Experimental demonstration of a continuous varifocal metalens with large zoom range and high imaging resolution

Varifocal lenses find significant applications in telescopy, photography, and microscopy. Conventionally, a varifocal lens is implemented by changing the axial distance between multiple conventional bulky refractive elements. Recent progress in metasurfaces offers an alternative based on ultrathin and lightweight metadevices, but suffering from a limited zoom range (typically no more than 2×) or numerical aperture (typically no more than 0.3). Here, we experimentally demonstrate a continuous varifocal metalens in the microwave band, which can be continuously zoomed by changing the mutual angle between two combined geometric metasurfaces with the same design. The results reveal that a 3.5× zoom range is realized when the mutual angle increases from 20° to 90°, with changes of the focal length from 295 mm to 85 mm and numerical aperture from 0.56 to 0.92. Furthermore, the diffraction-limited focusing and high imaging resolution are experimentally demonstrated.