Negative-index materials: New frontiers in optics

A lot of recent interest has been focused on a new class of materials, 0 the so-called left-handed materials (LHMs) or negative-index materials, which exhibit highly unusual electromagnetic properties and hold promise for new device applications. These materials do not exist in nature and can only be fabricated artificially; for this reason, they are called metamaterials. Their unique properties are not determined by the fundamental physical properties of their constituents, but rather by the shape and distribution of the specific patterns included in them. Metamaterials can be designed to exhibit both electric and magnetic resonances that can be separately tuned to occur in frequency bands from megahertz to terahertz frequencies, and hopefully to the visible region of the electromagnetic spectrum. This article presents a short history of the field, describes the underlying physics, and reviews the experimental and theoretical status of the field at present. Many interesting questions on how to fabricate more isotropic LHMs, on how to push the operational frequency to optical wavelengths, how to reduce the losses, and how to incorporate active or nonlinear materials in LHMs remain to be explored further.