Ocean turbulence is an important factor affecting the development of underwater wireless optical communication (UWOC). To improve the error characteristics of the underwater optical communication system, we propose a differential detection-based multi-receiver-multi-transmitter (MIMO) underwater laser communication transmission method. Additionally, we derive the expressions for calculating the average BER of the MIMO underwater wireless optical communication system with differential detection and non-differential detection in the case that the two transmitted beams are completely uncorrelated. The error characteristics of the MIMO system are simulated and analyzed from the perspective of ocean turbulence intensity and link distance. The simulation results show that the differential detection method has a lower average BER compared to the non-differential detection method in the case of moderate-to-strong ocean turbulence. In addition, the differential detection methods do not have the error floor effect, and non-differential detection methods have the error floor effect. The more the turbulence intensity affects the average BER of the MIMO UWOC system with the increase of the communication link distance, the more obvious is the effect of the turbulence intensity on the average BER of the MIMO UWOC system. Accordingly, the simulation analysis shows that the differential detection method is more suitable for the construction of communication links under long-distance and medium-strong turbulence.

White Rabbit (WR) is a technology based on fiber-optic networks that enables sub-nanosecond-level time synchronization and deterministic Ethernet data transmission among distributed devices. To investigate the transmission characteristics of WR technology over free-space optical links, this paper reports point-to-point single-link ranging experiments for WR over an approximately 1 km near-ground free-space optical link. For the 1 km fiber-optic link and the 1 km free-space optical link (scintillation index = 0.063), the intermediate precision of ranging after a power-cycle reboot is measured to be 5.829 mm (1σ) and 9.689 mm (1σ), respectively, while the ranging precision is 0.267 mm (1σ) and 1.353 mm (1σ), respectively. As the scintillation index of the free-space optical link increases from 0.063 to 0.168, the ranging precision degrades from 1.353 mm (1σ) to 2.221 mm (1σ). The results demonstrate that under a scintillation index of 0.063, both the intermediate precision of ranging after a power-cycle reboot and the ranging precision over the 1 km free-space optical link degrade compared with those of the 1 km fiber-optic link. Specifically, the intermediate precision of ranging after power-cycle reboot degrades to 1.66 times that of the fiber-optic link, and the ranging precision degrades to 5.07 times that of the fiber-optic link. Furthermore, it is also observed in this 1 km free-space optical link experiment that as the scintillation index increases from 0.063 to 0.168, the one-sigma standard deviation of ranging precision rises from 1.353 mm to 2.221 mm.

With the development of space laser networks, miniaturization and lightweight design have become inevitable trends in laser terminal development. In laser links, functions such as spot position measurement, ranging, and data transmission are usually performed by multiple independent units. Integrating these three functions can effectively reduce the size of the opto-mechanical structure and save space within the optical transceiver, thereby supporting the lightweight and compact growth of laser terminals. This paper presents an integrated scheme based on an optical direct-sequence spread-spectrum (DSSS) quadrant detector (QD) and regenerative codes, which enables spot position measurement, ranging, and data transmission through an optical transceiver. The core of this approach involves using a code tracking loop to perform correlation gain calculation, phase comparison, and demodulation of the pseudo-noise code-modulated laser signal, thereby achieving all three functions simultaneously. A desktop experimental system was built to test and verify the scheme’s accuracy and precision. The system achieved a ranging accuracy of 14 mm (1σ), a spot position measurement accuracy of 0.83 μm (1σ) at the target center, and a communication sensitivity of −31 dBm at a 10⁻⁴ bit error rate (BER) with a data rate of 1 Kbps. This study provides a reference for future lightweight optical terminals.