Abstract

The directional coupler has proven to be a versatile element in the fabrication of single-mode electrooptic devices. Low-loss optical switches, high-speed modulators, polarization converters, and wavelength filters have been fabricated using Ti waveguide couplers diffused into a LiNb0₃ substrate. Coupled-mode theory is normally applied to the coupling of step-profile waveguides.¹ More recently, the propagating beam method (PBM) has been applied to coupled fibers with idealized parabolic profiles.²³׳ To our knowledge, however, no attempt has yet been made to predict accurately the characteristic coupling length for diffused channel couplers from the fabrication conditions, which inelude initial Ti strip dimensions and diffusion conditions. We have applied the PBM to this problem, supplying only the coupler geometry, Ti mass deposited, and diffusion data, i.e., diffusion constant, time, and temperature. The calculated coupling lengths are in good agreement with those measured from fabricated Ti:LiNbO3 directional couplers.

© 1983 Optical Society of America