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Conflicting proposals hold back IEEE spec

Posted: 13 Feb 2013 ?? ?Print Version ?Bookmark and Share

Keywords:silicon photonics? Ethernet?

A handful of companies are facing a big decision as target date for drafting a spec to bring silicon photonics to market approaches. A key standards group is set to draft the spec by May, but so far none of the conflicting proposals from silicon photonics vendors appear to have adequate backing.

The IEEE 802.3bm group is setting a range of standards for low cost 40 and 100 Gbit/second Ethernet. They include a 4 x 25G module interface that silicon photonics vendors hope to use in 2014 to provide low cost, high speed links inside and between racks in data centres.

"Our biggest challenge is the different proposals from silicon photonic vendors are fairly evenly separated in votes," said Dan Dove, a director of technology at Applied Micro Circuits Corp., who chairs the group. "We have a lot of decision making in the next couple months," he said, noting proposals need a yes vote from three-quarters of the engineers attending.

"It's not uncommon at this stage in the standards process to have disparity, but... to get 75 per cent of the room to agree may be difficult," said Dove, a veteran of IEEE standard efforts.

The sticking point seems to be modulation schemes. In straw polls to date the group of 100 or so attending the meetings has been fairly evenly divided between four options:
? Fujitsu supports discrete multi-tone;
? Broadcom, Cisco and Luxtera back pulse amplitude modulation;
? Avago and Luxtera support parallel single mode;
? Huawei, IBM and Kotura want wavelength-division multiplexing.

"They all have their strengths and weaknesses, said Dove. "I would say the main sticking point is just sort of political logistics."

Intel keeps its power dry
Companies coming from an optical background typically are less familiar with complex modulation schemes such as PAM, and may consider it less technical viable. The group also takes costs and broad market adoption into consideration.

Ironically, Intel Corp. has not made any presentations to the group despite making a big splash recently by sampling 4x25G silicon photonics products based on a decade of research. It has only sent one engineer to the meetings so far, and that person did not attend on more than half of the meeting days.

Cisco is working on silicon photonics using 2.5-D chip stacks, said the head of Cisco's transceiver group, speaking at DesignCon. Start-ups Kotura and Luxtra shared their plans separately to field 4x25G silicon photonics in 2014. (see Kotura taps CMOS foundry for 100G photonics)

All four players hope to drive down 100G costs for a range of switches and other products. The meetings have drawn participants from a broad range of service, system and component vendors including Alcatel-Lucent, Deutsche Telekom, HP, Juniper, Microsoft and a range of start-ups. (see Cisco banks on silicon photonics for 2.5D, 3D ICs).

"The entire industry is investing to bring the cost of optics down, and when that happens we can get to products with multiple 100G ports," said Siddharth Sheth, vice president of marketing at Inphi Corp., speaking on a panel at the Linley Group event here this week.

- Rick Merritt
??EE Times

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