T1600 Calculating Optical Power Margin For Fiber-Optic Cable - Juniper T1600 Hardware Manual

T1600 Core Router Hardware Guide

T1600 Calculating Optical Power Margin for Fiber-Optic Cable

368
After calculating a link's optical power budget you can calculate the optical power margin
( ), which represents the amount of power available after subtracting attenuation or
P
M
link loss ( ) from the optical power budget (
LL
maximum LL :
P = P – LL
M B
A greater than zero indicates that the optical power budget is sufficient to operate
P
M
the receiver.
Factors that can cause link loss include higher-order mode losses, modal and chromatic
dispersion, connectors, splices, and fiber attenuation. Table 55 on page 368 lists an
estimated amount of loss for the factors used in the following sample calculations. For
information about the actual amount of signal loss caused by equipment and other
factors, refer to vendor documentation.
Table 55: Estimated Values for Factors Causing Link Loss
Link-Loss Factor
Higher-order mode losses
Modal and chromatic dispersion
Connector
Splice
Fiber attenuation
The following example uses the estimated values in Table 55 on page 368 to calculate
link loss ( ) for a 2 km-long multimode link with an optical power budget (
LL
Fiber attenuation for 2 km @ 1.0 dB/km= 2 dB
Loss for five connectors @ 0.5 dB per connector = 5(0.5 dB) = 2.5 dB
Loss for two splices @ 0.5 dB per splice =2(0.5 dB) = 1 dB
Higher-order loss = 0.5 dB
Clock recovery module = 1 dB
The power margin ( P ) is calculated as follows:
M
). A worst-case estimate of
P
B
Estimated Link-Loss Value
Single-mode—None
Multimode—0.5 dB
Single-mode—None
Multimode—None, if product of bandwidth and distance
is less than 500 MHz–km
0.5 dB
0.5 dB
Single-mode—0.5 dB/km
Multimode—1 dB/km
Copyright © 2010, Juniper Networks, Inc.
assumes
P
M
) of 13 dB:
P
B