Concentration profile calculation for buried ion-exchanged channel waveguides in glass using explicit space-charge analysis

Ionic conductivity inhomogeneity and its relation to space charge is analyzed in the case of a two-ion exchange for channel waveguide fabrication in optical glass. The space-charge evolution equation is derived and discussed in a general binary ion exchange context. This leads to an efficient algorithm which computes current-density nonuniformity in the field-assisted burying of ion-exchanged waveguides. The algorithm exhibits excellent agreement with the classic potential equation perturbed by nonhomogeneous ionic conductivity, and is appreciably faster. We show that the homogeneous current-density assumption is inaccurate for the calculation of the burying depth and waveguide size in the case of a realistic glass with nonlinear ionic diffusivity.