Transforming computers of the future with optical interconnects

Feb 23, 2012
This sketch shows an optically connected topology called "HyperX." Credit: Image courtesy of HP Labs

The ability to manufacture photonic interconnect components -- modulators, detectors, waveguides, and filters -- on silicon substrates has finally been realized, and these optical interconnect structures show great potential for intrachip and interchip applications. HP Labs is studying how this shift to light-based interconnects may revolutionize the way computers are built. Moray McLaren of HP will present his findings at the Optical Fiber Communication Conference and Exposition/National Fiber Optic Engineers Conference, March 4-8 in Los Angeles.

In order to build the next generation of very large supercomputers, it's essential that scientists and engineers find a way to seamlessly scale computation performance without exceeding extraordinary power consumption. It is widely agreed that the major challenge to scaling future systems will no longer be the CMOS (Complementary Metal–Oxide–Semiconductor) integrated circuit technology but rather the data movement among processors and memory. The rapidly evolving technology of photonic interconnects promises to deliver this increase in computing capabilities by providing ultra-high communication bandwidths with extreme energy efficiency and should therefore provide the impetus to move the technology from the lab into actual products.

The ability to manufacture photonic interconnect components—modulators, detectors, waveguides, and filters—on silicon substrates has finally been realized, and these optical interconnect structures show great potential for both intrachip and interchip applications.

HP Labs, the central research lab for Hewlett Packard (HP) in Palo Alto, Calif., is studying how this shift to light-based interconnects may revolutionize the way computers are built. Moray McLaren of HP will present his findings at the Optical Fiber Communication Conference and Exposition/National Fiber Optic Engineers Conference, taking place March 4-8 at the Los Angeles Convention Center.

"This is an exciting time because it's a big transition for the industry," says McLaren, a researcher in HP Labs' Exascale Computing Lab, focused on inventing computer fabrics for next-generation IT solutions using a cross-layer, interdisciplinary approach. "In many respects, it's one of the inevitable forces of technology that's been much-heralded for 10 years. There's finally industry-wide agreement that it will happen. We've reached the point where we can say that it's an essential technology—we'll need to have optical interconnects to deliver these machines in the 2017-2019 timeframe."

How will these optical technologies change the way computers are built? Computer architects hold essentially two views on the role photonics will play.

One widely held view is that photonic interconnects are simply "smarter wire," explains McLaren. "Today's computers are connected with copper cable up to a certain distance, currently about 8 meters, and as data rates continue to increase, this threshold will drop to less than a meter. And once the threshold is exceeded, the interconnect transitions from copper to optics."

While high-speed electronic interconnects are becoming increasingly range-limited, they still tend to cost less than optical interconnects. "The result is that people are contorting the way they build systems to use as many of the less expensive electronic connections as possible—and non-optimal wiring topologies," notes McLaren.

The other viewpoint suggests that the characteristics and capabilities of optical communication are sufficiently different to the way things are done electronically—meaning that we need to entirely rethink how to build computers.

"There are things that we might do differently because the characteristics of optical interconnects are different," McLaren points out. "One very simple example is that within a data center, distance isn't much of a factor after you've transitioned to an optical interconnect. Having paid the price of moving from the electronic domain into the optical domain, we can connect up any distance."

Another related topic that HP Labs is investigating, in terms of data centers, is pushing down power consumption. The power for computational parts is still reducing with Moore's Law, along with the shrinking size of the individual transistors. But the power related to electronic communication isn't shrinking nearly as much because it's tied to real-world connectors and cables that don't scale in the same way.

Two of the key benefits of photonics are that it has the potential to provide lower-power communication over certain distances, and moving into the optical world provides more headroom in channel capacity and bandwidth densities are much higher. "Photonic interconnects have very different properties than the electronic interconnects that underpin today's computer architectures. To gain the maximum benefit from emerging nanophotonic interconnects, it's necessary to reevaluate the design tradeoff at the system architect level," McLaren notes.

Techniques that have fallen out of use in the electronic domain due to signal integrity considerations, such as broadcast and circuit switching, can be exploited to significant advantage in optical interconnects. Moving forward, the development of integrated CMOS nanophotonics will be critical to achieving the objectives of the most demanding computer development programs.

