User Manual

Fiber-Optic and Network Cable Guidelines
M40 Internet Router Hardware Guide
52
Table 16 lists the estimated amount of loss for factors that cause link loss.
Table 16: Estimating Link Loss
In the following sample calculation for a 2 km-long multimode link with a power budget (
P
B
)
of 13 dB, the link loss (
LL) is the sum of the following factors:
 Fiber attenuation for 2 km @ 1.0 dB/km= 2 dB
 Loss for five connectors @ 0.5 dB per connector = 5(0.5 dB) = 2.5 dB
 Loss for two splices @ 0.5 dB per splice =2(0.5 dB) = 1 dB
 Higher-order loss = 0.5 dB
 Clock recovery module = 1 dB
The power margin is as follows:
P
M
= P
B
– LL
P
M
= 13 dB – 2 km (1.0 dB/km) – 5 (0.5 dB) – 2 (0.5 dB) – 0.5 dB [HOL] – 1 dB [CRM]
PM = 13 dB – 2 dB – 2.5 dB – 1 dB – 0.5 dB – 1 dB
P
M
= 6 dB
In the following sample calculation for an 8 km-long single-mode link with a power budget
(P
B
) of 13 dB, the link loss (LL) is the sum of fiber attenuation (8 km @ 0.5 dB/km, or 4 dB)
and loss for seven connectors @ 0.5 dB per connector, or 3.5 dB:
P
M
= P
B
– LL
P
M
= 13 dB – 8 km (0.5 dB/km) – 7 (0.5 dB)
P
M
= 13 dB – 4 dB – 3.5 dB
P
M
= 5.5 dB
In both examples, the calculated power margin is greater than zero, indicating that the link
has sufficient power for transmission and does not exceed the maximum receiver input
power.
Link-Loss Factor Estimated Link-Loss Value
Higher-order mode losses Single-mode—None
Multimode—0.5 dB
Modal and chromatic
dispersion
Single-mode—None
Multimode—None, if product of bandwidth and distance is less than 500
MHz–km
Connector 0.5 dB
Splice 0.5 dB
Fiber attenuation Single-mode—0.5 dB/km
Multimode—1 dB/km