Compositional Characterisation of Optical InGaSb-core Microfibres

Abstract

This thesis constitutes the first step on the way to understanding and applying the ternary InGaSb-semiconductor alloy in the field of nonlinear fibre optics. This semiconductor material is also interesting for applications in the infrared domain. Using InGaSb in the core has the potential to greatly influence especially the THz power delivery, since the bandgap and optical properties can be tuned by changing the composition. In this work the individual binary compounds, GaSb and InSb, and ternary compounds In0.3Ga0.7Sb and In0.5Ga0.5Sb have been hand-drawn into fibres. To determine the best candidates, different glasses and coatings were tested, those were AR-glass, AR-glass modified with NaKCl, DURAN and DURAN modified with Na2PO4. Investigation using SEM, EDS and Raman spectroscopy indicated that the core materials exhibit crystal structures with the expected phases, but also oxidation and diffusion of some of the glass and coating elements in the core, most prominent in the In-based fibres. DURAN seemed to be best suited for the GaSb-compound. This glass coated with Na2PO4 seemed to work best for the InSb-compound. The use of CO2-laser irradiation to heat the glass cladding and thereby recrystallise the core showed promising results upon formation of single crystal GaSb. Similar treatment of the In0.5Ga0.5Sb-core fibre looked, by XCT micrographs, to have homogenised the compound to some degree. It is suspected that a too small temperature and/or a too high translation velocity of the laser during process lead to constitutional undercooling with some local non-uniformities as result. However, critical assessment