Polarization-maintaining few mode fiber composed of a central circular-hole and an elliptical-ring core

We propose a novel waveguide design of polarization-maintaining few mode fiber（PM-FMF） supporting ≥10non-degenerate modes, utilizing a central circular air hole and a circumjacent elliptical-ring core. The structure endows a new degree of freedom to adjust the birefringence of all the guided modes, including the fundamental polarization mode. Numerical simulations demonstrate that, by optimizing the air hole and elliptical-ring core,a PM-FMF supporting 10 distinctive polarization modes has been achieved, and the effective index difference Δneff between the adjacent guided modes could be kept larger than 1.32 × 10-4 over the whole C +L band. The proposed fiber structure can flexibly tailored to support an even larger number of modes in PM-FMF（14-mode PM-FMF has been demonstrated as an example）, which can be readily applicable to a scalable mode division multiplexing system.