A Novel Hyperbolic Tangent Profile for Optical Fiber for Next Generation OAM-MDM Systems

In this work, we propose and theoretically/numerically investigate a novel parametric refractive index profile for few mode fibers, referred to as a hyperbolic tangent few mode fiber (HTAN-FMF). To the best of our knowledge, the HTAN-FMF is adopted for the first time, to simultaneously maximize the inter-channels separation and OAM purity. The proposed FMF achieves a wide separation between cylindrical vector modes ( $\geq 3\times 10\,\,^{\mathrm{ -4}}$ between TE0,1, HE2,1, and TM0,1). This enables low-level crosstalk and clearly overcomes recently reported levels in literature. On the other hand, simulations show that the generated and evaluated OAM modes are mostly high pure (≥ 99.9%) leading to intrinsic crosstalk as minimum as -30 dB during propagation through HTAN-FMF. Other propagation performance metrics of the proposed fiber including chromatic dispersion and differential mode delay are also evaluated over the C ITU-T band showing that HTAN-FMF has the potential to achieve stable OAM modes transmission. Bending insensitivity is numerically proved showing that the proposed FMF has the potential to enhance the transmission capacity and the spectral efficiency in next generation OAM mode division Multiplexing (OAM-MDM) systems.