Vector Brillouin optical time-domain analysis with Raman amplification and optical pulse coding

This paper proposes a new vector Brillouin optical time-domain analysis optical fiber sensor with large dynamic range and high signal-to-noise ratio that combines distributed Raman amplification with optical pulse coding. The optimized Raman pumping configurations are numerically simulated by solving the coupled differential equations of the hybrid Brillouin-Raman process, and experimentally investigated with respect to the Brillouin pump pulse. A vector network analyzer is adopted to extract both the amplitude and phase spectrograms of the Brillouin interaction in a distributed fashion which effectively lessens the impact of the Raman relative intensity noise transfer problem and achieve high accuracy measurement over a long sensing distance. Advanced pulse coding is further introduced to increase the sensing range under high spatial resolution. Initial experimental results of phase and amplitude from a custom built BOTDA system is presented. Compared to typically tens of kilometers measurement distance of conventional Brillouin optical time-domain analysis techniques, the proposed optical fiber Brillouin sensor has the potential to greatly enhances sensing range up to one hundred kilometers or greater, providing distributed temperature and strain monitoring of high spatial resolution and high sensing resolution in structures such as oil and natural gas pipelines.