Super-resolution imaging with a Bessel lens realized by a geometric metasurface.

In the super resolution imaging system, a lens and an axicon that can generate spherical wavefronts and non-diffracting Bessel beams respectively are both essential yet difficult to integrate using the traditional approach. We propose a new concept of a "Bessel-lens" to indicate unique optical elements that merge the functionalities of lenses and axicons simultaneously. The Bessel-lens is a mission that is extremely difficult if not impossible for state-of-the-art technology because of the exotic phase profile. Via the geometric phases in space-variant nanoslits, planar Bessel-lenses are designed and experimentally characterized for the first time to generate subdiffraction beams. Compared with a planar lens and axicon with the same dimensions and numerical aperture, the proposed Bessel-lens possesses a higher imaging resolution, which may find applications in microscopy, nanofabrication and dense data storage.