A new type Bragg fiber for supporting 50 orbital angular momentum modes

We propose a new type Bragg fiber to support 50 OAM modes transmission. The proposed Bragg fiber is composed of fiber core and dual claddings, which include a single-ring high refractive index inner cladding and periodic high-low refractive index outer cladding. Employing the COMSOL simulation software, we numerically demonstrate the transmission properties. The results show that the low nonlinear coefficients are less than 1.45 W-1/km, the total dispersion variations are less than 50 ps/(nm km and the confinement losses are at an acceptable level over the bandwidth from 1.2 mu m to 1.8 mu m. With these excellent properties, the proposed Bragg fiber could be a well-promising OAM fiber for optical communications. In addition, we discuss the effect of ellipticity and misalignment on the stability of OAM modes by using the 10ps-walk-off propagation length. It is proved that the misalignment has a greater effect on the OAM modes stability than that caused by the ellipticity, and the influence of the ellipticity and misalignment on transmission dispersion and confinement loss is relatively small.