The Multiplexing of Six Vortex Modes in a Multicore Photonic Quasi-Crystal Fiber

We propose a photonic quasi-crystal fiber which has five ring-shaped cores in the cross section. It realizes the multiplexing of 6 vortex modes. The fiber is based on SiO2 and has an octuple photonic quasi-crystal structure. It achieves four independent dual-core coupling pairs with the optimization of geometric parameters. By adjusting the thickness of five ring-shaped cores, the fundamental mode (HE11) in the small side ring-shaped fiber cores couple to different higher order vector modes (TE01, HE21, TM01, HE31) in the large center ring-shaped fiber core, which makes the light field transfer from small side cores to large center core and realizes the multiplexing of 6 vortex modes (TE01, $\text{OAM}_{ \pm 1,1}^ \pm $, TM01, $\text{OAM}_{ \pm 2,1}^ \pm $). The transmission characteristics are analyzed with supermode theory. The $\Delta {n}_{\text{eff}}$ of adjacent vector modes is larger than ${10}^{ - 4}$ due to the thin center ring core. The coupling length (${L}_c$) keeps in the order of ${10}^{ - 2}$ m between 1500--1600 nm and the coupling efficiency is larger than 90% in 1550 nm for four dual-core coupling pairs. We believe this design will have great potential in the field of all-fiber vortex mode division multiplexing.