Improving Soliton Transmission Systems through Soliton Interactions

Nonlinear interactions between neighboring pulses has always been a fundamental bottleneck in soliton transmission systems. Recently, coherent transceivers, digital signal processing (DSP) and the new nonlinear Fourier transform (NFT) theoretical framework has revived and generalized the field of soliton transmissions into nonlinear frequency division multiplexing (NFDM). We hereby demonstrate analytically and experimentally that one can considerably improve soliton transmission performance by intentionally allowing neighboring solitons to interact and collide during propagation and exchange positions at the receiver followed by standard NFT processing. This can be achieved by designing neighboring solitons' eigenvalues λ to have opposite signs in the real part while the magnitude |Re(λ)| is optimized for a given transmission distance so that neighboring transmitted pulses would have swapped their timing positions at the receiver. Experimental results for 6.13 Gbaud 1-soliton systems demonstrate a transmission reach improvement of 100% for 16APSK and 60% for 8PSK modulated on the b-coefficients. The proposed scheme eliminated a long-standing fundamental limitation in soliton transmissions, opened up new dimensions in transmitter signal design and receiver signal processing for nonlinear optical communication systems.