We present analytical expressions for the effective indices of a three-waveguide directional coupler, using the modified scalar coupled-mode theory. Our analysis takes into account all perturbation correction terms, all coupling coefficients, and all overlap integrals and leads to a simple analytical condition for maximum power transfer between the two outside guides.
© 1995 Optical Society of America
Sangeeta Srivastava and Enakshi Khular Sharma, "Analytical expressions for effective indices in a three-waveguide coupler," Opt. Lett. 20, 1005-1007 (1995)