Calculation of group velocity dispersion of hybrid modes in Bragg fibers using a modified linear combination method

A calculation method is presented for the group velocity dispersion of hybrid modes in Bragg fibers. The method is obtained by extending a linear combination approximation of TE and TM modes in an asymptotic expansion method, and its equation can be solved using the Ferrari method. Numerical results were compared by those of a multilayer division method having higher accuracy than the present method. It was confirmed that both linear combination approximation and modified linear combination method can be precisely used above a cladding index difference of ≈≈1.0 for HE and EH modes.