Abstract. Transformation optics is used to design a gateway that can block electromagnetic waves but allows the passage of other entities. Our conceptual device has the advantage that it can be realized with simple materials and structural parameters and can have a reasonably wide bandwidth. In particular, we show that our system can be implemented by using a magnetic photonic crystal structure that employs a square array of ferrite rods, and as the field response of ferrites can be tuned by external magnetic fields, we end up with an electromagnetic gateway that can be open or shut using external fields. The functionality is also robust against the positional disorder of the rods that make up the photonic crystal.

GENERAL SCIENTIFIC SUMMARY
Introduction and background. Transformation optics has paved the way for the development of optical devices that can realize novel functionalities that were thought to be possible only in science fiction. One such conceptual device that has attracted great public interest is a gateway that can block electromagnetic waves but that allows the passage of other entities. This device can be viewed as an implementation of a 'hidden portal' mentioned in fiction. However, the feasibility of such devices is limited by the very complex material parameters and the narrow bandwidth.

Main results. Here, we show that such gateway-type devices can actually be realized with simple parameters and they can have wider bandwidths such that the concept is closer to reality than previously thought. The structure can be implemented by using magnetic photonic crystal structures that are field tunable, resulting in an invisible electromagnetic gateway that can be open or shut using magnetic fields.

Wider implications. As there has been extensive work (both theoretical and experimental) on the design of double negative media (DNM) at various wavelengths, it would be reasonably feasible for the present gateway to be realized in the near future. Although it is still far away from hidden entrances like 'platform 9¾' in the Harry Potter novels, the interesting physics may fuel further research interest in transformation optics. The important message is that transformation optics can do more than making invisibility cloaks, it can actually generate all sorts of optical illusion effects.

Figure. (a) The DNM inside the device shuts EM waves out from the (physically open) gateway. (b) If we remove the DNM, the EM wave can propagate through the open gateway.

Received 6 May 2009
Published 13 August 2009