Dynamic Metasurface-Backed Luneburg Lens for Multiplexed Backscatter Communication

Backscatter communications is attractive for its low power requirements due to the lack of actively radiating components; however, commonly used devices are typically limited in range and functionality. Here, we design and demonstrate a flattened Luneburg lens combined with a spatially-tunable dynamic metasurface to create a low-power backscatter communicator. The Luneburg lens is a spherically-symmetric lens that focuses a collimated beam from any direction, enabling a wide field-of-view with no aberrations. By applying quasi-conformal transformation optics (QCTO), we design a flattened Luneburg lens to facilitate its seamless interface with the planar metasurface. The gradient index of the Luneburg lens is realized through additive manufacturing. We show that the flattened Luneburg lens with a reflective surface at the flattened focal plane is able to achieve diffraction-limited retroreflection, enabling long-range backscatter communication. When an interrogator transmits towards the metasurface-backed Luneburg lens, the device can modulate the reflected signal phase across a wide field of regard to communicate data. We experimentally show that the spatial control over the metasurface allows different bit streams to be simultaneously communicated in different directions. Additionally, we show that the device is able to prevent eavesdroppers from receiving information, thus securing communications.