- What is the maximal and economic switching rate of a current transistor? (it might be cheaper to produce several slower transistors who together have the same computing power)
Since modern processors run at around 3 Ghz and there are a bunch of transistors in a line to do one clock cycle, I guess the answer is around 30-300 Ghz (which is 1/1000 of the frequency of visible light). This question is a fundamental limit how much information can be processed in a single electrical wire, to process more, you need parallelism. - As light passing through a fibre is a electromagnetical wave, it can be (in theory) modulated the same ways radio waves are modulated: amplitude modulation/amplitude-shift key, frequency modulation/frequency-shift key, phase modulation/phase-shift key, (a combination of amplitude and phase modulation), OFDM. Which of these modulations are used in practice?
I know that through detuning lasers, one could probably archive frequency modulation and demodulate it through a phase-locked or frequency-locked loop, but I guess currently, most systems only use on-off/amplitude modulation on different wavelengths (WDM) because you just switch the laser or some filter in front of it on and off. - If electronics can only operate at a certain maximum frequency (see question 1), how can a single fibre transport more information than that?
I guess the only way, implemented right now, is through WDM.
Monday, September 22, 2008
Gigabit- and Terrabit-Router Questions
Here are a bunch of questions which I don't really know the answer to, but would like to know to understand the next two readings better.
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Actually these questions are not difficult if you look them up on the web. For example, terahertz transistors have been demonstrated in the lab in the last year.
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