Fig. 1. (a) Fiber propagation along cylindrical spiral wave-guide; (b) OAM light field distribution, (c) berry phase.

Fig. 2. (a) Path vector s; (b) linear momentum density P; (c) angular momentum density M with , .

Fig. 3. There is no higher-order OAM mode in the cross section of the optical fibers propagating in a straight line, and the optical field distribution is a circular aperture diffraction spot.

Fig. 4. The optical fiber cross section propagating in cylin-drical shape has a high-order OAM mode with: (a) ; (b) ; (c) ; (d) .