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A Look at Photonic Clocking
zymano writes "In an article on the Electronic Engineering Times site James Siepmann shares a few thoughts about Photonic Clocking. Siepmann states: 'Copper interconnects are reaching their limit as data-transmission bandwidth and processor speed continue to rise. [..] Photonic clocking not only solves the limitations of electronic clocking, but also reduces jitter, skew, delay, crosstalk and power consumption while maintaining clock signal integrity for longer distances.'" Are Photonic Processors the next logical step, or will the almighty buck shuffle them aside because of cost?
Are Photonic Processors the next logical step, or will the almighty buck shuffle them aside because of cost?
Yeah, 'cause technology never gets cheaper. Hey, I've got an AT&T 8086 PC with a lovely green monitor that you can have for $5000, if you act now...
Nice thing about a pulse of light is that it can be made to reach lots of places at the same time, or nearly so. Just a normal burst of light from a point source has a spherical wavefront, but this can be modified by optics in various ways. Having designed plenty of really fast stuff and having had to deal with skew problems, I can see the advantadge, if real use can be made of it. I think it might even be possible on silicon, which would be required for quick adoption -- after all, the LSI only has to receive, the clock light source can be made of anything. Making a hybrid of course drives costs way up, though. but at current profit margins for fast cpu's this may not be much of a real issue.
If photonic processors go into widespread usage, it will probably be because of the almighty buck and companies deciding that they can make more of it by producing photonic processors.
Profits and competition are the main reason for a lot of the recent advances in processor performance. Look at the processor introductions back when 486 and pentium processors were around and Intel didn't have any credible competition.
"When you sit with a nice girl for two hours, it seems like two minutes. When you sit on a hot stove for two minutes, it
The article didn't say a whole lot, did it? It just said, "Gee, wouldn't photonic clocking be nice". It didn't say a whole lot about how, and whether it's feasible.
So, I'll quickly fill in what I know. To do clock distribution you need two types of components: waveguides and detectors. Let's assume you are going to work in silicon...
Waveguides function as the optical wiring, and includes things like bends and splitters. Although perhaps not trivial, it is relative straight-forward to make waveguides in or on silicon. Detectors, on the other hand, are not so easy, at least at the wavelength most people are interested in, 1550 nm. There's a number of people researching Ge growth for detectors on Si, and this does have promise, but it's not ready yet. Another option would be bonding InGaAs, but that might always be too expensive.
Now, if you want to do full up optical communication, on chip, you'll want modulators, too. These have been demonstrated by Intel and Cornell in silicon, but only at speeds around 1 Ghz. Optical amplifiers would be nice, too, and this has been demonstrated (using Raman amplification) by Intel and UCLA. (I'm not sure Raman amplification can give you the sorts of amplification and efficiency you really need, though).
(Sorry, I won't be able to respond to any replies; at least not until Monday. I'm off to bed and I'm not planning to be near a computer tomorrow).
Distributing your clock with photons imples you have a photon wave guide. If you are going to build a photon wave guide then why not build an electrical wave guide. Electrical wave guides, like for example coax cable, have wave velocities that are faster than light in glass, so they would logically be even better. And you dont' need any special materials like you would for optical wave guides.
The problem might be that usually wave guides have to be the size of the wavelength to work right. ghz wavelength are larger than the chip. Thus you get forced towards the optical region by this considerarion.
But you can beat this two ways.
1) use negative index of refraction materials. Then the waveguide can be smaller than the wave length
2) use near field waveguides with amplification. When the wavelength is a lot larger than the waveguide then the wave becomes evanscent (decaying). So it can't propagate very far. But hey, that's okay because the chip is not very wide either, so we can tolerate some loss of signal. And we could toss in some amplification to offset it.
Some drink at the fountain of knowledge. Others just gargle.
Transistors don't need clocks, logic gates don't need clocks, but flip-flops do. The reason you need a clock is because the outputs of a bit of logic will be 'unstable' for a while the result is computed. The clock tells the next piece of the system when to read. In place of that, you'd need a 'done' signal, which would rase transistor counts quite a bit. Not to mention it would be very hard to find people who would know how to design these things. I think the future of the CPU involves different parts of the system operating on separate clocks, transferring data via a 'networking' type system. Computers connected via Ethernet don't need to have their clocks synched in order to work. Think of a simple instruction decoder. The decoder reads the instructions, and opens the right 'gates' in the CPU so that there is an electrical connection between the two registers and the ALU, and inside the ALU to the adder or subtractor, or whatever depending on what instruction you're trying to run. Then, the clock signals and tells the ALU that the registers are ready. Without the clock, the ALU might try to add the wrong things. (the ALU doesn't need a clock to work) In the future you could have some sort of system where the decoder just sends a message to the ALU telling it to setup the adder, and to the registry file to access these two registers. Then the register file will send the data to the ALU whenever it's ready.
autopr0n is like, down and stuff.