Abstract
The resolution of strain measurements using Brillouin scattering in an optical fiber depends on the pulse width of a pump laser pulse. It was considered that there was a lower limit for pulse width, since the line width of the Brillouin spectrum was broader for shorter pulses. This lower limit is about 10 ns and corresponds to a spatial resolution of 1 m. However, on the contrary, Bao et al. recently discovered a phenomenon in which the line width of the spectrum decreased for a very short pulse with a width of 1 ns when there was light leakage. In this paper, we analyze this phenomenon by solving coupled wave equations using a perturbation method, and clarify the cause of the phenomenon. We then propose an improved Brillouin measurement method using a two-step pulse inspired by the phenomenon and show that its spatial resolution is about 10 cm, which is one digit smaller than the present lower limit.
