Co-Packaged Optics And The Evolution Of Switch/Optical Interconnects In Data Centers

Driven by a need to reduce power and increase bandwidth density in data center network switches and other devices, the data networking industry is moving toward adoption of co-packaged optics (CPO). This paper provides a brief overview of the history of copper and optical interconnects, the limitations of existing interconnect solutions, and the future of co-packaged optics, including the benefits and challenges that co-packaged optics introduce.

As data network speeds continue to increase beyond 400Gbps, the power required to drive electrical signals even the relatively short distance from the switch ASIC near the center of a PCB to the pluggable modules at the front panel is becoming problematic. In addition, the devices needed to drive and receive high-speed data signals add significant latency, especially as transmit/receive clock periods get shorter. In 2018, the Consortium for On-Board Optics introduced the concept of “On-Board Optics” (OBO), as a means of reducing power and latency. OBO moves the optical engine from the front panel of the network device to a location on the PCB that is closer to the ASIC, thus reducing the amount of power required to drive the interface between the ASIC and OE. However, the industry is looking for further reduction in OE interface power to continue the progression of network speeds.

Future generations of switch ASICs running at 51.2 Tbps and faster to support 800GbE and 1.6TbE may incorporate co-packaged optics (CPO) so that data can be transmitted via light all the way to the switch ASIC package. Using CPO reduces the length of the electrical interface between the optical engine and the switch ASIC to perhaps a few millimeters, reduces the energy required to drive the signal, and cuts the latency associated with extracting the clock and data from the electrical signal. Pluggable optical modules using DesignWare 112G Ethernet PHY IP and DesignWare 112G Die-to-Die PHY IP are enabling next-generation CPO designs.

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