Fig. 1. Configuration of the BRFL and the operation principle of acoustic wave detection when (a) the probe light co-propagates with the acoustic wave and (b) the probe light counter-propagates with the acoustic wave.

Fig. 2. Configuration of the BRFL and the operation principle of acoustic wave detection when (a) the probe light co-propagates with the acoustic wave and (b) the probe light counter-propagates with the acoustic wave.

Fig. 3. (a) Spectrum measured on the OSA when the pump laser is turned on (red) and turned off (blue). (b) Distributed reflection spectra of the dynamic grating induced by the acoustic wave in the BRFL for the probe light photon energy downconversion process. (c) Reflectivity of the dynamic grating in the spatial domain along the Brillouin gain fiber. (d) Gaussian fitting of the reflection spectra of the dynamic grating at position of 10 m at maximum gain when the output powers of the BRFL are 10.3 mW, 7.62 mW, 5.23 mW, and 2.66 mW, respectively.

Fig. 4. (a) Spectrum of the reflected probe light measured on the OSA for the probe light photon energy upconversion process. (b) Distributed reflection spectra of the dynamic grating induced by the acoustic wave in the BRFL. (c) Reflectivity of the dynamic grating in the spatial domain along the Brillouin gain fiber. (d) Birefringence of the Brillouin gain fiber measured by the optical frequency redshifted probe light and optical frequency blueshifted probe light.

Fig. 5. (a) Spatial-time map of the acoustic wave intensity when the probe light experiences the photon energy downconversion process. The inset figure is the spectrum measurement of two beating modes when mode hopping occurs in the BRFL. (b) The spatial-time map of the acoustic wave intensity when the probe light experiences the photon energy upconversion process. (c) Schematic diagram of the acoustic wave detection process when the probe light experiences the photon energy downconversion process. (d) Schematic diagram of the acoustic wave detection process when the probe light experiences the photon energy upconversion process.

Fig. 6. Histograms of the temporal intensity statistical distribution near the lasing threshold at (a) high gain position and (b) low gain position for redshifted probe light measurement. Histograms of the temporal intensity statistical distribution above the lasing threshold at (c) high gain position and (d) low gain position for redshifted probe light measurement. Histograms of the temporal intensity statistical distribution near the lasing threshold at (e) high gain position and (f) low gain position for blueshifted probe light measurement. Histograms of the temporal intensity statistical distribution above the lasing threshold at (c) high gain position and (d) low gain position for blueshifted probe light measurement.