Calculating Power Margin For Fiber-Optic Cable For The Srx5400 Services Gateway - Juniper SRX5400 Hardware Manual

Calculating Power Margin for Fiber-Optic Cable for the SRX5400 Services
Gateway
After calculating a link's power budget, you can calculate the power margin (P
amount of power available after subtracting attenuation or link loss (LL) from the power budget (P
worst-case estimate of P
P = P – LL
M B
A P greater than zero indicates that the power budget is sufficient to operate the receiver.
M
Factors that can cause link loss include higher-order mode losses, modal and chromatic dispersion,
connectors, splices, and fiber attenuation.
factors used in the following sample calculations. For information about the actual amount of signal loss
caused by equipment and other factors, see your vendor documentation.
Table 44: Estimated Values for Factors That Cause 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
2 km-long multimode link with a power budget (P
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
assumes maximum LL:
M
Table 44 on page 163
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
lists an estimated amount of loss for the
Table 44 on page 163
) of 13 dB:
B
), which represents the
M
B
to calculate link loss (LL) for a
163
). A