Cladding mode suppression in bend-insenstivie fiber with epoxy-filled air holes

Reduction of bending loss has been recognized as an important aspect in optimizing single mode fibers for FTTH applications. Recently, introduction of several air holes around a germanium doped core has been intensively investigated for bending loss control. Such a fiber is called a bend insensity fiber (BIF). Usually larger air holes result in low bending loss for the core mode. However, the air hole layer forms another waveguide additional to the core, and there exist inner cladding modes guided with low loss. The cladding modes are excited at imperfect splices with single mode fiber, and they cause modal interference and intensity fluctuation. The trade off between the low bending loss and the cladding mode suppression, therefore, has been a main issue in design of BIFs. In order to effectively overcome the problem, we propose cladding mode strippers to be installed at two ends of the BIFs.