Experimental Demonstration of Hybrid LED-LD Based UOWC Link

In this paper, we have designed and experimentally characterized a hybrid light emitting diode (LED) and laser diode (LD) based underwater optical wireless communication (UOWC) link, which can be suitable for providing high-speed optical connectivity between onshore and submerged systems. An LED-based system is efficient for short-range communication whereas an LD-based system is for long distances. In this paper, we have experimentally demonstrated the establishment of a hybrid LED-LD UOWC link at a data rate of 10 Mbps over a 2.5 m water channel using a return to zero on-off keying (RZ-OOK) modulation scheme using an FPGA-based transmitter and receiver. We have also used offline data processing to quantify the bit error rate (BER) performance as a function of received optical power for tap water and turbid water channels. For the tap water channel, we have achieved a BER as low as 3.5 ×10 ⁻⁶ at - 35.1 dBm received optical power, whereas for turbid water the achieved BER is 1.8 × 10 ⁻⁵ at −31. 6 dBm of received optical power in absence of air bubble. In turbid water (and tap water) channel in presence of air bubbles the minimum achievable BER is around 3 × 10 ⁻⁴ (3 × 10 ⁻⁴ ) for −31.5 dBm (-35.5 dBm) of received power.