Design of 1-μm-band mode-detection OTDR for 40 km range measurement and its performance evaluation

This paper clarifies the requirements for applying 1-μm-band mode-detection optical time domain reflectometry (OTDR) to the loss monitoring of trunk cables with the goal of detecting slight changes in macro/micro-bending that are missed by conventional OTDR. In light of the requirements, the measurement system is enhanced through the use of coherent detection to fulfill the required range performance. Moreover, the enhanced system modulates the optical frequency and the state of polarization of the probe light during the measurement to suppress amplitude fluctuations in the backscattered waveforms. A field test is carried out to confirm the performance of the enhanced measurement system. The results demonstrate that the measurement range of over 40 km is achieved while amplitude fluctuations are reduced to as low as 0.02 dB.