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The design of bandgap-engineered all-solid photonic bandgap fibers based on a broken-ring structure is investigated in detail. Both density of states maps and Bloch mode field distributions are used to show how the bandgap structure can be engineered and a higher-order gap be greatly expanded by replacing the high-index germanium-doped rod in a repeating cell with a ring of several individual high-index rods. The strategy is that both the azimuthal and radial orders of the cladding LP modes can be controlled by the broken-ring parameters. In particular, the rod number determines the highest azimuthal order of the LP mode that is less affected by the broken-ring, and the bandgap width is largely affected by the rod size. The result of bandgap engineering is that the higher-order bandgap can be utilized to design all-solid photonic bandgap fibers with very broad transmission windows of 488 nm and 944 nm centered at 800 nm and 1550 nm, respectively, and with typical normal-zero-anomalous dispersion profiles.
Date of Publication: Nov.15, 2010