We report on the optical planar waveguide formation and modal characterization in a Ce:KNSBN crystal by triple helium ion implantation at energies of (2.0, 2.2 and 2.4 MeV) and fluences of (1.5, 1.65 and 2.25) x 10(15) cm(-2). The prism-coupling method is used to investigate the dark-line spectroscopy at wavelength of 632.8 and 1539 nm, respectively. The refractive index profiles of the waveguide are reconstructed by an effective refractive index method. It is found that the ion-beam irradiation creates slight increase of extraordinary index whilst decreases ordinary one in the guide region. The modal analysis shows, at wavelength of 632.8 nm, the fields of one TE and three TM modes are well restricted in the guiding region, which means the formation of non-leaky waveguide in the crystal. The damping coefficients of the waveguide are 0.6 and 1.6 cm(-1) for ordinary and extraordinary polarized light at 632.8 nm, respectively. (c) 2006 Elsevier B.V. All rights reserved.