The invention relates to an optical waveguide, in particular an optical fibre comprising a core, formed from a material based on rare-earth-ion-doped silica, covered by an optical cladding. Nanoparticles, at least some of which are metal nanoparticles, are dispersed in the material of the core. The optical devices, such as especially optical amplifiers, comprise an optical fibre having a core formed, from a material based on rare-earth-ion-doped silica covered with an optical cladding, nanoparticles, at least some of which are metal nanoparticles, being dispersed in the material of the core, and a pumping source delivering electromagnetic excitation radiation, which propagates in the core.