Researchers from the Hong Kong University of Science and Technology propose to use transformation optics [advanced metamaterials] to generate a general illusion such that an arbitrary object appears to be like some other object of our choice. This is achieved by using a remote device that transforms the scattered light outside a virtual boundary into that of the object chosen for the illusion, regardless of the profile of the incident wave. This type of illusion device also enables people to see through walls. Our work extends the concept of cloaking as a special form of illusion to the wider realm of illusion optics.
This type of illusion device also enables people to see through walls. Our work extends the concept of cloaking as a special form of illusion to the wider realm of illusion optics.
We note that some special illusion tricks by image projection using transformation
optics have been discovered, such as the shifted-position image of an object inside a metamaterial shell, the cylindrical superlens, the “superscatterer”, the
“reshaper” and the “super absorber”. Recently, we proposed an approach to
realize “cloaking at a distance” by using an “anti-object”. Here, by combining the “anti-object” cloaking functionality and the image projection functionality, we achieve a general form of illusion optics such that an object can be disguised into something else and the illusion device itself is invisible. This general form of illusion optics with arbitrary shape and generalized topology is proved mathematically as it is designed with transformation optics and the functionality is also demonstrated numerically.
In principle, the illusion optics allows us to remotely change the optical response of an object into that of any other object chosen for illusion at a selected frequency, without the need to change the constituents and shape of the true object or even cover its surface. This opens up interesting possibilities. For instance, an illusion waveguide or photonic crystal would allow the control of light propagation in actual free space; an illusion tip might perform near-field scanning optical microscopy without physically approaching a surface. However, the theoretical foundation of the illusion device is transformation optics and, as such, our theory relies on the validity and accuracy of a linear continuous medium that describes the homogenized electromagnetic fields in metamaterials. This requirement is crucial in the interface between the complementary medium and the “cancelled” object due to the high-intensity local fields as well as rapid oscillations there. The range of the virtual boundary also plays an important role. When it is large, the field at the boundary will be large as well. Another issue that we have not considered is loss, which will degrade the illusion effect unless the object is close to the device. If these issues and challenges can be solved with advances in metamaterial technologies, we should be able to harness the power of transformation optics to create illusions.