An Optically Transparent Reconfigurable Intelligent Surface with Low Angular Sensitivity

Recently, reconfigurable intelligent surfaces (RISs) have attracted extensive attentions from the communication community due to their powerful wavefront manipulation and signal modulation abilities. Optically transparent RISs are needed in some scenarios requiring both optical transparency and high-quality communication services. In RIS-based wireless communications, the channel reciprocity is an important factor to be considered since the electromagnetic responses of RISs usually depend on the incident and receiving angles. To address this problem, an optically transparent 2-bit RIS with low angular sensitivity is proposed. By applying a transparent dielectric substrate and metal-mesh-based patterns, the designed RIS achieves a light transmittance of 49.3%. Both the simulation and measurement results demonstrate the low angular sensitivity at transverse magnetic incidence from 0 degrees to 60 degrees. Moreover, beam steering experiments under various coding sequences and various incident angles are simulated and measured, and the results are consistent with the theoretically predicted results. A further study on the broadcast mode of the RIS shows that its phase response is weakly dependent to the incident and receiving directions.