A Broadband Achromatic Alvarez Metalens

Alvarez metalens, which consists of two layers of metasurfaces, has a focal length that can be altered by varying the relative lateral displacement. It garners significant interest due to its potential to replace the conventional bulk lens in ultra-compact varifocal imaging systems. However, the chromatic aberration limits its application under broadband illumination. For the first time, we demonstrate a broadband achromatic Alvarez metalens (BAAM) which is always free of chromatic aberration in the continuous zoom process. In the BAAM, the target phase profile of each componential metasurface can be described as a function of xy-coordinate and wavelength. The numerical results show that when the focal length ranges from 90 μm to 60 μm (the corresponding lateral displacement ranges from 0 to 2.8 μm), the designed BAAM is free of chromatic aberration over the wavelength range from 400 nm to 560 nm. Moreover, phase-profile functions are proposed to design an achromatic tunable beam deflector. These achromatic tunable devices may spark a revolution in optical systems.