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 弗兰克 埃芬博格
Huawei Technologies
USA
1700 Alma
Drive, Plano TX 75075
Office (732) 625
3002
Cell (908) 670
3889