ABSTRACT
This chapter concentrates on the developments in fibre lasers, with potential applications outside the domain of optical telecommunications, which has formed the driving motivation for so much fibre laser work. It reviews the developments based on zblan fibres, with particular emphasis on upconversion lasers and the use of fibre gratings to control the spectral properties of fibre lasers. The small cross-section area of the active core of the fibre means that a high pump intensity, and hence a high inversion density can be achieved for a modest pump power. A cursory examination of the energy levels of the triply ionised rare-earths, as shown in the ‘so-called’ Dicke diagram, suggests a wealth of potential transitions if each indicated energy level is considered as a potential upper laser level. The decay process of concern is a radiationless decay via the emission of one or more phonons.
