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Intel touts progress toward 50Gbps optical link

Apr 29, 2011 — by LinuxDevices Staff — from the LinuxDevices Archive — 1 views

Intel has reportedly shown working prototypes of silicon for a photonics link that moves data at 50Gbps. Capable of transmitting the equivalent of an entire HD movie every second, the technology will be ready to be integrated into PCs, embedded devices, and consumer electronics by 2015, according to the chipmaker.

At a company event this week, Intel demonstrated what it said were working prototypes of the chips that will be used to transmit and receive data optically, according to IDG News Service writer Agam Shah. Non-working mockups of the cables that will be used to carry the data were also displayed, the story adds.

Intel first announced its 50Gbps phototonics link last year in conjunction with the Integrated Photonics Research Conference held in Monterey, Calif. Justin Rattner, Intel chief technology officer and director of Intel Labs, said at the time that "the silicon photonics link … marks a significant achievement in our long term vision of 'siliconizing' photonics and bringing high bandwidth, low cost optical communications in and around future PCs, servers, and consumer devices."

Intel's silicon photonics transmitter and receiver
(Click to enlarge)

Intel previously claimed the silicon photonics interconnect (above) would work over distances of up to 50 meters (about 160 feet). But IDG's Shah now quotes Jeff Demain, Intel's strategy director of circuits and system research at Intel Labs, as saying the 50Gbps links will work up to 100 meters.

Demain is to have added that the silicon photonics technology — expected to be ready for commercial use by 2015 — will coexist with its earlier Light Peak interconnect. The latter currently runs at 10Gb/sec. over copper and is slated for an optical upgrade next year.

As we review later in this story, Intel now refers to Light Peak as Thunderbolt. The technology was brought to market in February on three Apple MacBook Pro notebook computers.

"We see (silicon photonics and Thunderbolt) … as complementary. It's the evolution of these connectors and protocols as they move forward," Demain was quoted as saying. Thunderbolt is more than a cable. It's a router chip that aggregates DisplayPort and PCI-Express."

According to Intel, its silicon photonics technology stems from a 2006 breakthrough, whereby the light-emitting properties of Indium Phosphide were combined for the first time with the light-routing capabilities of silicon in a single hybrid chip. The prototypes are said to include four silicon lasers, whose light beams each travel into an optical modulator that encodes data onto them at 12.5Gbps. The four beams are then combined and sent to a single optical fiber for a total data rate of 50Gbps, the chipmaker says.

At the other end of the fiber, a receiver chip separates the four optical beams and directs them into photo detectors, converting their data back into electrical signals. The transmitter and receiver are "assembled using low-cost manufacturing techniques familiar to the semiconductor industry," according to Intel.

More about Thunderbolt

Thunderbolt reached the market on three MacBook Pro laptops from Apple: a 13-inch model that starts at $1,199; a 15-inch model starting at $1,799, and a 17-inch model that costs $2,499. Still an Apple exclusive at this point, it can be recognized on all three portables by a DisplayPort-style interface decorated with a Thunderbolt icon (below).

Thunderbolt uses a DisplayPort-style connector

According to Intel, the key to Thunderbolt's abilities is a controller chip (below left) that allows both DisplayPort and PCI Express protocols to be carried over a single cable (below right). This controller offers "low latency with highly accurate time synchronization," and provides for bus-powered devices (up to 10 Watts), the company adds.

Intel's Thunderbolt controllers (left) are intended for PCs and up to six peripherals (right)
(Click either to enlarge)

Apple's MacBook Pro product page touts Thunderbolt as offering "two 10Gb/sec. data channels," while Intel says it features "dual-channel 10Gbps per port." This means "a full 10 Gb./sec of bandwidth can be provided for the first device, as well as additional downstream devices," the chipmaker adds.

A Promise storage device connected to Apple's new MacBook Pro via Thunderbolt
(Click to enlarge)

We interpret these claims as meaning that while Thunderbolt never offers more than 10Gb/sec. of bandwidth, it does not slow down when multiple devices are connected. According to Intel, Thunderbolt allows up to seven devices (a PC and six peripherals) to be connected to a single cable with almost no latency. The distance between each of the devices may be up to three meters (9.8 feet), the company adds.

Thunderbolt-ready peripherals such as LaCie's Little Big Disk include dual ports so they can be part of a daisy chain. Apart from Apple, vendors that have signed on include Aja, Apogee, Avid, Blackmagic, Promise, and Universal Audio, Intel said in February.

Thunderbolt requires no termination, unlike SCSI, but Intel says any DisplayPort device needs to be the last one in a chain (so, apparently, the interconnect will not support multiple monitors). Given that it relays both DisplayPort and PCI Express signals, Thunderbolt will make it "simple to create gigabit Ethernet, FireWire, or eSATA adapters using existing PCI Express device drivers," the chipmaker adds.

 Intel's 50Gbps silicon photonics link
Source: Intel
(click any of the images to play)

Further information

More information on Intel's silicon photonics research may be found on the company's website, here. A related presentation, white paper, and backgrounder, all in PDF format, may be found here, here, and here, respectively.

Further information on Thunderbolt may be found on Intel's Thunderbolt product page.

Jonathan Angel can be followed at

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