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Basic Concept
Fibre lasers are a special class of
lasers differing from the “classic design”. The optical
resonator consists of an optical fibre which can be coiled to a
drum providing extremely long amplification lengths.
Within this experiment, students are introduced to the basics of
optical pumping with subsequent application by means of an
Erbium doped optical fibre (EDF). This type of fibre is commonly
used as an amplifier in long distance telecommunication as a
so-called EDFA (Erbium Doped Fibre Amplifier). Due to its
particular properties, the EDF is a promising candidate as a
laser source for telecommunication. Furthermore, it can also be
used as an active fibre laser gyroscope.
Experimental Set-up
This experiment allows students to study the EDF in a linear as
well as a ring configuration. As a pump source a diode laser,
emitting around 100 mW at a wavelength of 980 nm, is applied.
Via a wavelength division multiplexer (WDM), the pump light is
coupled to the EDF. The other end of the EDF is connected to a
beam expander which delivers a parallel light bundle which is
coupled after a distance of 100 mm back into a patch fibre.
To close the ring this fibre is connected to the WDM. In common
applications, this “free space” propagating part is not used.
However, for experimental purposes a variety of demonstrations
can be done. By means of two thin glass plate - used as an
output coupler - a small fraction of the ring laser radiation is
coupled out for further analysis. Hereby counter propagating
ring modes can also be demonstrated and verified.
Additional optical components can be inserted like passive
Q-switch, birefringent tuner, etc. With the provided
photodetector and modulator, the time response like spiking and
life-time of excited states can be studied.
By means of a mirror, which is accomodated inside a ST
connector, the ring laser can be converted to a linear laser.
For this purpose, the connection to the external mode separator
is removed and the mirror plugged to the EDF. To monitor the
radiation, the now not used port of the WDM is available. |
