Eli5: How does data move through fiber optic cables?

Question

I understand that there are 1’s and 0’s (on/off) in binary code to transmit data, but does the light inside the fiber optic flash billions of times per second to simulate the 1’s and 0’s? Im also curious if copper ethernet cables work in a similar way to transmit data.

In: Technology

Answer 1

>does the light inside the fiber optic flash billions of times per second to simulate the 1’s and 0’s?

Kind of

Full blown flashing is inefficient, it only lets you send 1 bit per change so sending information at 1 Gigabit per second requires adjusting the state of the light every nanosecond. The flashing is very resistant to noise which is good for longer distance, but is an inefficient use of a cable.

Copper ethernet cables basically do this but rely on multiple wires to give you better bandwidth. They have a pair of wires where one is high and the other low for a 0 and low/high for a 1. Similar to above this isn’t very efficient which is why gigabit ethernet has to use all 4 pairs of wires in the cable, so each one only has to flip every 2 nanoseconds at most.

The better way to ram data through your wire is with a form of modulation. What if instead of having your little colored laser alternate between full on and full off, it went between off, 1/3 on, 2/3 on, full on. Now you can slip 2 bits into each state change! This is Amplitude Modulation.

Now take a red laser and a blue laser, they can both travel in the same channel without interfering, and amplitude module both of them. Now each state change you can have 1 of 4 red levels and 1 of 4 blue levels for 16 options (4 bits), this is QAM-16(Quadrature amplitude modulation – aka two signals being amplitude modulated together). Still using the same cable, but now we can get 16x as much through it.

Boost your transmitter and receiver precision so they can differentiate 16 different levels per color, now each transition carries 1 of 256 different options so you can get 8x as much data down the line as you could just having one laser turning on/off. This is handy because it can let you greatly upgrade the bandwidth of an existing fiber optic cable just by adjusting the equipment on the end and doesn’t require laying potentially hundreds of miles of new cable just for more bandwidth.