THE CASE FOR CO-PACKAGED OPTICS: LOWER POWER
As community site visitors continues to develop resulting from increased bandwidth purposes, corresponding to AI/ML (Synthetic Intelligence/Machine Studying), high-resolution video streaming and digital actuality, the pressure positioned upon information heart 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 3 years, which finally leads to doubling the velocity and will increase in energy of the host to pluggable optics electrical interface. Sadly, whereas Moore’s Regulation continues to permit us to scale our chips and gear (regardless of non-trivial technical challenges), its corollary, Dennard Scaling, has been useless 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 heart prospects, this has many implications. To proceed scaling a typical information heart constructed round a hard and fast electrical energy funds, each compute and networking should sustain with these new bandwidth calls for, however throughout the identical energy envelope as earlier than or face an costly improve.
Within the compute area, the requirement to stay inside a hard and fast energy funds has pressured adjustments:
- 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 corresponding to AI/ML inference and coaching.
Within the networking area, information heart topology compromises should happen to stay throughout the required energy envelope, and we should rethink how we design our gear.
Nevertheless, in our continued quest for modern designs, we wanted to proceed to innovate. That is the place co-packaged optics (CPO) are available in.
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 proportion 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 Swap 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 vital resolution. Lasers are extremely delicate to excessive temperature and expertise elevated failure charges when positioned in hotter environments (e.g. adjoining to a very popular swap ASIC). Shifting the lasers away from the excessive energy ASIC to cooler places throughout the system chassis leads to a number of enhancements:
- Lasers will be passively cooled to a decrease temperature, enabling them to be extra environment friendly in producing optical energy / Watt, decreasing system energy with out lively parts like a TEC (thermo-electric cooler).
- Lasers will be changed from the chassis faceplate. For the reason that 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 necessary to making sure CPO techniques have related MTBF (imply time between failure) to legacy techniques.
- The {industry} can standardize on the shape issue and design of the distant gentle 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} commonplace type issue.
Pillar #3 – Manufacturing-Confirmed Silicon Photonics Platform
To position optical parts very near the Swap ASIC silicon die, two orders of magnitude (over 100x) of miniaturization is required over present pluggable modules. To do that, many beforehand separate ICs (TIA, driver, modulator, mux/demux) have to be mixed collectively on a single IC. Cisco’s Silicon Photonics know-how permits this.
On this period of provide chain challenges, it is very important select a associate with confirmed, dependable know-how. Considered one of Cisco’s benefits within the CPO area is the expertise growing, optimizing, and transport thousands and thousands of Silicon Photonics-based optical modules.
CPO SYSTEM BENEFITS SUMMARY
On account of these improvements, the facility required for connecting the Swap ASIC to entrance panel pluggable optics will be lowered by as much as 50%, leading to a complete mounted 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 actual energy discount between:
- Cisco 8111-32EH, a standard 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 few 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 standard QSFP-DD or OSFP module). This requires optics and packaging innovation.
Any CPO structure should present the pliability to help all information heart 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 completely different wavelengths of sunshine on the identical fiber, every carrying 100Gbps. This implies 4 completely different wavelengths should be mixed collectively. That is usually completed utilizing an exterior lens, which takes up vital quantity.
Cisco has invented an modern method 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 operating directly
Integration of optical tiles on the Swap 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 whole system energy decreases, the thermal density within the heart 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 prospects to alter their infrastructure to help liquid cooling earlier than they wish 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.
Nevertheless, CPO poses extraordinarily complicated issues that system distributors and community operators should remedy earlier than vital deployments can start. For instance, it have to be dependable, serviceable, deployable, supply vital energy financial savings, and be cost-effective. That is the rationale for our demo at OFC. Cisco expects trial deployments coincident with the 51.2Tb swap cycle adopted by bigger scale adoption in the course of the 101.2Tb swap cycle.
We imagine it’s not a matter of if co-packaged optics will happen, it’s a matter of when. Cisco has experience in techniques, ASICs, and optics, which makes it one of many few corporations that may efficiently implement and deploy co-packaged optics in quantity. We stay devoted to investing for this inevitable transition, however sensible that it might be nonetheless some methods away.
You may go to our Cisco Silicon One web site to study extra about our industry-leading routing and switching silicon structure. You may go to our Cisco Optics web site to study 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 direction of 400G BASE-FR4 Baseline Proposal, IEEE March 2019
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