Inverse Filter in FDM-OTDR to Compensate for Phase Noise Induced Inter-Channel Crosstalk

We propose a scheme to compensate for inter-channel crosstalk (XT) caused by laser phase noise in frequency division multiplexing coherent optical time domain reflectometry (FDM-OTDR). To clarify the influence of laser phase noise in FDM-OTDR, we adopt a simple model assuming that the laser field spectrum including phase noise is approximated by a Lorentzian shape. With this simple model, the increase in inter-channel XT caused by spectral broadening can be described by using linear response theory. According to the linear response theory, we can compensate for the OTDR dead-zone degradation with a Wiener filter. We compare theoretical calculations of the OTDR trace with experimental results.