Calculating the Fiber-Optic Cable Power Budget for EX Series Devices
To ensure that fiber-optic connections have sufficient power for correct operation, calculate the link's
power budget when planning fiber-optic cable layout and distances to ensure that fiber-optic connections
have sufficient power for correct operation. The power budget is the maximum amount of power the link
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 for fiber-optic cable power budget (P
B
) for the link:
1. Determine values for the link's minimum transmitter power (P
T
) and minimum receiver sensitivity (P
R
).
For example, here, (P
T
) and (P
R
) are measured in decibels, and decibels are referred to one milliwatt
(dBm).
P
T
= – 15 dBm
P
R
= – 28 dBm
NOTE: See the specifications for your transmitter and receiver to find the minimum transmitter
power and minimum receiver sensitivity.
2. Calculate the power budget (P
B
) by subtracting (P
R
) from (P
T
):
– 15 dBm – (–28 dBm) = 13 dBm
Calculating the Fiber-Optic Cable Power Margin for EX Series Devices
Calculate the link's power margin when planning fiber-optic cable layout and distances to ensure that
fiber-optic connections have sufficient signal power to overcome system losses and still satisfy the minimum
input requirements of the receiver for the required performance level. The power margin (P
M
) is the amount
of power available after attenuation or link loss (LL) has been subtracted from the power budget (P
B
).
When you calculate the power margin, 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 worst-case levels. A power margin (P
M
) greater
than zero indicates that the power budget is sufficient to operate the receiver and that it does not exceed
the maximum receiver input power. This means the link will work. A (P
M
) that is zero or negative indicates
insufficient power to operate the receiver. See the specification for your receiver to find the maximum
receiver input power.
Before you begin to calculate the power margin:
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