Ion beams and γ rays are used to modify refractive index of polyallyldiglycol carbonate (PADC). Ion irradiations (H, Li, B) lead to optical waveguides the properties of which depend on the kind of ions, ion fluences and energy. Radiation damage consistently increases the refractive index. Measured variations of refractive index are given as function of deposited energy density (by ions or γ rays). It appears that index variations are principally linked to structural modification due to deposited energy.