Calculating Power Margin For Fiber-Optic Cable; Table 32: Estimated Values For Factors Causing Link Loss - Juniper acx1000 User Manual

Calculating Power Margin for Fiber-Optic Cable

Table 32: Estimated Values for Factors Causing Link Loss

Link-Loss Factor
Higher-order mode losses
Modal and chromatic dispersion
Connector
Splice
Fiber attenuation
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provide a margin of error, even though all the parts of an actual system do not operate
at the worst-case levels. To calculate the worst-case estimate of power budget (P
you assume minimum transmitter power (P
P = P – P
B T R
The following hypothetical power budget equation uses values measured in decibels
(dB) and decibels referred to one milliwatt (dBm):
P = P – P
B T R
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
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.
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.
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
Chapter 10: Transceiver and Cable Specifications
) and minimum receiver sensitivity (P
T
). A worst-case estimate of P
B
), which
M
assumes maximum LL:
M
Table 29 on page 78 lists an
),
B
):
R
91