Tuning the dispersion and single/multi-modeness in a hole-assisted fiber: A finite-element study

Using a vectorial finite element mode solver developed earlier, we studied a hole-assisted multi-ring fiber. We report the role of the holes in tuning the waveguide dispersion and the single/multi-modeness of the particular fiber. By correctly selecting the hole\´s size and position, a single-mode fiber with a relatively flat and low dispersion in the S-band of the third telecom window was obtained. We also report the observation of a mode-type which has never been reported before for ordinary fibers, which we label as a "ring" mode. This mode exists as a consequence of structural symmetry breaking due to the inclusion of the microstructural holes.