To reduce the coherent Rayleigh noise

a Brillouin Optical Time Domain Reflectometer（BOTDR）system based on self-heterodyne detection of Rayleigh and Brillouin scattering employing multi-wavelength source is proposed.The mechanism of multi-wavelength probe light generation by phase modulation and the principle of self-heterodyne detectionfor three-wavelength system are analyzed.A self-heterodyne detection BOTDR system employing single-wavelength and three-wavelength probe lights are constructed

and the self-heterodyne detection signal power and Brillouin frequency shift along the sensing fiber are obtained.The experiment results show that the power fluctuation generated by the coherent Rayleigh noise can be reduced effectively.The increment of signal-to-noise ratio is approximately to be 4.56 dB by employing three-wavelength probe light

and the root-mean-square error of Brillouin frequency shift fluctuation is reduced by 2.2 MHz when compared with that in the single-wavelength system.