Tunable THz co-coding beam splitting metasurfaces based on superconducting NbN and gold materials

Abstract

The tunable multi-beam has important roles in real-time detection, environmental sensing and so on. We demonstrate in this paper the tunable terahertz (THz) digital coding beam-splitting metasurfaces based on superconducting niobium nitride (NbN) and Gold materials. Based on the amplitude modulation (AM) mode of NbN, co-coding of phases and materials for tunable beam-splitting metasurfaces are proposed, including Regional Independent Modulation (RIM) and NbN + Gold Composite Modulation (CM). The variation of splitting beam number and ratio with temperature from the superconducting state to normal state is theoretically realized. The advantage of RIM can individually tune the intensity of certain beams without affecting others. Comparatively, CM design is more flexible, and different co-coding sequences can achieve diversity for far-field beams. To further increase the number of tunable beams, based on the 1-bit CM metasurfaces, the extension of 1D into 2D space by co-coding addition is discussed. As a verification of the theoretical method, tunable beam-splitting metasurfaces with main beams number ranging from 4 to 2, 2 to 3, and 16 to 8 at 0.85 THz are realized. The method proposed in this paper provides an effective approach for the design of amplitude tunable devices and NbN-based beam modulated metasurfaces.