Optical Multi-STAR-IRS Assisted Underwater Wireless Communication System

Optical intelligent reflecting surfaces (OIRSs) have emerged as a promising solution for enhancing reliability, coverage, and energy efficiency (EE) in optical wireless communication networks. However, their application in underwater wireless optical communication (UWOC) remains limited due to severe attenuation and the lack of adaptive non-line-of-sight (NLOS) support. To address these challenges, this paper proposes two novel optical simultaneously transmitting and reflecting intelligent reflecting surface (OSTAR-IRS) architectures: (i) a hybrid mirror-array and liquid crystal-based design (H-OSTAR-IRS), and (ii) a standalone liquid crystal-based OSTAR-IRS (LC-OSTAR-IRS). The proposed system integrates non-orthogonal multiple access (NOMA) and rate-splitting multiple access (RSMA) under energy splitting (ES) and mode switching (MS) operations with optimized power allocation. Numerical results demonstrate that the proposed H-OSTAR-IRS architecture achieves higher aggregate spectral efficiency (ASE) compared to LC-OSTAR-IRS, with improvements of up to approximately 20-30% depending on the multiple access scheme. In addition, RSMA consistently improves fairness across users. Furthermore, the MS mode achieves execution times below 3 seconds, highlighting its practical suitability and low computational complexity.