All-fiber pre- and post-data exchange in km-scale fiber-based twisted lights multiplexing.

Twisting light with orbital angular momentum (OAM) provides an alternative way to facilitate space-division multiplexing (SDM). Both twisted light (OAM modes) multiplexing transmission and data processing functions would be highly desired in a robust OAM-assisted SDM (OAM-SDM) network. In this Letter, we propose and demonstrate flexible all-fiber pre- and post-data exchange functions in a fiber-based OAM-SDM network. OAM₊₁ and OAM_-1 modes carrying 5  Gbit/s four-level pulse amplitude modulation signals are multiplexed to transmit through a 1.1 km OAM fiber in the system. Two simple and controllable data exchange control units are placed at the front end and the back end of the OAM fiber to demonstrate pre- and post-data exchange functions between the OAM₊₁ and OAM_-1 modes. The measured optical signal-to-noise ratio penalties at a bit-error rate of 2×10^-3 (enhanced forward-error correction threshold) for pre- and post-data exchange operations are less than 3.2 dB with crosstalk. The OAM data exchange functions could potentially enhance the flexibility of data management at network nodes in OAM-SDM networks.