Design calculations for directional couplers fabricated by Ti-diffused LiNbO(3) waveguides.

Coupling characteristics for designing a LiNbO(3) directional coupler fabricated by Ti diffusion have been investigated with a modified WKB method. The present analysis is verified by comparing the refractive-index change in the Ti-diffused LiNbO(3) waveguide derived from direct measurement and coupling length calculation. Coupling length variations due to refractive-index change, diffusion length waveguide spacing, and wavelength are described. Tolerances in coupling length mismatch and propagation constant differences affecting cross talk of the directional coupler are discussed.