This project will investigate transition metal (TM) and TM-rare earth (RE) codoped fibres. The investigation falls into two main areas: the study of the influence of various fabrication stages on the optical characteristics of the fibres, and the research into TM and TM-RE codoped fibres for tunable and visible upconversion lasers, and emission at telecommunications wavelengths. The proposal shows that relatively little work has been carried out on TM and TM-RE codoped fibres, and the study of which should produce an exciting source of new fibre devices. Also 'nanoparticle' doped fibres will be investigated. The importance of studying the influence of the fabrication conditions on the resulting optical characteristics of the fibres is discussed, along with the apparatus and methods that will be employed in doing so. The specific devices and program timetable are described, as is the relevance of the work to the European Community.