On Oct 30, 2020, at 9:03 AM, Tarko Tikan <tarko@lanparty.ee> wrote:

hey,

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.

Just to add to my original suggestion, we just did 100G-ZR4 over 30dB link with pre-FEC BER 3.174E-11.

As OP is asking for a solution for 25dB I don't see any reason why ZR4 would not work and why you would need coherent, amplifiers or any other additional solution except when you are limited by QSFP28 SFF power.

--
tarko