Example; Verifying Modal Bandwidth - 3Com CoreBuilder 2500 Getting Started Manual

D-4 A D: FDDI S
PPENDIX TANDARDS
Table D-4 Typical Losses for Connectors, Cables,
and Splices*
Type of Insertion
MIC connector
ST connector
(ceramic)
ST connector
(plastic)
ST connector
(stainless steel)
62.5/125 cable
8/125 cable
Bypass switch
Fusion splice
*A MIC-to-ST adapter connection and an ST-to-ST
connection are each considered 1 connector loss.

Example

Suppose that a link consisting of one km of
62.5/125 fiber with a maximum attenuation rating
of 1.75 dB/km is transmitting into one km of
50/125 fiber with a maximum attenuation rating of
3 dB/km. The fibers are joined using a fusion splice
rated at 0.3 dB and the link contains one in-line ST
connector rated at 0.6 dB. The calculation in
D-5 would arrive at the link loss attenuation value
for this linked fiber.
Loss
.6 dB
.6 dB
1.0 dB
.7 dB
1.0 to 3.0 dB maximum per km,
depending on cable quality
(nominal 2.0 dB)
.5 dB/km (AT&T Lightguide)
2.5 dB maximum
.1 to .3 dB depending on type used
(use .3 dB)
Table
Table D-5 Calculation Example for Link Loss
Attenuation Value
Type of Loss
Cable loss (62.5 mm)
Cable loss(50 mm)
Splice loss
ST connector loss
Insertion loss for mating unlike
fiber types
Total link attenuation
Because the resulting value, 7.85, does not exceed
the maximum attenuation value listed in
no adjustments are needed in the types of fibers
joined or how they are connected. The link meets all
of the specifications of the MMF-PMD standard.

Verifying Modal Bandwidth

Bandwidth for multimode fiber is referred to as
modal bandwidth because it varies based on the
modal field (or core diameter) of the fiber. The
bandwidth of an optical fiber is defined as the
lowest frequency at which the magnitude of the
baseband frequency response has decreased by 3 dB
compared to the magnitude at zero frequency.
Modal bandwidth is specified in units of MHz • km,
which indicates the amount of bandwidth supported
by the fiber for a one km distance.
Value
1 km (1.75 dB/km)
1 km (3 dB/km)
0.3 dB
0.6 dB
2.2 dB
7.85 dB
Table D-1,