Metasurfaces are flat structured surfaces that are designed to control the two-dimensional distributions of phase, polarization, and intensity profiles of optical waves. Usually, the optical response of metasurfaces is dispersive and polarization-dependent, which indicates the capability of using metasurfaces for information multiplexing using wavelengths and polarization states. However, most multiplexing techniques based on metasurfaces reported so far occur only in the spatial domain. Here, we experimentally demonstrate metasurface multiplexing by exploiting the degree of freedom of the spatial frequency domain. Specifically, we overlap two independent holographic images at high and low spatial frequencies and record them onto a single piece of metasurface hologram (meta-hologram). These two holographic images can be successfully separated from the reconstructed overlapped images by using two digital Gaussian filters. In addition, we demonstrate spatial frequency multiplexing by meta-nanoprinting, in which a complex multiplexed image (the combination of a cat image and a dog image) is recorded and demultiplexed with high fidelity. The presented spatial frequency multiplexing with metasurfaces suggests a route to increase the information channel and may contribute to the research and applications in optical information encoding, optical storage, optical information hiding, information security, compact displays, etc.
Keywords: meta-holography; meta-nanoprinting; metasurfaces; spatial frequency multiplexing.