A New Strategy for Transformation Optics With Index-Only Media

A new method to implement transformation optics is proposed. The method is simple but very effective. As long as the transformed regions in the virtual and physical spaces are finite, the material parameters obtained are free of zero or infinite values and can be realized by index-only media. It is the first time that the absence of zero values is guaranteed by the transformation scheme itself. The range for the refractive index is easy to control since the proposed scheme only requires the operation of stretching transformation. The designs of multibeam antennas, which convert the cylindrical waves to plane waves, are illustrated in this paper. The proposed method can be used to achieve many other electromagnetic and optical devices.