Fabrication of negative-index metamaterial (NIM) lenses (which can image beyond the diffraction limit) has made progress, but the creation of such lenses for the visible spectrum has been difficult due to high losses. Two kinds of NIM exist: double-negative (in which both the permittivity and permeability are negative), and single-negative (in which either the permittivity or permeability is negative). The first (much harder to make) has potentially higher performance. While single-negative metamaterials have been made that function with yellow light, double-negative materials have only been made for wavelengths as short as 725 nm.
Now, researchers at Zhejiang University (Hangzhou, China) and the Royal Institute of Technology (Stockholm, Sweden) have, at least theoretically, come up with a double-negative NIM geometry that could work down to UV wavelengths. They propose three types of silver structures—ring, disk, and nanowire—all of which have gaps that behave as magnetic dipoles that result in a negative permeability, but also decrease current strength, and thus loss. The nanowire-based device, although restricted to 2D structures, could be usable in the UV; the other two types are suitable for 3D structures, but work only in the visible. Contact Sailing He at [email protected].