The zero-dispersion characteristics are shown of coupled modes in twin waveguides when the medium of the substrate is iossy or active or when leakage exists. When the coupling strength of coupled modes composed of even and odd modes is critical, the phase velocities of these modes degenerate to make dispersion zero. The condition for zero dispersion is analytically obtained. The characteristics of reflection coefficients at various boundaries in the twin-waveguiding structure are studied in terms of the dual relation in the case in which the medium of the substrate is lossy or is active. The effect of the degenerate modes caused by leakage on the phase-shift characteristics of reflected waves at the prism-twin-waveguide boundaries is also studied.
© 1982 Optical Society of America
H. Kitajima, "Zero dispersion of coupled modes in twin waveguides and reflection characteristics at prism-twin-waveguide-coupling boundaries," J. Opt. Soc. Am. 72, 692-698 (1982)