ABSTRACT
We present a hybrid Brillouin/Rayleigh sensor for multiparameter sensing in optical fibers. The system makes use of a single laser pulse to excite both Rayleigh and Brillouin backscattering in the same optical fiber. In the detection path, the backscattered signals are separated based on their different wavelengths. The system is capable of determining simultaneously the Brillouin frequency shift (BFS) of the fiber, as well as the frequency contents of any vibration acting on the same fiber as recovered by phase sensitive OTDR (Ï-OTDR) measurements. The reported experiments show the possibility to perform simultaneous temperature and vibration measurements, as well as to perform dynamic strain measurements combining the information provided by slope-assisted Brillouin scattering measurements, with those provided by amplitude-based Ï-OTDR measurements.
ABSTRACT
In this paper, we analyze the performance of a distributed acoustic sensor at two different interrogation wavelengths. We show theoretically that, in a coherent optical time-domain reflectometry (OTDR) operating at 850 nm, the dynamic signal-to-noise ratio (SNR) is enhanced, compared to an identical configuration operating at 1550 nm. Such enhancement is maximum at the interrogating pulse input section, while decreasing along the fiber in virtue of the higher loss. Experimental tests, carried out using two heterodyne C-OTDR detection schemes operating at the analyzed wavelengths, confirm the SNR improvement.
