UC Santa Barbara

As demand for internet applications, cloud computation, and AI continue to grow, data center networks must scale to support increased traffic flow. While current intensity modulation links are an economical solution today, coherent links are an increasingly attractive option to improve performance. Conventional coherent link technologies that are used today in >40km transmission are based on power-hungry and expensive digital signal processing, and cannot be easily scaled to the high volumes required for data centers. Coherent links must be optimized for low power consumption and cost for reaches <2 km to make them viable for intra-data center networks. The enlarged link loss budgets from such links will also enable optical switching networks, which can dynamically reconfigure the network for improved server utilization, leading to vast improvements in overall data center energy efficiency.

The focus of this work is to develop energy-efficient coherent links with large link budgets for intra-data center networks. Design methodologies and architectural trade-offs for short-reach coherent link optimization will be presented. Using these techniques, custom electronic and photonic integrated circuits for coherent transmitters and receivers were designed, fabricated, assembled, and characterized. The first-ever full coherent link operating in the O-band was demonstrated with 56 Gbaud QPSK transmission. An O-band coherent link with custom packaged integrated circuits for both the transmitter and receiver was also demonstrated with 224 Gbps DP-QPSK transmission below the HD-FEC threshold with <10 pJ/bit power consumption expected for circuits including integrated optical gain. These results shows that optimized O-band coherent links can support high data rates and link budgets with attractive energy efficiency for future intra-data center networks.