element for enhancing the use of said doping element and an outer cladding which surrounds the core the invention is characterised in that the doping element is erbium and in that the enhancing element is selected from among antimony bismuth and a combination of antimony and bismuth according to the invention one such fibre is characterised in that the size of the nanoparticles is variable and is between 1 and 500 nanometres inclusive and preferably greater than 20 nm application_number US 80598910 A description types of glass that include bismuth or antimony have particularly interesting characteristics described below with the help of fig1 a and 1 b which represent amplification gains for materials comprising erbium as the doping element and antimony fig1 a or bismuth fig1 b as the enhancement element more precisely these fig1 a and 1 b represent the material 39 s amplification gain y axis 10 as a function of the wavelength of the amplified signal x axis 12 for fibres comprised of antimony curve 14 fig1 a or bismuth curve 16 fig1 b these gains being compared to those of a known fibre comprising aluminium as a doping agent curve 18 it thereupon becomes apparent that the respective properties of antimony sb and bismuth bi are interesting for processing an optical signal to wit expanding the curve sb of the gain medium 39 s gain or flattening said curve bi thus the usage of a filter intended to flatten the gain of a fibre is lower when the curve of the gain for that fibre is flattened as this reduction may limit the pumping energy required by said fibre by.