A planar optical waveguide was formed in a neodymium-doped calcium niobium gallium garnet (Nd:CNGG) crystal by using 500-keV He-ion implantation with a dose of 2 × 10 ions/cm at room temperature. The dark modes were observed by using a prism coupling method, and the refractive index profile was reconstructed using a reflectivity calculation method (RCM). The SRIM2006 code (stopping and range of ions in matters, code 2006) was used to simulate the damage profile in the ion-implanted sample. The photoluminescence spectra of the samples showed fairly good potential for used as a laser waveguide.