Simultaneous temperature and strain measurement with combined spontaneous Raman and Brillouin scattering

Abstract

We report on a novel method for simultaneous distributed measurement of temperature and strain based on spatially resolving both spontaneous Raman and Brillouin backscattered anti-Stokes signals. The magnitude of the intensity of the anti-Stokes Raman signal permits the determination of the temperature. The Brillouin frequency shift is dependent on both the temperature and the strain of the fiber; once the temperature has been determined from the Raman signal, the strain can then be computed from the frequency measurement of the Brillouin signal.

Simultaneous distributed strain and temperature sensing based on combined Raman–Brillouin scattering using Fabry–Perot lasers

“…As an additional point, while the anti-Stokes Raman intensity is measured by a simple direct-detection scheme, efficient detection in BFS measurements requires a coherentdetection receiver [2].…”

“…Distributed sensing commonly requires simultaneous measurements of temperature and deformations along the optical fiber, currently achieved by using measurement techniques based either on optical Brillouin scattering [1] or on hybrid Raman-Brillouin scattering detection [2]. Such nonlinear effects are generally exploited in measurement systems based on the optical time domain reflectometry (OTDR) principle.…”

“…The high noise in temperature trace from spontaneous Raman scattering (SpRS) has actually been identified in the literature [2] as the main limiting factor in temperature-strain measurements when using hybrid sensing schemes.…”

“…Furthermore, the common optical sources used for SpBS measurements are characterized by rather low output power levels (a few dBm at most); actually, in order to detect small BFS variations in the narrow-band Brillouin scattering (which is few tens of MHz in silica fibers), narrowband optical sources must be used. The most commonly used sources are distributed feedback (DFB) lasers or external cavity lasers [2], which are however characterized by low output power levels (below a few tens of mW).…”

Enhanced Performance of a Temperature-Compensated Submeter Spatial Resolution Distributed Strain Sensor

“…Temperature Resolution Strain Resolution [1] 20m 4°C 100µε [3] 10m 6°C 150µε [4] 5m 3.5°C 85µε [5] 1.3m 3°C 80µε [6] 32m 8.8°C 220µε [7] 10m 4.1°C & 27°C 140µε & 570µε In BOCDA a frequency swept laser output is split into two. One of which is frequency shifted by an amount close to the expected Brillouin frequency shift, and launched into the opposite end of the sensing fibre to the other un-shifted beam.…”