Refractive index profiles resulting from the fabrication of optical waveguides by diffusion techniques are measured using a reflection interferometric technique. In Cd-diffused ZnSe waveguides, the index variations are found to be complementary error functions that closely follow the composition changes for deep (>5 µm) diffusions. Shallow (<5 µm) diffusions produce waveguides in which the index profile is a complementary error function that differs significantly from the composition profile. The relationship between composition and refractive index is determined for Cd compositions less than 10%. Refractive index profiles in commercially available diffused glass waveguides (SELFOC rod and fibers) are also described.
W. E. Martin, "Refractive Index Profile Measurements of Diffused Optical Waveguides," Appl. Opt. 13, 2112-2116 (1974)