Calculating Power Margin For Fiber-Optic Cable; Table 63: Estimated Values For Factors Causing Link Loss - Juniper MX2020 Hardware Manual

Calculating Power Margin for Fiber-Optic Cable

Copyright © 2013, Juniper Networks, Inc.
Appendix E: Cable and Wire Guidelines and Specifications for the MX2020 Router
P = –15 dBm – (–28 dBm)
B
P = 13 dB
B
After calculating a link's power budget you can calculate the power margin (P
represents the amount of power available after subtracting attenuation or link loss (LL)
from the power budget (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 (HOL), modal and
chromatic dispersion, connectors, splices, and fiber attenuation.
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 63: 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 33 to calculate link loss (LL)
for a 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
Higher-order mode 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
), which
M
assumes maximum LL:
M
Table 63 on page 387
) of 13 dB:
B
387