Directional Coupler as an Electro-Optically Controlled Wavelength Division Demultiplexer

The number of passbands of the bandpass filter increases with the increasing of the difference of the propagation constants of the three waveguides of the directional coupler (i.e. electro-optically controlled). The allowed wavelengths (signals) which can be transmitted through the coupler´s waveguides (wavelength division demultiplexer, WDDM) become very large with asymmetric electrooptic materials. Then the problem of length of WDDM is treated by electro-optical control. In case of symmetric electrooptic materials of the three waveguides, the maximum number of the allowed signals occurrs with BaTiO₃. BaTiO₃, LiNbO₃ and BaTiO₃ are the best asymmetric materials. The design procedure of WDDM is done. The numerical results with five different electrooptic materials are presented as design curves.