  We demonstrate seamless channel multiplexing and high bitrate superchannel
transmission of coherent optical orthogonal-frequency-division-multiplexing
(CO-OFDM) data signals utilizing a dissipative Kerr soliton (DKS) frequency
comb generated in an on-chip microcavity. Aided by comb line multiplication
through Nyquist pulse modulation, the high stability and mutual coherence among
mode-locked Kerr comb lines are exploited for the first time to eliminate the
guard intervals between communication channels and achieve full spectral
density bandwidth utilization. Spectral efficiency as high as 2.625 bit/Hz/s is
obtained for 180 CO-OFDM bands encoded with 12.75 Gbaud 8-QAM data, adding up
to total bitrate of 6.885 Tb/s within 2.295 THz frequency comb bandwidth. Our
study confirms that high coherence is the key superiority of Kerr soliton
frequency combs over independent laser diodes, as a multi-spectral coherent
laser source for high-bandwidth high-spectral-density transmission networks.
