Geometric structure optimization of the ring-core fiber for high-order cylindrical vector beam modes transmission

The cylindrical vector beams (CVBs) as the spatially orthogonal modes in fiber provide additional degree of freedom for optical fiber communication. The ring-core fibers with a high refractive index area matching with the beam shape of CVBs are suitable for stable transmission of CVBs. We simulate and experimentally characterize the CVBs transmission in ring-core fibers with different geometric structure parameters. We demonstrated the transmission of CVBs from 2nd to 7th orders with mode purities higher than 80% and demonstrate the multiplexing communication of coaxial high order CVBs in ring-core fiber. The model we build to calculate the largest CVB mode number and order supported in the ring-core fiber are consistent with the experimental results of our three ring-core fibers. From the simulation results, the higher order CVB modes show larger effective refractive index differences and less crosstalk compared with the lower orders modes. According to the calculation, it is possible to transmit up to 4 mode groups of high order CVB modes in the ring-core fiber with optimized geometric parameters, given by the effective refractive index threshold of 2×10−3.