The 2.8 MeV Ni+ ion-implanted planar optical waveguide in Nd:YVO4 crystal is reported. The prism coupling method is used to measure the dark modes of the Nd:YVO4 waveguide. It is found that the effective refractive indices of all the extraordinary modes are lower than that of the substrate (n(e)), while the effective indices of the first three ordinary modes have a positive change compared with that of the substrate (n(o)). Both n(e) and n(o) profiles in the waveguide are reconstructed by reflectivity calculation method (RCM). (C) 2002 Elsevier Science B.V. All rights reserved.