Frequency division multiplexing OTDR with fast signal processing

A frequency division multiplexing optical time domain reflectometry (FDM-OTDR) is proposed and experimentally demonstrated. A phase modulator is employed to convert single frequency laser to multiple frequencies where four frequencies are adopted as the probe. Coherent detection between the backscattered Rayleigh signals of the four-frequency probe light pulses propagating in fiber under test (FUT) and original single frequency local oscillator (LO) only generates two intermediate frequencies (IFs) as the result of direct synthesizing of the same IFs. The two dominant IFs are processed by parallel computing method. Experimental results show that compared with conventional C-OTDR the FDM-OTDR is four times faster in fading noise reduction and can also bring a 1.9 dB single way dynamic range (SWDR) enhancement.

► A novel FDM-OTDR is proposed.
► Heterodyne IFs are shortened to be half by a directly synthesizing scheme.
► Parallel computing method is adopted for fast signal processing.