The angular response of thin diffractive optical elements is highly correlated. For example, the angles of incidence and diffraction of a grating are locked through the grating momentum determined by the grating period. Other diffractive devices, including conventional metasurfaces, have a similar angular behavior due to the fixed locations of the Fresnel zone boundaries and the weak angular sensitivity of the meta-atoms. To alter this fundamental property, we introduce angle-multiplexed metasurfaces, composed of reflective high-contrast dielectric U-shaped meta-atoms, whose response under illumination from different angles can be controlled independently. This enables flat optical devices that impose different and independent optical transformations when illuminated from different directions, a capability not previously available in diffractive optics.
Kamali, S. M., Arbabi, E., Arbabi, A., Horie, Y., Faraji-Dana, M. S., & Faraon, A. (2017). Angle-multiplexed metasurfaces: Encoding independent wavefronts in a single metasurface under different illumination angles. Physical Review X, 7(4). https://doi.org/10.1103/PhysRevX.7.041056