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ZyXEL
OLT-2300 Series Support Notes
All contents copyright
ٛ
2006 ZyXEL Communications Corporation.
32
uniformity specification in dB.
Typical uniformity specifications for a 1x32 splitter are in the range from 2 to 3 dB,
depending on the manufacturer.
What is the meaning of fixed attenuation and optical fiber attenuation?
Attenuation in the fiber plant arises from fixed components such as splitters and
patch panel (distribution frame) connectors, as well as from fiber attenuation. The
fiber attenuation varies with the fiber length and optical wavelength whereas the
attenuation of the fixed components does not. It is useful to think about the total
attenuation A as a combination of fixed and fiber attenuation, fiber
length-dependent terms, by
A (dB) = F (dB) +
α
(dB/km) * L (km) ,where
z
F is the fixed attenuation, and typical values are shown below:,
Attenuation
Fiber splice loss
0.3 dB
1:2 splitting loss in a 1:2 optical splitter
3.6 dB(max)
1:4 splitting loss in a 1:4 optical splitter
7.4 dB(max)
1:8 splitting loss in a 1:8 optical splitter
10.5 dB(max)
1:16 splitting loss in a 1:16 optical splitter
14 dB(max)
1:32 splitting loss in a 1:32 optical splitter
17.5 dB(max)
Fiber connector loss
0.2~ 0.3 dB
z
α
is the fiber attenuation coefficient in dB/km, typically, the
α
is 0.25dB/km at
1550nm/1490nm and 0.35dB/km at 1310nm.
z
L is the fiber distance in km.
What is the power budget value?
For minimum required received optical power at the optical receiver and available
maximum transmission optical power at the optical transmitter, the difference for
the optical transmission is called the
power budget
.
That is, the power budget=Tx output power- attenuation -Rx sensitivity, for
instance:
At the downstream direction (OLT->ONU), the OLT Tx power is +3dBm, and the
ONU sensitivity is -28dBm, then we can calculate that the downstream power
budget is 3-(-28) = 31dBm.
At the upstream direction (ONU->OLT), the ONU Tx power is +0dBm, and the
OLT sensitivity is -30dBm, then the downstream power budget is 0-(-30) =30dBm.
Because the downstream and upstream transmission is on the same single fiber,
so the available power budget of whole system in above case is 30dBm.