COLOR-CENTERS IN GERMANOSILICATE GLASS AND OPTICAL FIBERS

This review presents the state of the art of the study of germanium-re lated colour centres in silica glass and silica-based fibres. Most att ention is concentrated on the dominant colour centres such as the Ge-r elated oxygen-deficient centres and paramagnetic Ge(n) centres, all of them having ultraviolet absorption bands. The hypothetical models and formation mechanisms proposed so far for these colour centres are dis cussed in detail. The origins of the models and formation mechanisms a nd their weak and strong points are analysed. The origin of the less w ell studied Ge-related colour centres in the visible spectral range (G eH, GeX, drawing-dependent defects) is also discussed.