Where \(\varphi_{1}(r)\) is the required phase profile at the coordinate of \(r=\sqrt{x^{2}+y^{2}}\) along the plane of metalens, \(k_{0}={{2\pi}}/{\lambda}\) is the free-space wave vector, \(f_{1}\) and \(f_{2}\) are the nearest and farthest longitudinal focal lengths. Figure \ref{fig:2}(a) shows the required phase profiles for an achromatic bifocal metalens working at \(\lambda_{1}=460\) nm, \(\lambda_{2}=535\) nm and \(\lambda_{3}=610\) nm. The realized phases achieved by finite element method (FEM) study are plotted in Fig \ref{fig:2}(b) for each wavelength, separately.