Effect of laser linewidth on characteristics of -OTDR system

In order to optimize the phase sensitive optical time-domain reflectometer (-OTDR) system, a multi-intrusion detection system was built based on -OTDR principle. The effect of laser linewidth on system performance was studied theoretically and experimentally. 7km sensing optical fiber was used in system experiment. The theoretical analysis shows that with the increase of the laser linewidth, the ripples of backward coherent Rayleigh scattering detected by the system become gradually smooth, and the signal-to-noise ratio and location accuracy of system also decrease, so that the system can't locate and identify interference information. The experimental results show that when laser linewidth changes from 5kHz to 200kHz,the ripple of backward coherent Rayleigh scattering detected by the system also becomes gradually smooth, the signal to noise ratio of system decrease from 12dB to 3dB. The results of experiment is in agreement with the results of theoretical very well.