Geometric phase due to orbit–orbit interaction: rotating LP₁₁modes in a two-mode fiber

Abstract

Accumulation of geometric phase due to non-coplanar propagation of higher-order modes in an optical fiber is experimentally demonstrated. Vertically-polarized LP11 fiber mode, excited in a horizontally-held, torsion-free, step-index, two-mode optical fiber, rotates due to asymmetry in the propagating k-vectors, arising due to off-centered beam location at the fiber input. Perceiving the process as due to rotation of the fiber about the off-axis launch position, the orbital Berry phase accumulation upon scanning the launch position in a closed-loop around the fiber axis manifests as rotational Doppler effect, a consequence of orbit–orbit interaction. The anticipated phase accumulation as a function of the input launch position, observed through interferometry is connected to the mode rotation angle, quantified using the autocorrelation method.

From Imbert–Fedorov shift to topologically spin-dependent walking off for highly confining fiber-guided twisted light

“…One can conclude that these geometric phases in weakly guiding optical fibers would give rise to the polarization (or pattern, e.g. LP 11 ) rotation of light under the weakly opposite phase shifts between two opposite SAM (or OAM) components [26][27][28][29][30][31][32]. However, the strong SOI or geometric phase as in the high-contrast-index fibers can be regarded as the results of interaction between intrinsic angular momentum (usually SAM) and the centroid position of the reflected beam (extrinsic OAM), known as IF shift or SHE, following the principle of conservation of the total angular momentum of light [3,7,15].…”

“…It could cause polarization plane rotation of light (optical Magnus effect) when transmitting along a helically wound single-mode fiber, which was firstly used for experimental verification of Berry's phase [26]. In the few-mode fibers (FMFs), the polarization singular, topological birefringence and phase have been well revealed with the topological Berry phases by Volyar and Viswanathan, etc [27][28][29][30][31][32]. In the multi-mode fibers (MMFs), the SOI of light can induce a fiberlength dependent rotation of speckle patterns around the fiber axis generated by the coherent interference among multiple modes [33].…”