Design Principle for Realizing Low Bending Losses in All-Solid Photonic Bandgap Fibers

In this paper, the structural dependence of factor which mainly affects a bending loss property is theoretically investigated in all-solid photonic bandgap fibers (PBGFs). A design principle for realizing low bending losses is successfully figured out for the first-order photonic bandgap (PBG). In particular, one of the origins which causes the variation of bending loss property for each structural parameter is identified. In addition, we show that exploitation of a large pitch relative to a rod diameter, aiming to realize a large-mode area (LMA) structure, leads to a significant degradation of the bending loss property. Moreover, it is demonstrated that a V-value which is proposed for all-solid PBGFs is also reduced significantly for the LMA condition. The origin of the degradation is attributed to the newly-excited Bloch state which determines the second-order PBG edge.