Optical RIS-Aided Covert Visible Light Communications

This paper investigates a covert visible light communication (VLC) system, where a transmitter (Alice) aims to send confidential information to a legitimate user (Bob) while avoiding being detected by an unauthorized warden (Willie). To achieve this, we propose an optimization framework that controls both reflection by mirror array-based reconfigurable intelligent surface (mRIS) and refraction by liquid crystal-based RIS (LC-RIS) to reconstruct a desired covert optical transmission environment. Considering the covertness constraint with the strongest Willie aided by LC-RIS, we jointly optimize the rotation configuration of mRIS, the parameter of Bob's LC-RIS, and the average optical intensity of Alice by a proposed stepwise decoupling method. The simulation results show that the deployment of LC-RIS on Bob's receiver has a more significant impact on enhancing covert VLC performance compared to the deployment of mRIS.