An ultra-compact differential confocal sensor based on a system of metasurfaces

Owing to the powerful capability to manipulate light of the metasurface, here, we propose an ultra-compact differential confocal sensor based on two dielectric metasurface layers, in which the conventional focusing lens and beam splitter are replaced by the dielectric metasurfaces. We introduce the design of the dielectric metasurfaces based on truncated waveguide-type silicon nitride meta-atoms at the wavelength of 633 nm. The focusing performance of each metasurface was studied by the finite difference time domain method. Subsequently, the performance of the differential confocal system was simulated according to the ray tracing method. Metasurface-based optical sensors are expected to serve as the foundational elements of low-cost, miniaturized, and lightweight optical sensors in the future.