[Cerowrt-devel] Fiber bandwidth vs distance

Hal Murray hmurray at megapathdsl.net
Tue Dec 19 07:45:20 EST 2017

> I don't know the physics behind it, but people who have better insight  than
> I do tell me "it's hard" to run longer hops (if one wants any kind of  high
> bitrate). 

The buzzword is dispersion.  The speed of the photon varies slightly with 
color.  All the photons in a pulse are not the same color.  The farther they 
go, the more they spread out.  If they spread out far enough, they overlap 
neighboring bits and the receiver can't sort things out.

You would like all the photons in a pulse to be the same color.  Lasers are 
close.  Just not close enough.

The dimension of quality for fibers used to be megabit*miles.  (actually 
megabits/second)  That probably assumed a specific bandwidth of the light.  
For a given transmitter, you could go X miles at Y bits/sec, or 2*X at Y/2...

Sample data sheet:
Dispersion is the next to bottom section on the right of the first page.

> Todays laser links are in the few km per hop range, with is easily at  least
> one magnitude shorter than radio based equivalents. 

What's the bandwidth of those radio links?

These are my opinions.  I hate spam.

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