A planar optical waveguide has been formed in a LiB3O5 crystal using 6.0 MeV Cu+-ions with a dose of 1 x 10(15) ions/cm(2) at room temperature. Possible propagating modes were measured at a wavelength of 633 nm using the prism-coupling method. The refractive index profiles of the waveguide were reconstructed by an effective refractive index method and the beam propagation method was used to investigate the properties of the propagation modes in the formed waveguide. The results suggest that the fundamental TE0 and TM0 modes may be well-confined and propagate a longer distance inside the waveguide. The implantation process was also simulated using the transport of ions in matter code (TRIM), which indicates that the nuclear energy deposition may be the main factor for the refractive index change. (c) 2006 Elsevier B.V. All rights reserved.