Inverse design of a near-infrared metalens with an extended depth of focus based on double-process genetic algorithm optimization.

Metalens with extended depth of focus (EDOF) can extend the mapping area of the image, which leads to novel applications in imaging and microscopy. Since there are still some disadvantages for existing EDOF metalenses based on forward design, such as asymmetric point spread function (PSF) and non-uniformly distributed focal spot, which impair the quality of images, we propose a double-process genetic algorithm (DPGA) optimization to inversely design the EDOF metalens for addressing these drawbacks. By separately adopting different mutation operators in successive two genetic algorithm (GA) processes, DPGA exhibits significant advantages in searching for the ideal solution in the whole parameter space. Here, the 1D and 2D EDOF metalenses operating at 980 nm are separately designed via this method, and both of them exhibit significant depth of focus (DOF) improvement to that of conventional focusing. Furthermore, a uniformly distributed focal spot can be maintained well, which can guarantee stable imaging quality along the longitudinal direction. The proposed EDOF metalenses have considerable potential applications in biological microscopy and imaging, and the scheme of DPGA can be promoted to the inverse design of other nanophotonics devices.