User's Manual

Fiber Optics Powerwave
2 - 2 Rev. P1A9-Draft 2004-11 VM100 56/EN – User’s Manual
Fiber Optics in General
In the beginning, when fiber optics became in practical use, a ’first window’ with a
wavelength of 850nm was used. It had a loss of approximately 3dB/km.
As the technology developed, the ’second window’ at 1300nm became more attractive
because of the lower loss, below 1dB/km.
Today, the ’third window’ at 1550nm is the most attractive wavelength with a loss of
0.2dB/km for silica-based fibers.
The ’second window’ at 1300nm can today, with silica-based fibers, achieve a loss of
only 0.35dB/km.
The following figure illustrates the three ’windows’ where the loss is low over the usable
wavelength range.
Figure 2-2. The three wavelength windows
Figure 2-2 illustrates the losses for the three wavelengt windows, with silica-based
fibers.
The large absorption peaks in the diagram are caused mainly by moisture in the fiber,
and by scattering at shorter wavlengths.
Figure 2-2 also shows the visible light wavelegth band, the loss curve caused by
Rayleigh scattering at shorter wavelengths, and the loss curve caused by fiber molecule
absorption at longer wavelengths.
The wavelengts used by the FON boards in the repeaters are within the second window
(1310nm) and the third window (1550nm).
0
10
0
1600
5
600 800 1000 1200 1400
dB/km
1800 2000nm
Third
window
Second
window
First
window
Rayleigh
scattering
loss
Fiber
molecule
absorption
loss
Visible light