Rare earth ions in the glass amplifying medium: A proposal for new doping precursors

Though one of the recent major application breakthrough in the rare-earth (RE) field, is the general use of Erbium Doped Fibre Amplifiers (EDFA) for optical communications, such amplifiers are still bulky and expensive which limits them to terrestrial long trunk and under sea cable applications. In order to obtain compact amplifiers for the distribution network, doping concentration has to be increased up to the chemical and physical limits. It has been recently [1] proposed that the physical process of co-operative luminescence be closely related to chemical clustering and that using this effect with Yb3+ as a probing ion, clear signatures of RE clusters could be obtained for different glass compositions and RE concentrations. Developing this approach, a new doping principle is proposed [2]. It is based on the recognition that during crystal growing, the various atomic forces at the atomic scale are able to define atomic positions of atoms with the crystal cells regularity. In particular, in the case of a crystal with RE as constituents, the RE-RE distances are automatically fixed by the crystal nature. It is shown that introducing the doping RE into the glass composition through such precursor crystals with large RE-RE distances, allows some control of the clustering of RE ions after complete melting of the precursor. This is found to be independent of the final glass composition which so keeps some memory of the doping process.