Photonic metamaterials

Photonic metamaterials, also known as Optical metamaterials, are a type of electromagnetic metamaterial, which are designed to interact with optical frequencies which are terahertz, infrared, and eventually, visible wavelengths. As a type of metamaterial, the periodic structures are made up of single units called cells. These single units are much smaller than the wavelength of the radiated source.

Electromagnetic metamaterials in general are designed to operate at different frequencies. For example, prior and current research is in the microwave domain with physical periodic cell structures on the scale of millimeters. Because the optical wavelengths (a few microns) are much shorter than microwave frequencies, photonic metamaterial cell structures are on the scale of nanometers.

In a conventional material the response to electric and magnetic fields, and hence to light, is determined by the atoms. As a type of metamaterial, the photonic metamaterial is an artificially engineered structure. Therefore, each periodic cell is designed with specific parameters by which it interacts with the radiated field at optical frequencies. At the same time, however, metamaterials in general, which includes photonic metamaterials, are described as homogeneous materials, or in other words, utilizing an effective medium model.

Furthermore, demonstrating artificial magnetism at high frequencies, resulting in strong magnetic coupling, is contrasted with the usual or normal weak magnetic coupling of ordinary materials. This can then be applied to achieving negative index of refraction in the optical range, and developing approaches that show potential for application to optical cloaking. In addition, photonic metamaterials are an emergent tool in transformation optics.

Finally, regarding photonic crystals, the size and periodicity of the scattering elements are on the order of the wavelength rather than subwavelength. A photonic crystal cannot be described as a homogeneous medium so it is not possible to define values of ε or μ. However, photonic crystal materials are typically composed of insulators and therefore can exhibit very low losses, even at optical frequencies.

http://en.wikipedia.org/wiki/Optical_metamaterial