Explore further: Scientists reveal breakthrough in optical fibre communications

More information: McLaren's presentation at OFC/NFOEC, titled "Future computing architectures enabled by optical and nanophotonic interconnects," will take place Tuesday, March 6 at 5 p.m. in the Los Angeles Convention Center.

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User comments : 7

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BikeToAustralia
2 / 5 (4) Feb 23, 2012
Optical connections are different enough from electrical connections that the basic (electrical) design will not be viable. Innovation sells. If you do not adapt to changes you become extinct.

What makes optical connections so different? Make two electrical currents cross, you get sparks or interference, just like crossing two currents of water. Put a colored piece of plastic over one flashlight and another color for another flashlight. Cross the beams with the lights going to different places; the lights do not change each other.

Optical connections do not have as much of a problem with interference as electrical connections do. How many intelligent signals can be transmitted simultaneously, in both directions through an optical cable?

Nanoscale lasers communicating data (inside the computer case?) without the need for wires, traces or conduits. Oooh, look at all the pretty lights!
wealthychef
not rated yet Feb 23, 2012
The biggest hurdles in the future of supercomputing are power consumption and data transfer. Is this a twofer? Would be nice! Given the track record of technologies in blogs such as this one, I'm not holding my breath, but this does sound promising. I'd like to know more about bandwidth, latency and power consumption. These are the bottom lines. In a real computer, what's the speedup if you drop one of these guys in, best case?
Lurker2358
1 / 5 (1) Feb 23, 2012
Wealthychef:

Take a look at your Motherboard and other components in the computer.

Much of the area on any card is devoted to wires which need to navigate between and around components.

If you could remove all of the bus wires, and have only power supply wired, you'd save a lot of space on most components.

Further, if you could skip wires entirely, and transmit power optically as well, then you'd cut the needed space of many components even further.

Without wires, waste heat should be cut significantly, which means even less space wasted on cooling systems.

Optical interconnects should allow far faster computers with lower latency, particularly in servers, because you can often send the signal in a straight line, rather than around a wire navigating square or folded surfaces. You can simply send the optical signal across spaces, or possibly even between layers of multi-cored or multi-board systems.

Latency should decrease significantly at all scales of architecture..
infinite_energy
1 / 5 (1) Feb 23, 2012
Nothing travels faster than photons: not electrons.
You want the fastest computer: you have to use photons.
rwinners
not rated yet Feb 23, 2012
It's all about speed, but there are trade-offs. Photons are the faster, but electrons are working in the native medium. No need for translation.
Time will tell, but I think it will probably be a slow migration.
I mean, look at home electronics. Is wireless connectivity, even though easily available, becoming mainstream? I don't see it. People will not replace perfectly good electronics just to eliminate wire. edit: Well, not most people.
But they will make that choice when the current equipment becomes aged and infirm.
eric96
1 / 5 (1) Feb 24, 2012
@wealthychef

It's only as fast as the slowest link.
Not too long ago, the hard drive was the slowest link; that has changed to some extent with SSDs.
If you build a computer out of light, the choke point will again be the hard drive, but may also be the processor. A common transistor ( two switches, on and off ) made out of light would not be exponentially faster, then an electric one. A proper design would output much less heat and allow for higher clocks, but the same can be achieved with graphene; they would be toe to toe on the transistor level. Optics are unmatched however in bandwidth; data transfer. Still for the typical user, it's more of a question of the quantity of transistors. Intel solved a bandwidth issue with a ring bus, optical interconnects would be even better. At best, optical computers could be 10 times better over maturity of the technology unless then can make smaller optical transistors than silicons ones which I doubt.
eric96
1 / 5 (1) Feb 24, 2012
Correction,

@wealthychef

It's only as fast as the slowest link.
Not too long ago, the hard drive was the slowest link.
If you build a computer out of light, the choke point will again be the hard drive, but may also be the processor. A common transistor ( two switches, on and off ) made out of light would not be exponentially faster, then an electric one. A proper design would output much less heat and allow for higher clocks, but the same can be achieved with graphene. Graphene and silicon though have an additional advantage; you can make them much smaller than a light transistor. Also because light must be a product of electricity within a computer, it means the switching would not be faster on a computer made out of light. Because of all of these reasons, and because graphene can scale much smaller than silicon and light transistors, it is the clear winner hands down. Light is only good for data transfer, no benefit in switching speed (thinking).

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