Analysis and Assessment of Tube Thickness Variation Effect in Hollow-Core Inhibited Coupling Tube Lattice Fibers

Hollow-Core Inhibited Coupling Fibers have been the target of great investigation efforts due to their peculiar properties [1] . These features, in addition to their capability to handle high power levels, make this kind of fibers very attractive for a wide range of applications such as high-power lasing, light-gas interaction, plasma photonics, quantum physics, terahertz systems, and gas- and bio-sensing. The guidance mechanism of Inhibited Coupling (IC) fibers relies on the spatial mismatch between core modes and cladding modes (CLMs). In this way, the coupling between core and CLMs, caused by their spatial overlap, is dramatically reduced [1] . An effective way to strengthen this effect is to deploy hypocycloid core-contour (i.e. negative curvature) fiber designs [2] . A negative curvature core can be simply obtained by fabricating a cladding structure made of a layer of thin isolated glass tubes arranged around the hollow core (Tube Lattice Fibers – TLFs) [3] , [4] . Although TLFs have reached an extremely low transmission loss and are intensely developed [5] , [6] a gap remains between measured transmission and the theoretical minimum given by confinement loss (CL). This difference can be ascribed to geometrical non-idealities of the fiber structure, introduced during the fabrication process, even though a theoretical analysis showing the real reason for this gap is not yet available.