Utilization of a dispersion-shifted fiber for simultaneous measurement of distributed strain and temperature through Brillouin frequency shift

Abstract

In this letter, we propose and realize a new method that utilizes a dispersion-shifted fiber having compound compositions with different temperature coefficients in core to simultaneously measure the distributed strain and temperature based on Brillouin frequency shift. In a 3682-m sensing length of large-effective-area nonzero dispersion-shifted fiber, a temperature resolution of 5 C, a strain resolution of 60 , and a spatial resolution of 2 m are achieved simultaneously.Index Terms-BOTDR, Brillouin frequency shift, dispersion-shifted fiber. R ECENTLY, the fiber-distributed strain/temperature measurement based on the Brillouin scattering effect has been intensively studied. The Brillouin frequency shift is dependent on the temperature and strain conditions of the optical fiber, which provides the basis for a sensing technique capable of detecting these two parameters. The challenge, then, is to develop a technique to distinguish their individual contributions to the change in the Brillouin frequency of the optical fiber and to avoid the cross-sensitivity problem. Several techniques have been reported to accomplish the simultaneous measurement of fiber strain and temperature. In these methods, the one that uses a half of the fiber isolated from the effects of strain for temperature sensing [1], and another one that utilizes the fiber Bragg gratings combined with optical fiber [2] both require rather complicated sensing structure. Another technique that simultaneously measures the Brillouin power and frequency shift can achieve the fully distributed measurement of strain and temperature [3], but the temperature resolution is limited by the power measurement accuracy ( 0.013 dB for 1 C), which is very difficult to reach 0.05 dB over a considerable length of fiber and is very sensitive to environment.In this letter, we propose a new method that utilizes a dispersion-shifted fiber having compound compositions with different temperature coefficients in core as the sensing fiber to measure the distributed strain and temperature simultaneously. To prove this concept, the large-effective-area nonzero-dispersion-shifted fiber (LEAF), which has been reported to have multiple compositions in the fiber core [4] and now intensively deployed in Manuscript dense wavelength-division-multiplexing (DWDM) networks, is chosen as the test fiber. This technique needs only the measurement of Brillouin frequency shifts of the Brillouin spectra and can accomplish the high resolution and accuracy of temperature and strain measurement without modifying the sensing fiber.If an optical fiber has compound compositions in core, the multipeak structure in Brillouin spectrum of this optical fiber is arisen from the different acoustic velocities, which are due to different compositions or doping concentrations in the core [5]. From a previous experiment [3], the Brillouin frequency shift is dependent on strain and temperature of the standard single-mode fiber (SMF). In the case of an optical fiber with compound compositions in the core, the Brill...

Distributed discrimination of strain and temperature based on Brillouin dynamic grating in an optical fiber

“…A preliminary method is to use a specially-designed fiber with multiple Brillouin peaks that exhibit different frequency variations in temperature and strain [15][16][17]. As shown in Fig.…”

“…Although the preliminary method based on a specially-designed fiber [15][16][17] is a frequencybased measurement technique prior to the power-based one [22], it is still ill-conditioned and physically limited due to the correlated relationship among multiple peaks. …”

Comparison between standard SMF and nonzero dispersion shifted fibre LEAF for long range simultaneous temperature and strain measurements

“…It was reported that 99.7% of the temperature error and 94% of the strain error is attributed to errors arising from the intensity measurement [2]. An elegant solution recently proposed by Lee et al [3] is to use large effective area fibre (LEAF), which has multiple composition fibre core. The Brillouin spectrum of silica fibre depends on it structure and doping composition of the fibre core.…”

Optical pulse coding in hybrid distributed sensing based on Raman and Brillouin scattering employing Fabry–Perot lasers

“…A great part of distributed optical fiber sensors enables strain or temperature measurements. Those sensors allowing for simultaneous strain and temperature measurements are mostly based either on Brillouin scattering effect [2,3] or on combined Raman-Brillouin scattering effects [4], typically in conjunction with interrogating techniques based on optical time domain reflectometry (OTDR).…”