how do undersea cables transfer data from and to millions of people simultaneously?

Question

I understand it’s just signals and 1s and 0s but don’t the signals overlap in the undersea cables?

In: Engineering

Answer 1

[Time Division Multiplexing](https://en.wikipedia.org/wiki/Time-division_multiplexing). Lots of it.

Very high frequency (fast) modulation and demodulation (aka modems, but for fiber optics).

[Blinkenlights](https://en.wikipedia.org/wiki/Optical_fiber)

Edit: Looks like Fiber uses [Wavelength Division Multiplexing](https://en.wikipedia.org/wiki/Wavelength-division_multiplexing).

In Time Division Multiplexing, instead of sending one signal over one “wire,” multiple signals are broken up into multiple segments, which are sent one after another, in order to send multiple signals over one wire.

With Wavelength Division Multiplexing, the signals operate on different wavelengths (frequencies), which are able to work across the same wire without interfering with each other. Because fiber optics operate on light, these wavelengths manifest as different colors. Similar to how different radio frequencies can exist over the air, and you can tune a demodulator (a radio) to the frequency of the signal (radio station) you want to pick up.