Large negative dispersion in square solid-core photonic bandgap fibers

In this paper, a Ge-doping square solid-core photonic bandgap (PBG) fiber is proposed and the effective index of defect mode is investigated. Simulations show that, at the starting wavelength of the defect mode, n_effd (the effective index of defect mode) changes rapidly due to the PBG effect, which induces large negative dispersion in fiber. This mechanism is different from the mode coupling case in dual-core concentric fibers, and the dispersion characteristic is more robust to structural deviations.