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Optical Control of Light on a Silicon Chip
An anonymous reader writes "Researchers at Cornell University have demonstrated a device that allows one low-powered beam of light to switch another on and off, on silicon, a key component for future "photonic" microcircuits in which light replaces electrons for propagating signals. It is highly desirable to use silicon--the dominant material in the microelectronic industry--as the platform for these photonic chips.
The approach developed confines the beam to be switched in a circular resonator, greatly reducing the footprint required on the chip and allowing a very small change in refractive index to shift the material from transparent to opaque."
I believe that one of the reasons optical CPUs are attractive is that they WOULDNT need a huge heatsink. The heat in chips is caused by the losses when the transistors switch, optical CPUs don't have any transistors so don't have these losses. There will probably be a loss of light which could heat up the chip in a similar way, but I can't see why speed would have anything to do with it in an optical CPU. Speed effects the heat in electrical CPUs because higher speed = more switching = more switching losses per second. I don't THINK this would happen in an optical CPU because there is no gate capacitance to charge etc so the time a switch is partially on (highest losses) will be ridiculously small, so loss will occur for a shorter time = less heat. Probably.
There is very little loss in the FETs in a CPU either, until you start switching them really fast.
I'm pretty sure there will be switching losses in optical switches as well, especially while they are changing state. Optical CPUs probably won't need a heatsink until they become very advanced and operate way above the speeds achievable now, but its likely they will eventually. After all, the first few computers I had didn't need a heatsink either.
-Daniel
> Light travels about 10x faster than electrons in their optimal medium, so the potential processing speed limit is increased.
What?? I thought electrons traveled at the speed of light! AFAIK the advantage of optical over electrical is that the paths of photons can cross w/o interfering with each other, thus potentially allowing for smaller processors.
The unofficial
Ah, there was a discussion about this in a recent thread... can't remember which though. The electrons cannot travel with the speed of light because they have mass. But they don't need travel much anyway, because the information is transmitted via the electrostatic force which can be explained as the exchange of virtual (light-speed fast) photons. So the first electron in the wire gets pushed a bit and in turn pushes the second electron in the wire and so forth, much like when you push one end of a stick and automagically the other end moves too. In both cases the effect is not light-speedy but speedy nonetheless.
the most sexp i get is my paren-mode.
Diffraction and interferences are linear processes - you need a nonlinear process (such as the change in index used in the devices) to have one signal modify another.
given the same levels of power consumption
given this, the heat produced will be identical, and IAAEE.
Of course it's for "optical" switching!
;-).
Well, for the optical modules in a switch, anyway.
There's a much more obvious application for this than optical CPUs.
It's every optical networking component maker's wet dream to be able to modulate light on silicon, as this would bring down costs of optical modules for 10 Gb/s, 2.5Gb/s, etc. In principle, you could live without the expensive optical components (pin-diodes, EAMs) and do it all this on one single piece of silicon.
Now we just need to find a clever way of emitting light on silicon as well as finding a cost effective way of packaging ICs with optical fibres coming out of them
PS: Didn't Intel demonstrate optical modulation on Silicon already??
"What is the exact use for this?"
How many pins are on the latest AMD64? 939? 940? something like that. Optical interconnect could reduce that to single digits.
I'm not sure what loading concerns there are with optics... one problem I run into in my designs is needing to connect to many other devices, and that slows things down.