If the maximum data bandwidth is sent down a fibre optic cable, constantly, maxing out the cable's capacity, how much data is in transit over any given distance?
Perhaps I have an incorrect understanding of how this works, but I assume that the data packets are sent one after the other, in a line down the wire, not one at a time, so if a wire has a 1000GB/second bandwidth, it can have many of these terabyte 'seconds' going down the same wire at the same time.
Is this understanding in any way correct? If so, how much data can a fibre optic cable have in transit over x distance if sending maximum capacity throughout the length of the wire?
Best Answer
Let's say you transmit at 10 Gb/s. Then the bit period is 0.1 ns.
The index of refraction of glass is about 1.5, so the speed of propagation through the fiber is \$c/1.5\$, or about \$200\times10^6\ \mathrm{m}/\mathrm{s}\$.
So each bit occupies about 20 mm of length, and there are about 50 bits "in flight" in every meter of fiber.
If you want to know what happens when you use the "maximum data bandwidth" of the fiber, you'll have to define what you mean by that. In practical systems, the bandwidth isn't limited by the fiber but by the transmitters and receivers at each end. The number of wavelength division multiplexing channels that can be used is limited by nonlinear behavior that occurs in the fiber when the total power (across all channels) gets too high. So even that limit depends on the sensitivity of your receivers (which determines how low you can make the power in each channel).