Basic Concept

Fibre lasers are a special group 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 unused port of the WDM is available.