Optical Wireless Power Transmission under Deep Seawater Using GaInP Solar Cells

Optical wireless power transmission (OWPT) attracts attention because it enables wireless power transfer over longer distances than current wireless power transfer methods, irradiating laser light to a light-receiving element. In this study, an OWPT system was investigated under water and deep seawater using visible lasers with low optical absorption loss in water. Three laser beams (450 nm, 532 nm, and 635 nm) were transmitted through 30 cm, 60 cm, and 90 cm long tanks filled with tap water and deep seawater and were irradiated to 1.0 × 1.0 cm2 GaInP solar cells. The light reaching rate (ηop) of laser light and the system efficiency (ηsys) of the system (excluding the laser efficiency) were investigated. GaInP solar cells showed photo-electric conversion efficiencies of 30.6%, 40.3%, and 39.3% for 450 nm, 532 nm, and 635 nm irradiations, respectively. As a result, a 532 nm laser through a 90 cm water tank in tap water showed a 78.4% ηop and a 30.8% ηsys. Under deep seawater, a 532 nm laser through a 90 cm tank exhibited a 58.3% ηop and a 23.5% ηsys. A 532 nm green laser showed a higher efficiency than the other 450 nm and 635 nm lasers in this underwater system using GaInP solar cells.