Inversion of circular polarizaion in anisotropic fibers with a torsional acoustic wave

This article studies acousto-optical transformations of fiber modes in a circular single-mode anisotropic optical fiber with a traveling torsional acoustic wave of the fundamental order. For the first time, analytical expressions for resonant optical modes and the spectrum of propagation constants are obtained by applying a resonant perturbation theory to the scalar wave equation. This made it possible to consistently describe the experimentally demonstrated mutual transformation of linearly polarized LP0 fiber modes, while taking into account an optical frequency shift. A new effect of acoustically controlled sign inversion of the spin angular momentum of the fundamental mode is predicted. A possibility of generating entangled optical states in which the polarization direction and frequency of the optical beam are entangled has been established.