Copper–sodium ion‐exchanged glass waveguides are fabricated and characterized. Optical absorption andm‐lines spectroscopy analyses are presented. No stress‐induced birefringence is observed from refractive index profiles reconstruction, and the Cu+oxidation state is shown to mostly determine the refractive index change. Comparison between compositional in‐depth profiles and index profiles is allowed to obtain the variation in the electronic polarizability due to the Cu+–Na+exchange. The diffusion coefficient of Cu+in soda‐lime glass is also calculated. ©1996 American Institute of Physics.