An electro-optical switched directional coupler is fabricated in Y-cut $LiNbO_3$ by the Annealed Proton Exchange method. First, the effect of annealing is characterized by examining the coupling coefficient of passive directional couplers. It is found that by controlling the annealing time, the transfer length of directional coupler can be made widely variable. Initial crossover state tuning is performed by the annealing process and self-aligned electrodes are used in fabricating the directional coupler switch. The directional coupler switch has very good figures of merits; the measured crosstalk of -22.5dB and the switching voltage of 2.9V.
