The guided modes supported by two parallel, identical planar dielectric waveguides are investigated exactly by a quasi-optical technique and approximately by using the improved coupled-mode theory. The wave numbers obtained by the two methods are expanded into asymptotic series in terms of a suitable small parameter. By comparing the asymptotic series obtained by the two methods term by term, it is shown that the improved coupled-mode theory is asymptotically exact in the limit of weak coupling and not so in the strong-coupling regime. The merits and the defects of the improved coupled-mode theory are discussed.
© 1988 Optical Society of America
Original Manuscript: September 25, 1987
Manuscript Accepted: January 27, 1988
Published: June 1, 1988
Zi Hua Wang and S. R. Seshadri, "Asymptotic theory of guided modes in two parallel, identical dielectric waveguides," J. Opt. Soc. Am. A 5, 782-792 (1988)