Low crosstalk holey trench-assisted multi-core fiber supporting over 500 OAM modes

We propose what we believe to be a new design strategy for achieving low crosstalk in holey trench-assisted multi-core fiber (HTA-MCF), specifically designed to support broadband orbital angular momentum (OAM) modes. The proposed fiber structure features multiple cores with trench-assisted ring profiles, where the inclusion of air holes leads to a very low crosstalk while enabling the reliable transmission of numerous OAM modes. A theoretical analysis employing the finite element method (FEM) is performed. The simulation results demonstrate that the fiber supports 574 OAM modes at 1.55 μm and up to 518 OAM modes over O-E-S-C-L bands. The proposed HTA-MCF demonstrates exceptionally low inter-ring crosstalk, achieving below -208.34 dB between adjacent rings at 1.55 μm, and consistently maintaining crosstalk levels under -83 dB across the entire operational bandwidth after 100 km propagation. This performance is facilitated by a highly effective index difference (> 4.9×10^-4), ensuring stable mode isolation. Additional features include substantial effective mode area, nonlinear coefficients below 1.66 W^-1km^-1 at 1.55 μm, very low confinement loss ranging from 10^-12 to 10^-8 dB/m with mode qualities mostly above 90%, as well as purity greater than 99%. Additionally, it offers high tolerance to ellipticity and bending issues for higher-order modes. The proposed fiber structure is therefore highly promising for future high-capacity OAM-based multiplexing systems in optical communications.