Guiding properties of kagome-lattice hollow-core fibers

Photonic crystal fibers with kagome lattice are a particular kind of micostructured hollow-core fibers whose cross-section is characterized by a web of thin silica struts intersecting in a Star-of-David pattern. Such fibers show unusual properties, such as light confinement in the air-core in absence of a full photonic bandgap. The primary design parameter for such fibers is the strut thickness, which is responsible for the position and the width of the transmission bands. In this paper the guiding properties of hollow-core photonic crystal fibers with kagome lattice are investigated by means of a full-vector modal solver based on the finite element method. The fundamental mode effective index and confinement loss have been evaluated in a wide wavelength range, spanning from 300 nm to 1600 nm, accounting for the influence of the silica strut width on the transmission window. Moreover, the effects of selective alteration of the width and the shape of the silica struts surrounding the core have been analyzed. Simulation results show that the core-surrounding silica ring has the strongest effect on the transmission band, the loss level and the resonance wavelength position and, consequently, it should be carefully controlled during the fiber fabrication.