Semi-Analytical Modeling and Design of PANDA-Type Highly-Elliptical-Core Few-Mode Fibers

We design two PANDA-type fibers featuring stressapplying parts (SAP) and a highly-elliptical-core that each supports five spatial modes with two orthogonal polarization states, for a total of ten linearly polarized modes. In the first fiber, the added stress birefringence maximizes the modal birefringence so that it reaches half of the spatial mode separation, while in the second one it minimizes it. The stress birefringence in both fibers is calculated with a semi-analytical method that mitigates the need for finite element methods (FEM). We optimize the SAP parameters to control the stress distributions in the core and tailor the spacing between the effective refractive indices of the modes over the whole C+L bands. We show that the semi-analytical method can be used to optimize designs that either maximize or minimize modal birefringence. The effective index difference between all modes is increased to more than 5.3×10-4 in the highbirefringence design, whereas the spacing between the orthogonal polarizations within a spatial mode group is reduced to less than 1.05×10-5 in the low-birefringence design. The two fibers thus have potential for short range transmission either without MIMO or with 2×2 MIMO. Considering their array-like modal field distributions, reminiscent of those found in a rectangular waveguide, the fibers may facilitate coupling with integrated mode multiplexers.