Refractive index tailoring in congruent Lithium Niobate by ion implantation

Refractive index profiles of ion-implanted Lithium Niobate waveguides are investigated. Z⁺ and z⁻ congruent Lithium Niobate samples have been implanted with C³⁺ ions at a fluence of 4 × 10¹⁴ ions/cm². Dark m-lines measurements have been performed on ordinary (n_o) and extraordinary (n_e) indexes for three different wavelengths (532 nm, 632.8 nm, 818 nm) before and after the annealing process. A reconstruction of refractive index profiles by Reflectivity Calculation Method (RCM) is presented and commented. The literature data for nuclear damage regime have been collected and critically examined. n_o and n_e curves as function of the density of energy released in nuclear collisions, E_d, describing the effects of ion implantation on LN refractive indexes has been obtained on the basis of literature data. n_o depth profile, predicted according to n_o(E_d) curve, is in good agreement with the RCM reconstructed one. In the case of n_e, a satisfactory agreement has been reached only slightly modifying the n_e(E_d) curve and considering an alternative RCM profile structure.