Terahertz Logic Gate Operations in a Toroidal Metasurface

The applications of terahertz metamaterials are being actively explored in recent times for applications in high-speed communication devices, miniature photonic circuits, and bio-chemical devices because of their wide advantages. The toroidal resonance, a new type of metasurface resonance, has been examined with great interest to utilize its properties in terahertz metasurface applications. The study reports a proof of concept design of a toroidal metasurface that experimentally demonstrates logic gate operations in the terahertz frequency regime by passive tuning of the split ring resonators compromising the meta-atom design. The amplitude modulation is utilized as a method of determining the Boolean logic output of the system. The proposed metasurface could be further optimized for high amplitude modulations, as well as for active logic gate operations using tunable materials including graphene and ITO. The proposed metasurface consists of three split-ring resonators, and the near-field coupling between the adjacent resonators dictates the logic gate operations. The toroidal excitation in the metasurface is determined by a multipole analysis of the scattered powers of terahertz radiation. The proposed metasurfaces experimentally define AND Boolean logic gate at 0.89 terahertz, and OR Boolean logic gate at 0.97 terahertz. Numerical simulations support the experimentally obtained results. Additionally, we numerically report the excitation of NAND gate at 0.87 THz. Such toroidal logic-gate metasurfaces in the terahertz region could find applications in digitized terahertz circuits for photonic device applications.