Ultra-wide angle metalens design with ray-based and wave-based tools

Designing a metalens of millimeter scale or larger is challenging. We demonstrate how to combine a ray-based automatic design tool with a wave-based inverse design tool to design a mm-size ultra-wide angle metalens imaging system. The ray-based approach parametrizes the distribution of meta-atom design parameters over the surface with a polynomial, and treat the metalens similarly to a grating. The ray-based design tool considers both the transmission and the phase of the meta-atoms as functions of the incident angle. The ray-based approach is fast and robust. It can complete the optimization of a mm-size metalens in a few minutes. This design can then serve as a starting point for a wave-based inverse design tool. The wave-based inverse design tool is applied to further optimize the metalens with arbitrary distribution of meta-atom design parameters. The additional design freedom offered by the arbitrary distribution further increases the light collection efficiency and image resolution. Finally, the design performance is validated with a finite difference time domain (FDTD) algorithm. All analysis results agree well, show that the final ultra-wide angle metalens design is close to diffraction limited. These results demonstrate the effectiveness of our proposed workflow by taking advantage of both the ray-based and the wave-based design tools.