Abstract
M.Ing.
Data communications have increased tremendously over the last few years. Therefore, it
is important to use the potential large bandwidth of the existing optical fibre network to
satisfy the demand. Wavelength-division multiplexing (WDM) enables one to have
several channels on a single fibre while the system remains transparent for the bit rate
and format of the signals on the individual channels. Erbium doped fibre lasers have
narrow linewidths and the wavelength is tunable over the optical amplifier wavelength
range. They are therefore very attractive sources to test WDM systems. The exciting
possibility of simultaneous laser action at predetermined wavelengths X,, X2, ... , X, makes
the fibre laser a very important source for WDM systems.
In this work we concentrated on two ring laser configurations. The first one uses a
tunable Fabry-Perot filter, whereas the second one has a polarization filter for tunability
and wavelength selection. The Fabry-Perot filter had a finesse of 167, a bandwidth of
30.0 GHz and a free spectral range of 5010 GHz. This laser configuration was tunable
from 1546.52 nm to 1584.04 nm (37.52 nm) and the linewidth was less than 0.037 nm.
The polarization filter comprised a 31X-polarization controller, two XJ4-polarization
controllers, a X/2-polarization controller for wavelength tunability and a polarizer. This
ring laser was tunable from 1559.59 nm to 1568.69 nm (9.1 nm) and had a linewidth of
less than 0.037 nm. We obtained a slope efficiency of 17.6 % for the erbium doped fibre
laser.
For the first time computer software was developed that makes use of the Poincare sphere
and Jones matrices to present the state of polarization and the operation of a polarization
filter visually. The power spectra of both ring laser configurations were determined as a
function of the output coupling using signal flow diagrams and the power equations for
the ring laser. According to our knowledge, the influence of the output coupler on the
finesse and the linewidth of the fibre ring laser has been studied for the first time.