Ignoring hardware at either end and their technological limitations, what is the maximum theoretical bandwidth of fibre optic cables currently in use / being deployed in a FTTH type situations? I understand there's a limit to the number of freqencies or channels we can have in fibres, and each channel would have a theoretic max bandwidth too, I'd imagine?
I'm asking particularly to find out more about the current plan for a National Broadband Network in Australia, which is supposed to roll out fibre optics to almost every premises in the country. I'm interested in finding out how much data we can fit down the fibre before we have to dig it all up and replace it with newer fibres with higher bandwidth or some new medium we haven't started talking about yet. More general answers are interesting too.
Short answer: A good order of magnitude rule of thumb for the maximum possible bandwidth of an optical fibre channel is about 1 petabit per second per optical mode. So a "single" mode fibre (fibre with one bound eigenfield) actually has in theory two such channels, one for each polarisation state of the bound eigenfield.
Short answer: A good order of magnitude rule of thumb for the maximum possible bandwidth of an optical fibre channel is about 1 petabit per second per optical mode. So a "single" mode fibre (fibre with one bound eigenfield) actually has in theory two such channels, one for each polarisation state of the bound eigenfield.
I'll just concentrate on the theoretical capacity of a single, long-haul fibre; see roadrunner66's answer for discussion of the branching in an optical network. The fundamental limits always get down to a question of signal to noise in the measurement (i.e. demodulation by the receiver circuit). The one, fundamentally anavoidable, noise source on a fibre link is quantum shot noise, so I'll concentrate on that. Therefore, what follows will apply to a short fibre: other noise sources (such as Raman, amplified spontaneous emission from in-line optical amplifiers, Rayleigh scattering, Brillouin scattering) tend to become significant roughly in proportion to the fibre length and some power (exponent) of the power borne by the fibre.
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