The effects of air-hole size and lattice constant on the single-mode characteristics for photonic crystal fibers(PCFs) are analyzed in theories and the waveguide structure with large mode-field double-cladding photonic crystal fiber is designed.Then the high numerical aperture and large mode-field,ytterbium-doped double-cladding photonic crystal fiber is successfully fabricated with the patent technologies of independent intellectual property rights.The numerical aperture(NA) of its inner cladding is as hig...