Integrated electrooptic multielectrode tunable filter

We introduce a novel electrooptic integrated tunable filter for multiwavelength communication networks. The proposed device consists of an asymmetric co-directional coupler with multiple electrodes for attaining an alternating Δβ effect. The proposed structure can function as a multiplexer-demultiplexer and as a narrow bandwidth tunable filter, with conversion efficiency 1 within the entire tuning range. The amount of asymmetry in the waveguides can be achieved by combining a wide waveguide with low Δn fabricated by Ti:LiNbO₃ process with a second narrower waveguide with high Δn using proton exchange procedure. This combined technology would assure very narrow bandwidth in the 1 nm range. The demand of conversion efficiency 1 all over the tuning range is essential to several network architectures. We give the formulation for an asymmetric directional coupler with alternating Δβ, and show that the need for many electrodes is a must in order to reject the satellite passbands out from the tuning range. We give a simple expression for estimating the number of electrodes needed. Additionally, we give some suggestions in order to reduce the voltage applied to the electrodes for tuning