Designing the Fourier space with transformation optics.

We show that transformation optics can be applied to extend the functionalities of conventional optical devices. In particular, geometrically compressing the input facet of any conventional optical elements can extend the input spatial frequency bandwidth. As an example, we design a Fourier lens that can transform the image to its reciprocal space and operate for incident light of subwavelength profile. An explicit design employing metal-dielectric layers is given for realization.