Designs of functional metalenses at short wavelength via genetic algorithm optimization

The spectral region of short wavelength presents significant challenges for optical device and system designs due to the high photon energy and strong absorption characteristics. Metalenses have great potential for enabling single-chip wavefront shaping and function implementation for short wavelength beams, which can reduce energy loss and facilitate system integration. However, functional metalens design for this wavelength region remains largely unexplored. In this study, the metalenses with silicon-based nanohole layout were designed for the wavelength of 46.9 nm, using finite-difference time-domain simulations method. Two genetic algorithm -based design strategies were presented for functional metalenses, targeting extended depth-of-focus and energy-equalized multifocal performance. The study shows that the unit-cell design of the metalens have an average transmittance of 36% with reliable phase manipulation capability. The optimized EDOF metalens achieves a 2-3 times increase in depth of focus compared with a conventional metalens, while maintaining robust performance under off-axis incidence up to 20°. The energy-equalized multifocal metalens realizes clear focusing of multiple focal spots array with over 85% uniformity.