Connection Tech: 3 Common Interfaces Explained

Posted 02/16/2011 at 4:40pm | by The Maximum PC Staff

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Light Peak

Intel’s optical bus aims to supplement—or replace—most of your current connectors.

Make room in your desk drawer for more obsolete cables. Busses that rely on electrical signals might soon be replaced with fiber-optic alternatives that use light waves, if Intel has its way. “Electrical interconnects have some practical limits we’re starting to see,” says Victor Krutul, director of Intel’s optical I/O team. “When you go through a connector, you get reflections and noise; you get electromagnetic interference.”

Intel’s optical Light Peak technology replaces copper wires with laser pulses traveling through fiber-optic cable. Not only does it not suffer from any of copper’s shortcomings, it’s capable of transferring data at speeds up to 10Gb/s in 100-meter lengths. And Intel is already planning to scale the technology to 100Gb/s.

Rather than functioning as an entirely new data bus, Light Peak will serve as a wrapper for existing buses. A single cable will be capable of carrying USB 3.0, HDMI, and other digital signals at the same time. Intel is meeting with consumer-electronics manufacturers to develop a Light Peak standard and to form a consortium, although Intel has already defined much of the technology. We’ll explain how Light Peak works—from the controller chip to the optics and cable—and where USB 3.0 fits into all of this.

Controller Chips Ahoy

Light Peak is a bridging technology that begins and ends with Intel’s 12mm-square controller chip. This silicon sliver can drive two Light Peak ports and performs three primary tasks: enumeration, routing, and power management.

At the enumeration level, a handshake occurs, during which Light Peak devices identify themselves. Plug a Light Peak–enabled HDMI display and USB keyboard into your PC, for instance, and the Light Peak controller will be informed that you’ve connected an HDMI display to port one and a USB keyboard to port two.

From a routing perspective, the I/O controller inside the PC (or other device, as the case may be) transmits native bus signals—USB 3.0, DisplayPort, PCI Express, or what have you—to the Light Peak controller. The controller keeps the data intact, but translates it from electrical current to pulses of light capable of traveling over the fiber-optic cable. A Light Peak controller inside the receiving device—a NAS box, for example—then translates those pulses back into electrical current.

The transmitting Light Peak controller adds a header on top of the data packets, so that the receiving controller can identify them and send them on to the proper device. This all happens at the transport layer, so the OS doesn’t require any Light Peak software to for the hardware to work.

Power management is the third leg of Light Peak stool: Intel expects that Light Peak cables will include copper wire to carry electrical power as well as fiber optics for data. And when a device that’s connected via a Light Peak cable stops sending data—when you MP3 player finishes syncing to your PC, for example—the controller will automatically shut itself off to conserve power.

A Closer Look at Optics and Cables

Photo detectors, lasers, and other components transmit and receive Light Peak signals. The photo detector remains active at all times, looking for data. When a connected device produces a signal using its tiny laser (a 250-micron-square vertical cavity surface-emitting laser, or VCSEL, to be precise), the detector wakens its corresponding controller chip.

Intel will add lasers to reach 100Gb/s speeds. “With optical, you can use wavelength-division multiplexing, or WDM,” according to Krutul, “which is just a fancy word for saying I can put multiple colors of light on a fiber. One can use a prism-like device to mux [multiplex] the different colored lasers into the fiber [at one end], and a second one at the other end to demux [de-multiplex] them.”

Light Peak cables are bi-directional, utilizing a single 125-micron fiber-optic strand to send data and a second one to receive. The cables are 99 percent fabricated from glass; the balance of the material is a doping agent. Intel considered using plastic fiber, but opted for glass because it delivers superior bandwidth. As we’ve already mentioned, a copper strand will carry electrical current to power devices.

Each fiber strand boasts an active area of 62.5 microns, providing ample tolerance to envelop the lasers’ eight-micron beams. Intel specifies multi-mode strands, which means the light waves follow multiple paths as they travel down the strand. Multi-mode fiber delivers higher bandwidth than single-mode fiber (in which light waves travel in a straight path), but the signal can become distorted by the time it reaches the end of the strand. That’s why Light Peak cables will be limited to 100 meters.

Setting Standards

Intel hasn’t formally announced any OEM partners that will put Light Peak into consumer devices, although executives from Sony and Nokia have publicly announced their support for the technology. Intel is developing the Light Peak controller chip and has recruited Avago, Ensphere Solutions, FOCI, Foxconn, Foxlink, IPtronics, and SAE Magnetics to build the lasers, optics, and cables.

If you’re wondering where that leaves USB 3.0, which Intel has yet to support in any of its chipsets, Intel says not to worry. “Our work with Light Peak in no way signals a change of our support for USB 3.0,” Krutul says. “We expect that both of them will be in the market simultaneously—maybe even in the same PC.”

Intel had anticipated that Light Peak consumer devices would ship in 2010, but Krutul says the company has revised its target. “We expect companies will start announcing components at the end of 2010, and that we’ll see Light Peak integrated into computers and devices in 2011.”