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Dear All, I agreed at the last meeting to facilitate the development of
a more inclusive wavelength plan for the downstream. The current situation is that the PX30 budget would seem to
require cooled transmitters, and so the 6nm wide transmitter window centered at
1577nm is not an extra burden. However, for the PX10 and PX20 budgets, the OLT transmitter
may be an uncooled type, both because the output power is low, and because in
the case of PX10, the fiber distance is shorter and so dispersion control is
less needed. Therefore, there seems to be a justification for making the wavelength
band for the PX10 and PX20 types wider. So, the question then becomes: how to make the window wider?
It was discussed at the meeting that the wider window should contain the
narrow window inside of it. This has the possibility of defining a
universal ONT that can receive both the wide and narrow OLT signal. How
that actually works out in practice will have to be seen. One aspect to consider is the re-use of industry standard wavelength
plans, since then components are already available. From this
perspective, the CWDM wavelength at 1571 leaps out as a potential band. It
is true that the CWDM band is actually from 1563 to 1577 nm, but that is meant
for 0~70 C operation, and expansion to a 20nm width naturally occurs when the
-40 to +85 C operation is considered. So, proposal A would put the wider
wavelength band at 1560nm to 1580nm. Of course, this choice would make co-existence with the video
overlay impossible, with zero guard-band to the video band at 1550 to 1560nm. This
defeats the ¡®common ONT¡¯ idea, since it is impossible to make such an ONT.
Supposing we want to consider the coexistence with video for
these classes, then we must push the wavelength longer. Starting at 1574,
we could expand to a 1594nm. This is rather strange, having a center
wavelength at 1584, which is nearly the ¡®anti CWDM grid¡¯. We could call
this proposal B. On this alternative, we have sacrificed the compatibility
with those OTDR filters we heard about. This raises an inescapable
conclusion: to broaden the band, we will sacrifice either the video overlay or
the compatibility with certainly legacy OTDR filters. It should be noted
that there are even fewer system deployments with this particular OTDR
constraint than the video overlay. Combining the two motivations above, we turn to the next longer
CWDM wavelength: 1590nm. This would define the band to be 1580 to 1600nm;
called proposal C. In most PONs, this wavelength has no difficulties of
transmission. It also provides a 20nm guard-band from the video, which is
a little better than the 14 nm with the narrow plan. It is disjoint with
the narrow plan; however, it is in a part of the spectrum where the narrow plan
seems not to care. So, we could build an ONU that responds from 1576 to 1600,
and that would receive both signals. This is probably not the most
practical solution, but at least it is possible. So, that¡¯s sort of what we have: Option A: 1560 ~ 1580nm Option B: 1574 ~ 1594nm Option C: 1580 ~ 1600nm I¡¯ll stop at this point, and leave the ¡®floor¡¯ open for
comments. Sincerely, Dr. Frank J. Effenberger ¸¥À¼¿Ë °£·Ò²©¸ñ Huawei Technologies Office (732) 625 3002 Cell (908) 670 3889 |