Inverse designed metasurfaces can solve prescribed Fredholm integral equations at optical wavelengths. To this end, a mirror is included to provide the feedback required to perform the Neumann series that solves the equation.

OSA Technical Digest
doi.org/10.1364/CLEO_QELS.2021.FTh2M.7
Photonic Materials

Cordaro, A., Edwards, B., Nikkhah, V., Alù, A., Engheta, N., & Polman, A. (2021). Solving integral equations with inverse-designed metagratings at optical wavelengths. In CLEO: QELS 2021 - Part of Conference on Lasers and Electro-Optics. doi:10.1364/CLEO_QELS.2021.FTh2M.7