Metamaterial fibres for subdiffraction imaging and focusing at terahertz frequencies over optically long distances

Using conventional materials, the resolution of focusing and imaging devices is limited by diffraction to about half the wavelength of light, as high spatial frequencies do not propagate in isotropic materials. Wire array metamaterials, because of their extreme anisotropy, can beat this limit; however, focusing with these has only been demonstrated up to microwave frequencies and using propagation over a few wavelengths only. Here we show that the principle can be scaled to frequencies orders of magnitudes higher and to considerably longer propagation lengths. We demonstrate imaging through straight and tapered wire arrays operating in the terahertz spectrum, with unprecedented propagation of near field information over hundreds of wavelengths and focusing down to 1/28 of the wavelength with a net increase in power density. Applications could include in vivo terahertz-endoscopes with resolution compatible with imaging individual cells. Wire array metamaterials can be used to beat the fundamental diffraction limit of light, but most demonstrations have been limited to microwaves and very short propagation lengths. Tuniz et al. scale these metamaterial fibres up to the terahertz region over longer distances and show focussing down to λ/28.