The cross section of a real air-core photonic bandgap fiber (PBGF) with structural distortions is analyzed using a vectorial finite-element method and compared with an ideal structure. It is found that the properties of air-core PBGFs are extremely sensitive to changes of the structural parameters. Structural distortions in real fibers have significant impact on fiber properties such as bandwidth and tunneling loss. Numerical results show that the bandwidth of the real fiber is reduced by a factor of two, and the tunneling is increased by almost a factor of 10<sup>4</sup> when compared to an ideal cross section.
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