Cisco Touts Co

This week, Cisco showed its vision for co-packaged optics. Instead of simply showing that co-packaged optics are possible, it also showed why we need them and how it plans to tackle some of the deployment challenges.

This week, Cisco showed off its co-packaged optics demo switch. For those unfamiliar with the concept, the idea is to move the Silicon Photonics modules onto the switch package instead of using pluggable models.

Although Intel has stopped Barefoot development, we were able to take a look at an early generation co-packaged optics switch Hands-on with the Intel Co-Packaged Optics and Silicon Photonics Switch. (Ed: Maybe time for a thumbnail change on that, one of our very early videos.)

We also recently covered Broadcom Tomahawk 5 based 51.2T Bailly Co-Packaged Optics Switch Shown and the earlier version.

This is clearly the way the industry will evolve. One of the biggest reasons is power consumption. Here is Cisco’s chat showing just how much of a switch power can be reduced through co-packaged optics. For some sense, we have a 64-port 400GbE switch we are testing that can use over 2kW, and an enormous part of that (about half) comes from powering and cooling the optical modules. That is similar to the Cisco co-packaged optics demo above, but with traditional pluggable optics.

Cisco’s solution of co-packaging the optics means that one of the DSPs required to drive the signal across the PCB can be removed. That has enormous power savings, especially as speeds increase.

Putting a co-packaged optics module in the space of a chip footprint instead of a pluggable module creates another challenge: space. Here are four 800Gbps OSFP800 pluggable optical modules and a Cisco CPO module side-by-side. There is a lot of miniaturization including with the silicon photonics Mux/ Demux there.

One component that the pluggable modules need, but Cisco does not have is the light source. Cisco’s vision is to use an ELSFP (External Laser Small Form Factor Pluggable) module as a light source. Cisco says that the laser light sources are the least reliable parts of the optical modules. Thus, moving them away from the switch ASIC and to a field serviceable pluggable module helps solve the serviceability issue. We have seen others like Intel create a connector partly for this reason.

Field serviceability remains one of the biggest challenges to co-packaged optics since removing a switch if one of 64 or 128 links fails is not ideal. Cisco thinks that using remote pluggable light sources it can get close to traditional pluggable optics reliability.

Co-packaged optics are very cool for switch chips. At the same time, these are the leading edge devices for something we are expecting in the next 3-5 years becoming more commonplace. Chip-to-chip such as CPU-to-accelerator or even to CXL memory in systems is going to need longer reach and lower power options in the future. While Cisco and the networking world are trying to figure out how pluggable modules (with low-cost DACs) can be pushed, this is a broad topic for the industry that will need to be addressed. Co-packaged optics are no longer science fiction shown by a company every few years. There are teams of very bright engineers working on this across the industry today.