Inverse Design of Electromagnetic Phase Singularities.

The optical vortex has a rapidly changing spatial phase with orbital angular momentum centered by zero electromagnetic field intensity. It opens new strategies for optical communications, sensing, and imaging systems. Nevertheless, generating high-quality optical vortices at the appropriate wavelengths and polarizations is still challenging. In order to produce high-quality optical vortices, we optimize the 2D grating structure with nearly perfect absorption via inverse design in this work. We apply an inverse design, a broad-area computational optimization method, to generate multiple high-quality optical vortices within a 300 nmthick silicon. The grating-structure-based optimization shows nearly perfect absorption (97.02%). Our design shows the maximum purity of the optical vortex as 97.82% for mode 1 and 89.66% for mode -1, which can directly affect the quality of orbital angular momentum communication. Our design mechanism may open a new strategy for generating highquality optical vortices for optical communication, sensing, and many other applications.