With the growing demand of ocean exploration, underwater wireless communication has drawn great interest in recent years. Underwater acoustic communication suffers low bandwidth and high latency, while radio frequency signal attenuates rapidly in the water due to the skin effect. In contrast, underwater optical wireless communication (UOWC) exhibits distinct advantages such as high data rate and low latency, making it a promising solution for underwater wireless communication. However, the dynamic underwater environments and non-ideal device characteristics bring challenges for UOWC systems. Considering these challenges, the technological advancements and application prospects of UOWC are presented to provide reference for its future development.

Existing UOWC technologies primarily focus on channel equalization, modulation and coding, signal detection, tracking and multi-user access. Channel equalization for UOWC systems includes pre-equalization and post-equalization, where hardware-based pre-equalization is an effective approach to compensate for the nonlinear device characteristics at the transmitter side, and post-equalization typically employs signal processing techniques to eliminate the inter-symbol interference at the receiver side. Commonly used modulation schemes in UOWC include on-off keying, pulse amplitude modulation, pulse position modulation, and pulse width modulation. Channel coding schemes in UOWC are mainly categorized into block codes (e.g., Reed-Solomon code and Bose-Chaudhuri-Hocquenghem code) and convolutional codes (e.g., low-density parity-check code and Turbo code). Both model-driven and data-driven detection schemes have been proposed for UOWC systems based on various detectors. Tracking is an effective method to guarantee link stability and signal quality of UOWC, which can be classified into imaging and non-imaging categories. Multi-user access technologies in UOWC primarily include time division multiple access, code division multiple access, non-orthogonal multiple access, and hybrid schemes. Off-line or real-time UOWC systems have been developed incorporating these transmission technologies. Nevertheless, existing UOWC systems still face significant challenges such as dynamic underwater environments and non-ideal device characteristics, which require further development of UOWC technologies.

UOWC is considered as a promising underwater wireless communication technology, due to its distinct advantages including high data rate, low latency, and easy deployment. First, the UOWC channel characteristics are elaborated in the aspect of link and device, presenting the main challenges of UOWC in practical scenarios. Then, the advancements of UOWC technologies in channel compensation, modulation and coding, signal detection, tracking, and multi-user access are introduced subsequently. Next, the development progress of existing UOWC systems is reviewed. Finally, prospects and discussions are presented on the applications of UOWC. Future efforts involve adaptive transmission and integration of different communication technologies to construct intelligent ocean networks.