Researchers with the University of California at Santa Barbara, working in conjunction with Intel, announced Monday the next step in their joint plans to produce an entirely solid-state photonic processor assembly - a chip which processes data as light waves, without the need for microscopic, yet movable, parts.
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Member since:2006-07-25
Member since:2005-11-01
Well you sort of miss the point if you compare photons directly with electrons when comparing optical and electrical signals. In an electronic system, signals are usually conveyed as potential differences, and are therefore not directly limited to the speed at which electrons themselves can travel (i.e. their mobility in a semiconductor). Where "signal" is interpreted as a potential difference, an electrical signal propagates through a conductor very fast, approaching the speed of light. Of course, as you pointed out there are circuit delays introduced by various real factors (taking the CMOS example, parasitic capacitances and finite drain current to charge up the next MOSFET gate enough to drive it into strong inversion).
Still, the same delays will be present in any device that utilizes optics in the way that Intel is developing, thus my earlier comment. The issue is that the current optical modulators are still relatively "slow" compared to what is possible with modern loaded FETs. Maybe this will change, but I doubt these solid state optical modulators will ever be a whole lot faster than electronic transistors. In other words, I don't forsee this particular development path leading to an optical CPU. So we're back to my original assertion that the significance of lasers integrated with a high volume silicon process is largely for communications and perhaps, as some have mentioned, high speed interconnects. This latter option is pretty interesting for the massively parallel computer regime since optical interconnect busses wouldn't be subject to the crosstalk problems inherent with electrical signals in wires.
Member since:2006-07-30
Yes, you are right.
It's definately most interesting for communications.
Integrating some router IN the fibre optic itself would be really cool 
However, keep in mind that the technology is still quite young and might get faster over time.
Or is there any reason why it cannot?
Of course I'm talking propagation delay of components here, not speed of transmission - c is still rather limited ;-)
I'm really curious if it could allow for more 3d in computer design - it's just a shame to hardly use one dimension. I think it might because wires are not such an issue and if cooling does not get in our way it would allow for much smaller devices (potentially higher clock rate) to be built.
That being said I still find molecular computing way cooler if we can assure it does not get too hot.
Self assembling nano-structures would rock!
Member since:
2006-07-30
Hmm, not sure if I understand what you're trying to tell me...
I mean parallelisation can give you bandwidth but it cannot buy you less latency (at least not if the limiting factor is the speed of transmission).
But, of course, you are right that EM waves travel at the speed of light (which is, after all, an EM wave itself). Nevertheless electronic parts do have a propagation delay (bigger than their dimension/c) because the electrons have to move in order to establish a new state and they don't allways move as fast as light 'cause
a) they have mass and
b) there are things like resistors in their way
Also note that, talking of bandwidth, the skin effect can get in your way, which means that the current is only located at the surface which increases resistance.
On the other hand typical light already has a wavelength of 0.5µm, therefore having a frequency of about 6*10^14Hz which is pretty high.
But, as I said before, I'm not sure I got your point...
Edited 2006-09-20 12:38