Abstract: An X-geometry optical switch includes primary and secondary input branch waveguides merging at a junction, and first and second output branch waveguides optically coupled to the input branches at the junction. In a dual electrode configuration, one electrode is positioned on the primary input branch waveguide and the other electrode on one of the input branch waveguides. By applying a common or opposite polarity bias to the electrodes, changes in the waveguide refractive optical indices are produced so that light propagating through the primary input is directed to one of the output branch waveguides in accordance with adiabatic modal evolution. In another X-geometry optical switch, the electrode on the output branch is eliminated by fabricating the output branch waveguides to exhibit a natural index asymmetry. Accordingly, since there is a normal ON-OFF path designation without biasing, only the single electrode on the primary input branch waveguide is necessary to effect switching.