sensor based on dual-modulation is proposed, in which the scanning of the Brillouin gain spectrum (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 (∼10.8 GHz for silica fibers), while the tuning range of the frequency-agility modulation is required to cover only several-hundred MHz for the scanning of the BGS, which can significantly reduce the bandwidth requirement for the arbitrary waveform generator and ultimately reduce the cost of dynamic Brillouin sensors. With a 30-m fiber, an 11.8-Hz strain is measured with a spatial resolution of 1 m and a sampling rate of 200 Hz.