Frequency dependence of the optical force between two coupled waveguides.

We investigate the frequency dependence of the optical force between two coupled waveguides using the supermode theory. We show that the frequency dependence of the optical force in a coupled waveguide system is determined by the dispersion relations of uncoupled individual waveguides. We further numerically calculate the optical force of three representative coupled systems at different frequencies and show that these results agree well with the supermode analysis.