Measurement and extraction of the Giles parameters in Ytterbium-doped fibre
Date
2009-03
Authors
Hendriks, Adriaan Jacobus
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : University of Stellenbosch
Abstract
The role fulfilled by theoretical models is rapidly increasing due to lasers becoming appli-
cation driven to satisfy certain criteria and demands. Construction of high precision lasers
requires good theoretical models and consequently good approximations of the parameters
that such models are based upon. Despite the di erent model formalisms, most share a com-
mon set of input parameters, including fibre waveguiding properties, input powers, transition
cross-sections and overlaps between guided modes and the dopand distribution.
Experimental and numerical work which was aimed at obtaining the wide-band emission
and absorption cross-sections of fibre indirectly by means of the Giles parameters was done.
The Giles parameters were used rather than the well known ionic cross-sections primarily
because of the convenient encapsulation of the cumbersome overlap factors and the ionic
cross-sections within the Giles parameters. The wide band spectral characteristics of the
Giles parameters are indispensable in the design of fibre lasers and amplifiers, as they form
the key parameters for laser models.
These parameters are normally obtained utilizing absorption spectroscopy to obtain the
absorption cross-sections and models such as the Fuchtbauer Ladenberg relation, the Mc-
Cumber relation or uorescence spectroscopy to obtain the emission cross-sections. Recent
research however indicates that these methods are inaccurate in certain spectral regions. An
investigation was launched to extract the Giles parameters from measurements of the ampli-
fied spontaneous emission (ASE) and pump absorption in ytterbium-doped fibre for several
lengths of fibre and subsequent computer simulations, utilizing an ampli
fier model. The
Giles parameters are extracted with a fitting algorithm that adjusts the relevant numerical
values to minimize the least square difference between the numerical data obtained from the
amplifier model and the measured data.
Using the model devised in this project on literature data, the Giles parameters were
extracted and compared to the Giles parameters extracted in literature on the same data.
This comparison conforms the extraction of the Giles parameters, utilizing the model devised
in this project, as successful.
Subsequently the model devised in this project was applied to extract the Giles parameters
from experimental data measured at Stellenbosch, using a double cladding ytterbium-doped
fibre. Finally a fibre laser was built utilizing the double cladding ytterbium-doped fibre and
the output was measured. The Giles parameters extracted were then used in a fibre laser
model to calculate the output and compare it to the measurements taken. This served as
suffcient verification that the Giles parameters extracted can be used to model a fibre laser
effciently.
Description
Thesis (MSc (Physics))--University of Stellenbosch, 2009.
Keywords
Giles parameters, Ytterbium-doped fibre, Fibre laser, Dissertations -- Physics, Theses -- Physics