  Globally, the long-haul transmission of ultra-high bandwidth data is enabled
through coherent communications. Driven by the rapid pace of growth in
interconnectivity over the last decade, long-haul data transmission has reached
capacities on the order of tens to hundreds of terabits per second, over fiber
reaches which may span thousands of kilometers. Data center communications
however operate in a different regime, featuring shorter reaches and
characterized as being more cost and power sensitive. While integrated
microresonator frequency combs are poised to revolutionize light sources used
for high-speed data transmission over fiber, their use has been limited to
coherent detection schemes. In this paper, we demonstrate the use of
microresonator frequency combs pumped with a single laser for the transmission
of high-speed data, importantly using direct detection schemes. We achieve 120
Gb/s and 240 Gb/s aggregate data transmission for 30 Gb/s non-return-to-zero
(NRZ) and 60 Gb/s pulse modulation amplitude 4 (PAM4) modulation formats
respectively over 2 km of optical fiber, exceeding the reach, single lane data
rate, and aggregate data rates specified in Parallel Single Mode 4 (PSM4) and
Course Wavelength Division Multiplex 4 (CWDM4) multi-source agreements.
Remarkably, we achieve an extremely low power penalty of 0.1 dB compared to
back-to-back characterization. The results firmly cement CMOS-compatible
micro-resonator frequency combs based high-speed data transmission as a viable
technology for the cost and power sensitive data center transceiver industry.
