In Internet of Underwater Things (IoUT) scenarios, power-hungry devices need to periodically harvest energy to be alive. By dynamically controlling and redirecting the optical beam, reconfigurable intelligent surfaces (RIS) can enhance both the energy transfer and information reception processes, thereby improving the sustainability of low-power underwater devices. Simultaneous wireless information and power transfer (SWIPT) systems allows to harvest energy and receive data from the transmitted optical beam, thus feeding the low-power receiver (Rx) while downloading data. However, realistic underwater scenario can strongly affect the performance of such systems. This paper investigates the performance of ORIS-assisted SWIPT system under a realistic unified channel model for underwater optical wireless communications (OWC), considering both coherent and non-coherent detection schemes. Considering multiple attenuation losses, underwater turbulence, pointing error, and angle of arrival deviation, we derive the joint outage probability of an ORIS-aided SWIPT OWC system for different transmission protocols based on different resources that are allocated. Three approaches are investigatedi.e., (i)power-splitting (PS),(ii)time-switching (TS), and(iii)element-splitting (ES). While PS and TS are based on all-passive RIS elements, ES considers hybrid (active and passive) elements. Simulation results show enhanced performance obtained with ES approach for low signal-to-noise ratio (SNR), while PS outperforms ES for high SNR.

This paper presents a comprehensive performance study for the underwater optical wireless communication (UOWC) channel, accounting for the effects of attenuation, turbulence, pointing errors, and fluctuations in the angle-of-arrival (AOA), modeled by the Beer-Lambert model, the Fisher-Snedecor$\mathcal {F}$turbulence, Hoyt, and Rayleigh distributions, respectively. Considering the stochastic nature of UOWC, closed-form expressions for outage probability, average bit-error-rate (BER), and ergodic capacity are derived. The results revealed that increasing the field-of-view (FoV) reduces the impact of AOA fluctuations. Asymmetric two-dimensional beam misalignment exhibits better outage probability performance compared to symmetric misalignment. Furthermore, heterodyne detection consistently outperforms direct detection. When employing heterodyne detection, M-quadrature amplitude modulation (M-QAM) achieves superior BER performance. Additionally, as absorption increases with longer wavelengths, BER performance deteriorates. Narrower beamwidths improve ergodic capacity by enhancing received signal power.