Copyright 2006 OSA

Diffraction limits the resolution obtainable using conventional optics to approximately half the wavelength of light. All subwavelength information is contained in evanescent waves — non-propagating electric fields near the object surface that decay exponentially with distance. The key is to capture this information. Although conventional lenses can focus propagating waves, they are often too far from the object to detect the evanescent field. ‘Superlensing’ was recently proposed as a way of amplifying this field and making it easier to detect. However, superlenses, constructed from metamaterials, have their drawbacks. In addition to the large material losses predicted, the evanescent signal still decays with distance making it difficult to capture with a conventional optics system.

A team at Princeton University has come up with a proposal that may provide a way of imaging in the far-field at a resolution beyond the diffraction limit1. Their device, a so-called hyperlens, consists of a metamaterial with cylindrical symmetry. The material used needs to be highly anisotropic, so that in the radial-symmetry direction the electric permittivity is of opposite sign to that in the axial direction. Calculations show that the light carrying the subwavelength information is guided to the core of the lens. In a sense, the hyperlens converts the evanescent waves into propagating waves, which can then be imaged in the far-field. Independent theoretical studies of anisotropic metamaterials confirm that such far-field imaging should be possible2. If such a metamaterial could be fabricated, then this hyperlens could see the diffraction limit beaten once and for all.