ABSTRACT
Albert Einstein said once: “Œe important thing is not to stop questioning.” Indeed, it is the scientižc curiosity of a Russian physicist, Victor Veselago, in 1968 that led to the emergence of an entirely new area of modern optics: the optics of metamaterials [1-3]. In optics, interactions between light waves and materials are usually characterized by two parameters-dielectric permittivity ε and magnetic permeability μ-that explicitly enter Maxwell’s equations, or by their product, the index of refraction, dežned as n = ± εµ . In common transparent optical materials, the index of refraction and dielectric permittivity are positive numbers that are greater or equal to 1 and μ ≈ 1. Œe refractive index can be modižed to some degree by altering the chemical composition of the material or using electrical, thermal, or nonlinear e˜ects. Nevertheless, the refractive index is typically greater than one (air) and less than four (silicon). Veselago investigated in detail the question of whether or not ε and μ can simultaneously take negative values, leading to a negative index of refraction. It is noteworthy that the discussions of backward waves and negative index of refraction date back to the beginning of the twentieth century (see, e.g., [4]); nowadays, we can generalize Veselago’s question and ask whether one could engineer ε and μ (or n) to take any value beyond the limits imposed by nature. Meta in Greek means “beyond,” so the ultimate goal of metamaterials research is to create materials with properties and functionalities that have not been found in nature.
