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Crosstalk Reduction With Bidirectional Signal Assignment on Square Lattice Structure 16-Core Fiber Over WDM Transmission for Gradual Upgrade of SMF-Based Lines

C-band and L-band wavelength division multiplexing (WDM) transmission performance was improved by using bidirectional signal assignment (BSA) to reduce crosstalk (XT) in square lattice structure 16-core fiber. Transmission of 16 WDM channels with 256-Gb/s polarization multiplexed-16 quadrature amplitude modulation signals on a 50-GHz grid with a net spectral efficiency of 4 b/s/Hz over 55-km of 16-core fiber spans was achieved. Use of BSA to reduce XT extended the transmission distance to 880 km in both types of transmission. Furthermore, transmission was achieved over eight mixed spans consisting of 16-core fiber and conventional single-mode fiber (SMF), demonstrating the possibility of gradually upgrading standard SMF-based lines to multicore fiber-based lines. With BSA, six 16-core fiber spans can be acceptable if the Q penalty from XT is below 0.5 dB.