For our experimental demonstrations, we fabricated a silica fiber consisting of four coupled cores, each with a diameter of ~7.5 μm and a numerical aperture (NA) of 0.12. The neighboring elements were separated from each other by a distance (D) of 23 μm. To observe the tunneling suppression between opposite cores, it is essential that any cross couplings are suppressed so that the light propagation dynamics in the system are governed by nearest-neighbor interactions. To achieve this, we judiciously incorporated a fluorine-doped low-index core in the center of the fiber, having a diameter of ~5 μm. In the absence of any twist, when core #1 is initially excited, the light intensity in core #1 and core #3 varies along the propagation distance z according to I1(z) = cos4 κz and I3(z) = sin4 κz, as obtained after solving the dynamical modal evolution equations when ϕ = 0. In other words, light tends to tunnel between these two waveguide channels through core #2 and core #4, in a way similar to tunneling of electrons in a multiwell potential arranged on a circular geometry.

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