The sensing range of Brillouin distributed fiber sensors (BDFS) is typically in the order of tens of kilometers due to the attenuation of the optical fiber and restricted input pump power. This limits the use of BDFS in certain long range applications such as oil and gas pipeline monitoring; where maintenance and safety monitoring requires sensing lengths up to hundreds of kilometers. This deterioration in the sensing performance cannot be counteracted by indefinitely increasing the pump power injected into the sensing fiber; as nonlinear effects such as modulation instability, self-phase modulation, and significant pump depletion occurs within the sensing fiber. In this paper, we demonstrate an extended sensing range system for pipeline monitoring using Brillouin optical time domain reflectometry (BOTDR) combined with Raman amplification and inline erbium-doped fiber amplifier (EDFA). Variations in pump light power, propagation direction, and injection location are explored to allow full control over the signal amplification in any particular section of the total sensing fiber length. Thus, the signal-to-noise ratio (SNR) for a certain location along the length of the fiber can be enhanced to provide more useful localized information. By using a continuous wave 1480nm Raman laser, and 980nm-pumped inline EDFA, the proposed system is theoretically validated over 150 km sensing fiber.
Nageswara Lalam, Ping Lu, Michael Buric, and Paul R. Ohodnicki, "Enhanced performance of Brillouin distributed fiber sensor with hybrid amplification," Proc. SPIE 11000, Fiber Optic Sensors and Applications XVI, 1100003 (Presented at SPIE Defense + Commercial Sensing: April 16, 2019; Published: 14 May 2019); https://doi.org/10.1117/12.2518391.
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