Polarization Multiplexing Based UOWC Systems Under Bubble Turbulence

High-speed and turbulence-tolerant transmission links are required to meet the growing demand for underwater optical wireless communication (UOWC). However, most previous works were implemented in statically simulated underwater channels with uniform temperature and salinity gradients irrespective of bubble motion. This paper presents an experimental demonstration of a polarization multiplexing (PolMux) based UOWC system considering bubble-induced turbulence. A theoretical transmission model is built and experiments are carried out to investigate the impact of bubble turbulence on PolMux transmission. The general rules of bubble impairments are summarized by manipulating different bubble flow rates, positions and bubble-effected region thicknesses. Moreover, to mitigate these effects, subchannel pairwise coding is implemented to address the subchannel signal-to-noise-ratio (SNR) imbalance issue, and subcarrier pairwise coding is utilized to overcome the subcarrier SNR imbalance, reaching a sum data rate of 8.58 Gbps. This work evaluates the performance of PolMux-UOWC links in the presence of air bubbles and demonstrates the feasibility of pairwise coding to achieve high-speed transmission in UOWC systems with bubble turbulence.