Abstract

A waveguide-simulation program based on the beam-propagation method has been used to study Ti-indiffused LiNbO₃ waveguide structures. By modifying the double-moded branching structure of the conventional Y-junction design, the loss of the branching structure can be substantially reduced. For a 1° half-branching angle, the loss can be lowered from –1.2 dB to 0.2 dB. Experimental data confirm that the modified design indeed has a lower loss. In addition to the branching structure, waveguide bends are also needed to complete a Y-junction. Low-loss coherent coupling bends are simulated and measured. From the measured mode profile, the waveguide simulation program is used to obtain the diffusion parameters for the Y-cut, X- or Z-propagating waveguides. The coupling lengths of directional couplers fabricated on such substrates are calculated and compared with experimental measurements. Coupling between adjacent waveguide bends is simulated. Mismatched waveguides, as well as ion milling, are used to decouple adjacent waveguides. Results of simulation are compared with experimental data.

© 1990 Optical Society of America