Bianisotropic route to the realization and matching of backward-wave   metamaterial slabs
  A concept of backward-wave bianisotropic composite medium matched to free space is suggested. It is based on the use of a uniaxial bianisotropic structure embedded into a matrix with negative effective permittivity. Since bianisotropy is easier to achieve in the optical range than artificial magnetism, this concept is prospective for optical backward-wave metamaterials. As an example of possible realizations, a microwave Omega-composite combined with a wire lattice is analytically studied. 
Sergei A. Tretyakov, Constantin R. Simovski, Martin Hudlicka