That a paraxial light beam with spin angular momentum (SAM,σ ) propagating in a helical trajectory leads to the appearance of Rytov-Vladimirsky-Berry (RVB) phase has been a topic of extensive research for the past several decades. Recently, using geometrical optics approximation, it was shown that variations in the beam propagation direction leads to generic parallel transport law – a beam with intrinsic orbital angular momentum (IOAM, l ) behaves topologically similar to polarized beam containing only SAM but of magnitude proportional to the total angular momentum TAM = l ± σ . By considering the interaction of a beam with IOAM, propagating in a non-planar trajectory and hence with extrinsic orbital angular momentum (EOAM), in an inhomogeneous medium we study the parallel transport of fiber mode structure as a manifestation of orbit-orbit interaction. The resulting rotation of the transverse beam structure due to the parallel transport of the LP fiber mode propagating along non-planar ray direction is attributed to the ‘orbital’ Berry phase. The mode transformation is simulated based on the interference of the vector-vortex modes excited in the TMF. The LP mode rotation angle calculated as a function of the beam position at the fiber input is expected to show topological features that can be mapped onto orbital Poincaré sphere.
Pradeep T. Chakravarthy, Dinesh N. Naik, and Nirmal K. Viswanathan, "Parallel transport of fiber mode structure: orbit-orbit interaction," Proc. SPIE 10120, Complex Light and Optical Forces XI, 101200F (Presented at SPIE OPTO: February 01, 2017; Published: 27 February 2017); https://doi.org/10.1117/12.2252060.
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