THE CASE FOR CO-PACKAGED OPTICS: LOWER POWER
As community site visitors continues to develop resulting from increased bandwidth purposes, reminiscent of AI/ML (Synthetic Intelligence/Machine Studying), high-resolution video streaming and digital actuality, the pressure positioned upon information middle networks continues to extend. These insatiable calls for for extra bandwidth are leading to increased velocity and better density optics and ASICs. The mixture throughput of swap and optics units is doubling each two to a few years, which in the end leads to doubling the velocity and will increase in energy of the host to pluggable optics electrical interface. Sadly, whereas Moore’s Legislation continues to permit us to scale our chips and gear (regardless of non-trivial technical challenges), its corollary, Dennard Scaling, has been lifeless for some time. This implies the facility required for the brand new technology of swap and optics semiconductors is increased than the earlier one.
For Cisco’s Webscale information middle clients, this has many implications. To proceed scaling a typical information middle constructed round a set electrical energy finances, each compute and networking should sustain with these new bandwidth calls for, however inside the identical energy envelope as earlier than or face an costly improve.
Within the compute area, the requirement to stay inside a set energy finances has compelled modifications:
- Motion from single core to decrease frequency multicore CPUs (central processing items)
- Motion away from basic objective CPUs to targeted accelerators GPUs (graphics processing items) for purposes reminiscent of AI/ML inference and coaching.
Within the networking area, information middle topology compromises should happen to stay inside the required energy envelope, and we should rethink how we design our gear.
Nonetheless, in our continued quest for progressive designs, we would have liked to proceed to innovate. That is the place co-packaged optics (CPO) are available.
THE THREE PILLARS OF CO-PACKAGING OPTICS
Pillar #1 – Removing of a Degree of DSPs to Save Energy
As swap system speeds and densities have elevated, so has the share of the system energy consumed by entrance panel pluggable optics. At 25G/lane and sooner speeds, the need of lively DSP-based retimers has pushed up system energy.
One of many key improvements of co-packaged optics is to maneuver the optics shut sufficient to the Change ASIC die to permit elimination of this extra DSP (see Determine 1).
Pillar #2 –The Distant Mild Supply
In conventional pluggable optics, all sub-components of the optics reside within the pluggable modules. However as optics transfer nearer to the ASIC, the partitioning of the optical parts is a important resolution. Lasers are extremely delicate to excessive temperature and expertise elevated failure charges when positioned in hotter environments (e.g. adjoining to a highly regarded swap ASIC). Transferring the lasers away from the excessive energy ASIC to cooler areas inside the system chassis leads to a number of enhancements:
- Lasers may be passively cooled to a decrease temperature, enabling them to be extra environment friendly in producing optical energy / Watt, reducing system energy with out lively parts like a TEC (thermo-electric cooler).
- Lasers may be changed from the chassis faceplate. Because the lasers are the least dependable parts of the optics subsystem, making the sunshine supply accessible from the system entrance panel to permit simple insertion and elimination is vital to making sure CPO programs have related MTBF (imply time between failure) to legacy programs.
- The {industry} can standardize on the shape issue and design of the distant mild supply, which permits for multi-vendor sourcing. [Industry standard MSA for ELSFP (External Laser Small Form Factor Pluggable)] Cisco’s demo at OFC is the primary system demo to make use of the {industry} customary type issue.
Pillar #3 – Manufacturing-Confirmed Silicon Photonics Platform
To position optical parts very near the Change ASIC silicon die, two orders of magnitude (over 100x) of miniaturization is required over current pluggable modules. To do that, many beforehand separate ICs (TIA, driver, modulator, mux/demux) should be mixed collectively on a single IC. Cisco’s Silicon Photonics know-how permits this.
On this period of provide chain challenges, you will need to select a associate with confirmed, dependable know-how. One in all Cisco’s benefits within the CPO area is the expertise creating, optimizing, and delivery hundreds of thousands of Silicon Photonics-based optical modules.
