Sun Turns to Lasers to Speed Up Computer Chips

alphadogg writes to mention that Sun is attempting to move from the typical design of multiple small chips back to a unified single-wafer design. "The company is announcing today a $44 million contract from the Pentagon to explore replacing the wires between computer chips with laser beams. The technology, part of a field of computer science known as silicon photonics, would eradicate the most daunting bottleneck facing today's supercomputer designers: moving information rapidly to solve problems that require hundreds or thousands of processors."

Re:Are actuators faster than direct connections?

[TheRealMindChild]

I am not an expert in electricity by no means, but I have a fundamental understanding of it (or so I think). Energy is energy. With no resistance (don't overlook this point), light traveling via laser or via electrons flowing over a wire, the speed would be the same. Now, in reality, there IS resistance... there is always a "friction" or resistance (ohm) when energy is passing over a wire. In a vacuum, a laser will move as fast as energy can possibly travel. At least on paper.

Re:Are actuators faster than direct connections?

[isomeme]

Electrons in a superconductor (a material with zero resistance) do not travel at the speed of light.

Re:Why not...

[JustinOpinion]

To use the beloved transportation analogy: it's like moving your cargo off of trucks and onto a high-speed train. Yes it takes time to move cargo, but it's worth it if the time savings of the high-speed train are big enough (for long enough distances, the savings can be significant).

In this case, there may be a delay associated with signal processing, but if the optical transmission is sufficiently faster than an equivalent electrical one, then it's worth it. Considering that electrical signals themselves need to undergo various kinds of switching and processing anyway (data written or read from a bus), I don't know that converting to laser signals will add much of a delay.

Re:Why not...

[Arthur B.]

So do transistors. What's your point ? Analog computation ? Yurk.

Re:Are actuators faster than direct connections?

[JustinOpinion]

The article doesn't make it clear whether using optical communications is intended to reduce latency or increase bandwidth.

With respect to latency: the electrical signals travel at ~30% the speed of light, whereas the optical signals travel at ~70% the speed of light (it depends on refractive index, etc.). Over the distances we're talking about (as you said, mm to dm), that's only fractions of a nanoseconds delay savings [google.com]. This is on the order of a modern computer's switching time [google.com]. All this complexity to get rid of a one or two processor cycles of latency?

I suspect instead they are looking to increase bandwidth. An optical fiber can carry very high data rates. Moreover a single physical fiber can carry multiple simultaneous channels (e.g. different wavelengths of light). So the intention may instead be to create high-bandwidth links between various processors. Using on-chip lasers can make the entire assembly smaller and faster than the equivalent for electrical wires.

Really what they want, I think, is to implement the same kind of high-speed optical switching we use for transcontinental fiber-optics into a single computer or computer cluster. If you can put all the switching and multiplexing components directly onto the silicon chips, then you can have the best of both worlds: well-established silicon microchips that interface directly into well-understood high-speed optical switching systems.

Re:Are actuators faster than direct connections?

[arjay-tea]

It's not so much transit time, as parallelization where the big advantage is. Many frequencies of light can share the same medium without interfering with each other. Imagine many processors and memory chips streaming data to each other simultaneously, over the same backplane.

Re:Whenever anyone says 50%

[NeutronCowboy]

Absolutely. Personally, I do the same thing: if someone asks me about the likelihood of something happening about which I have no clue, I tell them flat out "50/50. Here, let me flip a coin." I expect the same thing to have happened here as well.

Now, someone please mod me redundant. Executive summaries should be discouraged wherever possible.

Re:Don't Shake the computer!

[vertinox]

how will dust be solved?

Why don't you crack open your 3.5" hard disk drive and find out why dust doesn't bother those sensitive platters? ;)

Re:Are actuators faster than direct connections?

[Anonymous Coward]

This idea absolutely correct. It is all about bandwidth. If you have several chips on the same board and want to send data between them, you either use board traces, or you build a custom package, but either way you have to use metal and you hit a wall. Even if you cover the entire surface of your chip in solder bumps you will never get as much bandwidth as you would like.

Think about where the bottlenecks are in your computer... memory and IO. You want a faster supercomputer, well you need more processors and more memory, but you always have that communication overheard. But what if your memory had a direct optical link to your processor?