Improved OAM mode purity and stability by ring-core fiber with single-sided gradient index profile

We proposed and investigated a novel ring-core fiber (RCF) with a single-sided gradient index (SSGI) profile, which allows orbital angular momentum (OAM) modes transmission with improved mode separation and mode purity. Thanks to the SSGI profile design, the separation degree between the vector eigenmodes in the proposed RCFs has been highly increased by 26.2%, compared to the one with the conventional graded-index (GI) RCF. Meanwhile, the OAM mode purity in the SSGI-based RCF is expected to surpass 99.9%. providing a weakened spin-orbital coupling compared to the graded-index (GI) fiber. Results show that the purity of the generated and evaluated OAM modes is greater than 99.9%, benefiting minimized intrinsic crosstalk of lower than -30 dB during OAM mode propagation.