Actively stabilized low-noise Brillouin fiber ring laser for Brillouin sensing

In this work we report the results of a theoretical and experimental study that we have carried out on a Brillouin optical time domain analysis (BOTDA) sensing scheme using a novel low-noise actively-stabilized fiber Brillouin ring laser (BRL) as probe source. The BRL laser is based on a short-cavity (SC), < 4 meters long, layout achieving double-resonance (DR) operation for both pump and probe signals; an active wavelength-locking circuit is used to stabilize the signal and tune the signal frequency over a range of ̴ 200 MHz range. The wavelength-locked SC-DR BRL shows spectral linewidth of approximately 10 kHz and RIN values of ~-145 dB/Hz across the (0-600) MHz range; pump-probe frequency shift can be efficiently tuned across the entire Brillouin gain spectrum of the sensing fiber with sub-kHz precision (200 Hz) and high temporal stability for timescale of BOTDA measurements (more than 100 ms). A preliminary BOTDA measurement using a wavelength-locked long-cavity (LC) BRL yielded a Brillouin frequency shift (BFS) uncertainty of 1,5 MHz corresponding to temperature and strain sensitivity values of 1 K and 25 με, respectively, and a spatial resolution of 5 m for 50 ns-long pump pulses.