Dual frequency probe based coherent optical time domain reflectometry

A new approach to enhance the performance of coherent optical time domain reflectometry(C-OTDR) is proposed. In this approach, single frequency light is converted to multi-frequency light using phase modulator (PM), while only two frequencies with the same light power level are adopted as the probe .Coherent heterodyne between the dual frequency probe and original single frequency local oscillator (LO) generates the same intermediate frequency (IF), which equals two IF signals automatically synthesizing in the process of coherent detection other than in IF signal processing circuit, so it doubles measurement speed. Experimental results show that compared with conventional single frequency probe based C-OTDR the dual frequency probe based C-OTDR has more quickly coherent Rayleigh noise (CRN) reduction capability and can bring a 3.0 dB dynamic range improvement.