Single LED-based 46-m underwater wireless optical communication enabled by a multi-pixel photon counter with digital output

Presently, most of the long-reach underwater wireless optical communication (UWOC) systems employ laser diodes rather than light-emitting diodes (LEDs) as the transmitters. Due to lasers' smaller divergence angles, those UWOC systems could realize longer communication links. Although LED-based long-reach UWOC has distinguished advantages, it suffers from very low received optical power. Fortunately, highly sensitive multipixel photon counter (MPPC) and energy efficient pulse position modulation (PPM) pave a way towards LED-based long-reach UWOC. In this paper, we investigated the underlying working principle of an MPPC and proposed a UWOC system based on single LED as well as a lens-free MPPC with digital output. The relationship between the MPPC p.e. threshold and its received optical power was theoretically studied and further proved by experimental results. Single 2.3-MHz, 3-W blue LED was used as the transmitter to generate 8-PPM to 64-PPM signals with a 5-MHz slot frequency. After a 46-m underwater transmission, the measured BERs were all below the forward error correction (FEC) limit, which were achieved with less than 100 incident photons during each pulse slot.