All,
I would like to kickstart some considerations in the group.
To review, the decisions made so far by the Task Force.
- All speed/distances upstream channels will use 1260 to 1280 nm. (This is quite solid, except for 10G 40km see below)
- 10G all distances downstream channels will use 1320 to 1340 nm. (This is also high confidence, except for 40km)
- For the LR budgets, reuse the LR specs from the two fiber links (except wavelength, TDP/TDEC, and loss budgets need reconsideration)
- For the ER budgets, reuse the ER specs from the two fiber links (except wavelength, TDP/TDEC, and loss budget need reconsideration)
- For the “Big Budget,” we are shooting for something like 25dB (true passive loss) – to be detailed.
- 25G all distances downstream channels will use 1300 to 1320 nm. (Note: this faces dispersion issues)
Non-motion: 50G downstream has not been discussed so much. My first order assumption is that it can use the same wavelengths s 25G, since it is using PAM4 and the channel bandwidth is about the same. But, this must be tested.
Some comments:
- 10G “ER” and “Big” specs: The fact is that if you want to go 40 km at 10G, the smart way to do it is to use the C band. The fiber loss differential between 1260 and 1550 is about
0.15 dB/km, which is 6 dB at 40km. That’s a lot. I think we could specify an economical “Big” 10G link that would reach an honest 40km (nonengineered) distance. In this case, we would not need the in between optical budget, or we could leave the 1330/1270
budget there for the BR20 spec. This is likely the cheapest way to get to the Big budget. What do people think? Should we explore the use of the C-band for the long 10G bidi? I think so.
- 25G: If I am to look at the 802.3cc specifications (which are the closest specs to what we need for 25G), I see that for 10km, they use the wavelength range 1295 to 1325; while for
40km, they use 1295 to 1310. They do this for dispersion reasons. So, the current agreed motion to use 1300-1320 nm for all distances I think can’t meet the TDEC specs at 40km. For the longer distances 25G BR20 and BR40, I would suggest that we use 1290
to 1310 nm. There are two big reasons for this choice: it matches the upstream wavelength of .3ca ONUs (and those should have good cost and high power), and it conforms to the .3cc ER max wavelength. Admittedly, this choice does limit the guard band to 10nm,
but this should present the same difficulty as a conventional CWDM filter, using collimated optics.
- For the 25G BR10 downstream wavelength, we can use a scaling argument. Namely, the 1310 max wavelength at 40km is 10nm away from the worst case dispersion zero. For 10km we can tolerate
4x worse dispersion, and since dispersion is almost linear in that region, we can go up to 1340nm. So, this would suggest that we can use the 1320 to 1340 nm downstream wavelength for the 25G BR10, which is the same as for 10G BR10 (keeping the possibility
of a dual rate module), and it makes the duplexing filter easier.
Please discuss, and if you agree or disagree, please say so. Thank you.
Sincerely,
Frank E,
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