完美涡旋光束在大气湍流传输中的螺旋相位谱分析

Abstract

Objective Vortex beam is a beam that carries orbital angular momentum (OAM). The perfect vortex beam (PVB) is a new type of beam that has emerged in recent years. Compared with other traditional vortex beams, the PVB has the property that the radius of the optical ring does not increase with the increase in OAM mode, which has attracted much attention in the field of freespace optical communication. Moreover, the different OAM modes of the vortex beam are orthogonal to each other and can be used to expand the channel capacity of optical communication systems. The OAM dimension of the vortex beam can also be used for signal coding, and since the number of modes of OAM modes is not limited (it can be any integer), it is theoretically possible to carry an infinite amount of bits of information in a single code element. However, vortex beam transmission in the atmosphere will be affected by atmospheric turbulence and produce distortion, and atmospheric turbulence makes its light intensity distribution uneven. Spiral phase distortion can result in the 研究论文 第 44 卷 第 6 期/2024 年 3 月/光学学报 transmitted to the far field, and the quantum number difference is 1, larger OAM mode at the emission indicates higher crosstalk probability. The crosstalk probability occurs mainly between two neighboring OAM states (Fig. 3). Furthermore, the variation of PVB light intensity with distance in atmospheric turbulence can reveal the evolution of the PVB light field (Fig. 4). In addition, the crosstalk probability curve of PVB has a significant feature in the state with a large refractive index structure constant near the ground: it first increases to a maximum with the transmission distance and then slowly decreases (Fig. 5).Conclusions In this paper, an analytical expression for the spiral phase spectrum of a PVB under non -Kolmogorov turbulence is derived theoretically. Theoretical models of OAM modal detection probability and crosstalk probability are developed. The results show that the atmospheric turbulence significantly causes the spiral phase spectrum expansion of the PVB. The detection probability curve of the PVB in the near field hardly varies with the OAM mode at the transmitter, while it varies significantly with the OAM mode at the transmitter when the beam is transmitted to the far field. This is because the PVB transmitted to the far field becomes a Bessellike beam, and its beam radius varies significantly with the OAM mode at the transmitter. Moreover, a long transmission distance of the PVB beam indicates a more severe negative impact of atmospheric turbulence. The detection probability of the beam after atmospheric turbulent transport decreases as the number of OAM modes at the transmitter, beam radius, refractive index structure constant near the ground, and turbulence coefficient increase. As the beam wavelength increases, the detection probability of the PVB after atmospheric turbulent transport increases. These results provide a certain reference value for the implementation of PVBs in atmospheric turbulence for optic...