[Noisebridge-discuss] Hot off the IEEE press

[Charles Collicutt]

On Thu, Sep 09, 2010 at 04:58:36PM -0700, Glen Jarvis wrote:
> I've been waiting for a breakthrough for something like an 'optical
> transistor' and have been theorizing to anyone who will listen how this much
> make things faster (totally non-qualified talk -- like those who sit in a
> bar and give advice on how to 'rule the country'). But, it does make sense
> that optical will be much faster than electrical.

Disclaimer: I don't really know what I'm talking about, I just happen to have
attended a tutorial on silicon photonics at a conference recently.

It depends on what you mean by "faster". Signal mobility is about the same
for electrical signals in copper as it is for optical signals in a waveguide.
That means that optical latency will never be lower than electrical latency.

The main advantages of photonics are that power consumption is independent of
the length of the cable/waveguide (at least for the lengths we are interested
in, i.e. on-chip up to datacentre cabling) and signal integrity is better due
to the lack of the crosstalk that plagues electrical signaling.

Electrical signaling has serious power and integrity issues, which mean that
communication bandwidths do not scale with computational power. ITRS
predictions for electrical interconnects over the next decade are not
promising. We're basically going to have to switch to photonics or we're
going to end up with lots of really fast processors talking to each other
really slowly. (NB: I was told this by people with a vested interest in
photonics.)

Anyway, my impression is that we're not there yet, with the exception of
"active cabling" there isn't really any photonics outside the lab yet, but
we'll probably all have photonic interconnects in a decade or two.

I haven't heard anything about optical transistors. Why would they be a good
thing?

-- 
Charles

"The dinosaurs became extinct because they didn't have a space program.
 And if we become extinct because we don't have a space program, it'll
 serve us right!"
         -- Larry Niven, quoted by Arthur C. Clarke in 2001
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