Experimental Verification of Signal Quality Difference Induced by Differential Modal Loss and Modal Crosstalk on Optical MIMO Transmission and its Compensation by Equipartition Multiplexing

We investigate experimentally the signal quality difference induced by differential modal loss and modal crosstalk (XT) in few-mode fiber during optical MIMO transmission. We measure the modal loss and modal XT properties of two LP mode fibers in the presence of tension and confirm that the coexistence of differential modal loss and modal XT leads to a signal quality imbalance even with MIMO digital processing. In addition, to compensate for the signal quality imbalance, we employ a novel equipartition multiplexing technique at the transmitter used in a mode-division-multiplexed transmission to equalize the mode-dependent impairment, and successfully achieve a two LP mode multiplexed transmission with a low signal quality difference.