All-Fiber Multiplexing and Transmission of High-Order Circularly Polarized Orbital Angular Momentum Modes With Mode Selective Couplers

We have demonstrated an all-fiber high-order circularly polarized (CP) orbital angular momentum (OAM) modes (de) multiplexing system based on second-order mode selective couplers (SMSCs). Such SMSCs combining standard single mode fiber and ring core fiber (RCF) are fabricated by a fusing and pulling technique, in which the RCF supports second-order vector modes (HE31 and EH11). During a pulling process, the HE31 and EH11 modes could be excited along the coupling region through evanescent wave interaction. By adjusting the polarization states, the excited secondorder modes are transformed into two sets of second-order CP OAM (CP-OAM(+/- 2)) modes and then transmit along the RCF. The second-order CP-OAM(+/- 2) modes, carrying a 2.95-Gb/s orthogonal frequency division multiplexing signals filled with the 16-level quadrature amplitude modulation signals, are successfully (de) multiplexed and propagated over a 3.7-km RCF. The experimental investigations show that the developed system to multiplex and transmit CP-OAM(+/- 2) can achieve forward error correction threshold that the received optical power is larger than -13 dBm. The obtained results show that the OAM modes can be generated, (de) multiplexed, and effectively transmitted in the RCF with favorable performance by the designed SMSCs.