Calculating Power Budget And Power Margin For Fiber-Optic Cables; How To Calculate Power Budget For Fiber-Optic Cables - Juniper QFX5100 Hardware Manual

An efficient optical data link must have enough light to exceed the minimum power that the receiver
requires to operate within its specifications. In addition, the total dispersion must be within the limits
specified for the type of link in the Telcordia Technologies document GR-253-CORE (Section 4.3) and
International Telecommunications Union (ITU) document G.957.
When chromatic dispersion is at the maximum allowed, its effect can be considered as a power penalty
in the power budget. The optical power budget must allow for the sum of component attenuation,
power penalties (including those from dispersion), and a safety margin for unexpected losses.

Calculating Power Budget and Power Margin for Fiber-Optic Cables

IN THIS SECTION

How to Calculate Power Budget for Fiber-Optic Cables | 99

How to Calculate Power Margin for Fiber-Optic Cables | 100
Use the information in this topic and the specifications for your optical interface to calculate the power
budget and power margin for fiber-optic cables.
TIP: You can use the Hardware Compatibility Tool
transceivers supported on your Juniper Networks device.
To calculate the power budget and power margin, perform the following tasks:
How to Calculate Power Budget for Fiber-Optic Cables
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 ), you assume minimum transmitter power (P
B
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):
to find information about the pluggable
) and minimum receiver sensitivity (P
T
99
):
R