Specifications

Ethernet Design Considerations
RADring
Installation & Operation Manual
7-6 Fiber Optic Design Considerations 3/11/98 12:25
Losses in Optical Fibers
Losses are expressed in dB.
Losses (dB) = 10log
P
P
in
out
Where P
in
is the power coupled into the fiber, and Pout is the power
reaching the other end of the fiber.
Typical losses of graded-index fibers at a wavelength of 820mm (the
common LED wavelength) are as follows:
50/125 micron: 3.0 - 3.5dB/km
62.5/125 micron: 3.5 - 4.0dB/km Multimode
100/140 micron: 4.5 - 5.0dB/km
Calculation of Optical Link Budgets
The maximum link attenuation (optical "link budget") equals the power
coupled into the fiber at transmitter side minus receiver sensitivity.
Table 7-1 Typical Values of Link Budgets
Fiber type Output Power Sensitivity Link Budget
50/125 micron -22 dBm -32 dBm 10 dB
62.5/125 micron -18 dBm -32 dBm 14 dB
100/140 micron -14 dBm -32 dBm 18 dB
Losses in Optical Fibers
Typical losses that must be considered when calculating losses in actual fiber
optic links are as follows:
Cable Losses 3-5 dB/km
Connector Losses 1 - 2dB/connector
Splice Losses 0.1 - 0.3dB/splice
Aging,, Temperature 3dB
The values given above are to be used as guidelines. Always use cable and
connector losses specified by the manufacturer.
Connectors are the weakest point. The "cost" of a "bad" connector may be as
high as 1 km of fiber.
Note
Do not design in too many connectors!