Slow-light enhanced optical forces between longitudinally shifted   photonic-crystal nanowire waveguides
  We reveal that slow-light enhanced optical forces between side-coupled photonic-crystal nanowire waveguides can be flexibly controlled by introducing a relative longitudinal shift. We predict that close to the photonic band-edge, where the group velocity is reduced, the transverse force can be tuned from repulse to attractive, and the force is suppressed for a particular shift value. Additionally the shift leads to symmetry breaking that can facilitate longitudinal forces acting on the waveguides, in contrast to unshifted structures where such forces vanish. 
Yue Sun, Thomas P. White, Andrey A. Sukhorukov
physics.optics