Annual Report 2005 - IPHT Jena

Die nachfolgend präsentierten Ergebnisse in diesem
Jahresbericht machen die hohe Attraktivität
der Forschung zu optischen Fasern und Faseranwendungen
deutlich und bieten in Kombination
mit dem komplementären Arbeitsgebiet zur
photonischen Instrumentierung im IPHT breite
zukünftige Anwendungsmöglichkeiten.
OPTIK / OPTICS
40
2.2. Scientific Results
2.2.1 Flame hydrolysis technique (FHD)
for the preparation of advanced
optical materials
(C. Aichele, St. Grimm, M. Köhler,
K. Schuster)
The flame hydrolysis technique allows the production
of highest quality silica. This material is
primarily used for planar optical waveguide
devices and components or for the deposition of
substrate tubes by OVD (Outside Vapor Deposition).
To utilize the potential of this technology we
are engaged in new applications.
The recent concentration of microlithography on
an excitation wavelength of 193 nm requires an
improvement of the optical materials and devices
used.
For high power density and excellent replication
quality, materials are necessary which provide
special, very well-defined properties in terms of
optical quality as well as type and distribution of
the dopant hydrogen. The flame hydrolysis technique
enables the preparation of a high-quality
quartz glass material combined with the implementation
of different dopant distributions in a
wide range.
Fig. 2.1: FHD-configuration.
A further miniaturization of the structure at the
same excitation wavelength can be achieved by
what is known as immersion lithography. Aqueous
fluids (immersions) with a still higher refractive
index than standard materials and good optical
transparency are particularly suitable for
these processes.
By flame hydrolysis it is possible to prepare highly
pure, oxidic particles with a main size of about
5–10 nm and a narrow particle size distribution.
These oxidic materials can be used as additives
to water to increase its refractive index for application
as an immersion medium.
Figure 2.1 shows the burner configuration used
for the FHD technique.
2.2.2 Materials for fibre lasers: Preparation
and properties
(S. Unger, A. Schwuchow, S. Grimm,
V. Reichel, J. Kirchhof)
Recently, the performance of rare earth doped
high-power silica fibre lasers has been dramatically
increased with output powers beyond 1 kW,
high efficiency and excellent beam quality.
This progress is due to new design concepts
such as non-symmetrical double clads and large
mode area core structures, but also by careful tailoring
of the material properties. Extreme power
load and complicated fibre structures make high
demands on preparation technology and materials.
However, up to now still little is known about
the influence of the material and the preparation
technology on the laser efficiency.
Here, the absorption and emission properties of
silica based ytterbium doped preforms, made by
Modified Chemical Vapor Deposition (MCVD)
and solution doping, and of the drawn fibres were
investigated in dependence on the atmosphere
during the preform collapsing.
The preparation was carried out under oxidizing
and reducing conditions (helium/carbon monoxide/hydrogen).
The absorption measurements on
preforms and fibres with nominally identical compositions
have shown the following results:
– All Yb doped preform samples show the typical
Yb 3+ absorption in the wavelength region
between 800 and 1100 nm, and the absorption
coefficient is not remarkably changed by modifications
during the preparation process.