Abstract: A glass planar waveguide structure, typically on a glass wafer or chip, has a core region, a contiguous narrow cladding region encompassing the core region, and an outer region practically extending over the rest of the wafer. The core region and the outer region are implanted with outside ions by ion diffusion, whereby the refractive index of the core and of the outer region are similar. The outer region forms an artificial waveguide to enhance the uniformity of physical properties of the wafer, e.g. stress, and reduce birefringence of the core.