Metamaterials for optical security

In this letter we introduce the concept of optical security marks based on photonic metamaterials. We propose that a metamaterial with strong negative magnetic activity in the visible wavelength regime can be used to create a security mark that can be incorporated in any object to ensure its authenticity. The sophisticated nanofabrication processes needed to manufacture the metamaterial contribute to avoid counterfeiting. To illustrate the concept, a particular configuration consisting of silver nanohoops is analyzed.