Spectral properties of asymmetrical optical directional couplers with periodic structures

A comparison is made of co- and contradirectional couplers with periodic structures, with a view to their suitability as WDM devices for integrated optical systems. Expressions are obtained for the spectral response within the framework of a coupled-mode theory. It is shown that the competition between direct Bragg, Bragg-exchange and codirectional coupling in the contradirectional coupler leads to shifting and constriction of the stop bands. Calculations are made for a codirectional coupler with a new type of meander structure and for the contradirectional coupler.