Creating Illusion Effects Using Transformation Optics

In this chapter, we show how to create illusion effects using metamaterials. We will see that a passive metamaterial device can be designed such that when it is placed next to or covering an object, the scattered fields of the object and the device together will be changed to be exactly the same as the scattered fields due to another object. Simply put, we can turn an object optically and stereoscopically into another one. For instance, an apple can be made to look like a banana. If we make a measurement of the electromagnetic fields at the designed working frequency, there is no way to distinguish optically between the true object and the illusion. The theory on realizing such an optical illusion effect is called illusion optics. Invisibility can be regarded as a special case of the illusion effect, in which the object is turned optically to a volume of free space. A metamaterial does not need to encircle the object to create the illusion effect. Furthermore, if we use this method to implement invisibility, the cloaked object will not be blinded by the cloak as in the cases of normal invisibility cloaks. The design of illusion optics is based on the replacement of optical spaces, where the material parameters are determined using the technique of transformation optics. One unique route to achieve illusion effects is to employ the idea of complementary media. Materials designed using complementary media typically contain negative refractive index components, and no extreme constitutive parameters values are needed. Slight variations of the scheme can create a variety of interesting illusion effects. For example, we can make an object appear larger in size, rotated, or located at other positions. Illusion optics may lead to some plausible applications, such as small or reduced form-factor optical devices that exhibit the same optical functions as much larger instruments or even super-absorbers that can absorb significantly more than their geometric cross-sections.