Novel Inter-Core Crosstalk Measurement Method Using a Loopback and Bidirectional OTDR Technique

Uncoupled multi-core fibers (MCFs) have been reported to increase transmission capacity. One of the issues of MCFs is inter-core crosstalk (XT), which deteriorates communication quality. Measurement of the amount of XT is essential; however, the measurement methods require a measurement system separate from that of standard single-mode fiber (SMF) measurements. In this paper, we propose a novel inter-core XT measurement method using a loopback and bidirectional optical time-domain reflectometer (OTDR) technique. In this measurement, an OTDR is connected to the excitation core at one end of an MCF, and a dummy SMF is connected to the excitation and measured cores at another end. A measured OTDR waveform comprises an excitation core, a dummy SMF, and a measured core. Further, an XT peak appears at the midpoint of the measured OTDR waveform. An XT of homogeneous MCF can be easily calculated from their peak height. The fiber attenuation of excitation and measured cores can be calculated from these waveforms, and the amount of XT and fiber attenuation can be measured simultaneously. Furthermore, in this method, XT can be measured using only OTDR devices, which are the same measurement system as that of the standard SMF. We discussed the measurement mechanism and calculation method of XT amounts and compared the measured XT values with those obtained from the general measurement method using a power meter. We confirmed accurate measurements up to 80 km length of homogeneous MCF; however, the measured error increased when the length was close to the OTDR's noise level.