OAM Modes Exchanging by Controlling Polarization of Vortex Beams Propagating Through an FMF-Based Polarization Controller

Abstract

In order to exchange OAM modes in a space-division multiplexing (SDM) system, an OAM-mode-exchange concept between the first-order vortex beams (L = and −1), which is achieved by controlling the polarization of vortex beams propagating over a few-mode-fiber-based polarization controller (FMFPC), is proposed. A step-index fiber is also designed and manufactured for switching the propagated OAM beams. The feasibility of the proposed concept is not only exploited and simulated in principle, but is also verified through experiments. The simulated results show that SDM-based vortex beams (L = and −1) can be mutually exchanged by appropriately controlling the phase difference (with respect to the polarization of propagated vortex-beams) between two first-order-linear-polarized-mode beams ( $\text {LPM}_{\text {11ax/ay}}$ and $\text {LPM}_{\text {11bx/by}}$ ). An experimental setup is also proposed and established for verifying the feasibility of the proposed concept in practice. The measured experimental results are consistent with the simulation, and demonstrate that the proposed scheme is correct and reliable. To evaluate the performance of the proposed scheme, bit error rates (BERs) and constellation graphs (CGs) with respect to the exchanging ways, loop numbers, and fiber lengths, are employed and investigated, respectively. The measured BERs and CGs demonstrate that the performance can be further improved with the decrease of fiber length and crosstalk, and also can be enhanced when the coiled loops is set as an appropriate value.