Currently, optical properties of lenses are limited by the refractive indices of conventional materials. Typically, lenses are made of silicon-based materials that have refractive indices smaller than 2. Due to this constraint, it is extremely hard for people to shorten the focal distances of conventional lenses beyond certain limitation. So far, facing this challenge, researchers developed gradient index lenses and many other types of lenses. These innovative lenses have better focusing properties such as the Full Width at Half Maxima (FWHM) and focal lengths than those of the conventional ones, but still there are needs to make things even better. To further improve the focusing properties, we believe the hope is on metamaterials.
In our design, the lens is composed of metamaterials in metal-grating. Intuitively, it is quiet weird to use this kind of metamaterials to build lenses, since metals have very high absorptions and are mostly opaque to light. Even though the light can transmit though the slits in the metal grating, as the slits are very narrow in width, the transmittance of the lens should be very low. However, interestingly, this is not true. Previously, it has been shown that the spherical metal-grating metamaterials lenses have very good focusing properties . In our project, to verify how good are the matamaterials nanoslit lenses, we are going to use COMSOL Multiphysics to simulate several different setups and look specifically 1. focal length, 2. full width at half maximum, and 3. transmittance of them.
Zijian Wu, Yan-Qin Lu, & Jung-Tsung Shen, Jun. 23. (2015). Planar-convex metallic gratings as elective refractive lenses. Manuscript submitted for publication.