Wavefront Selective Modal Excitations for Optimally Informative Sensing in Fano-Resonant Metasurfaces

Fano-resonant metasurfaces governed by quasi-bound states in the continuum have recently sparked an enormous interest in the sensing community due to their spectacular sensitivity to nanoscale disturbances. Here, a plane wave or focused illumination is typically used to excite the quasi-BIC modes. In this paper, we theoretically demonstrate how structuring an incident excitation leads to a gain in information about relevant nanoscale perturbations to be detected. We analyze the full eigenmode spectrum of a dielectric quasi-BIC metasurface, and uncover eigenmodes that are incompatible with trivial illuminations such as plane waves. By utilizing the concept of "maximum information states," that was recently developed by the wavefront shaping community, we engineer incident excitations that can selectively excite these quasi-BIC modes. By using information theory, we quantitatively demonstrate that such wavefront selective modal excitations can be more informative than conventional excitations based on plane waves.