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Emission
and Absorption
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Laser
Diodes
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Optical
Fibers
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Coupling
Light to Fibers
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An
important step in optical fiber technology has
been done with the development of fibers that able
to amplify light through stimulated emisson. Erbium
is a metallic rare earth element that is used to
amplify light signals sent along fiber-optic-cable.
If this chemical element is doped in a glass fiber
and light is pumped through it, the result is an
Erbium-Doped Fiber Amplifier (EDFA). These amplifiers
provide al large gain, which occurs when the fiber
is "pumped" by additional light input
at a wavelength shorter than 1.55 µm, e.g.
a wavelength of 980 nm.
Also, large output power is obtained
and near quantum-limited noise performance
in the 1.55 µm spectrum. EDFAs
enable the user transmitting an optical
signals over very long distance without
the need for electronic
signal regeneration. Up to now, EDFAs could only operate suffciently
in a restricted wavelength range, called the C-band (Coventional band)
transmission window, which is between 1530 nm and 1565 nm.
This educational kit teaches the principle of an EDFA by
using a open frame set-up that shows all single components
instead of a closed "black
box". A 1550 nm laser signal source is coupled into a 17 m Er
doped fiber. With the help of a 980 nm laser diode the Er fiber is
pumped an the result of optical amplification con be shown an measured
in a impressive way to the students. All necessary mechanical, optical
and electronic components for the EDFA system shown in the figure below
are included. The measurments require an 100 MHz oscilloscope, which
can be ordered an an option.
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