Spin-orbit interactions of a vector twisted beam in gradient index fibers

In order to study the spin-orbit interaction of vector twisted beams in gradient index (GRIN) fibers, the generalized Huygens-Fresnel integral and ABCD transmission matrix method were employed to obtain the cross-spectral density matrix-element expressions of a class of radially polarized twisted Gaussian-Schell model beams in GRIN fibers, and a detailed analysis of the transmission process was performed. The spatial distribution characteristics of light intensity, polarization state, spin angular momentum and orbital angular momentum during the transmission process were analyzed in detail. The results show that the polarization state distribution of the beam gradually changes and generates spin angular momentum during the transmission process, and periodic spin-orbit interconversion occurs and reaches the conversion extreme at the focal plane L/2. The design of the spot shape and polarization ellipse of the beam can be achieved by tuning the twist factor and coherence length. The research results show a broad application potential and prospect in fiber optic high-capacity communication and encrypted communication.