Doped-Core Octagonal Photonic Crystal Fiber with Ultra-Flattened Nearly Zero Dispersion and Low Confinement Loss in a Wide Wavelength Range

In this article, an octagonal photonic crystal fiber is proposed, in which the core region and four air holes in the inner ring have a refractive index of 1.43. Compared with the hexagonal photonic crystal fiber, the octagonal photonic crystal fiber has less confinement loss. To study the propagation characteristics of the proposed photonic crystal fiber, the finite-difference time-domain method with perfectly matched layer boundary conditions has been used. By properly optimizing the design parameters of the proposed octagonal photonic crystal fiber, an ultra-flattened nearly zero dispersion of 0 ± 0.1 ps/nm.km in the wavelength range of 1.25 μm to 1.65 μm is made feasible, and for wavelengths shorter than 1.65 μm, confinement losses of less than 7 × 10−7 dB/km have been achieved.