Hyperlens

Hyperlens is a device that employs hyperbolic metamaterials to reveal details smaller than the diffraction limit. The key idea is that certain anisotropic materials have a hyperbolic dispersion relation, allowing the propagation of very high spatial frequencies that would be evanescent in ordinary media. In cylindrical or spherical geometries, a hyperlens maps near-field, subwavelength features into propagating waves that expand as they travel outward, effectively magnifying the image and making subdiffraction information detectable in the far field.

Implementation often uses multilayer metal-dielectric stacks or nanowire composites designed to realize the required anisotropy at optical or infrared frequencies. In a cylindrical or spherical hyperlens, high-k components excited by a subwavelength object travel through the lens and are converted into lower-k waves with increasing radius, producing a magnified image beyond the conventional diffraction limit.

History and limitations: The concept arose from the study of hyperbolic metamaterials in the mid-2000s, with experimental demonstrations following. Practical challenges include intrinsic losses in metal components, limited operational bandwidth, and fabrication sensitivity, which can reduce image contrast and resolution. Despite these constraints, hyperlenses have been explored for near-field imaging, sub-diffraction microscopy, and lithography concepts, highlighting the potential of metamaterial-based approaches to surpass diffraction.