Distributed optical fibre sensors based on spontaneous Brillouin scattering employing multimode Fabry-Pérot lasers

Proposed and characterised is the use of multi-longitudinal mode Fabry-Pérot laser sources, in distributed optical fibre sensors based on spontaneous Brillouin scattering, for simultaneous strain and temperature measurements. Experimental results show that, by using such multi-longitudinal mode lasers, it is possible to measure the Brillouin spectrum, even if the overall laser spectral linewidth is larger than the Brillouin frequency shift. In this case, a suitable receiver scheme, combining optical and electrical heterodyne detection, is needed. Results report an increase in the threshold value of the input peak power before onset of nonlinear effects, allowing for a better sensing performance compared to single-longitudinal mode lasers.