THE CASE FOR CO-PACKAGED OPTICS: LOWER POWER
As community visitors continues to develop attributable to larger bandwidth purposes, resembling AI/ML (Synthetic Intelligence/Machine Studying), high-resolution video streaming and digital actuality, the pressure positioned upon knowledge middle networks continues to extend. These insatiable calls for for extra bandwidth are leading to larger pace and better density optics and ASICs. The combination throughput of swap and optics gadgets is doubling each two to a few years, which in the end leads to doubling the pace 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 ability required for the brand new era of swap and optics semiconductors is larger than the earlier one.
For Cisco’s Webscale knowledge middle prospects, this has many implications. To proceed scaling a typical knowledge middle constructed round a hard and fast electrical energy funds, 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 house, 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 models)
- Motion away from normal objective CPUs to targeted accelerators GPUs (graphics processing models) for purposes resembling AI/ML inference and coaching.
Within the networking house, knowledge 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 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 – Elimination 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 energetic 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 elements is a essential choice. 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 inside the system chassis leads to a number of enhancements:
- Lasers might be passively cooled to a decrease temperature, enabling them to be extra environment friendly in producing optical energy / Watt, decreasing system energy with out energetic elements like a TEC (thermo-electric cooler).
- Lasers might be changed from the chassis faceplate. For the reason that lasers are the least dependable elements of the optics subsystem, making the sunshine supply accessible from the system entrance panel to permit simple insertion and elimination is essential to making sure CPO methods have related MTBF (imply time between failure) to legacy methods.
- 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 kind issue.
Pillar #3 – Manufacturing-Confirmed Silicon Photonics Platform
To put optical elements 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 expertise permits this.
On this period of provide chain challenges, it is very important select a companion with confirmed, dependable expertise. One among Cisco’s benefits within the CPO house is the expertise growing, optimizing, and delivery hundreds of thousands of Silicon Photonics-based optical modules.
CPO SYSTEM BENEFITS SUMMARY
On account of these improvements, the ability required for connecting the Change ASIC to entrance panel pluggable optics might be diminished 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 show these subsequent steps – a side-by-side comparability of the actual energy discount between:
- Cisco 8111-32EH, a standard 32-port 2x400G 1RU router absolutely 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 among the key benefits of Cisco’s expertise improvement.
Built-in Silicon Photonics Mux/Demux for 400G FR4
One of many challenges of co-packaging optics is the requirement to miniaturize the optical elements to suit on an ASIC package deal (over 100x decrease quantity than a standard QSFP-DD or OSFP module). This requires optics and packaging innovation.
Any CPO structure should present the flexibleness to assist all knowledge middle optics varieties, 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 finished utilizing an exterior lens, which takes up vital quantity.
Cisco has invented an progressive manner 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 without delay
Integration of optical tiles on the Change ASIC package deal requires innovation in package deal 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 standard 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 package deal.
Different distributors use liquid cooling to handle this larger thermal density.
Cisco has labored with key companions to develop superior warmth sink applied sciences, which permit standard, dependable air cooling to proceed for use as a substitute of forcing prospects to alter their infrastructure to assist 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 expertise and is investing to make sure we’re prepared for this inevitable transition.
Nonetheless, CPO poses extraordinarily complicated issues that system distributors and community operators should clear up earlier than vital deployments can start. For instance, it should be dependable, serviceable, deployable, supply vital 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 imagine it’s not a matter of if co-packaged optics will happen, it’s a matter of when. Cisco has experience in methods, 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 practical that it could be nonetheless some methods away.
You’ll be able to go to our Cisco Silicon One web site to study extra about our industry-leading routing and switching silicon structure. You’ll be able to go to our Cisco Optics web site to study extra about our pluggable optics choices and Silicon Photonics expertise.
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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