As the largest ecosystem covering 71% of Earth’s surface, the ocean harbors abundant biological resources, mineral deposits, and energy reserves, holding irreplaceable strategic value for sustainable development. With rapid advancements in marine resource exploitation, environmental monitoring, and military applications, traditional acoustic communication technologies can no longer meet the growing demand for high-speed data transmission in modern ocean exploration. Underwater wireless optical communication (UWOC) technology has emerged as a pivotal development direction in underwater communications due to its remarkable advantages of high bandwidth (up to Gbit/s level), low latency (ms level), and low power consumption. This technology demonstrates vast application prospects in submarine observation networks, underwater internet of things (IoT), marine resource exploration, and military security. However, the complexity and uniqueness of marine environments, including high water attenuation, dynamic turbulence effects, platform position uncertainty, and intense background light interference, pose significant challenges for practical UWOC implementation. Therefore, systematically reviewing UWOC research progress and analyzing its development trends carry substantial theoretical and practical significance for advancing this technology.

Progress Recent years have witnessed breakthrough developments in three key aspects of UWOC technology transmission, propagation, and reception.

In transmission technology, significant efforts have focused on developing high-power blue-green lasers and micro-LED arrays. Notably, Tsinghua University-Berkeley Shenzhen Institute developed a blue single-layer quantum dot micro-LED achieving 2 Gbit/s transmission over 3 m underwater with a bit error rate below the forward error correction threshold (Fig. 1). National Chiao Tung University implemented a semipolar InGaN/GaN green micro-LED array achieving 3.129 Gbit/s communication rates (Fig. 1). Advanced modulation formats like 16-QAM OFDM have substantially improved spectral efficiency, with experiments demonstrating 12.5 Gbit/s transmission over 1.7 m underwater (Fig. 2). University of Science and Technology of China realized 1 Gbit/s transmission over 130 m using PAM4 modulation with avalanche photodiode detectors.

In propagation technology, beam shaping techniques have achieved important breakthroughs in complex underwater environments. Bessel beams and Airy beams exhibit superior anti-interference capabilities under turbulent and bubbly conditions due to their unique non-diffracting and self-healing properties (Fig. 3). Beijing University of Posts and Telecommunications developed Bessel beams using fiber micro-axicon technology that effectively mitigate signal attenuation caused by absorption and Mie scattering. Fudan University’s 2024 proposal of self-focusing Airy beams combined with wavelength division multiplexing increased system data rates by 91%. Multi-dimensional multiplexing techniques including wavelength division, polarization, and orbital angular momentum multiplexing have dramatically enhanced system capacity. Fudan University achieved 20.09 Gbit/s over short distances using wavelength division multiplexing (Fig. 4), while Ocean University of China verified the feasibility of orbital angular momentum multiplexing at 20 Mbit/s rates (Fig. 4).

Reception technology has seen remarkable progress in high-sensitivity detectors and advanced signal processing algorithms. The application of single-photon avalanche detectors (SPAD) and silicon photomultipliers (SiPM) significantly improved communication performance under low-light conditions. Xi’an Institute of Optics and Precision Mechanics achieved 0.34 bit^-1 receiver sensitivity using 32-PPM modulation with high-performance photon-counting detectors (Table 2). In signal processing, deep learning-assisted equalization methods demonstrate outstanding advantages. Fudan University first introduced Gaussian kernel-aided deep neural network equalizers into underwater visible light communication systems, achieving 1.5 Gbit/s transmission over 1.2 m underwater. In 2025, Beijing University of Posts and Telecommunications proposed a machine vision-based intelligent turbulence perception mechanism that effectively addresses turbulence effects caused by thermohaline gradients and bubbles.

Engineering prototype development and sea trials have achieved notable accomplishments worldwide. The Xi’an Institute of Optics and Precision Mechanics developed a series of prototypes demonstrating outstanding performance in deep-sea applications, with their LED array-based system achieving 20 Mbit/s communication rates at 3509 m depth in the South China Sea aboard the “Deep Sea Warrior” manned submersible (Fig. 10). In practical applications like submarine pipeline laying monitoring, their prototypes successfully transmitted HD video in real-time over 18 m@c=0.5 m^-1 (equivalent communication distance under Class I water quality conditions: 300 m) under sea state 4?5 conditions (Fig. 11). Internationally, Sonardyne’s BlueComm system has been practically deployed for unmanned underwater vehicle swarm communications, supporting rates up to 500 Mbit/s (Table 4).

UWOC technology has made significant progress in both theoretical research and engineering applications after years of development, yet still faces challenges in communication distance and environmental adaptability. Based on current research and technological trends, future UWOC development will focus on the following aspects.

1) Extended range and higher rates. Developing higher-power blue-green lasers, optimizing beam shaping techniques, and adopting more efficient modulation schemes may break through current distance limitations. The U.S. Navy has initiated research on high-energy high-repetition-rate lasers targeting systems exceeding 1 Gbit/s over 100 m.

2) Multi-modal communication integration. Hybrid systems combining optical, acoustic, and RF communications will become a major trend. The marine space-time reference network (Fig. 12) demonstrates the concept of an integrated air-space-ground-sea network that leverages the strengths of various communication methods.

3) Integrated communication and sensing. Future UWOC systems will not only transmit data but also enable environmental sensing and target detection through optical signal analysis, providing richer data support for marine research.

4) Intelligent and autonomous systems. Deep integration of artificial intelligence will enhance system adaptability. Deep learning-based channel estimation, signal processing, and link optimization algorithms will enable intelligent responses to complex marine environmental changes.

5) Standardization and practical implementation. As the technology matures, establishing unified communication protocols and performance evaluation standards will be crucial for transitioning UWOC from laboratory research to large-scale practical applications.