Hole-assisted polarization-maintaining few-mode fiber

We propose a novel polarization-maintaining few-mode fiber by introducing four identical circular side-holes surrounding an elliptical ring core. In addition to the parameters of ring core, this kind of fiber endows new degrees of freedom to adjust the modal birefringence of guided modes. Numerical simulations indicate that such fiber could support 10 distinct polarization modes, including the effectively separated fundamental modes. The influences of side-hole size and positions on the polarization-maintaining property are investigated for the 10-mode fiber. With appropriate parameters of side-holes, the minimum effective refractive difference (Δneff) between adjacent modes is 1.65 × 10−4 at 1550 nm. Compared with the fiber excluding side-holes, the modal effective refractive indexes are decreased while most Δneff values are enlarged in the proposed fiber. Moreover, all the Δneff values could be higher than 1.52 × 10−4 over a bandwidth ranging from 1510 nm to 1630 nm. The chromatic dispersion covering the broadband is analyzed subsequently. Furthermore, 16 vector modes could be guided in the proposed fiber structure with modified parameters. The proposed fiber is capable of supporting extended modes and might be a promising candidate toward high-capacity spatial-division-multiplexing communications.