Terabit interconnect to take hold in the data centre

Intel and Corning have further detailed their 1.6 Terabit interface technology for the data centre.

The collaboration combines Intel's silicon photonics technology operating at 25 Gigabit-per-fibre with Corning's ClearCurve LX multimode fibre and latest MXC connector.

Silicon photonics wafer and the ClearCurve fibres. Source: Intel

The fibre has a 300m reach, triple the reach of existing multi-mode fibre at such speeds, and uses a 1310nm wavelength. Used with the MXC connector that supports 64 fibres, the overall capacity will be 1.6 Terabits-per-second (Tbps).

"Each channel has a send and a receive fibre which are full duplex," says Victor Krutul, director business development and marketing for silicon photonics at Intel. "You can send 0.8Tbps on one direction and 0.8Tbps in the other direction at the same time."

The link supports connections within a rack and between racks; for example, connecting a data centre's top-of-rack Ethernet switch with an end-of-row one.

James Kisner, an analyst at global investment banking firm, Jefferies, views Intel’s efforts as providing important validation for the fledgling silicon photonics market.

However, in a research note, he points out that it is unclear whether large data centre equipment buyers will be eager to adopt the multi-mode fibre solution as it is more expensive than single mode. Equally, large data centres have increasingly longer span requirements - 500m to 2km - further promoting the long term use of single mode fibre.

Rack Scale Architecture

The latest details of the silicon photonics/ ClearCurve cabling were given as part of an Intel update on several data centre technologies including its Atom C2000 processor family for microservers, the FM5224 72-port Ethernet switch chip, and Intel's Rack Scale Architecture (RSA) that uses the new cabling and connector. 

Intel is a member of Facebook's Open Compute Project based on a disaggregated system design that separates storage, computing and networking. "When I upgrade the microprocessors on the motherboard, I don't have to throw away the NICs [network interface controllers] and disc drives," says Krutul. The disaggregation can be within a rack or between rows of equipment. Intel's RSA is a disaggregated design example.

The chip company discussed an RSA design for Facebook. The rack has three 100Gbps silicon photonics modules per tray. Each module has four transmit and four receive fibres, or 24 fibres per tray and per cable. “Different versions of RSA will have more or less modules depending on requirements," says Krutul. Intel has also demonstrated a 32-fibre MXC prototype connector.

Corning says the ClearCurve fibre delivers several benefits. The fibre has a smaller bend radius of 7.5mm, enabling fibre routing on a line card. The 50 micron multimode fibre face is also expanded to 180 microns using a beam expander lens. The lenses make connector alignment easier and less sensitive to dust. Corning says the MXC connector comprises seven parts, fewer than other optical connectors.

Fibre and connector standardisation are key to ensure broad use, says Daryl Inniss, vice president and practice leader, components at Ovum.

"Intel is the only 1310nm multimode transmitter and receiver supplier, and expanding this optical link into other applications like enterprise data centres may require a broader supply base," says Inniss in a comment piece. But the fact that Corning is participating in the development signals a big market in the making, he says. 

Intel has not said when the silicon photonics transceiver and fibre/ connector will be generally available. "We are not discussing schedules or pricing at this time," says Krutul.

Silicon photonics: Intel's first lab venture

The chip company has been developing silicon photonics technology for a decade.

"As our microprocessors get faster, you need bigger and faster pipes in and around the servers," says Krutul. "That is a our whole goal - feeding our microprocessors."

Intel is setting up what it calls 'lab ventures', with silicon photonics chosen to be the first.

"You have a research organisation that does not do productisation, and business units that just do products," says Krutul. "You need something in between so that technology can move from pure research to product; a lab venture is an organisational structure to allow that movement to happen."

The lab ventures will be discussed more in the coming year.