High efficiency dual-wavelength achromatic metalens via cascaded dielectric metasurfaces

Multiple-wavelength, frequency-adjustable planar metalenses are of great concern in optical imaging and microscopy systems. Here we propose a novel approach to design a high efficiency dual-wavelength achromatic metalens (DAM). This is different from the mostly reported multiple-wavelength achromatic devices which realize their functions at the expense of sacrificing the efficiency by partitioning the structure plane to several sections. In our designed DAM, the doublet approach is adopted and phase shifts on both sides are superimposed to modulate the focal length at a certain wavelength. With elaborate design, focal lengths at two discrete wavelengths can be regulated to own the same value. With such a strategy, DAM for different focal lengths (f = 20μm and 30μm) with focusing efficiency as high as 70% are demonstrated. Our work provides a general design scheme for multiple-wavelength, high efficient wavefront engineering and holds potential applications in designing optical achromatic devices.