dark fiber and sfp distance limitations

Rene Avi rene.avi at gmx.net
Sat Jan 2 14:22:39 UTC 2010

On 02.01.2010 13:22, Richard A Steenbergen wrote:
> 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. 

Respectfully disagree here - been there (googled^H^Hmarket research, 
talked to both manufactures and resellers for the last year), bought 
sample and went through lab tests. Still was unable to find 
trustful/working EDFAs near the cost of a pair of 40dB SFPs. 200km SFPs 
are even cheaper than 'original' Cisco CWDM-SFPs (standard 80km). We 
have them on stock for resale (no commercials intended here), so this 
price indication is near real-time ;)

> 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.

It depends on the requirement - of course.

When Mike is heading for 10G DWDM demand levels he will probably have to 
amplify and cromatic-disperse-compensate with 120km G.652 (depending on 
the transceiver type) in any case. There are plenty of commercial 
solutions available for such spans, or he can try a building-block 

My point is to skip EDFAs in a single 1G 120km fiber setup for 
commercial aspects, let alone technical reasons (complexity, safety), if 
there is no requirement for more bandwidth. IMHO even with multiple 1G 
CWDM-style setups, but your mileage may of course vary.

> 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 

In Mikes scenario this might be as a +10dB pre-amp would do the trick 
with low power, but a post-amp (+17dB gain with levels around 
-20..-30dBm to get some additional power budget) is what I would use if 
EDFAs are a stringent requirement.

Most new long-haul transport systems have an automatic power-off feature 
  for optical protection (e.g.the splice teams after a fiber 
cut/disconnect) now because of this.

 > (i.e. you're in far more danger from someone with a green
> laser pointer ordered from the Internet :P). 

Agreed, but failed to save the whales - 

> 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.

Or stare in the beam at 500mW/27dBm without noticing because it is 
infrared, and there is no eyelid closure reflex. I tend not to take 
chances for my colleagues and me but as common knowledge says it is 
everyones own decision to look into the laser with the remaining good eye.

Rene Avi

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