Transformation optics with windows

Transformation optics is a recent paradigm for designing metamaterial structures that behave, to light, like curved spaces. The headline application, invisibility cloaking, has created much interest with scientists and the public alike. Transformation-optics devices built from metamaterials have many limitations, for example the very high cost of creating even tiny volumes of the nano-structured materials required for operation in the visible wavelength range, and the very narrow wavelength band over which metamaterials have the desired properties. Pairs of microlens arrays that are separated by the sum of their focal lengths form arrays of micro-telescopes. Such arrays are pixellated windows (each telescope is one pixel) that change, over a limited field of view but also over a wide wavelength range, the light-ray direction of transmitted light rays like the interface between different materials. In principle, they can also be manufactured cheaply and in bulk. By exploiting the fact that these windows are (in principle) perfectly imaging [S. Oxburgh and J. Courtial, J. Opt. Soc. Am. A 30, 2334 (2013)], we demonstrate that such windows, when combined into suitable structures, are pixellated transformation-optics devices. This new class of transformation-optics device can be macroscopic in size, and so such devices offer a very different compromise to metamaterial transformation-optics devices. This should significantly widen the applicability of transformation optics.