  Forces arising from overlap between the guided waves of parallel,
microphotonic waveguides are calculated. Both attractive and repulsive forces,
determined by the choice of relative input phase, are found. Using realistic
parameters for a silicon-on-insulator material system, we estimate that the
forces are large enough to cause observable displacements. Our results
illustrate the potential for a broader class of optically-tunable microphotonic
devices and microstructured artificial materials.
