From Volumetric to Planar Multiplexing: Phase-Coded Metasurfaces without the Bragg Effect

Metasurfaces consisting of planar subwavelength structures with minimal thickness are appealing to emerging technologies such as integrated optics and photonic chips for their small footprint and compatibility with sophisticated planar nanofabrication techniques. However, reduced dimensionality due to the 2D nature of a metasurface poses challenges to the adaptation of a few useful methods that have found great success with conventional optics in 3D space. For instance, Bragg diffraction is the foundation of the well-established technique of phase-coded multiplexing in volume holography. It relies on interference among the scattered waves from multiple layers across the thickness of a sample. In this work, despite losing the dimension in thickness, a metasurface is devised to experimentally demonstrate phase-coded multiplexing by replacing free-space light with a surface wave in its output. The in-plane interference along the propagation of the surface wave resembles the Bragg diffraction, thus enabling phase-coded multiplexing in the 2D design. An example of code-based all-optical routing is also achieved by using a multiplexed metasurface, which can find applications in photonic data processing and communications.