Optical receiving systems with single-lens structures have problems such as low receiving efficiency and small field of view when applied to underwater optical wireless communication systems. In this study, a design scheme for a double-layered fly-eye-lens optical system with wide-angle focusing is proposed. Based on the analysis of the LED light source transmission model and seawater channel, the optical-power receiving equation of the fly-eye lens system is deduced. The fly-eye-lens receiving system was designed and simulated using Zemax according to the geometrical optics principle of the lens array. An experimental device for measuring the insertion loss and receiving efficiency of an underwater blue-green LED communication system was built, and the optical power of the receiving optical system was experimentally measured. For the link distances of 1, 3, and 5 m, the received optical power of the double-layered-compound eye system was higher than that of the single-layered system, with a power increase of 72%, 65%, and 60%, respectively. The results show that the double-layered fly-eye-lens receiving antenna can significantly improve the optical power received by the receiving end; therefore, this antenna structure has strong practicability and good development prospects in the field of underwater optical wireless communication.

Vortex beams have a broad application prospect in the fields of information modulation, detection, and identification of targets because they carry orbital angular momentum. First, the related theories of vortex beam and bidirectional reflection distribution function are introduced. Differential surface element method is a numerical calculation method that discretizes the problem domain into small panels, approximates the properties of the problem, and transforms it into a system of algebraic equations. The expression for the backscattered intensity of a vortex beam illuminating a typical target (sphere, cylinder, cone, and dome) is derived by combining the scattering theory and the differential surface element method, and simulations are carried out. Finally, the theoretical analysis was verified by the experiments. The results show that: for different targets, the difference between the backscattered power curves of the vortex beam is larger, which is conducive to target identification; for the same target, the peak range of the backscattered power curve of the vortex beam is wider, which is conducive to the detection of multiple angles; when the typical target is a sphere and the material is different, the peak value of the backscattered power curve of the vortex beam changes with the change of the material but the trend of the change is basically the same.

Spot detection technology plays an important role in modern scientific research and application. Due to its advantages of high detection sensitivity, simple signal processing, and strong anti-interference ability, four-quadrant detectors have been widely used in spot detection technology and are the key components in acquisition, tracking, and pointing systems. Firstly, the spot models commonly used in spot detection and the principle of four-quadrant detector spot detection were introduced. Then, the research results of four-quadrant detector spot detection at home and abroad, as well as the factors affecting the accuracy of four-quadrant detector spot detection and the commonly-used spot detection algorithms were analyzed. The four-quadrant detector spot detection system was introduced, including the beam alignment detection system, four-quadrant detector tracking communication composite system and micro-nano laser communication system. Finally, the development prospects of spot detection technology was prospected.

The propagation of a laser beam in an underwater environment gives rise to attenuation caused by absorption and scattering as well as fading caused by turbulence. These effects lead to a decrease in light power and fluctuations in light intensity. To account for variations in water velocity, flow direction, and distance in communication links, field measurements were conducted in rivers and ocean nearshore waters. Based on these measurements, a model for an underwater wireless optical channel was developed. Our study involves the measurement and analysis of light intensity fluctuation, loss of received light power, and the structure constant in various underwater regions. Additionally, the investigation examines the variation of the bit-error rate in relation to different signal-to-noise ratios. The results suggest that the river displays attributes of low turbulence, whereas the ocean’s nearshore waters exhibit a moderate level of turbulence under the specified circumstances. As the velocity of the water increases, the scintillation index of the received optical signal also increases, indicating a higher degree of signal instability. When transmitting horizontally, the scintillation index of the received optical signal remains unaffected by the direction of water flow. Furthermore, as the distance between the transmitter and receiver increases, the scintillation index of the received optical signal intensifies, indicating a greater level of signal instability. The presence of the external interference factors can increase turbulence intensity. Within a depth range of 60 cm underwater, the turbulence intensity at different depths remains basically unchanged.