Diversity gain in cylindrical vector beam multiplexing

Cylindrical vector beam (CVB) provides an attractive prospect in enhancing the capacity density of optical communication via mode multiplexing. However, the mode coupling in few-mode fiber will disturb the mode power distribution of CVBs randomly, which causes crosstalk and signal fading, severely degrading the system performance and even interrupting communication. Here, we propose a diversity gain strategy to mitigate the crosstalk and signal fading in CVB multiplexing communication. By performing multi-input multi-output equalization on the receiving signals and estimating the channel matrix by solving the optimal mode channel weights, the diversity gain is performed to equalize the crosstalk-induced noise components and random signal errors, and the crosstalk and signal fading are mitigated. As a proof of concept, we experimentally demonstrate a multi-dimensional multiplexing communication (320 channels combined by 4 CVBs and 80 wavelengths), and 7.5 Tbit/s QPSK-OFDM signals are transmitted in 5 km few-mode fiber. We show that after diversity gain, the bit-error-rate is improved by about 2–3 orders of magnitude, and the communication outage of 60 % is completely suppressed. These validate that the diversity gain effectively eliminates crosstalk and signal fading caused by mode coupling in CVB multiplexing transmission over few-mode fiber, which significantly enhances communication capacity while greatly improving the stability and reliability of the communication system. It provides an effective solution for future high-capacity and long-distance optical communication.