Abstract
Sub-meter distributed optical fiber sensing based on Brillouin optical time-domain analysis with differential pulse-width pairs (DPP-BOTDA) is combined with the use of optical pre-amplification and pulse coding. In order to provide significant measurement SNR enhancement and to avoid distortions in the Brillouin gain spectrum due to acoustic-wave pre-excitation, the pulse width and duty cycle of Simplex coding based on return-to-zero pulses are optimized through simulations. In addition, the use of linear optical pre-amplification increases the receiver sensitivity and the overall dynamic range of DPP-BOTDA measurements. Experimental results demonstrate for first time a spatial resolution of ~25 cm over a 60 km standard single-mode fiber (equivalent to ~240 k discrete sensing points) with temperature resolution of 1.2°C and strain resolution of 24 με.
Highlights
Distributed optical fiber sensors for temperature and strain measurements are commonly based on Brillouin optical time-domain analysis (BOTDA), exploiting stimulated Brillouin scattering (SBS)
Note that distributed sensing with a sub-meter spatial resolution is very important for many applications, such as for structural health monitoring (SHM), where centimeter-scale detection of cracks in civil engineering structures can lead to early diagnosis of structural damage and prevention of catastrophic events
We report on the implementation of a long-range DPP-BOTDA sensor based on Simplex coding [5]
Summary
Distributed optical fiber sensors for temperature and strain measurements are commonly based on Brillouin optical time-domain analysis (BOTDA), exploiting stimulated Brillouin scattering (SBS) This technique allows for a sensing distance of several tens of km with a spatial resolution down to about 1 meter [1, 2], which is limited by the acoustic phonon. The use of 511-bit Simplex coding, combined with return-to-zero (RZ) modulation format with an optimized duty cycle and linear optical pre-amplification at the receiver, provides significant SNR enhancement and improved sensing performance, attaining a spatial resolution of 25 cm over 60 km standard single-mode fiber (SMF), with a resolution in Brillouin frequency shift (BFS) measurements of ~1.2 MHz, corresponding to ~1.2°C / ~24 με temperature/strain resolution respectively
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