Objective This study investigates the transmission characteristics of Laguerre-Gaussian (LG) vortex beams carrying orbital angular momentum (OAM) in underwater environments, with a particular focus on the effects of different turbulence intensities on beam quality and stability. By employing an improved Nikishov model that incorporates low-frequency subharmonic compensation, this research validates the transmission characteristics of LG beams with various topological charges (l=1,2,3,4) over a transmission distance of 0-40 meters. The analysis of light intensity, phase distribution, and spot drift index aims to provide theoretical support and experimental guidance for optimizing underwater optical communication systems.

Methods An improved Nikishov model incorporating low-frequency subharmonic compensation is employed to generate accurate oceanic phase screens. The multi-phase-screen method, combined with angular spectrum propagation, is utilized to simulate the propagation of LG vortex beams through turbulent ocean conditions. The study evaluates the impact of turbulence intensity on beam drift and peak signal-to-noise ratio (PSNR) by comparing the results under weak, moderate, and strong turbulence conditions.

Results and Discussions The results indicate that the beam drift and transmission instability increase with higher turbulence intensity and topological charge. Under weak turbulence conditions (C_n² = 9.0×10⁻¹³, σ_R²=0.1), the root mean square (RMS) value of the spot centroid drift for l=1 is 0.098 mm, while under strong turbulence (C_n² = 1.3×10⁻¹¹, σ_R²=1.5), the RMS value for l=4 increases to 0.473 mm. The PSNR of the LG beams decreases linearly with transmission distance, with a higher rate of decline in stronger turbulence. For instance, under weak turbulence, the PSNR for l=1 drops from 48.96 dB to 27.39 dB over 40 meters, whereas under strong turbulence, it decreases from 37.68 dB to 14.87 dB. Research indicates that low-order LG beams are more suitable for short-range underwater optical communication.

Conclusions This study refines the Nikishov phase screen model via low-frequency compensation, reducing the phase structure function deviation from 12.6% to 3.8%. Simulations demonstrate that LG beams with topological charge l=1 exhibit optimal turbulence resilience over 40 m coastal propagation (PSNR: 28-45 dB, RMS drift: 0.098 mm), whereas l=4 beams destabilize under strong turbulence (σ_R²=1.5). These findings validate low-order OAM modes as preferred candidates for robust short-to-medium range underwater optical communication links.