Mikael Malmström

Abstract
The objective of this thesis was to explore the usefulness of all-fiber
modulators for laser applications. In particular refractive index change
was achieved in the core of the studied fiber-components, with either the
elasto-optic effect or the electro-optic effect. This was realized with the
aid of electrodes placed inside the fiber cladding and ran along the core
and provided either stress in the core due to thermal expansion, or an
electric field over the core. The electrodes consisted of low melting-point
alloys, such as BiSn and AuSn, which were pushed into the hole-fibers
used, in the liquid state which then solidified to form continues electrodes
filling the entire space in the hole.
Together with an analyzer such as a polarizer or an interferometer
the achieved refractive index modulation in the core could then be
translated into amplitude modulation of the guided light, which was
subsequently utilized for switching fiber-lasers to generate, cavity
dumped, Q-switched, or mode-locked pulses. The fast rise/fall-time of the
elasto-optic devices was only a few nanoseconds owing to fast thermal
expansion of the electrodes, the maximum repetition rate, however, was
limited to a few tens of kHz, due to slow thermal processes. The electrooptic
fiber components displayed similar rise/fall-time, although, with a
much higher cut-off frequency of ~ 16 MHz.
The electro-optic all-fiber switch was also employed to select singe
pulses at 1 MHz repetition rate out of a 7 MHz train of pulses.
Additionally, simulations using the finite element method were
performed in order to gain insight and explain the underlying processes of
the observed response of a long period grating written in a 2-hole fiber
with electrodes, when applying HV-pulses to one of the electrodes.
The thesis show that the all-fiber components used show great
potential of becoming price-worthy high damage threshold components
for laser applications in the future.