Is Co-packaged Optics Just Around the Corner?

Optical engines co-packaged with switching ASIC are likely to offer an alternative to pluggable optical transceivers in mega datacenters. The pluggables were first introduced two decades ago for connections in enterprise networks and became the ubiquitous solution for optical connectivity across a variety of applications. Over 1 billion units of pluggable transceivers were shipped in the last ten years, including more than 500 million for the fiber to the home or the building (FTTx) market. More than ten million transceivers were shipped for connections inside mega datacenters operated by Amazon, Facebook, Google, Microsoft, and other cloud companies. However, the industry is starting to look for an alternative to the pluggable transceivers to reduce the power consumption of next-generation Ethernet switches.

Facebook and Microsoft recently launched the Co-Packaged Optics (CPO) Collaboration. The goal of CPO is “the adoption of common design elements that will provide guidance for suppliers in the design and manufacturing of co-packaged optics.” Leading switch ASIC vendors, including Broadcom and Cisco, are also investing in the development of these new solutions. There are quite a few technical challenges, but if everything goes as planned, consumption of pluggable transceivers by the Top 5 Cloud companies will start to decline in 2027-2028, as shown in the Figure.

Figure: Shipments of Ethernet transceivers and opto-chiplets to Top 5 Cloud companies (includes products with data rate of 100GbE and above with reach of 100m and 500m only).

This forecast was developed for a study commissioned by ARPA-E ENLITENED program, which funds the development of next-generation optical connectivity and switching technologies. The main goal of this program is to reduce the power consumption of datacenter switches by a factor of ten.

IBM is among a few companies selected for Phase 2 ARPA-E funding this year. IBM was the first one to co-package optical engines with switching ASICs, as part of a DARPA funded supercomputer project in 2004-2008. It might have been slightly ahead of its time, which is not unusual for DARPA-funded projects. IBM is developing very low power co-packaged optics based on VCSEL arrays for the ENLITENED project, including double wavelength VCSELs for Phase 2 of the program. Other teams funded by ARPA-E are planning to use silicon photonics technology.

Co-packaged optics promises to eliminate power to drive several inches of copper traces connecting a switching ASIC in the middle of a PCB board to optical transceivers plugged at the board edge or faceplate. Co-packaging involves simpler SerDes interfaces that not only consume less power but reduce latency.

The development of new technologies for opto-chiplets has to overcome many engineering challenges. Our forecast predicts that all these challenges can be resolved ahead of the early demand for these products in 2023-2024. Nevertheless, the engineers are the ones responsible for making these resolutions happen.

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