  We study the optical force between two coupled parallel identical nanofibers
using the rigorous array mode theory. We show that the forces of the even array
modes are attractive, while the forces of the odd array modes are repulsive. We
examine the dependencies of the optical forces on the array mode type, the
fiber radius, the light wavelength, and the fiber separation distance. We show
that, for a given power and a given separation distance, the absolute value of
the force achieves a peak when the fiber radius and the light wavelength are
appropriate.
