transcievers/amplifiers for 150 km fiber run

Lamar Owen lowen at
Sat Oct 11 16:25:23 UTC 2008

On Friday 10 October 2008 14:50:11 Fletcher Kittredge wrote:
> We are looking to light a two strand fiber link of about 95 miles (or
> 150km).   It would be worth a lot to us not to have repeaters.   We are
> hoping for Gigabit Ethernet.   Sonet is possible but a less attractive
> solution.  Are there options for this sort of distance?   The longest
> current link we have is about 65 miles.  I understand the transmission
> characteristics of the fiber will effect distance of transmission.

EDFA's can extend your power budget a few dB.  Chromatic dispersion could 
still be an issue, though.

Used units that had previous homes in CATV supertrunk applications should work 
well, at least for GigE; up to 120mW is easily possible (I have a few 65mW 
(18.1dBm) EDFA's that came as part of a donation).  You hit the input of the 
EDFA with your ZX (1550nm) transceiver's transmit on each end, and don't look 
at the lit fiber or even a reflection of the lit fiber (IOW, wear laser 
safety goggles).  And don't even think about looping the EDFA output back 
around without many dB of attenuation.

At this power level you will have to use angle polish connectors at the EDFA 
output (the green SC/SPC or FC/APC ones) or you can burn out the pump laser 
with the reflections.

You also will need to notify your carrier's tech department of the power level 
with which you're lighting that fiber, as even several km down fiber from an 
EDFA is in Class IIIB laser territory.

A bare Cisco ZX GBIC or SFP is rated to light 70km of ordinary singlemoder 
fiber, and up to 100km of either premium (low-loss) or dispersion-shifted 
(which is also low-loss) singlemode fiber.  The rated output is between 0 and 
+5dBm (1 and 3.2 mW) for the ZX laser.  The link budget is 23dB for the 
standard ZX optics.  With a high-gain EDFA outputting 13 more dBm of power 
(20 times the power) you can get a link budget for loss of 36dB; which could 
increase your range 40km, on ordinary fiber.

So, in a nutshell, you'd take the TX from a ZX SFP or GBIC, a few feet worth 
of jumper to an EDFA, and light the fiber (with APC connectors only) from the 
EDFA output.  You do this at both ends.

More information about the NANOG mailing list