OIF addresses 800-gigabit coherent interfaces

The OIF has started work on 800-gigabit coherent interfaces, a follow-on to its 400-gigabit 400ZR specification work.

Two requirements are being addressed: an 800-gigabit dense wavelength division (DWDM) interface with a 80-120km span for data centre interconnect, and an unamplified single-channel fixed-wavelength 2-10km coherent link for campuses.

The need for 800 gigabit

Tad Hofmeister

“When we hit that 90 per cent mark on 400ZR, we had people stand up and say: ‘We are ready to start 800ZR’,” says Karl Gass, OIF, physical link layer working group – optical vice-chair.

But completing the work has taken time. “The first 90 per cent of a project takes about half the time and the last 10 per cent takes the other half,” says Gass.

So only in mid-2020 did the OIF’s attention turn to the new standard, starting with determining the use cases.

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Features added around 400ZR aims to bring order to 400ZR+

The OIF has started a project to combine Flexible Ethernet (FlexE) technology with the 400ZR coherent interface standard.

Karl Gass400ZR is designed to transmit a 400 Gigabit Ethernet (GbE) signal over at least 80km using coherent optical transmission.

Adding FlexE technology will enable 4x100GbE signals to also be transmitted.

Separately, the OIF has started a project to create a 96 gigabaud (GBd) coherent driver modulator specification. Such a symbol rate enables 800 gigabits of data to be sent using a single carrier.

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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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OIF moves to raise coherent transmission baud rate

The Optical Internetworking Forum (OIF) has started modulator and receiver specification work to enhance coherent optical transmission performance. The OIF initiative aims to optimise modulator and receiver photonics operating at a higher baud rate than the current 32 Gigabaud (Gbaud).

"We want the two projects to look at those trade-offs and look at how we could build the particular components that could support higher individual channel rates,” says Karl Gass of Qorvo and the OIF physical and link layer working group vice chair, optical.  

Karl Gass

The OIF members, which include operators, internet content providers, equipment makers, and optical component and chip players, want components that work over a wide bandwidth, says Gass. This will allow the modulator and receiver to be optimised for the new higher baud rate.

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