The invention relates to a substrate (1), especially a glass substrate, coated with at least one dielectric thin-film layer deposited by sputtering, especially magnetically enhanced sputtering and preferably reactive sputtering in the presence of oxygen and/or nitrogen, with exposure to at least one ion beam (3) coming from an ion source (4), characterized in that said dielectric layer exposed to the ion beam has a refractive index that can be adjusted according to the parameters of the ion source, said ion source being a linear source.