Fig. 1. Schematic diagram of vortex beams propagating in underwater turbulence. L₁, L₂, thin lenses; SPP, spiral phase plate; M₁, M₂, reflectors

Fig. 2. The practical photos of the experimental device. (a) Weak turbulence; (b) strong turbulence

Fig. 3. The scintillation of the vortex beam with m=2 transmitted to 3.6 meters in weak underwater turbulence with the SA =2.42 ‰

Fig. 4. The intensity patterns of the vortex beam with m=2 propagating in both the weak and strong underwater turbulences with salinity of 0. (a) z=3.6 m, weak turbulence; (b) z=3.6 m, strong turbulence; (c) z=5.4 m, weak turbulence;(d) z=5.4 m, strong turbulence

Fig. 5. The intensity patterns of the vortex beam with m=2 propagating in both the weak and strong underwater turbulences with the salinity of 2.42 ‰. (a) z=3.6 m, weak turbulence; (b) z=3.6 m, strong turbulence; (c) z=5.4 m, weak turbulence; (d) z=5.4 m, strong turbulence

Fig. 6. Scintillation index of the vortex beam with m=2 varying with propagation distance in the water turbulence with different salinities in (a) weak turbulence and (b) strong turbulence

Fig. 7. The effect of salinity on scintillation index of the vortex beam with m=2 at 3.6 m propagation distance in (a) weak turbulence and (b) strong turbulence

Fig. 8. Scintillation index of the vortex beam with m=2 at 3.6 m propagation distance in (a) weak turbulence and (b) strong turbulence

Fig. 9. Experimental device of direct long-distance transmission

Fig. 10. Scintillation indices of the vortex beam and the Gaussian beam varying with propagation distance (no turbulence)