Calculating Power Margin For Fiber-Optic Cable; Table 18: Estimated Values For Factors Causing Link Loss - Juniper Internet Router M160 Hardware Manual

Calculating Power Margin for Fiber-Optic Cable

After calculating a link's power budget (using the equation described in
"Calculating Power Budget for Fiber-Optic Cable" on page 72), you can
calculate the power margin (
available after subtracting attenuation or link loss (
(
P M = P B – LL
A
to operate the receiver.
Factors that can cause link loss include higher-order mode losses, modal and
chromatic dispersion, connectors, splices, and fiber attenuation. Table 18
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 18: Estimated Values for Factors Causing Link Loss

The following example uses the estimated values in Table 18 to calculate link loss
(
The power margin (
). A worst-case estimate of
P B
greater than zero indicates that the power budget is sufficient
P M
Link-Loss Factor
Higher-order mode losses
Modal and chromatic dispersion
Connector
Splice
Fiber attenuation
) for a 2 km-long multimode link with a 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
) is calculated as follows:
P M
), which represents the amount of power
P M
) from the power budget
LL
assumes maximum
P M
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
Network Cable Specifications and Guidelines
Preparing for Router Installation
:
LL
) of 13 dB:
P B
73