Performance Improvement of Space-Division Multiplexed 128-Gb/s PDM-QPSK Signals by Constructive Superposition in a Single-Input-Multiple-Output Configuration

We propose digital constructive-superposition to improve the performance of space-division-multiplexed (SDM) signals, and demonstrate a Q^2-factor improvement of 2.2(3.6)dB by constructively-superimposing 2(3) SDM copies of a 128-Gb/s PDM-QPSK signal after 2688-km transmission over a seven-core-fiber.