Narrowing Brillouin gain spectrum for BOTDA sensor

A novel BOTDA method based on differential pi-phase-shift-pulse pair is proposed for narrowing the Brillouin gain spectrum. Theoretical analysis and experimental results demonstrate that the proposal could achieve 17 MHz Brillouin gain spectrum linewidth with a fixed spatial resolution of 2.5 m. The Brillouin gain spectrum linewidth is 3 times narrower than that obtained using conventional single-pulse based BOTDA method with same spatial resolution, resulting in,5 times frequency accuracy improvement. Furthermore, the sharper rising/falling edge of the Brillouin frequency shift profile resulting from the narrowed Brillouin gain spectrum could obtain more precise temperature/strain information along the fiber.