Comb-Driven Coherent Optical Transmitter for Scalable DWDM Interconnects

Abstract: Driven by the growing demand for large-scale artificial intelligence applications, disaggregated compute nodes and high-radix switches in next-generation computing clusters are set to surpass the capacity of current optical interconnect technologies. Such a surge turns several aspects of transmitters into critical bottlenecks: shoreline bandwidth density and energy efficiency are effectively limiting the scalability. We present a comb-driven coherent optical transmitter architecture on a Si/SiN platform that provides the bandwidth density, energy efficiency, and compact footprint required for such co-packaged-enabled optical interconnects. We evaluate scalability through critical building blocks, including ultra-compact microring-assisted Mach--Zehnder modulators (MRA-MZMs) and dense wavelength-division multiplexing (DWDM) interleavers. Single-tone experiments demonstrate a net line rate of 400 Gbps per polarization (16-QAM, 120 GBd) in silicon within the O-band, achieving a record shoreline density of 4 Tbps/mm while consuming only 10 fJ/bit for modulation. We also demonstrate transmission rates of up to 160 GBd QPSK in back-to-back and 100 GBd over 7 km of fiber without dispersion compensation. Using a quantum-dot frequency comb, six 100 GHz-spaced WDM channels transmit 1.08 Tbps over 5 km. System-level analyses show that by leveraging advanced modulation formats through the integration of wavelength and polarization multiplexing, our proposed architecture can realistically support combined transmission rates exceeding 10 Tbps per fiber within practical limits of power consumption and packaging, outlining a clear path toward future petabit-scale interconnects.