hyperlenses

Hyperlenses are lenses constructed from hyperbolic metamaterials, engineered media with an anisotropic dielectric response whose dispersion relation is hyperbolic. They enable the conversion of evanescent, subwavelength components of an optical field into propagating waves that can reach the far field, allowing imaging of features smaller than the conventional diffraction limit.

The operating principle relies on hyperbolic dispersion in uniaxial metamaterials, where the permittivity tensor components have opposite signs. This creates hyperbolic isofrequency surfaces that support high-k waves, which would be evanescent in ordinary media but can propagate within the lens. In cylindrical or spherical geometries, a hyperlens maps near-field angular variations into magnified far-field variations, effectively translating subwavelength detail into a magnified, detectable image.

Fabrication and performance considerations include metal-dielectric multilayers and nanowire composites that realize Type I or Type II hyperbolic metamaterials, typically targeting infrared to optical frequencies. Practical devices face material losses, limited bandwidth, polarization sensitivity, and stringent fabrication tolerances. Early demonstrations showed subdiffraction imaging in the near field, confirming the basic concept, though real-world performance remains constrained by these challenges.

Applications and outlook involve high-resolution optical imaging, nanoscale sensing, and potential roles in lithography and inspection. While hyperlenses offer a route to surpass the diffraction limit with metamaterial concepts, they are generally viewed as components of imaging systems rather than universal replacements for conventional lenses, owing to losses, efficiency, and integration considerations.