Avoiding imaging artifacts from resonant modes in metamaterial superlenses

Superlenses are imaging components that can overcome the diffraction limit associated with conventional dielectric lenses. An ideal superlens is a flat infinite slab of homogeneous double-negative material with $\ensuremath{\varepsilon}\phantom{\rule{0.16em}{0ex}}=\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\phantom{\rule{0.16em}{0ex}}=\phantom{\rule{0.16em}{0ex}}\ensuremath{-}1$ embedded in air, which achieves perfect imaging by restoring all the spatial frequency components of an object to the image plane. It has been shown that any deviation from these homogeneous material parameter values limits the resolution of the lens and introduces a surface mode resonance with fields that dominate the image. While material loss can suppress the resonant mode, loss also reduces spatial resolution. In this paper, we investigate resonant modes arising in metamaterial superlenses of infinite and finite extent and show how they cause imaging artifacts and reduce imaging fidelity. We choose a well-studied periodic structure consisting of an array of magnetodielectric cylinders for the lens medium under test. We demonstrate that the presence of these artifacts can lead to erroneous interpretation of the standard two-source resolution test for lenses. We show that artifacts can be mitigated by introducing point defects into the array, which move the resonant modes to higher spatial frequencies and, in the case of finite lenses, suppress their amplitudes through radiation losses. This strategy enables more robust and reliable subwavelength imaging performance, improves the spatial resolution of the metamaterial lens, and reduces the deleterious effects of material losses.