Optical Metamagnetism and Negative-Index Metamaterials

A new class of artificially structured materials called metamaterials makes it possible to achieve electromagnetic properties that do not exist in nature. In this article, we review the recent progress made in the area of optical metamaterials, specifically artificial magnetism and negative-index metamaterials. It was predicted that nanostructured metamaterials could provide magnetic responses and negative refractive indexes at optical frequencies. To date, optical metamagnetics have been fabricated to demonstrate magnetic responses in the infrared range and across the entire visible spectrum. Metamaterials showing negative refractive indexes, also called negative-index materials (NIMs), have also been demonstrated in the infrared range and at the border with the visible spectral range. Additionally, we report the results of a sample that displays NIM behavior for red light at a wavelength of 710 nm and another sample that displays double-negative NIM behavior at 725 nm. Both observations represent the shortest wavelengths so far at which NIM behavior has been observed for light. We also discuss the fabrication challenges and the impact of fabrication limitations, specifically the effect of surface roughness of the fabricated structures, on the optical properties of the metamaterials.