Test Method of Splice Points for Constructing Uncoupled Multi-Core Fiber Transmission Line With Low Inter-Core Crosstalk

A key requirement for transmission systems using uncoupled multi-core fibers (MCFs) is the far-end crosstalk (XT), as it limits the transmission capacity and distance of the system. Far-end XT is determined by both the losses of each core and the mode coupling between cores. They occur not only in all system components such as the MCFs themselves and the related input-output devices but also at splice points generated when constructing transmission lines. Therefore, telecommunication carriers have to test the construction quality of the splices to keep the far-end XT of uncoupled MCF transmission lines low. In this work, we numerically investigate how splices in the transmission line using MCFs affect the far-end XT. On the basis of this investigation, we present how to determine the requirements for each splice and propose a method using general-purpose optical time domain reflectometers (OTDRs) for testing the construction quality of the splices to suppress the far-end XT. We also conduct experiments that demonstrate the validity of our numerical investigation. The proposed method will be useful for testing the quality of construction work at the splice points of MCF transmission lines since it can be implemented using general-purpose OTDRs without introducing new instruments.