Design of Single-Mode and Low-Bending-Loss Hole-Assisted Fiber and Its MPI Characteristics

Bending-loss insensitive fibers (BIFs) have been receiving increasing attention with a view to improving FTTH network installation and maintenance. Several BIFs have been proposed and developed to realize a lower bending loss, and hole-assisted fiber (HAF) can realize both excellent bending loss characteristics and other properties compatible with conventional single-mode fiber (SMF). In this paper, we numerically clarify a design that provides both an allowable bending radius of 5 mm and other properties comparable to conventional SMFs. The calculated results also reveal the much wider single-mode bandwidth of HAF with both a low bending loss and a comparable MFD to that of SMF. We then discuss the applicability of HAF based optical cord for short-length transmission and reveal the sufficiently low multi-pass interference (MPI) characteristics of single-mode HAF, which are independent of the existence of a mode field diameter (MFD) mismatch. Although a large MFD mismatch degrades the MPI characteristics of HAF with a longer cut-off wavelength, we reveal a way to improve the MPI for such a HAF by utilizing the sweep fusion splicing technique.