Influence of the laser frequency drift in phase-sensitive optical time domain reflectometry

The influence of the laser frequency drift on the operation of phase-sensitive optical time domain reflectometry ($\varphi$-OTDR) systems is considered. Theoretical results based on a new numerical $\varphi$-OTDR model demonstrating the influence of the laser frequency instability on a signal are reported. This model is verified based on experimental data. It has been used to calculate the signal-to-noise ratio (SNR) of the system for different parameters of the laser source stability. As a result, quantitative requirements for lasers used in $\varphi$-OTDR systems are formulated.