Juniper PTX10001-36MR - How to Calculate Power Margin for Fiber-Optic Cables

How to Calculate Power Margin for Fiber-Opc Cables
Aer calculang a link's power budget, you can calculate the power margin (P
M
), which represents the
amount of power available aer subtracng aenuaon or link loss (LL) from the power budget (P
B
). A
worst-case esmate of P
M
assumes maximum LL:
P
M
= P
B
– LL
P
M
greater than zero indicates that the power budget is sucient to operate the receiver.
Factors that can cause link loss include higher-order mode losses, modal and chromac dispersion,
connectors, splices, and ber aenuaon. Table 31 on page 69 lists an esmated amount of loss for the
factors used in the following sample calculaons. For informaon about the actual amount of signal loss
caused by equipment and other factors, refer to vendor documentaon.
Table 31: Esmated Values for Factors Causing Link Loss
Link-Loss Factor Esmated Link-Loss Value
Higher-order mode losses Single mode—None
Mulmode—0.5 dB
Modal and chromac dispersion Single mode—None
Mulmode—None, if product of bandwidth and distance is less than 500 MHz-
km
Faulty connector 0.5 dB
Splice 0.5 dB
Fiber aenuaon Single mode—0.5 dB/km
Mulmode—1 dB/km
The following sample calculaon for a 2-km-long mulmode link with a power budget (P
B
) of 13 dB uses
the esmated values from Table 31 on page 69. This example calculates link loss (LL) as the sum of ber
aenuaon (2 km @ 1 dB/km, or 2 dB) and loss for ve connectors (0.5 dB per connector, or 2.5 dB) and
two splices (0.5 dB per splice, or 1 dB) as well as higher-order mode losses (0.5 dB). The power margin
(P
M
) is calculated as follows:
P
M
= P
B
– LL
69