138-Tb/s Mode- and Wavelength-Multiplexed Transmission Over Six-Mode Graded-Index Fiber

We report on the multiplexing of 12 spatial and polarization channels and 120 wavelength channels in the C -band, each carrying 16 quadratic-amplitude modulation symbols at 30 GBd over graded-index few-mode fiber. A combination of multiple fiber spools with positive and negative modal dispersion values is exploited to form a 59-km link with 0.35-ns differential mode group delay. The link is placed inside a sixfold synchronized recirculating loop transmission setup. Photonic lanterns with low insertion and mode-dependent loss are employed to excite the six spatial modes in the few-mode fiber. A net transmission rate of 138 Tb/s at a spectral efficiency of 34.91 b/s/Hz over 590 km is demonstrated.