CPO SYSTEM BENEFITS SUMMARY
Because of these improvements, the facility required for connecting the Change ASIC to entrance panel pluggable optics may be decreased by as much as 50%, leading to a complete fastened system energy discount of as much as 25-30%.
CISCO’S OFC DEMONSTRATION OF CO-PACKAGED OPTICS (CPO)
At OFC 2023, Cisco is proud to display these subsequent steps – a side-by-side comparability of the true energy discount between:
- Cisco 8111-32EH, a traditional 32-port 2x400G 1RU router totally populated with 2x400G-FR4 pluggable optics modules (64x400G FR4) based mostly on the Cisco Silicon One G100 ASIC
- Cisco CPO router populated with a full complement of co-packaged Silicon Photonics-based optical tiles driving 64x400G FR4 additionally based mostly on the Cisco Silicon One G100 ASIC with CPO substrate
KEY ADVANTAGES
Cisco’s CPO demonstration at OFC 2023 highlights a number of the key benefits of Cisco’s know-how growth.
Built-in Silicon Photonics Mux/Demux for 400G FR4
One of many challenges of co-packaging optics is the requirement to miniaturize the optical parts to suit on an ASIC bundle (over 100x decrease quantity than a traditional QSFP-DD or OSFP module). This requires optics and packaging innovation.
Any CPO structure should present the flexibleness to assist all information middle optics sorts, together with these utilizing parallel single mode fiber, e.g. 4x100G DR4, and CWDM (coarse wave division multiplexing) e.g. 400G FR4.
400G FR4 makes use of 4 totally different wavelengths of sunshine on the identical fiber, every carrying 100Gbps. This implies 4 totally different wavelengths should be mixed collectively. That is usually carried out utilizing an exterior lens, which takes up important quantity.
Cisco has invented an progressive means to do that mux/demux on the Silicon Photonics IC, which we’re demonstrating as a part of the OFC demo.
A number of modules working directly
Integration of optical tiles on the Change ASIC bundle requires innovation in bundle mechanical design (to make sure mechanical reliability), energy supply (to ship present to each the swap ASIC and the optical tiles in a small space), and thermal cooling (to take away the upper energy density).
Cisco’s demo has a full complement of optical tiles drawing their full energy.
Enhanced thermal design to allow typical air cooling
One other of the challenges of integrating optics with swap ASICs is whereas complete system energy decreases, the thermal density within the middle of the system grows, as a result of optics transfer from the entrance panel to the ASIC bundle.
Different distributors use liquid cooling to handle this increased thermal density.
Cisco has labored with key companions to develop superior warmth sink applied sciences, which permit typical, dependable air cooling to proceed for use as an alternative of forcing clients to vary their infrastructure to assist liquid cooling earlier than they need to.
CISCO IS THE RIGHT CHOICE FOR OF CO-PACKAGED OPTICS (CPO)
Cisco acknowledges the potential advantages of CPO know-how and is investing to make sure we’re prepared for this inevitable transition.
Nonetheless, CPO poses extraordinarily advanced issues that system distributors and community operators should clear up earlier than important deployments can start. For instance, it should be dependable, serviceable, deployable, provide important energy financial savings, and be cost-effective. That is the explanation for our demo at OFC. Cisco expects trial deployments coincident with the 51.2Tb swap cycle adopted by bigger scale adoption throughout the 101.2Tb swap cycle.
We consider it’s not a matter of if co-packaged optics will happen, it’s a matter of when. Cisco has experience in programs, ASICs, and optics, which makes it one of many few firms that may efficiently implement and deploy co-packaged optics in quantity. We stay devoted to investing for this inevitable transition, however reasonable that it could be nonetheless some methods away.
You possibly can go to our Cisco Silicon One web site to be taught extra about our industry-leading routing and switching silicon structure. You possibly can go to our Cisco Optics web site to be taught extra about our pluggable optics choices and Silicon Photonics know-how.
REFERENCES:
[1] Traverso et al, Built-in Silicon Photonics Transmitters, IEEE Xplore, August 17, 2022
[2] Welch et al, In the direction of 400G BASE-FR4 Baseline Proposal, IEEE March 2019
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