The various paths to co-packaged optics

Near package optics has emerged as companies have encountered the complexities of co-packaged optics. It should not be viewed as an alternative to co-packaged optics but rather a pragmatic approach for its implementation.

Co-packaged optics will be one of several hot topics at the upcoming OFC show in March.

Placing optics next to silicon is seen as the only way to meet the future input-output (I/O) requirements of ICs such as Ethernet switches and high-end processors.

Brad Booth

For now, pluggable optics do the job of routing traffic between Ethernet switch chips in the data centre. The pluggable modules sit on the switch platform’s front panel at the edge of the printed circuit board (PCB) hosting the switch chip.

But with switch silicon capacity doubling every two years, engineers are being challenged to get data into and out of the chip while ensuring power consumption does not rise.

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Preparing for a post-pluggable optical module world

Part 1: OIF: ELSFP, XSR+, and CEI-112G-Linear

The OIF is working on several electrical and optical specifications as the industry looks beyond pluggable optical transceivers.

One initiative is to specify the external laser source used for co-packaged optics, dubbed the External Laser Small Form Factor Pluggable (ELSFP) project. 

Nathan Tracy

Industry interest in co-packaged optics, combining an ASIC and optical chiplets in one package, is growing as it becomes increasingly challenging and costly to route high-speed electrical signals between a high-capacity Ethernet switch chip and the pluggable optics on the platform’s faceplate.

The OIF is also developing 112-gigabit electrical interfaces to address not just co-packaged optics but also near package optics and the interface needs of servers and graphics processor units (GPUs).

Near package optics also surrounds the ASIC with optical chiplets. But unlike co-packaged optics, the ASIC and chiplets are placed on a high-performance substrate located on the host board.

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The compound complexity of co-packaged optics

Part 1: The OIF’s co-packaging initiative

Large-scale data centres consume huge amounts of power; one building on a data centre campus can consume 100MW. But there is a limit as to the overall power that can be supplied.

Jeff Hutchins

The challenge facing data centre operators is that networking, used to link the equipment inside the data centre, continues to consume more and more power.

That means less power remains for the servers; the compute that does the revenue-generating work.

This is forcing a rethink regarding networking and explains the growing interest in co-packaged optics, a technique that effectively adds optical input-output (I/O) to a chip.

Two industry organisations - the OIF and The Consortium for On-Board Optics (COBO) - have each started work to identify the requirements needed for co-packaged optics adoption.

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OIF to double data rate with a 224G electrical interface

• The OIF will develop a faster electrical signalling standard 
• The 224-gigabit standard will make optical modules sleeker 
• It will also help data centre operators keep up with ever-growing software workloads

Nathan TracyIt was just a matter of time before the OIF started on the next electrical interface standard beyond 112 gigabits-per-second (Gbps).

There have been announcements of new 800-gigabit optical modules along with growing interest in co-packaged optics, where optical interfaces are added alongside semiconductor chips.

Nathan Tracy, TE Connectivity and OIF president, says member companies will need to be creative to develop a 224-gigabit electrical interface. Getting signals to travel at such speeds over workable distances will be a challenge.  

The project, to kick-off in August, will begin with a study phase that will help identify the interface types needed.  

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The OIF’s 400ZR coherent interface starts to take shape

Part 2: Coherent developments

The Optical Internetworking Forum’s (OIF) group tasked with developing two styles of 400-gigabit coherent interface is now concentrating its efforts on one of the two.

When first announced last November, the 400ZR project planned to define a dense wavelength-division multiplexing (DWDM) 400-gigabit interface and a single wavelength one. Now the work is concentrating on the DWDM interface, with the single-channel interface deemed secondary. 

Karl Gass"It [the single channel] appears to be a very small percentage of what the fielded units would be,” says Karl Gass of Qorvo and the OIF Physical and Link Layer working group vice chair, optical, the group responsible for the 400ZR work.

The likelihood is that the resulting optical module will serve both applications. “Realistically, probably both [interfaces] will use a tunable laser because the goal is to have the same hardware,” says Gass.   

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Micro QSFP module to boost equipment port densities

Twelve companies are developing a compact Quad Small-Form-Factor Pluggable (QSFP) module. Dubbed the Micro QSFP (μQSFP), the multi-source agreement (MSA) will improve by a third the port count on a platform's face plate compared to the current QSFP.

Nathan Tracy

The μQSFP will support both copper and optical cabling, and will have an improved thermal performance, benefitting interfaces and platforms.

“There is always a quest for greater port density or aggregate bandwidth,” says Nathan Tracy, technologist at TE Connectivity and chair of the μQSFP MSA.

The challenge for the module makers is to provide denser form factors to increase overall system traffic. “As we go to higher densities, we are also increasing the thermal load,” says Tracy. “And so now it is a mechanical and a thermal [design] problem, and both need to be solved jointly.”

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OIF shows 56G electrical interfaces & CFP2-ACO

The Optical Internetworking Forum (OIF) is using the OFC exhibition taking place in Los Angeles this week to showcase the first electrical interfaces running at 56 Gigabit. Coherent optics in a CFP2 pluggable module is also being demonstrated.

“The most important thing for everyone is power consumption on the line card”

The OIF - an industry organisation comprising communications service providers, internet content providers, system vendors and component companies - is developing the next common electrical interface (CEI) specifications, as well as continuing to advance fixed and pluggable optical module specifications for coherent transmission including the pluggable CFP2.

“These are major milestones that the [demonstration] efforts are even taking place,” says Nathan Tracy, technologist at TE Connectivity and the OIF technical committee chair.

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