dark fiber and sfp distance limitations

Richard A Steenbergen ras at e-gerbil.net
Sat Jan 2 12:22:03 UTC 2010

On Sat, Jan 02, 2010 at 12:35:15PM +0100, Rene Avi wrote:
> With regards to suggested EDFA amplification tricks and similar: If
> the requirement is not > 150km at 1G or 80km at 10G/DWDM then I personally
> strongly disencourage the use of optical amps. 200km / 41dB 1G SFPs
> are available with costs way below dual EDFAs plus spare, and the
> chance for the untrained to get eye damages in the process of
> implementation is far less. So put some laser googles at around 400
> USD/each to the purchase list. If one decides to do so then add a
> post-amplifier on each *end* of the fiber link to increase the signal
> before hitting the receiver, and do not pump in star-wars class laser
> power at the beginning ;) .

Depends where you buy your EDFAs, I suspect you could probably get them
for less than the cost of a single channel of super long reach optics if
you tried hard enough. If you needed to add DWDM later on, and/or
dispersion compensation for 10G links the EDFAs will be needed anyways,
so sometimes it just makes sense to solve the problem once with an amp
rather than trying to solve it on a per-channel basis.

You're also vastly exagerating the power of what are effectively metro
reach amps, you're really in no danger of making an eye hazard unless
you start slapping on ultra long-haul 1500+km transport gear with class
3B lasers (i.e. you're in far more danger from someone with a green
laser pointer ordered from the Internet :P). Remember that 1550nm is
infrared and very effectively filtered by the human eye, so even a
+17dBm output EDFA (the max output for most metro systems) is still
going to be class 1M and effectively safe as long as you don't stare at
it in a microscope.

Richard A Steenbergen <ras at e-gerbil.net>       http://www.e-gerbil.net/ras
GPG Key ID: 0xF8B12CBC (7535 7F59 8204 ED1F CC1C 53AF 4C41 5ECA F8B1 2CBC)

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