Theoretical investigation of the transverse optical force between a silicon nanowire waveguide and a substrate

We present a study of transverse optical forces arising in a free-standing silicon nanowire waveguide. A theoretical framework is provided for the calculation of the optical forces existing between a waveguide and a dielectric substrate. The force is evaluated using a numerical procedure based on finite-element simulations. In addition, an analytical formalism is developed which allows for a simple approximate analysis of the problem. We find that in this configuration optical forces on the order of pN can be obtained, sufficient to actuate nano-mechanical devices.