Calculating Power Budget And Power Margin For Fiber-Optic Cables; Calculating Power Budget For Fiber-Optic Cable; Calculating Power Margin For Fiber-Optic Cable - Juniper T640 Hardware Manual

T640 Core Router Hardware Guide
Related
Documentation

Calculating Power Budget and Power Margin for Fiber-Optic Cables

446
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 less than the limits specified for the type of link in 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 on page 446
1. Calculating Power Budget for Fiber-Optic Cable on page 446
Calculating Power Margin for Fiber-Optic Cable on page 446
2.

Calculating Power Budget for Fiber-Optic Cable

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
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

Calculating Power Margin for Fiber-Optic Cable

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.
an estimated amount of loss for the factors used in the following sample calculations.
) and minimum receiver sensitivity (P
T
). A worst-case estimate of P
B
), which
M
assumes maximum LL:
M
Table 71 on page 447
Copyright © 2013, Juniper Networks, Inc.
),
B
):
R
lists