Adverse effect of the Brillouin optical time-domain analysis system caused by self-phase modulation

Compared with strict rectangular pulse, the real rectangular pulse has power transients like the rising edge, failing edge and the oscillation times, which will cause self-phase modulation (SPM), leading to the BGS broadened or even be out of shape, and then result in the decline of the system measuring accuracy. Brillouin gain spectrum (BGS) can no longer maintain Lorentz line profile along the sensing fiber. In this paper, a model is established based on the nonlinear Schrodinger equation (NLSE) in regular single mode fiber (SMF) concerning the effects of pumping pulse power transients on the BGS. The noise is also taken into consideration to imitate the physical truth.