A novel large-mode-area Bragg fiber （BF） is proposed for selectively suppressing the amplified spontaneous emission （ASE） of Yb. Confinement loss can be effectively lowered by adding a layer of F-doped glass near the core of this fiber. The BF can achieve effective suppression of ASE of Yb when the bend radius is 0.15 m at wavelength lower than 1.13 μm in theory, and eliminate LP 11 mode in mode competition in wavelength range of 1.15 1.2 μm.
