Interference Fading Elimination With Single Rectangular Pulse in $\Phi$-OTDR

The interference fading, which is detrimental for signal retrieval in phase-sensitive optical time-domain reflectometry (Φ-OTDR), is analyzed in frequency domain, and a novel spectrum extraction and remix method is proposed to achieve fading-free operation for Φ-OTDR with heterodyne detection. The operation principle is theoretically analyzed, and it is well confirmed by both simulation and experimental results. This method utilizes single rectangular probe pulse and makes full use of its spectral contents. Therefore, no complicated pulse modulation is required and the signal processing executed in digital domain is simple.