Coupled multiple waveguide systems

The coupled-mode equations for systems of four and five planar coupled waveguides are investigated to determine transmission characteristics of interest. By proper selection of the coupling coefficients in a system of "synchronous" waveguides, full transfer can be achieved from one outermost guide to the guide on the opposite side. In the five-waveguide system, an excitation of the center guide can be fully transferred to a symmetric excitation of the outer guides. Sinusoidal modulation of the propagation constants leads to transfer functions with desirable properties for sampling applications. The analysis for synchronous waveguides is extended to waveguide systems of arbitrary order. Expressions for the coupling coefficients of an th order system are given for each of the two types of transfer characteristics described above.