Calculating the Power Budget for Fiber-Optic Cable for the SRX3600
Services Gateway
To ensure that fiber-optic connections have sufficient power for correct operation, you need to calculate
the link's power budget, which is the maximum amount of power it can transmit. When you calculate the
power budget, you use a worst-case analysis to 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
B
), you assume minimum transmitter power (P
T
) and minimum receiver sensitivity (P
R
):
P
B
= P
T
– P
R
The following hypothetical power budget equation uses values measured in decibels (dB) and decibels
referred to one milliwatt (dBm):
P
B
= P
T
– P
R
P
B
= –15 dBm – (–28 dBm)
P
B
= 13 dB
RELATED DOCUMENTATION
Signal Loss in Multimode and Single-Mode Fiber-Optic Cable for the SRX3600 Services Gateway | 93
Attenuation and Dispersion in Fiber-Optic Cable for the SRX3600 Services Gateway | 94
Calculating the Power Margin for Fiber-Optic Cable for the SRX3600 Services Gateway | 95
Calculating the Power Margin for Fiber-Optic Cable for the SRX3600
Services Gateway
After calculating a link's power budget, you can calculate the power margin (P
M
), which represents the
amount of power available after subtracting attenuation or link loss (LL) from the power budget (P
B
). A
worst-case estimate of P
M
assumes maximum LL:
P
M
= P
B
– LL
A P
M
greater than zero indicates that the power budget is sufficient 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 29 on page 96 lists an estimated amount of loss for the
95
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