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Long-distance enhanced fourier transform by hyperbolic gradient-index metalens

A new hyperbolic gradient-index metalens is demonstrated at terahertz (THz) frequency, which can realize enhanced Fourier transform with extended spatial frequency bandwidth. The bandwidth can be extended to 2.5k0 (k0 is the wave-vector in air), which is 2 to 3 times of conventional lens. Furthermore, the working distance can be larger than one wavelength, and the input and output surfaces are flat, which provides conveniences for system integration. The metalens has potential applications on super-resolution imaging working over long distances.