Limitation of effective area for large-mode-area all-solid photonic bandgap fibers

The bending characteristics of all-solid photonic bandgap fibers (AS-PBGFs) are investigated for aiming to achieve large mode area (LMA) and effectively single-mode operation with a practically allowable bending radius for Yb-doped fiber applications. Through detailed numerical simulations, the impacts of the order of photonic bandgap (PBG) on the bending performance are evaluated and the limitation of core-size enlargement due to bending loss (BL) increase in the AS-PBGFs with a one-cell core structure is pointed out. In addition, it is found that the AS-PBGFs having a seven-cell core can achieve sufficient differential BL between the fundamental mode (FM) and the higher-order modes (HOMs) and a much larger effective area limit as compared with previously-reported index-guiding LMA fibers, by taking into account practical constraints.