Abstract

A beam propagation method (BPM) provides a useful approach to the simulation of most guided-wave devices because (1) it treats the guided and the radiating fields with the same formalism; (2) it can analyze device structures which vary along the propagation direction.¹ Instead of the 3-D BPM approach, which usually needs a supercomputer, we used a 2-D BPM approach to model Ti-diffused directional couplers on LiNbO₃ fabricated by Alferness et al.,² Noda et al.,³ and Feit et al.⁴ The 1-D effective-index profile was calculated to replace the transverse 2-D refractive-index profile. The input variables were optical wavelength, diffusion temperature, diffusion time, and the thickness, width, and locations of the titanium strips. The anisotropic diffusion constants and the relation between refractive-index change and titanium concentration found in Ref. ⁵ were used in computation. However, since different fabrication conditions and wavelengths were used by different groups, slight adjustments of the diffusion lengths and the index change vs Ti concentration were necessary to fit all data.

© 1987 Optical Society of America