An investigation of the spectroscopy and laser performance of thulium in a variety of optical fibre hosts
This thesis presents the results of a three-year investigation into thulium-doped optical fibres with the aim of examining the suitability of various host glasses for device applications. The first report of lasing in a silica-based fibre at 820nm, of the 3F4 - 3H6 transition of the Tm3+ ion, is presented. The laser was pumped in-band at 785nm and lasing was observed at a launched power threshold of 40mW. A slope efficiency of 29% was measured. The possibility is examined of high-power operation, via a cladding-pumped geometry using a high-power diode-laser pump, potentially a simple means for converting the low-brightness output of the diode laser into a high-brightness source at ~820nm. A modified lead germanate glass, suitable for fibre fabrication, is considered as a host for both fibre lasers and planar technology waveguide lasers. Laser operation at 1.9µm, of the 3H4 - 3H6 transition of the Tm3+ ion, is reported in an ion-implanted planar waveguide. This was the first 2µm planar technology waveguide laser and the first waveguide laser in which the waveguide has been fabricated in a glass host by ion implantation. The non-radiative relaxation rates of thulium in a tantalum-doped silica fibre host, fabricated by a standard solution-doping technique, have been investigated. Fluorescence decay components for the 3F4 and 3H4 levels are observed which are significantly longer than those observed in thulium-doped germanosilicate or aluminosilicate fibres. This is interpreted as a reduction in the multi-phonon decay rate due to the formation of a low-vibrational-energy microenvironment around the rare-earth ion.