Propagation of light in a CdSxSe1–x planar waveguide structure with a variable band gap along the surface

An investigation was made of the conditions of propagation of light in waveguides having different band gaps E_g formed by two-stage diffusion in the same cadmium sulfide substrate. The efficiency of mode matching at the junction of two waveguides was determined as a function of changes in E_g and the length of the transition zone. Zero-order modes were the most efficiently coupled and as the mode number increased, the matching efficiency decreased. When waveguides having values of E_g differing by 0.12 eV were coupled, the optical energy transfer efficiency was higher than 80%. The overlap integral method used to calculate the efficiency of matching of the waveguide fields ensured a satisfactory agreement with the experimental results.