Multispectral metasurface hologram at millimeter wavelengths.

We demonstrate a computer-generated metasurface hologram in which four distinct images are encoded at four different W-band (75-110 GHz) frequencies. The metasurface hologram consists of a planar array of resonant metamaterial elements excited by a collimated reference beam incident on the hologram at an oblique angle. Each of the images is encoded by a subset of metamaterial elements that are resonant at the specific excitation frequency and are spatially positioned to achieve a desired phase distribution in the plane in conjunction with the reference wave. The phase-only hologram is optimized using the Gerschberg-Saxton algorithm. The four well-defined images are produced at specific distances within the Fresnel zone of the aperture.