We examine coupled-mode theory in the very-weak-coupling limit and show that in multiwaveguide systems with dissimilar waveguides the overlap integrals of the recent, more-sophisticated theory should be included to ensure accurate solutions. Using the old theory in this limit may lead to errors reaching 100% in calculated coupling length.
© 1988 Optical Society of America
Amos Hardy, William Streifer, and Marek Osinski, "Weak coupling of parallel waveguides," Opt. Lett. 13, 161-163 (1988)