Full-duplex modulating retroreflector based UWOC system using MEMS grating modulator and SiPM

In this paper, a single source full-duplex modulating retroreflector based underwater wireless optical communication (UWOC) system is proposed and experimentally demonstrated. A green laser is used and directly modulated for the downlink data transmission, and a reflective MEMS grating modulator is employed in the uplink to reflect and modulate the transmitting light. A large field-of-view (FOV) fisheye lens is mounted before the MEMS grating modulator to extend the field of view of the transceiver. The received signal in uplink, of which light beam travels through the underwater channel twice, is detected by a highly sensitive silicon photomultiplier (SiPM). The BER performance of the system is comprehensively investigated at different received optical powers and different incident angles. Experimental results show that the system can achieve 200-kbps uplink data rate and at 1.6-Gbps downlink data rate simultaneously at a wide field-of-view at 130°, offering a promising system design for practical applications such as data collection and controlling of small and lightweight underwater devices. To the best of our knowledge, it is the first time that Modulating retroreflector (MRR) based full-duplex UWOC system with only one light source has been experimentally demonstrated and studied. The achievable transmission distances of the proposed system at different water types are estimated, which are about 49 m and 15 m, in pure sea water and clear ocean water respectively.