  Anomalous optical coupling properties between two silicon wires in a silicon
slot waveguide embedded in epsilon-near-zero (ENZ) metamaterials are proposed
and demonstrated. The dependences of optical field enhancement in the slot
region and transverse optical force on the slot size and the permittivity of
surrounding material are studied in details. It is demonstrated that the
optical field in the slot region is significantly enhanced due to the giant
index contrast at the slot interface between silicon wires and ENZ
metamaterials, but the optical mode coupling between silicon wires is greatly
reduced so that the transverse optical force is suppressed into almost zero.
Moreover, metal-dielectric multilayer structures are designed to realize ENZ
metamaterials in the slot region for achieving the electric field enhancement.
