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Cisco Demonstrates Co-packaged Optics (CPO) System at OFC 2023


As community site visitors continues to develop as a consequence of larger bandwidth purposes, resembling AI/ML (Synthetic Intelligence/Machine Studying), high-resolution video streaming and digital actuality, the pressure positioned upon knowledge heart networks continues to extend.  These insatiable calls for for extra bandwidth are leading to larger pace and better density optics and ASICs.  The mixture throughput of change and optics gadgets is doubling each two to 3 years, which finally ends in doubling the pace 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 ability required for the brand new technology of change and optics semiconductors is larger than the earlier one.

For Cisco’s Webscale knowledge heart prospects, this has many implications.  To proceed scaling a typical knowledge heart constructed round a set electrical energy finances, 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 house, the requirement to stay inside a set energy finances has pressured adjustments:

  • Motion from single core to decrease frequency multicore CPUs (central processing items)
  • Motion away from normal objective CPUs to centered accelerators GPUs (graphics processing items) for purposes resembling AI/ML inference and coaching.

Within the networking house, knowledge heart topology compromises should happen to stay throughout the required energy envelope, and we should rethink how we design our gear.

Nonetheless, in our continued quest for modern designs, we wanted to proceed to innovate. That is the place co-packaged optics (CPO) are available in.


Pillar #1 – Removing of a Stage of DSPs to Save Energy

As change 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 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 important 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 change ASIC).  Shifting the lasers away from the excessive energy ASIC to cooler areas 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, decreasing system energy with out energetic elements like a TEC (thermo-electric cooler).
  2. Lasers could 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 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} customary kind issue.

Pillar #3 – Manufacturing-Confirmed Silicon Photonics Platform

To position optical elements very near the Change 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) should be mixed collectively on a single IC.  Cisco’s Silicon Photonics expertise permits this.

Determine 2 – 4x OSFP800 vs. Cisco 3.2T CPO module (>100x quantity discount)

On this period of provide chain challenges, you will need to select a accomplice with confirmed, dependable expertise. One among Cisco’s benefits within the CPO house is the expertise creating, optimizing, and delivery tens of millions of Silicon Photonics-based optical modules.

Determine 3 – Cisco 106.25Gbps/lane Silicon Photonics SISCAP modulator [1] (a) First technology siscap configuration; (b) driving siscap; (c) measured pam4 53gbaud transmit waveform (106.25Gbps) from second technology siscap and driver


On account of these improvements, the ability required for connecting the Change ASIC to entrance panel pluggable optics could be decreased by as much as 50%, leading to a complete mounted system energy discount of as much as 25-30%.

Determine 4 – 51.2T system energy discount from pluggable to CPO



At OFC 2023, Cisco is proud to show these subsequent steps – a side-by-side comparability of the true 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
Determine 5- Cisco’s OFC 2023 CPO Demo System (in 128x400G FR4 chassis configuration)


Cisco’s CPO demonstration at OFC 2023 highlights among the key benefits of Cisco’s expertise 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 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 heart 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 performed utilizing an exterior lens, which takes up important 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.

Determine 6 – 400G FR4 module block diagram (highlighting mux/demux) [2]

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 change 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 change 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 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 vary their infrastructure to assist liquid cooling earlier than they need to.


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 remedy earlier than important deployments can start.  For instance, it should be dependable, serviceable, deployable, supply 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 change cycle adopted by bigger scale adoption throughout the 101.2Tb change 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 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 lifelike that it might be nonetheless some methods away.

You may go to our Cisco Silicon One web site to be taught extra about our industry-leading routing and switching silicon structure. You may go to our Cisco Optics web site to be taught extra about our pluggable optics choices and Silicon Photonics expertise.


[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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