Quadratic Vortex Optical Pin Beam With OAM Mode Anti-Degradation Characteristic

Orbital angular momentum (OAM) signal mode crosstalk and energy loss induced by atmospheric turbulence are challenging phenomena commonly occurring in high-capacity and high-speed OAM-based free-space optical communications. In this paper, we combine the optical pin beam (OPB) that resists atmospheric turbulence with the quadratic vortex phase (QVP) to realize a communication transmission beam based on weakening the degradation of the OAM signal mode. The probability densities of a single OAM mode of an optical pin vortex beam carrying a QVP (QVP-OPVB), after passing through an anisotropic non-Kolmogorov turbulent atmosphere, are theoretically derived. Through numerical simulation, it is found that QVP can be regarded as a superposition of multiple OAM modes, and the energy transfer between OAM modes during the propagation can compensate for the degradation of the OAM spectrum caused by atmospheric turbulence. Compared to the OAM spectra of the Gaussian vortex beam carrying QVP (QVP-GVB), the QVP-OPVB has better anti-crosstalk performance in a turbulent environment with a long propagation distance and a small receiving aperture. This beam has applications in free-space optical communication to enhance the interference resistance of the communication link.