Coupling Plasmonic System for Efficient Wavefront Control.

Efficient and flexible manipulation of electromagnetic waves using metasurfaces has attracted continuous attention in recent years. However, previous studies mainly apply sole resonance effect to accomplish the task. Here, we show that introducing a meta-coupling effect would reveal further physical insights in the electromagnetic wave control. To demonstrate this, a reflection-type coupling system composed by two identical linear resonances in a metal-insulator-metal configuration is theoretically proposed using the coupled-mode theory, whose phase diagram can be well controlled upon the coupling changes. Such intriguing optical property is verified by a double C-shaped resonator in the terahertz regime, where the coupling effect can be tuned by changing their either relative distance or rotation. More importantly, the reflection phase shift around the working frequency can be efficiently engineered without having to change the dimensions of the resonators. Two efficient anomalous metasurface deflectors are designed and experimentally characterized, whose maximum measured efficiency is more than 70%. The proposed controlling strategy further enriches the designing freedoms of metasurfaces and may find broad applications in realizing efficient and tunable functional devices.