Directly modulating the distributed feedback laser diode(DFB-LD) by small signal current can restrain the stimulated Brillouin scattering(SBS) in coherent optical time domain reflectometer(COTDR).The optical spectrum characteristics and the relationship between the threshold value of stimulated Brillouin scattering and the spectrum width are analyzed,and the optical circuit and electrical circuit are designed to restrain stimulated Brillouin scattering.Theoretical analysis and experimental result show that ...