Application of coupled-mode theory to nearly parallel waveguide systems

The improved coupled-mode theory is extended and applied to multiwaveguide systems consisting of any number of nonparallel guides, such as Y-junction laser arrays and directional couplers. The impact of the improved analysis on the design of devices containing nonparallel sections is illustrated by an example of Ti-indiffused LiNbO3 directional couplers. It is shown that the overall performance of the device may be significantly affected by the nonparallel sections.