This work reports the impact of He ion implantation conditions on the depthdependent refractive index profile n(z) defining optical waveguides in 95.5% Pb(Zn 1/3 Nb 2/3 )O 3 -4.5%PbTiO 3 (4.5% PZN-PT). Two hypotheses are investigated. The first is that n(z) follows the same functional form as the energy deposited into the lattice for all implantation conditions. The second is that the effective refractive indices for fully confined propagating modes can be accurately predicted by a simple step-function analytical approximation. Experimentally observed prism-coupled reflectivity data are collected from 4.5% PZN-PT samples implanted with 1.0 MeV He ions for doses varying from 7.5 · 10 14 ions/cm 2 to 1 · 10 17 ions/cm 2 and with 3.8 MeV He ions for doses varying from 1 · 10 15 ions/cm 2 to 5 · 10 16 ions/cm 2 . For doses less than 5 · 10 16 ions/cm 2 , the data are consistent with a functional form of n(z) following that of the energy deposited to the lattice. The confined modes are accurately described by a step-function approximation to n(z). These data and analyses result in the ability to design waveguides in PZN-PT through choosing implantation conditions that deposit the appropriate energy profile. This is not the case for the highest implantation doses, potentially signaling a difference in the type of structural modification that occurs.