Design and characteristics of ellipse-assisted ring-core fiber for space division multiplexing

We propose a novel ellipse-assisted ring-core fiber characterized by an elliptical region of low refractive index in the core. The proposed fiber proves effective in eliminating the spatial degeneracy of the LPmn mode groups and keeping the birefringence properties at a low level. This fiber, with optimized structural parameters, can guide 9 modes over the entire C-band. The simulation results show that the effective refractive index difference (Δneff) between adjacent modes at 1530–1565 nm falls within the scope of (3.1 ∼ 6.64) × 10−4. At the same time, the polarization separation level of each mode is lower than 3.23 × 10−6, which is 2 orders of magnitude lower than the degree of spatial mode degeneracy separation. This fiber design has good application prospects in space division multiplexing systems.