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Comment by networkchad | Hacker News Reader

Most simple answer is you can cram N number of light streams via WDM (wave division multiplexing). You transmit N number of parallel streams on different wavelengths.

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Thanks for that -- And is something analogous not possible for electrons in a wire?

The highest frequency you can practically send long distances over coax is around 1-2GHz. When I had a cable modem the highest I saw was 900MHz. Therefore, regardless of what encoding scheme you use you will never get more then a couple GHz of bandwidth.

Visible light starts at 400THz so right off the bat you get 10k times more more headroom before physics becomes the limiting factor.

I was thinking somehow that the response / recovery time of the silicon detectors to react to the laser pulses would be a limiting factor, is that at all valid?

Like, you cannot blink faster than <x> nanoseconds and get a CCD(?) to see it properly. (I'm sure it's not like a CCD with readout, etc. but whatever mechanism is the correct one, is there some natural minimum read time?)

It's analogous to frequency multiplexing in radio (and radio carried over a wire -- which high speed codings like modern Ethernet or PCIe are, in practice). For example, sending one channel on a carrier at 100 MHz, and another at 102 MHz. These days potentially thousands of carriers may be used in parallel. Practical bandwidths in radio are limited to a few gigahertz at most, though. By comparison the visible spectrum is several hundred thousand GHz wide. There's much more bandwidth to work with at optical frequencies.

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