In photonic bandgap (PBG) fibers, light is confined by a photonic bandgap caused by a periodic structure of air holes in the cladding regions. The doubly degenerate fundamental mode in ideal PBG fiber structures becomes slightly nondegenerate in actually produced fibers, and this causes polarization instability and polarization mode dispersion. Here, to avoid these problems, we propose a novel absolutely single-polarization PBG fiber structure with an elliptical-hole lattice core. A PBG fiber with a single-polarization bandwidth of 420 nm is numerically demonstrated. Furthermore, based on the proposed fiber structure, we report another single-polarization PBG fiber that has two absolutely single-polarization bands being orthogonal to each other.
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