Heterodyne slope-assisted Brillouin optical time-domain analysis for dynamic strain measurements

We propose a slope-assisted Brillouin sensing scheme based on the interaction between a phase modulated probe and a pulsed pump. The modulation frequency of the probe is chosen so that both first-order modulation sidebands lie within the Brillouin gain spectrum generated by the pump field. Owing to stimulated Brillouin scattering (SBS), a phase modulation to intensity modulation conversion occurs in the probe field upon interaction with the pump, producing a beat note whose amplitude grows with detuning from the SBS resonance. We show that the ratio between the amplitude of the heterodyne signal and the direct component of the probe gain provides a means for performing pump-power independent dynamic strain measurements, therefore improving the conventional slope-assisted brillouin optical time-domain analysis.