Analysis of fundamental mode of photonic crystal fiber by imaginary-distance beam propagation method

The imaginary-distance beam propagation method (IDBPM) is successfully employed to investigate the effective index of the fundamental mode in the air-filled silica index-guiding photonic crystal fibers (PCFs). A PCF characterized by a hexagonal distribution of air holes with a central defect is taken as example. The convergence behavior of the modal index versus the air hole radius is investigated. It is demonstrated that the converging speed is proportional to the air hole radius. The modal birefringence in the HE state is numerically investigated and demonstrated to strongly depend on the precision of the numerical mesh.