“…Improvements of IDFs, which will be explained next, have been attempted so as not to exceed the bending loss (both macro-and micro-bending) of initial IDF. The performances of ribbon-slot cable and loose-tube cable using initial IDF were also confirmed and reported in [19,20], and reliable performances were also reported. With these fabrications and experiments of initial IDF, the performance potential and basic properties were well understood, and improvements have been done based on these results.…”