Eigenmode matching and propagation theory of square meander-type couplers

The coupling efficiency of square meander-type or grating-assisted codirectional couplers has been calculated so far by common coupled mode theory. The theory presented calculates coupling efficiency, period length, dispersion behavior, etc. on the basis of the propagation of both eigenmodes of the asymmetrical coupler, using mode matching at the boundaries, which can be described as a rotation between the two eigenmodes of the undisturbed waveguide. This method is very fast, simple, accurate and gives a good insight into the physical behavior. Some examples verified by BPM calculations show the significance of this new theory.<>