Structural design and performance analysis of wide-band and large-mode-field double cladding photonic crystal fiber

A unique double-cladding photonic crystal fiber structure was designed, consisting of two layers of circular air holes in the outer cladding and two layers of ortho-octagonal air holes in the inner cladding, and the core material was a multi-component glass with rare-earth doped bismuth. The finite element method combined with scattering boundary conditions was used to analyze the mode field area, limiting loss, effective refractive index, time-averaged power and other characteristics of this structure. The results show that the corresponding mode field area and limiting loss at wavelengths of 1 310 nm, 1 550 nm and 1 600 nm is 726.5 μm², 1.24×10⁻⁸ dB.km⁻¹; 731.26 μm², 1.32×10⁻⁸ dB.km⁻¹; 732.28 μm², 1.72×10⁻⁸ dB.km⁻¹, respectively. The time-averaged power z-component at wavelength of 1 550 nm is up to 313 W·m^-2, which can be used as a reference for gain medium of high-power lasers and provide a new option for wide-band tunable lasers.