100G over 100 km of dark fiber

Fri Oct 30 15:16:10 UTC 2020

On 10/30/20 10:27 AM, Vincentz Petzholtz wrote:
> If it’s just a single 100G channel needed you could try 100GBASE-ZR4. Specified for 80km, 30db power budget they could actually reach more the 80km.
> Dispersion should also be „no" problem in the 1310nm length. I have to say that I never tried this on 100km distance without coherent solutions.

If you end up marginal with the ZR4 at the receive end, you may be able 
to use a silicon optical preamp to make up the margin.

If you are at the noise floor already (ZR4 receivers are pretty good), 
you may just need to dump more power into the line.  I recently came 
across the PDFA (like an EDFA but the fiber is doped with Praseodymium 
instead of Erbium) which operate on the 1310 band and can push upwards 
of 20-23dBm of power out.  They are not cheap (low 5 figures), but they 
are cheaper than coherent and will still let you run on 1310 so you 
don't have chromatic dispersion issues.  With good (ER4 or ZR4) 
receivers good down to -20dBm or so, you've got 30-33dB of link budget 
which should just about make your 100km if it's decent fiber.  They're 
also usable as a pre-amp (different configuration optimized for gain and 
noise figure instead of power, similar to EDFA preamps) and have 
performance potentially better than silicon amps in that situation.

The 1550 PAM4 pizza box EDFA+Mux+DCM that others have mentioned may also 
work and end up even cheaper, but I normally see those for 40-60km or 
"up to" 80km with them really pushing the link budget at that point.

Honestly, I'd be tempted to just suck it up and do a coherent solution, 
though I admit it would probably be at least 2x the cost.  You can 
probably get a 200G carrier, though.
-- 
Brandon Martin