High Sensitive BOTDR Demodulation Method by Using Slow-Light in Fiber Grating

To improve the sensitivity of Brillouin optical time domain reflecting (BOTDR) based on the Mach-Zehnder interferometer (MZI), a novel method was proposed by using fiber grating (FG). The FG was introduced not only as a filter to reduce the noise caused by Fresnel reflection and Rayleigh scattering, but also as the slow-light medium to improve the sensitivity of MZI used in BOTDR. Both uniform and nonuniform FGs were modeled, and then their transmission and group index spectra were calculated. By calculating the sensitivities of BOTDR demodulation, it was found that the power of noise light could be greatly reduced when nonuniform FG was utilized. Meanwhile, the phase and relative output power sensitivities of BOTDR demodulation could be improved to almost 20 times as large as the ones based on double-pass MZI. Besides, the sensitivity of BOTDR distributed sensor could also be improved.