Cascaded Optical Reconfigurable Intelligent Reflecting Surfaces for Multi-Hop Optical Wireless Communications

Optical reconfigurable intelligent reflecting surface (ORIS), as a new type of programmable optical communication equipment, can reconstruct the optical channel environment and expand the application scenarios of optical wireless communications (OWC), which have attracted widespread attention. However, with the increasing demand for OWC scale in B5G and even 6G scenarios, the coverage range of a single ORIS (below 300 m) can no longer meet communication needs. Cascaded ORISs’ technology has become an inevitable trend in the development of ORIS, which has not been deeply studied in existing work. To address the above challenges, in this paper we set up cascaded ORISs in a typical long-distance free space optcis (FSO) scenario and conduct a detailed analysis of their channels and performance. This system employs cascaded ORISs to extend ORIS coverage and expand the overall scale of the FSO system, thereby enabling the FSO link to evolve from a traditional point-to-point configuration to a broader, spatially distributed communication layout. The physical model of multiple ORISs’ cascades and the effect on their communication performance are analyzed in detail. Meanwhile, the closed-form expressions of the bit error rate (BER) and outage probability of the multi-hop cascaded ORISs-assisted FSO system are derived and verified by simulations. Based on the theoretical results and simulation results, the influence of each parameter on the system performance is carefully analyzed, which provides guidance for the design of the actual system.