A study of the spectroscopic and laser properties of some rare earth doped glass optical fibres
This thesis describes a study of the spectroscopy of some rare earth doped silica and fluorozirconate glass optical fibres. The application of these fibres in efficient, low threshold lasers is also described. Most of the work has been carried out on monomode silica fibres where the rare earths investigated have included ytterbium (Yb3+) thulium (Tm3+), holmium (Ho3+) and erbium (Er3+ ). Yb fibre lasers of high efficiency (67% slope efficiency at 974nm and 77% at ~1.04µm) have been demonstrated together with lasers of wide tunability (from 1.0µm to 1.16µm). Tm3+ fibre lasers operating near 2µm have been demonstrated with photon conversion efficiencies (above threshold) in excess of 80%. A tuning range of more than 250nm has also been demonstrated. A Ho3+ doped silica fibre laser operating at 2.04µm has been demonstrated but the efficiency was found to be low as a consequence of the high non-radiative decay rates in the silica host. An Er3+ fibre laser operating at 1.56µm has been studied with excitation taking place through energy transfer from Yb3+ ions. Energy transfer from Yb3+ to Tm3+ has also been investigated with upconversion of infra-red pump photons to the blue being observed. The thesis ends with the results of a study on Tm3+ and Er3+-doped fluorozirconate fibres where reduced non-radiative decay rates compared to silica allow; many more laser transitions to be studied. Suggestions are also made for possible areas of future study in the field of rare earth doped fibres.