Exploiting Gold Nanoparticles for Secure Visible Light Communications

Visible light is a proper spectrum for secure wireless communications because of its high directivity and impermeability. To make visible light communication (VLC) even more secure, we propose to exploit recently synthesized gold nanoparticles (GNPs) with chiroptical properties for circularly polarized light. Carefully synthesized GNPs can differentially absorb and retard the left and right circularly polarized light, and a GNP plate made by judiciously stacking many GNPs can elaborately manipulate the amplitudes and phases of left and right circularly polarized light. In the proposed VLC system with multiple transmitters, each transmitter is equipped with a GNP plate and a linear polarizer while the legitimate receiver is equipped with only a linear polarizer. A new VLC channel model is first developed by representing the effect of GNP plates and linear polarizers in the circular polarization domain. Based on the new channel model, the angles of linear polarizers at the transmitters and legitimate receiver are optimized considering the effect of GNP plates to increase the secrecy rate in wiretapping scenarios. Simulation results verify that when the transmitters are equipped with the GNP plates, the secrecy rate around the legitimate receiver is significantly improved due to the chiroptical properties of GNP plates even if a nearby eavesdropper sets the linear polarizer angle same as the legitimate receiver.