Four wave mixing techniques are used to induce refractive-index gratings in Eu-doped glasses. When the Eu3+ ions are resonantly excited, superimposed transient and permanent gratings are formed. The former is characteristic of population grating, while the latter is attributed to local structural modifications of the glass host induced by high energy "phonons" localized around the Eu3+ ions. The result suggest the use of such gratings for de-multiplexing applications
