By investigating the influence of the difference of refractive index between core and cladding(nco-ncl),normalized frequency(V)and core radius(α)on both the intramodal and intermodal nonlinear coefficients(NCs)respectively,we design a novel weakly-coupled four-mode fiber with low nonlinearity.In general,under the premise of ensuring the low NCs between two non-degenerate modes,this design can reduce the intermodal NCs(<0.5 W-1·km-1)between two degenerate modes and optimizes the parameters of differential group delays(DGDs)and chromatic dispersion.The optimized few mode fiber(FMF)is eligible for transmission and mode de-multiplexing in the receiver.
