Dispersion properties of hollow-core photonic bandgap fibers based on a square lattice cladding

In this paper the dispersion properties and confinement loss of hollow-core photonic bandgap fibers (PBGFs) based on a square lattice (SL) with rounded square air-holes was investigated for the first time, by using a full-vector finite element method (FEM). The waveguide group velocity dispersion (GVD) curves with different core diameter D, air hole size d, rounded diameter dc and hole pitch Λ are presented. The influence of the number of cladding rings on dispersion and confinement loss were also calculated. It was found that as Λ or d increases, the width of PBG becomes wider, and that D and the number of cladding rings have a smaller influence on waveguide GVD. The ratio between bandgap width and central wavelength in our simulation is about 38.1%, which is larger than that of hollow-core PBGFs with triangular lattice (TL) (∼25%). By simulation, the desired zero dispersion wavelength or desired dispersion slope could be obtained by properly choosing the value of dc or Λ. Compared to TL PBGF, at least nine cladding rings is needed to achieve the confinement loss less than 0.1 dB/m for future application.