On 26.11.2024 05:31, Mark Tinka wrote:
But getting 100G beyond 10km without amplification and dispersion compensation means you will need to go coherent.
NRZ-based 100G-ZR4 says it will do 80km, but real life has shown things can be vastly different, primarily due to generally poor fibre characteristics.
I agree on the struggle with bad fiber, and we've had to use 100G ER4 "Lite" on links around 10km before too. But I think you are a little too pessimistic with putting the limit of what NRZ can do at 10km. From my experience 30km is also possible with NRZ. We have a few ER4 and ER4 "Lite", that is Flexoptix Q.161HG.40 and Q.161HG.25, running between cities, with one span being a bit over 30km. That one is muxed parallel to our DWDM, so take an additional 2.5dB for our filters.
That said, you might find OpenXR's latest work exciting for GPON. That group has put out a 400G coherent plug that uses digital subcarriers (wavelengths nested within a wavelength) to deliver 16x 25G channels in a p2mp topology, right in the plug itself. It can run both in normal or BiDi mode, and certainly makes future GPON and Active-E p2mp architectures very interesting.
That's very interesting, even if we don't use PON. I hadn't heard of this before. On the face of it, it sounds expensive to have to use a 400G capable coherent receiver for a 25G customer. But I'm curious to see how the prices shake out in the end, with potential mass adoption. Best, Joel -- Joel Busch, Network SWITCH Werdstrasse 2, P.O. Box, 8021 Zurich, Switzerland