THE CASE FOR CO-PACKAGED OPTICS:  LOWER POWER

As community site visitors continues to develop attributable to increased bandwidth functions, reminiscent of 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 increased velocity and better density optics and ASICs.  The mixture throughput of swap and optics gadgets is doubling each two to 3 years, which in the end ends in 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 era of swap and optics semiconductors is increased than the earlier one.

For Cisco’s Webscale knowledge middle clients, this has many implications.  To proceed scaling a typical knowledge middle constructed round a set electrical energy finances, each compute and networking should sustain with these new bandwidth calls for, however throughout the similar 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 common function CPUs to targeted accelerators GPUs (graphics processing items) for functions reminiscent of AI/ML inference and coaching.

Within the networking area, knowledge middle 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 revolutionary designs, we wanted 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 Stage 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 quicker 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 Gentle 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 essential choice.  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).  Shifting the lasers away from the excessive energy ASIC to cooler places throughout the system chassis ends in a number of enhancements:

1. Lasers could 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).
2. Lasers could 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 straightforward insertion and elimination is vital to making sure CPO techniques have related MTBF (imply time between failure) to legacy techniques.
3. 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} normal 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 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 accomplice with confirmed, dependable expertise. One in every of 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

On account of these improvements, the facility required for connecting the Swap ASIC to entrance panel pluggable optics could be lowered 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 reveal these subsequent steps – a side-by-side comparability of the true energy discount between:

• Cisco 8111-32EH, a traditional 32-port 2x400G 1RU router absolutely populated with 2x400G-FR4 pluggable optics modules (64x400G FR4) primarily based 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 primarily based 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 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 parts to suit on an ASIC package deal (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 help all knowledge 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 completely different wavelengths of sunshine on the identical fiber, every carrying 100Gbps. This implies 4 completely different wavelengths must be mixed collectively.  That is usually performed utilizing an exterior lens, which takes up vital quantity.

Cisco has invented an revolutionary 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 working without delay

Integration of optical tiles on the Swap 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 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 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 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 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 expertise and is investing to make sure we’re prepared for this inevitable transition.

Nevertheless, CPO poses extraordinarily advanced 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 rationale 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 techniques, 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 real looking that it might be nonetheless some methods away.

You’ll be able to go to our Cisco Silicon One web site to be taught extra about our industry-leading routing and switching silicon structure. You’ll be able to go to our Cisco Optics web site to be taught 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 the direction of 400G BASE-FR4 Baseline Proposal, IEEE March 2019

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